APPLICATION NOTE ICP-Optical Emission Spectroscopy Authors: Lori Foglio Lee Davidowski Ken Neubauer PerkinElmer, Inc. Shelton, CT Meeting the USP <232>/<233> Regulation for Elemental Introduction Impurities in Pharmaceutical The U.S. Pharmocopeia is in the process of revising the analytical Products with ICP-OES protocols for the analysis of metals in pharmaceutical products. A detailed summary of the methodology and the changes is available1, so only a brief description will be given here. The new methods that will be enacted are USP Chapters <232> and <233>, which deal with inorganic content in pharmaceutical products that enters the body through consumption, inhalation, or injection directly into the blood stream. With the exception of large volume parenterals, the upper concentration limits of inorganic elements which can enter the body are based on a maximum permissible daily exposure (PDE) – these are defined in Chapter <232> and shown in Table 1 for orally consumed medications. Table 1. USP <232> Oral Permissible Daily Exposure of Inorganic Elements in Drug Products Element Oral PDE (µg/day) Cadmium (Cd) 5 Lead (Pb) 5 Inorganic Arsenic (As) 15 Inorganic Mercury (Hg) 15 Iridium (Ir) 100 Osmium (Os) 100 Palladium (Pd) 100 Platinum (Pt) 100 Rhodium (Rh) 100 Ruthenium (Ru) 100 Molybdenum (Mo) 180 Nickel (Ni) 600 Vanadium (V) 120 Copper (Cu) 1300 However, ICP-OES is also an appropriate analytical technique for medications with low daily doses, such as allergy, blood pressure, and sleep-aid medicines. In addition, since ICP-OES can handle higher levels of dissolved solids than ICP-MS, samples do not need to be diluted as much. This combination of low daily doses and smaller dilutions allows ICP-OES to meet the USP <232>/<233> criteria for a variety of medications. To analytically determine a person’s exposure to the elements in Table 1, the maximum dose of the medication must be taken into account, as well as the dilution factor used in sample preparation prior to analysis. USP <232>/<233> defines this level as the “J” value, which is determined with the following formula: J= PDE Maxium Daily Dose * Dilution Factor where: PDE = maximum permissible daily exposure in µg/g Since ICP-MS has very high sensitivity, it is the most applicable technique to meet the requirements of USP <232>/<233> as it can measure the low concentrations from medications with high daily doses and large dilution factors, which result in lower J values. Maximum Daily Dose = the maximum dose of the medicine, in grams Dilution Factor = the dilution factor used in sample preparation for analysis From this equation, it is evident that the J value will vary by medication, with larger daily doses (such as analgesics and cold remedies) having much smaller J values than medications with smaller daily doses (such as allergy and blood pressure medications). When considering an appropriate analytical technique to meet the requirements of USP <232>/<233>, the medication must be considered. This work demonstrates that the PerkinElmer Optima® 8300 ICP-OES can meet the USP <232>/<233> requirements for medicines with low daily doses, focusing on over-the-counter allergy and antacid medications. Although a wide variety of prescription medications would also be appropriate for ICP-OES, these were not analyzed due to difficulty in attaining samples. It should also be noted that analyses for osmium were not performed due to safety concerns regarding the formation of OsO4 gas and its safe disposal. Experimental Samples and Sample Preparation All medications in this work were purchased at local stores and selected for their low maximum daily doses: 1-2 tablets/day. All sample digestions were done in a PerkinElmer Titan MPS™ Microwave Sample Preparation System using low-pressure vessels. A single tablet of each medication (0.1 – 0.3 g) was added to a digestion vessel, followed by 5 mL of concentrated nitric acid, 2 mL of 30% H2O2, and analyte spikes, as required. The vessels sat uncapped in a fume hood for ten minutes and were then placed into the microwave and digested according to the program in Table 2. After completion, the contents of the digestion vessels were transferred to autosampler tubes and diluted to the appropriate volume with 18 MΩ deionized water. The appropriate dilution factor depended on the medication being analyzed. An advantage of ICP-OES compared to ICP-MS is its ability to handle high levels of total dissolved solids, which allow for smaller dilutions. The internal standard (Y, 100 μg/L) was added to all standards and samples, post-digestion. Calibration standards were made in 15% (v/v) nitric acid to match the acid content of the samples. Table 2. Titan MPS Microwave Digestion Program 2 Step Temperature (°C) Pressure (bar) Ramp (min) Hold (min) Power (%) 1 140 30 5 10 70 2 190 30 5 20 90 3 50 30 1 10 0 Instrumental Parameters All analyses were done on an Optima 8300 ICP-OES operating in axial view mode. The instrumental parameters used are displayed in Table 3, while the elements and wavelengths are shown in Table 4. To aid with method development, Universal Data Acquisition2 was used to help identify interferences. Table 3. Instrumental Parameters Results and Discussion Table 5 shows the medications evaluated in this work and their associated J values. Table 5. Elements and Associated J Values for the Medicines Studied Element Allergy Relief-1* (µg/L) Allergy Relief-2* (µg/L) Acid Reducer (µg/L) 67 Cd 170 170 Parameter Value Pb 170 170 67 Instrument Optima 8300 ICP-OES As 500 500 200 Nebulizer SeaSpray Hg 500 500 200 3300 3300 1300 Glass cyclonic, unbaffled Ir Sample Uptake Rate 1.5 mL/min Pd 3300 3300 1300 Nebulizer Gas Flow 0.55 L/min Pt 3300 3300 1300 Plasma Gas Flow 10 L/min Rh 3300 3300 1300 Auxiliary Gas Flow 0.2 L/min Ru 3300 3300 1300 1500 W Mo 6000 6000 2400 Axial Ni 20000 20000 7900 V 4000 4000 1600 Cu 43000 43000 17000 Spray Chamber RF Power Plasma View Mode Table 4. Elements and Wavelengths Element Wavelength (nm) Cd 226.502 Pb 220.353 As 188.979 Hg 194.168 Ir 224.268 Pd 340.458 Pt 265.945 Rh 343.489 Ru 240.272 Mo 202.031 Ni 221.648 V 290.880 Cu 327.393 * Two different formulations of the same allergy relief medicine were studied. Both contained the same level of active ingredient and daily dosage – only the inactive ingredients and tablet size differed. Calibration curves were constructed with a blank and two calibration standards with concentrations of 0.5J and 2J, as specified in USP Chapter <233>. All calibration curves gave linear regressions > 0.9999. To meet the repeatability requirements of USP <233>, six separate tablets of the same medication were digested with a spike at the J value. Tables 6 and 7 show the results for the allergy and acid reducer medicines; all have relative standard deviations significantly less than the 20% criteria defined in the method. (It should be noted that none of the elements in the method were detected in any of the unspiked tablets.) Table 6. Results for Analysis of Six Separate Acid Reducer Tablets Element Tablet 1 (µg/L) Tablet 2 (µg/L) Tablet 3 (µg/L) Tablet 4 (µg/L) Tablet 5 (µg/L) Tablet 6 (µg/L) %RSD Cd 70.8 69.7 70.5 69.6 69.2 69.8 0.9 Pb 68.7 71.3 64.7 66.7 66.6 69.4 3.5 As 203 203 204 200 199 203 1.0 Hg 181 188 182 183 185 185 1.2 Ir 1450 1450 1440 1450 1450 1450 0.5 Pd 1380 1300 1320 1290 1300 1300 2.6 Pt 1270 1260 1260 1270 1270 1270 0.5 Rh 1290 1280 1280 1300 1280 1290 0.5 Ru 1290 1280 1270 1290 1290 1280 0.4 Mo 2380 2350 2350 2350 2360 2360 0.6 Ni 8170 8160 8080 8160 8200 8180 0.5 V 1660 1660 1650 1660 1670 1670 0.4 Cu 19200 19700 19000 19300 19500 1950 1.3 3 Table 7. Results for Analysis of Six Separate Allergy Relief Tablets Element Tablet 1 (µg/L) Tablet 2 (µg/L) Tablet 3 (µg/L) Tablet 4 (µg/L) Tablet 5 (µg/L) Tablet 6 (µg/L) %RSD Cd 171 172 170 170 168 172 0.9 Pb 167 165 168 169 164 168 1.2 As 497 508 501 496 490 502 1.3 Hg 498 508 500 498 494 507 1.1 Ir 3390 3390 3420 3380 3360 3430 0.7 Pd 3510 3470 3430 3420 3390 3500 1.4 Pt 3310 3300 3260 3260 3240 3300 0.9 Rh 3230 3230 3200 3170 3160 3240 1.0 Ru 3300 3290 3270 3260 3230 3310 0.9 Mo 6330 6340 6290 6270 6200 6330 0.8 Ni 20000 20100 20200 20000 19900 20300 0.7 V 4030 4040 4070 4020 4000 4070 0.7 Cu 44900 45100 44800 44500 44000 45000 0.9 To determine the ruggedness of the method, samples were analyzed on three separate days, and the results compared. Table 8 shows the relative standard deviations from a three-day analysis of both the acid reducer and allergy relief medications, all of which are well below the USP <233> requirement of 25% RSD over three days. Table 8. RSDs for Acid Reducer and Allergy Relief Tablets Over Three Days Element Acid Reducer % RSD over Three Days Allergy Relief % RSD over Three Days Cd 1.1 0.4 Pb 1.4 0.2 As 1.6 1.1 Hg 3.2 0.8 Ir 1.7 0.8 Pd 7.7 1.2 Pt 1.2 0.5 Rh 2.3 3.7 Ru 0.3 0.8 Mo 0.5 0.2 Ni 1.2 0.5 V 1.5 0.4 Cu 0.9 0.9 The accuracy of the method was assessed by determining pre-digestion spike recoveries of 0.5J and 1.5J, as specified in the method. Table 9 shows the recoveries for the acid reducer and allergy medicines, all well within the 70-150% window specified in the method. Table 9. Spike Recoveries (%) for Acid Reducer and Allergy Medicines Acid Reducer 0.5J 1.5J Allergy Relief 0.5J 1.5J Cd 100 99.2 98.3 92.3 Pb 98.0 100 101 97.6 As 104 97 96.4 95.5 Hg 92.4 93.5 104 97.8 Ir 108 112 105 95.8 Pd 91.7 96.6 102 98.0 Pt 101 97.5 100 99.2 Rh 94.9 96.9 101 98.0 Ru 94.3 98.9 106 108 Mo 94.3 97.1 103 96.3 Ni 99.2 99.0 99.1 94.0 V 99.7 99.3 98.3 94.8 Cu 108 110 101 95.0 Element Conclusion This work has demonstrated that the Optima 8300 ICP-OES from PerkinElmer can meet and exceed the requirements of USP Chapters <232>/<233> for medications with low daily doses, as demonstrated with allergy relief and acid reducer tablets. The ability of ICP-OES to handle high levels of dissolved solids allows for minimal dilution of the samples. These low dilution factors, combined with low daily doses, allow ICP-OES to meet the USP <232>/<233> criteria for a variety of medications. References 1. “Implementation of USP New Chapters <232> and <233> on Elemental Impurities in Pharmaceutical Products”, PerkinElmer Inc., 2014 2. “Universal Data Acquisition on the Optima ICP-OES”, PerkinElmer Inc., 2009-2014 PerkinElmer, Inc. 940 Winter Street Waltham, MA 02451 USA P: (800) 762-4000 or (+1) 203-925-4602 www.perkinelmer.com For a complete listing of our global offices, visit www.perkinelmer.com/ContactUs Copyright ©2014, PerkinElmer, Inc. All rights reserved. PerkinElmer® is a registered trademark of PerkinElmer, Inc. All other trademarks are the property of their respective owners. 011799_01