JOURNAL OF COSMETIC SCIENCE 408 melting and mixing together eleven tubes of lipstick (same brand and shade, but several lot numbers). These lipsticks were placed in a beaker submerged in a water bath at 85°C and stirred with a propeller-type mixer. Initial attempts to completely dissolve a lipstick sample using typical microwave- assisted HNO3 digestion were unsuccessful. A cloudy, white suspension remained after the treatment. Also, replicate results for a single lot of lipstick showed variations in Pb recovery for different lipstick portion sizes and maximum digestion temperatures (see Table I). The portion size and temperature effects on Pb recovery suggested that microwave-as- sisted digestion with HNO3 was incomplete for Pb and that levels of Pb recovered would vary depending on digestion parameters. Therefore, other preparation procedures were investigated that might achieve total recovery of Pb. A dry ash procedure was tried in which a lipstick sample was heated gradually to 540°C and held at that temperature for an hour. The resulting residue was treated with HNO3 and HCl but would not com- pletely dissolve. The acid leachate was diluted with water and analyzed by ICP–MS. Results were variable and lower compared to values obtained with microwave-assisted acid diges- tion. Similarly, sodium carbonate fusion at 1075°C resulted in a residue that would not completely dissolve in HNO3 or HCl and produced variable values for Pb. The results indicated that some Pb must be associated with the undissolved refractory mineral matter in the lipsticks and suggested that HF would be necessary to break down the minerals. Based on work of other investigators (10), the initial HF dissolution procedure used 0.3-g portions of lipstick, 7 ml HNO3 + 2 ml HF, and sealed Tefl on microwave digestion ves- sels. A two-step procedure was used for digestion. The vessels were heated to 130°C over 15 minutes and held at that temperature for three minutes before ramping to 200°C over 15 minutes and holding for an additional 30 minutes. The vessels were allowed to cool to 50°C and then were vented. Initially 6 ml of 4% boric acid was then added to each vessel and the solutions were heated to 170°C over 15 minutes and held for ten minutes to complex the HF. Boron forms a strong complex with fl uoride according to the reaction shown in equation 1. After cooling and venting, the solutions were diluted to a fi nal vol- ume of 200 ml for ICP–MS analysis. However, the digests were still cloudy, with a ge- latinous precipitate appearing upon centrifugation. Also, results varied depending on the analytical portion. Equation 1 is as follows: 4HF + B(OH)3 → HBF4 + 3H2O (1) Therefore, an excess of boric acid was used to dissolve any insoluble fl uorides. The revised HF digestion procedure used 30 ml of 4% boric acid and resulted in clear solutions for all Table I Analytical Portion and Temperature Effects on Pb Determined After Digestion with Nitric Acid Portion size (g) Maximum digestion temperature (°C) μg Pb/g 0.3 240 1.4 0.1 240 2.1 0.3 200 0.5

DETERMINATION OF TOTAL LEAD IN LIPSTICK 409 lipstick samples and no variation in ICP–MS values for lipstick portion sizes ranging from 0.1 to 0.4 g (see Figure 1). The fi nal method parameters are outlined in Table II. For each lipstick sample, duplicate portions and portions fortifi ed at 0.5 and 1.0 μg Pb/g were digested. A Pb solution in 1% HNO3 was used for fortifi cation. Each digestion batch of 12 vessels also included a blank, a blank + 0.02 μg Pb/g, an organic Pb RM (0.100 μg Pb/g in base oil 20), and an RM with mineral content (estuarine stediment, SRM 1646a). RESULTS METHOD VALIDATION Accuracy of the method was demonstrated by measuring recoveries of Pb from RMs and from fortifi ed lipstick samples. Since no lipstick-type RM was available, several RMs were analyzed representing varying matrix types. NIST 1635 trace elements in coal (complex matrix, organics) NIST 8435 whole milk powder (high fat matrix) NIST 1084a wear metals in oil and SPEX ORG-PB8-2Y/Z lead in base oil 20 (oily matrices Figure 1. Portion size effect before and after adding excess boric acid. Table II Final Method Parameters ● 0.3-g lipstick portion ● 2 ml HF + 7 ml HNO3 ● CEM XP-1500+ vessels, MARS Microwave Digestion System ● Heat in two steps to 200°C, hold for 30 min: Stage Power (watts) Ramp (min) Pressure (psi) Temperature (°C) Hold (min) 1 1200 15:00 0800 130 3:00 2 1200 15:00 0800 200 30:00 ● Cool to 50°C, vent, add 30 ml 4% boric acid ● Heat to 180°C, hold for 10 min ● Dilute to 200 ml