Fact-checked by Grok 2 weeks ago

Elemental analysis

Elemental analysis is a core analytical technique in chemistry that determines the elemental composition of a substance by identifying and quantifying the atoms of each element present, often expressed as mass percentages to establish empirical or molecular formulas.^[1] It serves both qualitative purposes, detecting which elements are in a sample, and quantitative purposes, measuring their precise amounts, independent of the sample's molecular structure or functional groups.^[1] This method is indispensable for verifying compound purity, typically requiring results within ±0.4% of theoretical values for publication in scientific journals.^[2] Historically rooted in early combustion methods developed in the 19th century, elemental analysis has evolved with advancements like Fritz Pregl's microanalysis techniques, which earned him the 1923 Nobel Prize in Chemistry for enabling analysis of milligram-scale organic samples.^[3] Modern approaches rely on sophisticated instrumentation to handle diverse sample types, from organic compounds to metals and environmental materials. Key techniques include combustion analysis for carbon, hydrogen, nitrogen, sulfur, and oxygen (CHNSO), which involves high-temperature oxidation followed by gas chromatographic separation and detection.^[4] Spectroscopic methods such as atomic absorption spectroscopy (AAS), which measures light absorption by vaporized atoms for trace-level detection (down to ppm), and inductively coupled plasma mass spectrometry (ICP-MS), offering ultra-low detection limits (ppt) for multi-element isotope analysis, are widely used for their sensitivity and speed.^[5] Surface-sensitive variants like X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) provide localized elemental mapping in materials such as semiconductors and polymers.^[1] Applications span multiple disciplines, including pharmaceutical development for purity confirmation, environmental monitoring for pollutant detection in soil and water, geological surveys for mineral composition, and forensic science for trace evidence analysis.^[4] In organic synthesis, it corroborates reaction outcomes and assesses homogeneity, though challenges like calibration errors in outsourced services can lead to inaccuracies if not properly managed.^[2] Despite its power, the technique demands rigorous sample preparation—such as accurate weighing for microanalysis—and adherence to standards to ensure reliability across non-destructive (e.g., XRF) and destructive (e.g., combustion) methods.^[1]

Fundamentals

Definition and Principles

Elemental analysis is a fundamental branch of analytical chemistry dedicated to identifying (qualitative analysis) and quantifying (quantitative analysis) the elements present in a sample, including their isotopic composition when relevant for tracing origins or environmental pathways. This process applies to diverse materials such as solids, liquids, gases, and biological tissues, providing insights into chemical composition independent of molecular structure or functional groups.^[6]^[7] The core principles of elemental analysis rely on exploiting chemical reactions, physical properties like density or melting point, or interactions with electromagnetic radiation such as absorption or emission spectra to isolate, detect, or measure elements. Methods are broadly classified as destructive, which alter or consume the sample (e.g., through combustion to convert elements into measurable gases), or non-destructive, which preserve the sample's integrity (e.g., X-ray fluorescence spectroscopy that excites atoms without chemical change). These approaches ensure detection across a wide range of concentrations, from major components to trace levels, while accounting for the sample's overall matrix.^[8]^[6]^[9] Sample preparation is a critical initial step to render heterogeneous or complex samples amenable to analysis, often involving dissolution in acids to break down matrices or ashing via controlled heating (typically 450–600°C) to oxidize organic matter and yield inorganic residues. However, fundamental challenges include matrix effects, where co-existing components suppress or enhance signals, and interferences from overlapping spectral lines or chemical similarities that can distort results. Mitigation requires careful method selection and calibration to maintain accuracy.^[10]^[11] In quantitative elemental analysis, results are commonly expressed as percentage composition by mass, calculated via the general equation:

\% \text{ Element} = \left( \frac{\text{mass of element}}{\text{mass of sample}} \right) \times 100

This mass balance principle underpins the conversion of raw measurements (e.g., from detectors) into interpretable elemental abundances, ensuring stoichiometric consistency.^[12]

Applications

Elemental analysis plays a pivotal role in organic chemistry, particularly for structure elucidation and confirming the purity of synthesized compounds. By determining the percentages of carbon, hydrogen, nitrogen, and other elements, it verifies empirical formulas and supports the characterization of new molecules, often complementing techniques like NMR spectroscopy.^[13]^[14] In inorganic materials science, elemental analysis is essential for composition verification, ensuring the precise elemental makeup of alloys, ceramics, and semiconductors to meet performance standards. This process identifies major, minor, and trace elements, aiding in quality control during manufacturing and defect analysis.^[15]^[16] Environmental science relies on elemental analysis for detecting pollutants such as heavy metals in soil and water, enabling the assessment of contamination levels and ecosystem impacts. Techniques like ICP-MS quantify trace elements to monitor bioavailability and mobility, supporting remediation efforts.^[17]^[18] In pharmaceuticals, elemental analysis assesses purity by identifying and quantifying impurities, including elemental contaminants that could affect drug safety and efficacy. Compliance with guidelines like ICH Q3D involves risk-based testing to control trace metals in active ingredients and excipients.^[19]^[20] Forensic science employs elemental analysis to examine trace evidence, such as glass fragments or paint chips, linking materials to crime scenes through unique elemental signatures. This aids in source identification and reconstruction of events.^[21]^[22] Geological applications focus on mineral analysis, where elemental profiling determines rock and ore compositions to inform exploration and resource evaluation. It reveals formation conditions and economic viability by quantifying elements like iron, copper, and rare earths.^[23]^[24] A key example is ensuring regulatory compliance, such as adhering to EPA limits for heavy metals in water and waste, where methods like EPA 200.7 detect elements at parts-per-billion levels to protect public health.^[25]^[26] In nanotechnology, it profiles impurities in nanomaterials, preventing defects that could compromise applications in electronics or medicine.^[27] Broader impacts include contributions to sustainable practices, such as analyzing recycled materials for elemental purity to promote circular economies and reduce waste. In food safety, it tests for contaminants like heavy metals in products, ensuring compliance with standards and minimizing health risks.^[28]^[29]^[30]

Historical Development

Classical Foundations

The foundations of elemental analysis as a quantitative scientific discipline were laid in the late 18th century by Antoine Lavoisier, who pioneered precise measurements in combustion experiments to refute the phlogiston theory and establish the role of oxygen in chemical reactions.^[31] Lavoisier's work, beginning around 1772, involved carefully weighing reactants and products—such as phosphorus and sulfur gaining mass upon burning—to demonstrate the conservation of mass, a principle he formalized in his 1789 Traité élémentaire de chimie.^[31] These experiments not only quantified elemental compositions in simple compounds but also enabled the synthesis and analysis of water as a compound of hydrogen and oxygen in 1783, marking a shift from qualitative observations to empirical, weight-based determinations.^[31] In the 1830s, Justus von Liebig advanced these combustion techniques specifically for organic substances, developing an apparatus in 1831 that allowed accurate determination of carbon, hydrogen, and oxygen content.^[32] Liebig's method involved combusting the sample to produce carbon dioxide and water vapor, which were then absorbed and weighed using a "Kaliapparat" (potassium hydroxide bulbs for CO₂) and calcium chloride tube for H₂O, enabling routine elemental percentages in complex molecules.^[32] This innovation revolutionized organic chemistry by providing a standardized, reproducible protocol that built directly on Lavoisier's quantitative principles. Early techniques emphasized manual precipitation and titration for isolating and measuring elements. Gravimetric precipitation, developed throughout the 18th and 19th centuries, relied on forming insoluble compounds like silver chloride (AgCl) to quantify chloride ions by weighing the dried precipitate after adding silver nitrate to the sample solution.^[33] Complementing this, volumetric titrations emerged in the 18th century, with Étienne François Geoffroy describing the first acid-base titrations in 1729 and François Antoine-Henri Descroizilles inventing the burette in 1791, allowing precise volume measurements to determine elemental content indirectly through reactions like acid neutralization.^[34] Key milestones included the refinement of the analytical balance in the late 18th century, which Joseph Black and others adapted for chemical use to achieve milligram precision in weighings, essential for accurate mass-based analysis.^[35] By the early 19th century, these tools enabled chemists like John Dalton to derive the first empirical formulas from weight percentages obtained via combustion and precipitation, as outlined in his 1808 A New System of Chemical Philosophy, where atomic ratios were inferred from proportional masses in compounds like water and carbon dioxide.^[36]

Instrumental Advancements

The evolution of instrumental methods in elemental analysis began in the early 20th century with Fritz Pregl's pioneering work on quantitative microanalysis of organic substances. Between 1912 and 1923, Pregl developed techniques that enabled accurate determination of carbon, hydrogen, nitrogen, and other elements in milligram quantities of samples, drastically reducing the sample size required compared to classical methods and making analysis feasible for scarce biological materials.^[3] This innovation earned Pregl the Nobel Prize in Chemistry in 1923 for inventing the method of micro-analysis of organic substances.^[3] In the 1930s, the introduction of advanced spectroscopic techniques marked a significant shift toward more precise and automated detection. Emission spectroscopy, particularly with controlled arc and spark sources, gained prominence for its improved stability and sensitivity in qualitative and quantitative elemental identification, building on earlier flame-based observations but enabling routine laboratory use.^[38]^[39] These developments laid the groundwork for post-war instrumental proliferation by addressing limitations in excitation sources and spectral resolution. Following World War II, atomic absorption spectroscopy (AAS) emerged as a transformative technique in the 1950s, primarily through the efforts of Alan Walsh at CSIRO in Australia. Walsh's 1955 conceptualization and subsequent development of AAS allowed for highly sensitive detection of metals by measuring light absorption by ground-state atoms in a flame or graphite furnace, offering detection limits in the parts-per-billion range and revolutionizing trace metal analysis in environmental and clinical samples.^[40]^[41] The 1960s brought further innovation with the advent of inductively coupled plasma (ICP) sources, independently advanced by researchers like Stanley Greenfield and Velmer Fassel, which provided high-temperature plasmas (up to 10,000 K) for superior atomization and excitation, enabling multielement analysis with reduced interferences compared to flame-based methods.^[42]^[43] The integration of mass spectrometry with ICP in the late 1970s and 1980s propelled elemental analysis into the realm of ultra-trace detection and isotopic studies. Inductively coupled plasma mass spectrometry (ICP-MS), first demonstrated around 1980 by teams at Iowa State University and refined commercially by 1983, combined ICP's efficient ionization with MS's high-resolution mass separation, achieving femtogram-level sensitivity for most elements and facilitating applications in geochemistry and toxicology.^[44]^[45] This hyphenation extended to speciation analysis, where techniques like gas chromatography coupled with ICP-MS (GC-ICP-MS) emerged in the 1990s and beyond to separate and quantify organometallic species, such as alkylated metals in environmental matrices, by leveraging chromatographic separation prior to elemental detection.^[46]^[47] By the 2020s, instrumental advancements emphasized portability, automation, and intelligent data handling to meet demands for on-site and high-throughput analysis. Portable X-ray fluorescence (XRF) devices, such as handheld models from Bruker and Thermo Fisher, have become standard for non-destructive field-based elemental screening, offering real-time analysis of alloys, soils, and artifacts with detection limits down to 10-100 ppm for key elements like lead and arsenic.^[48]^[49] Automation in sample introduction and instrument control, integrated into modern ICP and AAS systems, has reduced manual intervention, while AI-assisted algorithms for spectral deconvolution and interference correction—evident in software updates from vendors like Agilent—enhance accuracy in complex datasets, processing multivariate signals to identify trace elements amid matrix effects.^[50] These trends, including hyphenated systems like GC-ICP-MS, continue to address speciation challenges in emerging fields such as nanomaterials and biofuels.

Qualitative Methods

Chemical Identification Tests

Chemical identification tests encompass traditional wet chemistry procedures that detect the presence of specific elements through characteristic reactions, color changes, or precipitates, without providing quantitative data. These methods rely on simple reagents and observable outcomes, making them accessible for preliminary laboratory confirmation of elemental composition in inorganic and organic samples. Developed primarily in the 19th century, they form the backbone of qualitative elemental analysis, particularly for metals, halogens, nitrogen, and sulfur. One classical approach is the flame test, which identifies certain metal ions by the unique colors they impart to a flame when heated. For instance, sodium ions produce a persistent yellow flame due to the excitation and emission of electrons at specific wavelengths. This test is performed by dipping a platinum or nichrome wire into the sample solution and placing it in a Bunsen burner flame, observing the coloration after cleaning the wire to avoid contamination. Limitations include interference from other ions, which can mask weaker colors, and its inapplicability to non-volatile or colorless-emitting elements. For organic compounds, the sodium fusion test, known as Lassaigne's test and developed by Jean-Louis Lassaigne in 1843, detects halogens, nitrogen, and sulfur by fusing the sample with sodium metal to form water-soluble ionic compounds. The resulting sodium extract is then tested: halogens form precipitates with silver nitrate (white for chloride, pale yellow for bromide, yellow for iodide), nitrogen is detected by treating the extract with iron(II) sulfate, followed by iron(III) chloride and acidification, yielding Prussian blue if sulfur is absent, and sulfur produces a violet color with sodium nitroprusside or black lead sulfide precipitate.^[51] This method is rapid and integral to qualitative organic analysis. Additional procedures include the Beilstein test for halogens, where a copper wire coated with the sample is heated in a flame, yielding a green color from volatile copper halides, though it fails to distinguish between halogens and can give false positives from nitrogenous compounds or acids. For specific metals like nickel, dimethylglyoxime reagent in ammoniacal solution forms a bright red precipitate of the nickel dimethylglyoxime complex, confirming the ion's presence with high selectivity. The silver nitrate precipitation test specifically identifies chloride ions through an insoluble white silver chloride precipitate, which dissolves in ammonia, aiding differentiation from other halides. These tests offer high specificity for targeted elements using minimal equipment, ideal for small-scale confirmations in educational or field settings, but they are susceptible to interferences from co-existing ions or compounds, requiring careful sample preparation to ensure reliability. They serve as a complementary, low-tech alternative to instrumental methods for initial elemental screening.

Spectroscopic Detection

Spectroscopic detection in elemental analysis relies on the principle that atoms emit or absorb electromagnetic radiation at wavelengths characteristic of their electronic structure, enabling identification of elements without altering the sample's chemical composition. When atoms are excited by an external energy source, such as light, electrons, or particles, they transition between energy levels, producing spectra with unique line patterns that serve as fingerprints for each element. This method is particularly valuable for qualitative analysis, as it allows simultaneous detection of multiple elements in complex matrices, often with minimal sample preparation.^[52] X-ray fluorescence (XRF) is a prominent non-destructive technique for surface elemental analysis, where high-energy X-rays irradiate the sample, ejecting inner-shell electrons and causing outer electrons to emit characteristic fluorescent X-rays as they fill the vacancies. These X-rays are detected and sorted by energy, revealing the presence of elements from sodium to uranium in solids, liquids, or powders. XRF's non-destructive nature makes it ideal for analyzing valuable or irreplaceable samples, such as artifacts or alloys, where it excels in detecting major and minor constituents in inorganic materials like metals and minerals.^[53] Atomic emission spectroscopy (AES) facilitates multi-element detection by exciting atoms in a high-temperature source, such as a flame, arc, or plasma, leading to the emission of light at specific wavelengths corresponding to electronic transitions. The emitted spectrum is dispersed and analyzed to identify elements based on their unique emission lines, allowing for the simultaneous observation of dozens of elements in a single measurement. AES is widely applied to solutions and gases, providing rapid screening for metals and non-metals in environmental and industrial samples.^[54]^[55] X-ray photoelectron spectroscopy (XPS), also known as electron spectroscopy for chemical analysis (ESCA), identifies elements and their chemical states in the surface layers of solids by measuring the kinetic energy of photoelectrons ejected when the sample is irradiated with soft X-rays. The binding energy of these electrons, calculated from their kinetic energy and the X-ray photon energy, provides element-specific signatures, while shifts in binding energy reveal oxidation states or bonding environments. XPS is surface-sensitive, probing depths of 1-10 nm, and is essential for studying thin films, catalysts, and semiconductors where elemental speciation is critical.^[56]^[57] Particle-induced X-ray emission (PIXE) extends XRF principles by using accelerated charged particles, typically protons, to induce X-ray emission from trace elements in a sample. The particles penetrate deeper than X-rays, exciting inner-shell electrons and producing characteristic X-rays that are detected for elemental identification, with particular sensitivity for elements from sodium to uranium at parts-per-million levels. PIXE is advantageous for thin samples or those requiring high spatial resolution, such as biological tissues or geological sections, and complements other methods for low-concentration detection.^[58] Modern enhancements, such as synchrotron-based XRF, leverage the intense, tunable beams from synchrotron radiation sources to achieve superior sensitivity and spatial resolution compared to laboratory XRF systems. These facilities enable micro- and nano-scale mapping of elements in heterogeneous samples, detecting traces below parts-per-billion in fields like environmental science and materials research, by exploiting the high brilliance and polarization of synchrotron X-rays to minimize background noise.^[59]^[60]

Quantitative Methods

Gravimetric and Volumetric Approaches

Gravimetric analysis is a classical quantitative method in elemental analysis that determines the amount of an analyte by converting it into an insoluble precipitate of known composition, which is then isolated, purified, and weighed./08%3A_Gravimetric_Methods/8.02%3A_Precipitation_Gravimetry) The process begins with digestion of the sample to ensure complete precipitation, followed by filtration to separate the precipitate from the solution, and ignition to convert it to a stable form suitable for weighing.) A representative example is the determination of sulfate ions, where the sample is treated with barium chloride to form barium sulfate (BaSO₄), an insoluble precipitate that is filtered, dried, and weighed.^[61] The concentration of the analyte is calculated using the formula:

\% \text{Analyte} = \left( \frac{\text{MW}_\text{analyte}}{\text{MW}_\text{precipitate}} \right) \times \left( \frac{\text{mass}_\text{precipitate}}{\text{mass}_\text{sample}} \right) \times 100

where MW denotes molecular weight./08%3A_Gravimetric_Methods/8.02%3A_Precipitation_Gravimetry) For sulfate analysis, this yields the percentage of SO₄²⁻ based on the mass of BaSO₄. Gravimetric methods achieve high accuracy, typically better than ±0.1% relative error, making them reliable for macro-level determinations.^[62] However, limitations include errors from co-precipitation, where impurities adsorb onto or incorporate into the precipitate, potentially leading to positive or negative biases in the measured mass./08%3A_Gravimetric_Methods/8.02%3A_Precipitation_Gravimetry) Volumetric analysis, another foundational quantitative approach, measures the volume of a reagent solution of known concentration required to react completely with the analyte in the sample, often through titration./Analytical_Sciences_Digital_Library/Contextual_Modules/Volumetric_Analysis) This method is particularly useful for determining elements like oxygen and certain metals. For dissolved oxygen in water, the Winkler method involves adding manganese(II) sulfate and an alkaline iodide-azide reagent to form a precipitate that liberates iodine proportional to the oxygen content; this iodine is then titrated with sodium thiosulfate using starch as an indicator.^[63] In complexometric titrations, ethylenediaminetetraacetic acid (EDTA) serves as a versatile reagent that forms stable chelates with metal ions such as calcium and magnesium, allowing their quantification by titrating to a color change with indicators like Eriochrome Black T.) These techniques, rooted in 19th-century classical chemistry, remain valuable for validating results from contemporary instrumental methods.^[64]

Atomic and Mass Spectrometry Techniques

Atomic absorption spectroscopy (AAS) is a widely used technique for the quantitative determination of metal elements in samples by measuring the absorption of light by free atoms in the gaseous state. Developed by Alan Walsh in 1955, AAS relies on the principle that atoms absorb radiation at specific wavelengths corresponding to electronic transitions from ground to excited states.^[65] Flame AAS, the most common variant, involves aspirating the sample into a flame where it is atomized, allowing for rapid analysis of concentrations typically in the parts-per-million range. For lower detection limits, graphite furnace AAS (GF-AAS) uses a heated graphite tube to progressively dry, ash, and atomize the sample, enabling detection down to parts-per-billion levels for trace elements.^[66] Inductively coupled plasma optical emission spectrometry (ICP-OES) extends atomic techniques to simultaneous multi-element analysis with high sensitivity. In ICP-OES, the sample is introduced into a high-temperature argon plasma (around 6000–10,000 K) generated by radio-frequency induction, where elements are excited and emit characteristic light wavelengths that are detected and quantified. Pioneered by Velmer Fassel in the 1970s, this method achieves detection limits in the ppb range for over 70 elements, making it ideal for complex matrices like environmental and geological samples.^[67]^[68] Mass spectrometry techniques enhance elemental analysis by separating ions based on mass-to-charge ratios, providing isotopic information and ultra-trace detection. Inductively coupled plasma mass spectrometry (ICP-MS), introduced by Robert Houk and colleagues in 1980, ionizes the sample in an argon plasma and uses a mass analyzer (e.g., quadrupole) to detect ions, achieving femtogram-level sensitivity for most elements and enabling isotopic ratio measurements critical for geochronology and environmental tracing. Neutron activation analysis (NAA), originating from the work of George de Hevesy and Hilde Levi in 1936, involves irradiating the sample with neutrons to produce radioactive isotopes, whose gamma emissions are measured via high-resolution spectroscopy for non-destructive multi-element quantification at ppb to ppm levels, particularly useful for light elements like oxygen and rare earths.^[69]^[70] Quantitative procedures in these techniques rely on calibration curves constructed from standard solutions of known concentrations, where signal intensity (absorbance in AAS, emission intensity in ICP-OES, ion counts in ICP-MS and NAA) is plotted against concentration to ensure linearity and accuracy, often spanning 3–5 orders of magnitude. Internal standards, such as scandium or indium added to all samples and standards, compensate for matrix effects, signal drift, and instrument variability by normalizing analyte signals, improving precision to better than 5% relative standard deviation. Recent hyphenated methods like laser ablation ICP-MS (LA-ICP-MS), developed in the 1980s, couple a laser for direct solid sampling with ICP-MS to enable spatial elemental mapping in materials such as alloys and biological tissues, providing micron-scale resolution for in situ analysis without dissolution. These instrumental methods are often validated against gravimetric techniques for accuracy and applied in environmental monitoring for pollutant tracking.^[71]^[72]^[73]

Combustion Analysis

CHNS Procedures

The CHNS procedure for elemental analysis of organic compounds relies on high-temperature combustion in an oxygen-rich environment, typically at 900–1000°C, to quantitatively convert the elements into measurable gaseous products. During this process, carbon is oxidized to carbon dioxide (CO₂), hydrogen to water vapor (H₂O), nitrogen to dinitrogen (N₂), and sulfur to sulfur dioxide (SO₂). These combustion products are then separated, often via gas chromatography, and quantified using detectors such as thermal conductivity or infrared sensors, with absorption or trapping steps employed to isolate specific gases for accurate measurement.^[74]^[75] Variants of the CHNS procedure adapt classical methods to specific elements or sample constraints. The Dumas method, originally developed for nitrogen, involves complete combustion followed by reduction of nitrogen oxides to N₂, integrated into modern CHNS analyzers for simultaneous multi-element detection. Adaptations of the Pregl micro-method enable analysis of milligram-scale samples by optimizing combustion efficiency and gas handling for trace-level accuracy in organic matrices. For samples containing halogens (extending to CHNX analysis), quantitative determination requires sodium fusion, where the compound is fused with sodium metal to convert halogens to sodium halides (NaX), which are then extracted and quantified via precipitation or titration to avoid interference in the primary combustion step.^[74]^[76]^[77] The percentages of each element are derived from the masses of the combustion products using stoichiometric ratios, accounting for the atomic masses relative to the molecular masses of the gases. For carbon, the calculation is:

\% \mathrm{C} = \left( \frac{12}{44} \times \frac{\text{mass of } \mathrm{CO_2}}{\text{mass of sample}} \right) \times 100

For hydrogen:

\% \mathrm{H} = \left( \frac{2}{18} \times \frac{\text{mass of } \mathrm{H_2O}}{\text{mass of sample}} \right) \times 100

For nitrogen, since the molecular weight of N₂ matches the combined atomic weight of two nitrogen atoms:

\% \mathrm{N} = \left( \frac{28}{28} \times \frac{\text{mass of } \mathrm{N_2}}{\text{mass of sample}} \right) \times 100 = \frac{\text{mass of } \mathrm{N_2}}{\text{mass of sample}} \times 100

For sulfur:

\% \mathrm{S} = \left( \frac{32}{64} \times \frac{\text{mass of } \mathrm{SO_2}}{\text{mass of sample}} \right) \times 100

These formulas assume complete combustion and calibration against standards to correct for instrumental factors. The core CHN analysis can be extended with add-ons for sulfur (CHNS) or oxygen (CHNSO), where oxygen is often calculated by difference after accounting for other elements and ash content.^[78]^[79]^[74]

Instrumentation and Variants

Core instruments for combustion analysis in CHNS elemental determination primarily consist of automated CHNS analyzers equipped with thermal conductivity detectors (TCD) for nitrogen quantification and infrared (IR) sensors for simultaneous detection of carbon, hydrogen, and sulfur gases.^[79]^[80] These systems operate via high-temperature combustion, converting sample elements into measurable gases like CO₂, H₂O, N₂, and SO₂, with TCD measuring thermal differences in carrier gas mixtures and IR sensors detecting specific molecular absorptions.^[81] Representative automated platforms include the PerkinElmer 2400 Series II CHNS/O analyzer, which enables rapid, sequential analysis of multiple elements in organic materials through integrated furnace and detection modules.^[82] Variants extend beyond standard CHNS to specialized adaptations, such as oxygen analysis using the Unterzaucher method, which involves pyrolysis of the sample in a helium or nitrogen stream at temperatures around 1120°C to form carbon monoxide (CO), followed by manometric or coulometric measurement of CO after purification.^[83] For sulfur-specific determination, particularly in coal and coke, the Eschka method employs fusion of the sample with a mixture of magnesium oxide and sodium carbonate, followed by combustion, sulfate extraction, and gravimetric titration to quantify total sulfur content.^[84] Modern integrations incorporate gas chromatography (GC) for enhanced separation of combustion products, allowing precise resolution of overlapping peaks in complex matrices before detection, as seen in systems like the Thermo Scientific FlashSmart analyzer with GC columns.^[85] Advancements in these instruments emphasize flash combustion techniques, where samples—whether solids, liquids, or viscous materials—are rapidly oxidized in a tin capsule at temperatures exceeding 1800°C, ensuring complete conversion and minimal residue for accurate multi-element analysis.^[86] In the 2020s, eco-friendly variants have emerged with reduced carrier gas consumption and no need for reference gases, such as the VELP EMA 502 analyzer, which lowers oxygen usage and maintenance while maintaining high precision through compact, low-emission designs.^[87] Complementary software advancements, like the Eager Smart suite in Thermo systems or the DataApex EA Extension, automate peak integration by adjusting thresholds for width, height, and baseline, improving data processing efficiency in CHNS workflows.^[88]

Interpretation and Quality Control

Empirical Formula Determination

Empirical formula determination involves deriving the simplest whole-number ratio of atoms in a compound based on its elemental composition data, typically obtained from quantitative methods such as combustion analysis or spectrometry.^[78] The process begins with the mass percentages of each element, which are converted to moles by assuming a 100 g sample for convenience, dividing the mass of each element by its atomic mass, and then finding the ratio of these mole values.^[89] This ratio is simplified by dividing all mole values by the smallest one, and if necessary, multiplying by a small integer to yield whole numbers, resulting in the empirical formula.^[90] To illustrate, consider a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. Assuming a 100 g sample yields 40 g C, 6.7 g H, and 53.3 g O. Converting to moles: carbon (40 / 12.01 ≈ 3.33 mol), hydrogen (6.7 / 1.01 ≈ 6.63 mol), oxygen (53.3 / 16.00 ≈ 3.33 mol). Dividing by the smallest value (3.33) gives a ratio of C:H:O ≈ 1:2:1, so the empirical formula is CH₂O.^[91] The sum of the percentages should ideally equal 100%, with deviations typically under 0.4% indicating acceptable data quality from the analysis.^[2] For organic compounds analyzed via combustion, the empirical formula provides the base ratio, but determining the molecular formula requires additional information, such as the molar mass obtained from mass spectrometry. The molar mass is divided by the empirical formula mass to find the integer multiple n, yielding the molecular formula as (empirical formula)ₙ. For instance, if mass spectrometry indicates a molar mass of 170 g/mol for a compound with empirical formula C₆H₁₃ (mass 85 g/mol), then n ≈ 2, giving C₁₂H₂₆.^[78] This integration ensures the formula reflects the actual molecular structure rather than just the atomic ratio.^[89]

Error Analysis and Standards

In elemental analysis, errors can be broadly classified into systematic and random categories, each arising from distinct sources that impact the accuracy and precision of results. Systematic errors, which consistently bias measurements in one direction, include incomplete combustion in CHNS analysis, where refractory elements or high inorganic content lead to underestimation of carbon, hydrogen, nitrogen, and sulfur by failing to fully oxidize the sample. Calibration drift in spectrometric techniques, such as gradual shifts in instrument response over time due to environmental factors or component aging, introduces proportional biases that accumulate during extended runs. Matrix effects in inductively coupled plasma (ICP) methods represent another systematic issue, where sample components alter nebulization efficiency or plasma conditions, suppressing or enhancing analyte signals by up to 20-35% depending on acid concentration and viscosity mismatches. Random errors, conversely, vary unpredictably and stem from sources like sample inhomogeneity, where uneven distribution of elements within a solid or powdered sample causes replicate measurements to fluctuate, contributing to variability in observed standard deviations. Quality control measures are essential to mitigate these errors and ensure reliable elemental quantification. Certified reference materials (CRMs), such as those from NIST, provide well-characterized elemental compositions for validating method accuracy, with values traceable to international standards and used to detect biases by comparing measured against certified concentrations. Blank corrections address contamination by subtracting signals from reagent or procedural blanks, particularly critical in trace analysis to prevent overestimation from background interferences. Precision is typically assessed using relative standard deviation (RSD), with macro-level elemental analysis (e.g., >1% concentrations) achieving RSD values below 1% under optimal conditions, indicating high repeatability across instruments like flash combustion analyzers. Adherence to international standards further enhances reliability in elemental analysis laboratories. The ISO/IEC 17025 guidelines require laboratories to implement risk-based quality management, including competence documentation, equipment calibration, and proficiency testing to produce valid results with demonstrated impartiality. Recent interlaboratory studies (as of 2023) have questioned the traditional ±0.4% absolute deviation requirement for confirming compound purity in publications, suggesting it may be overly strict and lead to rejection of valid samples in up to 10% of cases; some journals have since adopted more flexible guidelines based on statistical validation, while others retain the standard.^[92]^[93] To address variability in multi-run datasets, modern statistical tools like analysis of variance (ANOVA) are employed for validation, separating repeatability from intermediate precision by partitioning variances within and between experimental groups. Metrological traceability to SI units is ensured through calibration hierarchies linking measurements to primary standards, often via CRMs, minimizing propagation of uncertainties and supporting comparability across global labs.

References

[1]
https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Physical_Methods_in_Chemistry_and_Nano_Science_(Barron)/01%3A_Elemental_Analysis
[2]
Elemental Analysis–A Powerful but Often Poorly Executed Technique
Jul 6, 2022 · Elemental analysis is a broad term utilized to describe multiple techniques to identify the atomic composition of matter.Missing: definition reliable
[3]
Fritz Pregl – Facts - NobelPrize.org
Prize motivation: “for his invention of the method of micro-analysis of organic substances”. Prize share: 1/1. Work. In nature organisms are composed of an ...
[4]
Elemental Analysis - an overview | ScienceDirect Topics
Elemental analysis (EA) is an analytical technique applied in chemistry to determine the elemental composition of chemical compounds and their composites.Missing: reliable | Show results with:reliable
[5]
Most Common Elemental Analysis Techniques - AZoM
Some of the most common techniques used in the laboratories today are X-ray fluorescence (XRF), absorption atomic spectroscopy (AAS), and inductively coupled ...Missing: reliable | Show results with:reliable
[6]
1: Elemental Analysis - Chemistry LibreTexts
Mar 21, 2021 · Elemental analysis determines the quantity of a particular element within a molecule or material. It can be qualitative or quantitative.Missing: reliable | Show results with:reliable
[7]
Elemental Analysis - an overview | ScienceDirect Topics
Elemental analysis is a destructive method which requires acidic sample digestion before dilution and analysis which is rather expensive. However, a huge ...Skeletal Examination And... · Humic And Fulvic Compounds · Glass: Analysis
[8]
How Does an Elemental Analyzer Work? - AZoM
May 5, 2021 · Elemental analysis is the process where a sample of material is analyzed for its elemental composition, i.e. the amount of elements present in ...
[9]
Elemental Analysis - An Introduction - Malvern Panalytical
Elemental analysis is critical for product quality and safety, providing insights into the chemical makeup of materials. Techniques include XRF, PFTNA, LIBS, ...
[10]
Ashing - an overview | ScienceDirect Topics
Ashing is defined as a sample preparation method involving the heating of a sample in an open dish or crucible to oxidize organic matter, ...
[11]
Matrix effects demystified: Strategies for resolving challenges in ...
Oct 28, 2023 · To overcome this, sample preparation techniques play a crucial role. Proper sample preparation methods can mitigate the effects of matrix ...
[12]
5.7 Determining Empirical and Molecular Formulas - UCF Pressbooks
Key Equations · % X = mass X mass compound × 100 % · molecular or molar mass ( amu or g mol ) empirical formula mass ( amu or g mol ) = n formula units/molecule ...
[13]
An International Study Evaluating Elemental Analysis - PMC
For organic and organometallic compounds, high-field 1H and 13C NMR can be used to show purity. Ideally, elemental analysis (±0.4%) should be included for small ...
[14]
Applications in Organic Chemistry - Mass Spectrometry Lab - NTNU
Elemental composition confirmation. Mass spectrometry is without a doubt an indispensable tool for the chemistry disciplines like organic and organometallic ...
[15]
Inorganic Analysis - Intertek
Inorganic analysis involves various analytical methods that can qualitatively or quantitatively determine the inorganic and elemental composition of solids or ...
[16]
Elemental Analysis of Materials - HORIBA
Elemental analysis of materials is the process of identifying and quantifying the chemical elements in a sample to determine its composition.
[17]
Elemental Speciation Analysis in Environmental Studies
Nov 19, 2021 · Speciation analysis is a key aspect of modern analytical chemistry, as the toxicity, environmental mobility, and bioavailability of elemental analytes are ...
[18]
Quantifying Pollutants: Elemental Analysis Methods for Cleaner Air
Jan 17, 2024 · Elemental analysis via EDXRF and WDXRF is key in identifying PM sources, aiding air quality management and pollution control strategies.
[19]
Trace Metals Testing and Elemental Analysis for Pharmaceuticals
Elemental analysis and trace metals testing of pharmaceuticals is critical to drug product quality control and commercial release.
[20]
[PDF] ICH guideline Q3D (R2) on elemental impurities Step 5
Nov 12, 2014 · This guideline presents a process to assess and control elemental impurities in the drug product using the principles of risk management as ...
[21]
The smallest traces of crime: Trace elements in forensic science
Trace elements can be valuable as traces collected at crime scenes and during corpse examination, aiding in determining characteristics like the sex or age of ...
[22]
What Role Does SEM Play in Trace Evidence Analysis?
SEM plays a pivotal role in trace evidence analysis by providing high-resolution imaging, elemental analysis, and detailed surface characterization of trace ...
[23]
Geologic and Mineral Analysis | Thermo Fisher Scientific - US
Quickly determine the elemental composition of geologic and mineral samples using characteristic X-rays. As every element has a unique electron orbit, when ...
[24]
[PDF] Analytical Techniques for Elemental Analysis of Minerals
Elemental analysis of minerals is one of the most important routine working methods in. Earth sciences, since information on the elemental composition of ...
[25]
Method 200.7: Determination of Metals and Trace Elements in Water ...
Apr 21, 2025 · This method for preparation and analysis of drinking water samples to detect and measure compounds containing arsenic, thallium and vanadium.
[26]
Metals | US EPA
Mar 10, 2025 · This module addresses water column contamination by metals and metalloids that commonly cause toxic effects. These include arsenic, cadmium, ...
[27]
Evaluation of elemental impurities and particle size distribution in ...
We developed an asymmetric flow field-flow fractionation hyphenated to inductively coupled plasma mass spectrometry (AF4-ICP-MS) to assess elemental impurities.
[28]
From Mining to Recycling: Why Elemental Analysis Matters for ...
Oct 10, 2025 · Elemental fingerprints support quality control, process optimization, and sustainable practices. Comprehensive analysis enables safer, more ...
[29]
An Overview of Elemental Analysis in Recycling - AZoCleantech
Dec 15, 2023 · Elemental analysis helps determine the elemental composition of a substance. The concept of circular economy is essential for sustainability ...Missing: safety | Show results with:safety
[30]
Food Safety Testing: Analytical Methods for Contaminants and ...
For elemental analysis, Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Atomic Absorption Spectroscopy (AAS) are the gold standards. ICP-MS is a ...<|control11|><|separator|>
[31]
Antoine Laurent Lavoisier The Chemical Revolution - Landmark
Lavoisier showed an early inclination for quantitative measurements and soon began applying his interest in chemistry to the analysis of geological samples, ...Missing: pioneer sources
[32]
Justus von Liebig: Great Teacher and Pioneer in Organic Chemistry ...
May 1, 2023 · In 1831, Liebig developed an apparatus for determining the carbon, hydrogen, and oxygen content of organic substances (i.e., elemental analysis) ...
[33]
https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Analytical_Chemistry_2.1_(Harvey)/08%3A_Gravimetric_Methods/8.02%3A_Precipitation_Gravimetry
[34]
The development of the titration methods : Some historical annotations
The early history of titrimetric analysis coincides with the development of chemical industries, for which rapid methods of analysis were essential.Missing: volumetric elemental
[35]
The evolution of the analytical balance - ResearchGate
Aug 9, 2025 · This work intends to describe the historical evolution of the balance based on its technical improvement.
[36]
(PDF) 19th Century Atomism and the Empirical Nature of the ...
May 10, 2025 · 19th Century Atomism and the Empirical Nature of the Chemical Atom: Dalton Against Lavoisier ; The development of such a quantitative chemical ...<|control11|><|separator|>
[37]
(PDF) Fritz pregl, inventor of quantitative elemental microanalysis of ...
Aug 5, 2025 · Fritz Pregl was awarded the 1923 Nobel Prize in Chemistry for developing organic elemental micro-analysis of milligram amounts of sample.
[38]
A history of atomic absorption spectroscopy - ScienceDirect
Spectrochemical analysis originated with the work of Kirchoff and Bunsen in 1860 but found relatively little application until the 1930s. Arc-spark emission ...Missing: introduction | Show results with:introduction
[39]
Optical Emission Spectrometer --history of development at home ...
Mar 29, 2022 · In the 1930s and 1940s, controlled arcs and electric sparks were used as excitation light sources, which improved the stability of spectral ...
[40]
Atomic absorption spectroscopy - CSIROpedia
Feb 21, 2011 · The concept of atomic absorption spectroscopy (AAS) came to CSIRO scientist Alan Walsh in a flash of inspiration as he was gardening at his ...
[41]
A Timeline of Atomic Spectroscopy
Oct 1, 2006 · This timeline provides a short history of the experimental and theoretical development of atomic spectroscopy for elemental spectrochemical analysis.
[42]
History of inductively coupled plasma atomic emission spectral ...
The first instrument for ICP spectral analysis was produced in Germany by KONTRON about 1 year later. It was exhibited at the XVII Colloquium Spectroscopicum ...Missing: elemental | Show results with:elemental
[43]
[PDF] CHAPTER 4 Inductively Coupled Plasma—Atomic Emission ...
Greenfield et al. developed plasma-based instruments in the mid 1960s about the same time flame-based instruments such as FAAS and FAES (Chapter.
[44]
The Top 10 Milestones in MS - The Analytical Scientist
Nov 5, 2021 · The coupling of inductively coupled plasma with MS (ICP-MS) made mass spectrometry a major player in trace elemental analysis. Earlier work ...
[45]
40 Years Old and Still Solving Problems: Evolution of the ICP-MS ...
Mar 1, 2023 · This is in contrast to the 1970s and 1980s, when, for example, the fundamentals of ICP-MS research were carried out predominantly in academia.Missing: onward | Show results with:onward
[46]
Hyphenated ICP-MS Techniques for Speciation Analysis
Mar 1, 2009 · The authors discuss speciation analysis methods that enable scientists to identify and measure the quantities of one or more individual chemical species in a ...
[47]
GC-ICP-MS: A very sensitive hyphenated system for speciation ...
Aug 11, 2007 · GC-ICP-MS: A very sensitive hyphenated system for speciation analysis · Brief summary: Gas chromatography for the separation of elemental species.
[48]
Handheld XRF Spectrometers for Elemental Analysis - Bruker
Handheld / portable X-ray fluorescent (XRF) analyzers have the capability to non-destructively quantify or qualify nearly any element from Magnesium to Uranium.
[49]
[PDF] XRF Technology in the Field - Thermo Fisher Scientific
Portable handheld XRF analyzers are lightweight, easy to handle and can be operated with minimal training. They provide elemental analysis anytime, anywhere, in ...
[50]
https://www.agilent.com/cs/library/applications/5990-9473EN_icpmsSpeciationHB_lr.pdf
[51]
X-Ray Fluorescence Spectroscopy - an overview - ScienceDirect.com
X-ray fluorescence (XRF) spectroscopy is defined as a high-energy analytical technique that provides information about the elemental composition of a sample ...
[52]
X-Ray Fluorescence (XRF) - SERC (Carleton)
An X-ray fluorescence (XRF) spectrometer is an x-ray instrument used for routine, relatively non-destructive chemical analyses of rocks, minerals, sediments ...
[53]
Atomic Emission Spectroscopy - an overview | ScienceDirect Topics
Atomic emission spectroscopy (AES) is defined as a technique that analyzes multiple elements simultaneously by introducing an analyte solution into a ...
[54]
[PDF] Atomic Emission Spectrometry - NanoQAM
Atomic emission spectrometry (AES) uses excited atoms to produce spectra for elemental analysis. Plasma sources are widely used in AES.
[55]
X-Ray Photoelectron Spectroscopy (XPS - SERC (Carleton)
Aug 13, 2021 · X-ray photoelectron spectroscopy (XPS) is a surface sensitive, non-destructive technique used routinely to analyze the outermost ~10 nm (~30 atomic layers) of ...<|separator|>
[56]
X-ray photoelectron spectroscopy: Towards reliable binding energy ...
The purpose of this review is to critically evaluate the status quo of XPS with a historical perspective, provide the technique's operating principles, resolve ...
[57]
Particle‐Induced X‐Ray Emission - Campbell - Wiley Online Library
Oct 15, 2002 · Particle-induced x-ray emission (PIXE) is an elemental analysis technique that employs a mega-electron-volt energy beam of charged particles ...
[58]
Synchrotron-Based X-Ray Fluorescence Microscopy as a Technique ...
Synchrotron-based X-ray fluorescence microscopy (XFM) is a powerful elemental imaging technique now enabling a wide range of studies within plant sciences.
[59]
Elemental and Chemically Specific X-ray Fluorescence Imaging of ...
Aug 7, 2014 · Synchrotron radiation based confocal micro-XRF was employed to unravel the tissue-specific three-dimensional (3D) distribution of metals ...
[60]
[PDF] Gravimetric Analysis
Gravimetric analysis is one of the most accurate and precise methods of macroquan-titative analysis. In this process the analyte is selectively converted to ...
[61]
[PDF] Chapter 8
The accuracy of a total analysis technique typically is better than ±0.1%, which means that the precipitate must account for at least 99.9% of the analyte.
[62]
The Winkler Method - Measuring Dissolved Oxygen - SERC (Carleton)
The Winkler Method is a technique used to measure dissolved oxygen in freshwater systems. Dissolved oxygen is used as an indicator of the health of a water ...
[63]
The principle of Gravimetric Analysis - BYJU'S
It is used to determine the atomic masses of many elements to six-figure accuracy. It provides little room for instrumental error and does not require a ...
[64]
The application of atomic absorption spectra to chemical analysis
1955–1956, Pages 108-117. Spectrochimica Acta. The application of atomic absorption spectra to chemical analysis. Author links open overlay panel. A. Walsh.Missing: seminal paper
[65]
Atomic Absorption Spectroscopy, Principles and Applications
Jan 24, 2024 · Walsh had already realized in the 1950s that the main difficulty of atomic absorption was "that the relations between absorption and ...
[66]
Inductively coupled plasma. Optical emission spectroscopy
Inductively coupled plasma. Optical emission spectroscopy. Click to copy article linkArticle link copied! Velmer A. Fassel ...Missing: original | Show results with:original
[67]
[PDF] Inductively Coupled Plasma Optical Emission Spectrometry
Jun 13, 2008 · Inductively coupled plasma optical emission spectrometry (ICP OES) is a powerful tool for the determination of many elements in a variety of ...
[68]
Inductively coupled argon plasma as an ion source for mass ...
Article December 1, 1980 ... Pollution of water resources and application of ICP-MS techniques for monitoring and management—A comprehensive review.Missing: original | Show results with:original
[69]
Discovery of neutron activation analysis - ScienceDirect.com
It is well known that George Hevesy and Hilde Levi were the original discoverers of neutron activation analysis. However, there were many other researchers ...
[70]
[PDF] Fundamentals and new approaches to calibration in atomic ...
Sep 10, 2019 · Advantages and limitations of the external standard calibration (EC), internal standardization (IS) and standard additions (SA) methods are ...<|control11|><|separator|>
[71]
Traditional Calibration Methods in Atomic Spectrometry and New ...
It consists of adding a reference element called internal standard (IS) to all samples, calibrations standards and the analytical blank, and using the analyte- ...
[72]
LA-ICP-MS imaging in the geosciences and its applications to ...
Jan 5, 2021 · Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) mapping is a rapidly expanding field in the geosciences.
[73]
[PDF] CHNS Elemental Analysers - The Royal Society of Chemistry
Apr 29, 2008 · In its simplest form, simultaneous CHNS analysis requires high temperature combustion in an oxygen-rich environment and is based on the ...
[74]
MICROANALYSIS - Elemental Analysis Method for CHN via CHN/O ...
Mar 5, 2020 · The sample is broken down via combustion in an oxygen atmosphere at 1000°C. At this temperature, the desired elements react with the oxygen to ...
[75]
[PDF] 2400 Series II CHNS/O Elemental Analysis
In the presence of excess oxygen and combustion reagents, samples are combusted completely and reduced to the elemental gases CO2, H2O, N2 and SO2. Users have ...Missing: procedure | Show results with:procedure
[76]
Determination of halogens in organic compounds by ion ...
Determination of halogens in organic compounds by ion chromatography after sodium fusion ... A feasible method for indirect quantification of L-T 4 in ...
[77]
Stoichiometry: Elemental Analysis
The composition of a compound is often expressed in terms of the weight percent of each element in the compound. For example, ethanol has the formula C2H6O. One ...
[78]
TruSpec Micro - CHN/CHNS/O - LECO Corporation
This combustion converts carbon to CO2, hydrogen to H2O, nitrogen to N2, and sulfur to SO2. The combustion gases are swept from the furnace, through scrubbing ...Missing: procedure | Show results with:procedure
[79]
Organic elemental analyzer UNICUBE - Elementar
In just a single analysis the user can simultaneously collect CHN data with the thermal conductivity detector and sub-µg sulfur data with the IR detector.
[80]
Carbon, Sulfur, Oxygen, Nitrogen and Hydrogen Analyzers - HORIBA
The C/S and O/N/H instruments combine electric furnaces and detection systems. Two techniques are used for detection (IR absorption and TCD) depending on the ...Missing: sensors | Show results with:sensors
[81]
DETERMINATION OF ORGANIC OXYGEN - UIC Inc.
The method is generally applicable to organic oxygen. Inorganic forms of oxygen are determined if the components are reduced or oxygen displaced at 1120oC.
[82]
ISO 334:2020
### Summary of the Eschka Method for Sulfur Determination in Coal and Coke (ISO 334:2020)
[83]
[PDF] Thermo Scientific FlashSmart: The Elemental Analyzer
The gas chromatography IC (GC) provides a “real” picture of the analytical process during combustion (CHNS) and pyrolysis (O). GC technique provides you with ...
[84]
[PDF] Elemental Analysis: CHNS Determination of Organic Liquids and ...
For CHNS determination, the FlashSmart Analyzer operates with the dynamic flash combustion of the sample. Liquid samples are injected by a syringe into the ...
[85]
https://tools.thermofisher.com/content/sfs/brochures/SN-42259-OEA-GC-Separation-Method-FlashSmart-SN42259-EN.pdf
[86]
EA - Elemental Analysis Extension | DataApex
EA Extension provides an interactive and automated tool for determining the Carbon, Hydrogen, Nitrogen, Oxygen, and Sulfur (CHNS-O) content of unknowns.
[87]
3.8: Determine Empirical Formula from Combustion Analysis
### Process for Empirical Formula from Combustion Analysis
[88]
Empirical and Molecular Formulas - FSU Chemistry & Biochemistry
(1) For each element, multiply the molecular weight by the percentage composition (expressed as a decimal). (2) Divide each element's answer from (1) by its ...
[89]
[PDF] Spring 2024 CHM 2045 Exam 1 Review - Academic Resources
What is the empirical formula of a compound that is 40% C, 6.71% H, and 53.3% O? What is the molecular formula given that the molar mass is 240.24 g/mol? a ...
[90]
[PDF] Chapter 3 – Composition of Substances and Solutions
1) Confirm the percentages total to 100%. 2) Assume there are 100 g of compound present. (Then the amount of each element present in grams will equal the ...