The Determination of Metals in Cosmetics
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APPLICATION NOTE ICP-Mass Spectrometry Authors Zoe Grosser, Ph.D. Lee Davidowski, Ph.D. Laura Thompson PerkinElmer, Inc. Shelton, CT 06484 USA Introduction The Determination of Cosmetics of one form or another have been used since the beginning of time. Metals in Cosmetics The U.S. Food and Drug Administration (FDA) defines today’s cosmetics as: “1. articles intended to be rubbed, poured, sprinkled, or sprayed on, introduced into, or otherwise applied to the human body or any part thereof for cleansing, beautifying, promoting attractiveness, or altering the appearance, and 2. articles intended for use as a component of any such articles; except that such term shall not include soap.” 1 The U.S. FDA has not regulated metals in cosmetics except in the case that zirconium is prohibited in aerosol preparations and mercury can only be used (generally as a preservative) when no other alternative is possible. They do have the authority to protect consumers against contamination deemed to be deleterious to health. Proposition 65 in California requires notice when concentrations in a product may cause exposure to hazardous components exceeding a prudent level. A letter from the Attorney General of the State of California discusses the level of concern and calculates that based on documented lipstick use, a concentration of 5 mg/kg would be the level of concern requiring listing.2 The regulations in Canada include statements about heavy metals, and although low concentrations may be difficult to avoid, concentrations above the levels listed in Table 1 (Page 2) require special scrutiny. Measurements in this work are performed using ICP-MS. Table 1. Canadian metal concentrations of concern in Elements chosen for examination are commonly considered cosmetics.3 to be toxic, although there are others that might be consid- Metal Concentration (mg/kg) ered hazardous as well, such as antimony, included on the Lead 10 Canadian list. Arsenic 3 Cadmium 3 Experimental Mercury 3 Samples of a variety of commercially available lipsticks (Figures 1 and 2), nail polishes, and skin creams (for evening Antimony 5 tone, lightening age spots) were purchased and prepared in duplicate. Nail polishes were painted onto tared weighing The European Union (EU) has also developed a list of more paper and allowed to dry before weighing into the digestion than 1000 compounds that are banned for use in cosmetic vessel (Figures 3 and 4). Microwave digestion was used manufacturing. They further limit the amount of these (Multiwave™ 3000, PerkinElmer®, Shelton, CT USA) to obtain compounds that may be found naturally-occurring in the clear solutions. Six mL of nitric and 0.5 mL of hydrofluoric product. For example, strontium peroxide may be found in acid (GFS Chemical™, Columbus, OH USA) were added to rinse-off hair care preparations, but is limited to containing PTFE vessels with approximately 0.3-0.5 g of sample and the less than 4.5% as strontium in the ready-to-use product.4 digestion program shown in Table 2 applied. The samples were ® Examining the notices of recall in the U.S. for products then transferred and diluted to 50 mL with ASTM Type I manufactured in various parts of the world show that a water. The samples were fairly homogeneous and in number of items which have been recalled are cosmetics. a form that allowed a representative sample to be easily For example, skin whitening cream from several Caribbean taken. If the samples were solids, grinding, blending or other countries was put on an import alert because the level of procedures might be necessary to ensure a more homogeneous mercury measured in the product was 8%.5 Another alert sample to be measured. Preparing replicate samples will allow was issued for eye colors including Kohl, Kajal, or Surma. us to evaluate if our homogeneity assumption is accurate. In addition to being an unapproved coloring agent, the material was found to contain lead (Pb). There has also been Table 2. Microwave digestion program. recent concern about lead in lipstick, uncovered through Step Power Ramp Hold Fan 6 testing. The U.S. FDA has not recalled lipstick and states 1 750 10:00 10:00 1 they will do further testing.7 The guidance mentioned for 2 1200 10:00 10:00 1 lead relates to the limited guidance available for food, where a letter stating that 0.1 mg/kg of Pb in candy is the 3 0 15:00 3 maximum tolerable limit for acceptable children’s exposure. An ELAN® DRC-e ICP-MS (PerkinElmer, Shelton, CT USA) This application note will evaluate the levels of several was used for measurement of chromium, cadmium, lead, heavy metals in lipstick, nail polish and skin cream. Based mercury, arsenic, selenium, and antimony. The instrumental on candy guidance in the U.S. and the limits set in Canada, conditions are shown in Table 3 (Page 3). Mercury was also either graphite furnace atomic absorption (GFAA), inductively measured using the SMS 100 Mercury Analyzer (PerkinElmer, coupled plasma optical emission spectroscopy (ICP-OES), Shelton, CT USA) which uses a combustion system, requiring or inductively coupled plasma mass spectrometry (ICP-MS) no sample preparation and generating no waste. Instrumental would be appropriate, based on the amount of sample conditions are shown in Table 4 (Page 3). taken for digestion and the final volume of solution. Figure 1. A variety of commercially- Figure 2. Lipstick was weighed prior Figure 3. Nail polish was dried on Figure 4. The nail polish and tared available lipsticks were analyzed. to microwave digestion. tared paper before digestion. paper were weighed into the digestion vessel. 2 Table 3. ICP-MS instrumental conditions. Table 4. Mercury system instrumental conditions. Nebulizer Quartz Concentric Parameter Spray Chamber Quartz Cyclonic Dry 400 °C for 200 s RF Power 1500 W Decomposition 800 °C for 350 s Integration time 1000 ms (per analyte) Catalyst 600 °C Replicates 3 Catalyst wait period 60 s Reaction Gas for arsenic O2 = 0.6 mL/min Gold trap 600 °C for 30 s RPq for arsenic as 91 AsO 0.5 Measurement 100 s Oxidant gas flow 350 mL/min Arsenic analysis employed cell technology to remove the chloride interference arising from either natural chlorine Results and Discussion content, salt added to a supplement material or hydrochloric acid used in sample preparation, which can degrade the Sample preparation is an important contributor to the detection limit. This cell allows a gas to react with the results, especially when it influences the consistency and sample, and under controlled conditions, the interference is information provided by the results. An article by several chemically separated from the analyte. Figure 5 shows how researchers, including the U.S. FDA, discussed the need the Dynamic Reaction Cell™ (DRC™) operates. Detection for a small amount of hydrofluoric acid (HF) in the digest limits are improved compared to other approaches and the to ensure better consistency and recovery of all the metal, precision in varying matrices is more consistent. An instrument including that which might be protected from other acid detection limit for arsenic measured in 1000 mg/L NaCl was attack by a silica particle.9 The question always becomes: shown to be 2.3 ng/L, comparing favorably to detection is it better to report the total metal content or the portion limits of 0.6-1.8 ng/L, measured in 1% nitric acid solution, that might be bioavailable? Even if lipstick is consumed and using this technique.8 exposed to hydrochloric acid in the digestion process, lead enclosed in silica particles will not be released and is there- fore unable to cause harm. The digestion here used HF and therefore reports a total metal value with more confidence, although it may not be all bioavailable. Several performance criteria were evaluated to ensure the method was operating as expected and the sample prepara- tion had been performed correctly. Table 5 (Page 4) shows the results for NIST® reference material Typical Diet (1548a) digested at the same time as the cosmetics, using the same conditions and acids. Although Typical Diet is not a cosmetic matrix, it has some of the same components. The fat content may not be comparable to all of the skin cream or lipstick Figure 5. Dynamic reaction cell (DRC) operates with the PerkinElmer ELAN® ICP-MS to react and remove interferences without allowing types, depending on their formulation. competing reactions to add other interferences. The mass for selenium measurement was chosen to avoid interference from calcium, which may be present in cosmetics. Since this work was completed, the NexION® 300 ICP-MS has been introduced by PerkinElmer, Inc. and performance is expected to be the same or better than the ELAN DRC-e ICP-MS. 3 Table 5. NIST® 1548a Typical Diet certified reference material. Element and Mass 1548a – 1 (mg/kg) 1548a – 2 (mg/kg) Average (mg/kg) Certificate Value % Rec Cr 52 0.135 0.118 0.127 – Cd 111 0.036 0.038 0.037 0.035 106 Hg 202 < DL < DL 0.005* Pb 208+207+206 0.045 0.046 0.046 0.044 104 Se 82 0.231 0.251 0.241 0.245 98.4 AsO 91 0.183 0.192 0.188 0.20 93.8 Prepared at the same time as the cosmetics, using the same procedure. * Informational value, not certified. Recoveries of the certified values were within ±20%, indicating acceptable performance. Table 6. Estimated detection limits in the solid cosmetic. Element and Mass µg/g Detection limits were estimated from digested blanks run Cr 52 0.044 during the analysis. The standard deviation was multiplied by three and adjusted by the dilution of the solid during Cd 111 0.00069 digestion to give an estimate in the original cosmetic material.