Pentavalent antimony (Sb(V)) is a trace elemental impurity of increasing regulatory concern in cosmetics, since antimony and its compounds are prohibited as intentional ingredients in the EU and China and only technically unavoidable traces are tolerated. This article explains the professional laboratory methods used to determine Sb(V) and total antimony in cosmetic products, including mild extraction, HPLC-ICP-MS speciation, ICP-MS/ICP-OES digestion analysis, and hydride generation atomic fluorescence spectrometry, together with detection limits, quality-control requirements, and compliance applications.
Technical Overview
Antimony (Sb, CAS 7440-36-0) is a toxic metalloid that occurs in the environment and in consumer products mainly as two inorganic oxidation states: trivalent antimony, Sb(III), and pentavalent antimony, Sb(V). Antimony and its compounds are listed as prohibited cosmetic ingredients in the EU (Regulation (EC) No 1223/2009, Annex II) and in China's Safety and Technical Standards for Cosmetics (2015 Edition), meaning they must never be added intentionally, while only technically unavoidable traces from raw materials, process water, equipment, or packaging are tolerated. Industry screening values for such traces are typically in the range of 0.5–1 mg/kg for total antimony, in line with the reference levels cited in the SCCS Notes of Guidance and comparable national practice.
Speciation, not just total content, is scientifically important. In oxygenated, near-neutral aqueous systems such as lotions, toners, and shampoos, pentavalent antimony exists predominantly as the antimonate complex Sb(OH)6−, which is highly soluble, mobile, and potentially bioaccessible. Although Sb(III) is generally the more acutely toxic form, Sb(V) often represents the dominant leachable fraction that can migrate from packaging or dissolve from mineral-based colorants. Measuring the Sb(III)/Sb(V) distribution therefore provides far more meaningful information for exposure assessment and root-cause investigation than a single total-antimony figure.
Typical sources of antimony contamination in cosmetics include mineral fillers and pigments (talc, mica, clays, iron oxides, ultramarines), low-grade titanium dioxide, process water, and antimony trioxide catalyst residues that can leach from PET packaging into aqueous formulations. A robust testing strategy therefore combines total antimony determination after digestion with species-preserving extraction and chromatographic separation.
Testing Samples
Leave-On Skin and Lip Products
Creams, lotions, serums, sunscreens, lipsticks, and lip glosses are high-priority matrices because residues remain on the skin or may be incidentally ingested. Lip products with mineral pigments and petroleum-wax bases typically require 0.5–1 g of homogenized sample per determination, and at least three retail units should be submitted to account for batch heterogeneity.
Color Cosmetics and Powder Products
Eyeshadows, pressed powders, blushes, foundations, and mineral makeup frequently contain talc, mica, and synthetic fluorphlogopite substrates that can carry antimony impurities. Powder samples are homogenized by coning and quartering; siliceous matrices may require hydrofluoric acid digestion when total antimony verification is needed. Powder inhalation exposure also makes speciation-relevant, water-extractable antimony data valuable.
Rinse-Off and Aqueous Products
Shampoos, body washes, cleansers, toners, and sheet-mask essences are usually packaged in PET bottles, where residual antimony catalyst can migrate into the product over shelf life. These low-viscosity, water-rich matrices are the simplest for Sb(V) determination because mild aqueous extraction preserves the native speciation well.
Raw Materials and Packaging Materials
Supporting programs cover pigments and lakes, talc and mica powders, titanium dioxide, glycerin, process water, and PET bottle preforms or finished containers. Packaging migration testing fills the container with a simulated aqueous product and stores it under accelerated conditions (for example, 40 °C for 10–30 days) before measuring dissolved Sb(V).
Testing Items
Accredited third-party laboratories typically offer the following test items for antimony in cosmetics, with method limits of quantification (LOQ) in the range of 0.005–0.01 mg/kg for speciation work:
- Pentavalent antimony, Sb(V), expressed as mg/kg of antimony in the finished product
- Trivalent antimony, Sb(III), the companion species separated in the same chromatographic run
- Speciation distribution: the Sb(III):Sb(V) ratio and the percentage of total antimony present as Sb(V)
- Total antimony after closed-vessel microwave digestion (regulatory screening parameter)
- Water-extractable or leachable antimony, relevant to migration and bioaccessibility studies
- Mass-balance verification: sum of extracted species versus digested total, with acceptable recovery typically 80–120%
Testing Methods
Species-Preserving Sample Preparation
Speciation analysis begins with a mild extraction designed to avoid changing the oxidation state of antimony. A typical protocol homogenizes 0.2–0.5 g of sample with 10 mL of 20–50 mmol/L EDTA solution (or an ammonium tartrate buffer), sonicates for 30–60 minutes at ambient temperature, then centrifuges and filters through a 0.22–0.45 µm membrane. EDTA complexes Sb(III) and prevents its oxidation to Sb(V) during handling. Strong mineral acids, oxidants, and elevated temperatures are strictly avoided; extracts are protected from light, held at 4 °C, and analyzed within 24–48 hours.
HPLC-ICP-MS Speciation (Primary Method)
The reference technique for Sb(V) is anion-exchange high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry. A polymeric strong-anion-exchange column (PRP-X100 type) is operated isocratically with an EDTA-based mobile phase at pH 4.5–5.0 and about 1.0 mL/min, under which Sb(V) elutes as the antimonate anion before the EDTA-complexed Sb(III), with chromatographic resolution Rs ≥ 1.5. The ICP-MS detector monitors m/z 121 and 123 for antimony, with tellurium or rhodium as internal standard. Instrument detection limits reach 0.02–0.1 µg/L per species, translating to sample-based LOQs of roughly 0.005 mg/kg. Species identification is confirmed by retention-time matching within ±2% against standards prepared in the same extraction buffer.
Total Antimony by Digestion and ICP-MS or ICP-OES
For regulatory screening of total antimony, 0.2–0.5 g of sample undergoes closed-vessel microwave digestion with nitric acid and hydrogen peroxide (adding hydrofluoric acid only for siliceous matrices such as talc and mica). Quantification follows the instrumental principles of ISO 17294-2 (ICP-MS) or ISO 11885 (ICP-OES), using 121Sb with interference checking on 123Sb and matrix-matched or standard-addition calibration for high-organic matrices such as lipsticks. Digested-total data also serve as the mass-balance benchmark for the speciation extraction.
Hydride Generation Atomic Fluorescence Spectrometry (HG-AFS)
As a cost-effective alternative for total antimony at trace levels, HG-AFS follows the approach of ISO 17378 for water-quality determination. Sb(V) is first pre-reduced to Sb(III) using a thiourea–ascorbic acid or potassium iodide–L-cysteine system; sodium borohydride in hydrochloric acid then generates stibine, which is atomized and measured by atomic fluorescence. Detection limits below 0.1 µg/L are achievable, making the technique well suited to high-throughput screening, provided the matrix does not suppress hydride formation.
Quality Control and Method Validation
Testing is performed within an ISO/IEC 17025 quality framework. Each batch includes reagent blanks, duplicate samples (relative deviation <10%), matrix spikes at relevant levels with 80–120% recovery, and certified reference materials where available. Calibration uses at least five points with r² ≥ 0.999, retention-time stability within ±2%, and reported results carry an expanded measurement uncertainty generally below 25%.
Applications
Pentavalent antimony testing supports multiple points in the cosmetics quality and compliance chain:
- Product registration and notification dossiers, where safety assessments must demonstrate that antimony traces comply with prohibited-substance requirements
- Verification of supplier certificates of analysis for mineral pigments, talc, mica, and titanium dioxide before production release
- Packaging safety evaluation, quantifying Sb(V) migration from PET containers over accelerated and real-time shelf-life studies
- Root-cause investigation when total-antimony screening flags an out-of-specification batch, distinguishing raw-material input from packaging or equipment contribution
- Children's cosmetics and sensitive-category risk assessments, where water-extractable and speciated data strengthen the exposure evaluation
- Stability and post-market surveillance programs for water-rich products stored in antimony-containing plastics
FAQ
Why measure Sb(V) separately instead of only total antimony?
Total antimony tells you how much is present, but not how it behaves. Sb(V) is the dominant soluble, mobile species in aqueous cosmetics and the primary form that leaches from PET packaging; the Sb(III):Sb(V) ratio helps identify contamination sources and supports a more accurate exposure assessment.
What detection capability and sample quantity are required?
HPLC-ICP-MS speciation typically achieves an LOQ of about 0.005–0.01 mg/kg, well below the 0.5–1 mg/kg screening values commonly applied. A practical submission is 5–10 g of finished product (or the equivalent retail units) plus a completed application form; only 0.2–0.5 g is consumed per determination, with the remainder retained for confirmation.
How is interconversion between Sb(III) and Sb(V) prevented during testing?
Laboratories use EDTA-buffered mild extraction at ambient temperature, avoid oxidizing acids, protect extracts from light, and analyze within 24–48 hours. Method validation includes analyzing species-spiked matrix samples through the full procedure to demonstrate that species recovery falls within the 80–120% acceptance window.
What regulatory limits apply to antimony in cosmetics?
Antimony and its compounds are prohibited as intentional ingredients in the EU and China, and appear on comparable prohibited lists in other jurisdictions. Traces must be technically unavoidable and kept as low as reasonably achievable; industry screening values of approximately 0.5 mg/kg (SCCS-referenced) to 1 mg/kg total antimony are widely used, with Sb(V) reported as a constituent portion of that total.
How long does testing take, and can difficult matrices be handled?
Standard turnaround is typically 7–10 working days, with express service in 3–5 days available for urgent cases. Waxy lipsticks, high-silica powders, and heavily pigmented products are handled through extraction optimization, standard-addition calibration, and, where total-antimony confirmation is needed, digestion protocols appropriate to siliceous matrices.
