Arsenic Analysis of Chemical Sample Granules: Testing Methods, Standards, and Applications

Arsenic analysis of chemical sample granules is an essential quality control and regulatory compliance procedure for manufacturers of fertilizers, catalysts, polymer pellets, inorganic salts, and mineral-based products. Because arsenic is a highly toxic, carcinogenic element whose regulatory limits are increasingly set in the low mg/kg or even µg/kg range, accurate determination of total, soluble, and speciated arsenic in particulate chemical materials is critical. This article explains how accredited third-party laboratories handle sampling, digestion, instrumental measurement, and quality control for reliable arsenic testing of granular chemical samples.

Technical Overview

Arsenic (As) is a naturally occurring metalloid that enters chemical products through raw ores, phosphate rock, industrial acids, recycled streams, and process water. Classified as a Group 1 human carcinogen by international health authorities, arsenic is strictly regulated across nearly every chemical value chain, from fertilizers and water treatment chemicals to food-contact polymers, electronic-grade reagents, and catalysts.

Granular and particulate chemical samples present two distinct analytical challenges. First, arsenic is rarely distributed homogeneously within or between particles, so representative sampling and size reduction are as important as the measurement itself. Second, many granular products—fused salts, ceramics, siliceous catalysts, glass frits—are chemically resistant and require aggressive digestion (aqua regia, hydrofluoric acid, or fusion) before instrumental quantification. A valid arsenic result therefore depends on the entire analytical chain: sampling plan, homogenization, digestion, interference-free measurement, and quality control conducted under ISO/IEC 17025-accredited conditions.

Typical regulatory benchmarks illustrate the sensitivity required: the EU Fertilising Products Regulation (EU) 2019/1009 caps arsenic at approximately 40 mg/kg in most fertilizer categories, Chinese national fertilizer standards (GB 38400, GB/T 23349) enforce comparable limits, toy safety standards (EN 71-3, ISO 8124-3) restrict migratable arsenic at sub-mg/kg levels, and food chemical or reagent grade specifications (JIS K 8000 series and equivalent national standards) commonly specify arsenic limits of 1 to 3 mg/kg.

Testing Samples

Inorganic Salts and Industrial Chemicals

Sodium, potassium, calcium, and ammonium salts, pigments such as titanium dioxide and iron oxides, and acids or alkalis in solid form are routinely screened for arsenic as part of reagent grade verification and downstream product certification. High-purity grades often require reporting limits below 0.1 mg/kg, which favors ICP-MS determination.

Fertilizer and Soil Amendment Granules

Phosphate fertilizers, NPK compounds, organic fertilizers, and liming materials are the largest industrial group tested for arsenic, since phosphate rock is a well-known arsenic carrier. Regulatory limits in China, the EU, and other jurisdictions require total arsenic data on a dry weight basis, typically obtained by aqua regia digestion followed by ICP-OES, ICP-MS, or hydride generation techniques.

Polymer and Plastic Granules

PE, PP, PVC, and engineering plastic pellets intended for food contact, toys, or drinking-water applications are analyzed for total arsenic and, where required, migratable arsenic. Microwave digestion with nitric acid (with hydrogen peroxide for carbon-rich matrices) is the standard preparation route.

Catalysts, Adsorbents, and Molecular Sieves

Alumina carriers, zeolites, silica gels, and spent hydrotreating catalysts contain silicon and refractory metals that resist conventional acid attack. Accurate arsenic closure in these matrices demands hydrofluoric acid digestion or alkali fusion, followed by careful matrix matching during measurement.

Ceramic, Glass, and Mineral Raw Materials

Feldspar, quartz, clay, talc, glass frit, and other mineral powders used in ceramics, coatings, and fillers are digested with nitric–hydrofluoric acid mixtures in closed vessels to recover both lattice-bound and adsorbed arsenic.

Water Treatment Chemicals

Aluminum and iron coagulants, flocculants, and disinfectant precursors are tested because process-chemical impurities transfer directly into drinking water. Limits are expressed as maximum contribution to treated water, requiring low-level ICP-MS methodology.

Testing Items

Depending on the regulatory context and the end use of the material, the following arsenic determinations are typically requested for granular chemical samples:

• Total arsenic content, reported in mg/kg on a dry weight basis.
• Water-soluble arsenic, relevant for fertilizers and salts with direct environmental exposure.
• Acid-soluble or aqua regia extractable arsenic, the standard basis for fertilizer and soil-related limits.
• Leachable arsenic, assessed through waste acceptance leaching tests (EN 12457 series) or hazardous waste identification leaching procedures (GB 5085.3).
• Migratable arsenic from polymers and coated materials, per EN 71-3 or ISO 8124-3 toy safety methodologies.
• Arsenic speciation, separating As(III), As(V), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) by HPLC coupled with ICP-MS, important for toxicological assessment and process diagnostics.

Testing Methods

Sampling and Sample Preparation

Representative sampling follows international practice for industrial chemicals (e.g., ISO 8213), combining multiple increments across the lot, followed by riffling or cone-and-quartering. Because arsenic heterogeneity is particle-size dependent, samples are ground to 250 µm or finer—75 µm or finer for visibly heterogeneous materials—using non-contaminating mills (zirconia or agate). Moisture is determined separately at 105 °C so results can be reported on a dry weight basis, and method blanks track any contamination introduced during grinding.

Digestion and Extraction

For total or pseudo-total arsenic, microwave-assisted digestion with aqua regia or nitric acid–hydrogen peroxide (aligned with ISO 12914 and ISO 11466 principles) is the workhorse method, typically using 0.1–0.5 g of sample. Siliceous matrices require the addition of HF, following approaches consistent with ISO 14869-1, with boric acid added afterwards to complex residual fluoride and protect the instrument. Alkali fusion with lithium metaborate is reserved for the most refractory glasses and ceramics. Extraction-based tests (water, dilute acid, or regulated leaching fluids) use milder conditions defined by the applicable EN, GB, or ISO procedure.

ICCP-MS Determination

Inductively coupled plasma mass spectrometry (ISO 17294-2 methodology) is the reference technique for low-level arsenic, achieving method quantification limits of roughly 0.01–0.05 mg/kg in digested solids. Since arsenic is monoisotopic at mass 75, chloride-rich digests are corrected using helium collision mode or oxygen mass-shift (AsO+ at m/z 91) to eliminate the 40Ar35Cl+ polyatomic interference. Germanium is the customary internal standard.

ICP-OES Determination

Inductively coupled plasma optical emission spectrometry (ISO 11885 methodology), monitoring the 188.979 nm or 193.696 nm arsenic lines, is well suited to fertilizer and mineral samples where limits are in the mg/kg range and sample throughput is high. Typical method limits are near 0.5–1 mg/kg in the solid.

Hydride Generation AAS/AFS and Colorimetric Methods

Hydride generation atomic absorption or atomic fluorescence spectrometry remains a robust, cost-sensitive option with detection capability around 0.05–0.2 mg/kg. Arsenic(V) must first be pre-reduced to As(III) with potassium iodide–ascorbic acid in hydrochloric acid before sodium borohydride generates arsine (AsH3). Classical limit tests based on Gutzeit or silver diethyldithiocarbamate colorimetry, still referenced in national reagent specifications such as the JIS K 8000 series and corresponding GB chemical reagent standards, are used for simple pass/fail grade checks.

XRF Screening

Energy-dispersive X-ray fluorescence provides rapid, non-destructive screening of granules and powders at roughly the 5–10 mg/kg level. It is valuable for incoming material checks and contamination triage, but positive or borderline findings are always confirmed by digestion plus ICP-MS or hydride generation, because granular geometry and matrix effects limit XRF accuracy.

Quality Control and Data Integrity

Accredited third-party laboratories operating under ISO/IEC 17025 support each batch with method blanks, laboratory duplicates, matrix spikes (typical acceptance 75–125% recovery), and certified reference materials such as fertilizer, soil, or polymer standards. Control charts, instrument daily optimization, and reported measurement uncertainty provide the documented traceability required for regulatory submissions and export documentation.

Applications

Arsenic data on granular chemical samples directly support compliance, safety, and process decisions across many industries:

• Fertilizer registration, labeling, and export market access under GB 38400, GB/T 23349, and (EU) 2019/1009.
• Raw material qualification and supplier audits for polymer, ceramic, and catalyst producers.
• Food-contact and toy material compliance demonstrating migration below EN 71-3 and ISO 8124-3 limits.
• Hazardous waste classification of spent catalysts, filter media, and process residues using GB 5085.3 and EN 12457 leaching criteria.
• REACH-related substance assessment, safety data sheet refinement, and SVHC screening for arsenic compounds.
• Drinking water treatment chemical certification, where trace impurities in coagulants must not transfer to finished water.
• Contamination investigations, comparing arsenic in finished granules against incoming raw materials, additives, and equipment contact surfaces.

FAQ

How much sample should be submitted for arsenic analysis of granules?

A minimum of 50–100 g of homogenized granular material is recommended; for visibly heterogeneous lots or referee testing, 250 g or more allows the laboratory to perform proper splitting and replicate analysis. Fine, well-milled powders can be accepted in smaller quantities.

What detection limits can be expected?

With ICP-MS after closed-vessel digestion, method quantification limits of 0.01–0.05 mg/kg are routinely achieved. Hydride generation AAS/AFS reaches roughly 0.05–0.2 mg/kg, ICP-OES about 0.5–1 mg/kg, and XRF screening about 5–10 mg/kg.

Why do high-chloride or high-calcium samples need special ICP-MS handling?

Arsenic has only one stable isotope (m/z 75), where 40Ar35Cl+ and 40Ca35Cl+ polyatomic ions overlap. Collision-mode helium kinetic energy discrimination or oxygen mass-shift to m/z 91 resolves this interference and prevents false positives in salt- and chloride-rich digests.

Which digestion is correct for silica-rich catalysts and ceramic granules?

Nitric–hydrofluoric acid microwave digestion, with post-digestion boric acid complexation, recovers lattice-bound arsenic in aluminosilicates, zeolites, and glass frits. Aqua regia alone under-recovers arsenic in these matrices and is only appropriate for total-recovery matrices like salts, fertilizers, and polymers.

What is the difference between total and leachable arsenic?

Total (or aqua regia extractable) arsenic measures how much arsenic exists in the particle, reported in mg/kg. Leachable arsenic measures what dissolves under a defined extraction fluid—such as the GB 5085.3 procedure or EN 12457 compliance tests—and is expressed in mg/L, which is the basis for waste classification and environmental release assessment.

How long does arsenic testing take?

Standard total arsenic analysis by ICP techniques is typically completed within 5–10 working days, including digestion batch QC. Speciation by HPLC-ICP-MS and fusion digestion of refractory matrices may require additional time and should be confirmed with the laboratory in advance.