a p p l i c at i o n N o t e Atomic Absorption Authors: Lee Davidowski, Ph.D. Lorraine Foglio PerkinElmer, Inc. Shelton, CT 06484 USA The Determination of Minerals and Metals in Multi-Mineral/MultiVitamin Tablets by Flame Atomic Absorption Spectroscopy Introduction There are many mineral dietary supplements available in today’s marketplace to ensure that mineral deficiencies do not occur in one’s diet. The mineral content of these products must be verified for quality control (QC) purposes. Furthermore, the Nutritional Labeling and Education Act of 1990 mandates accurate labeling of all food supplements sold in the U.S. which means accurate testing of the products is mandatory. In many labs, this task is accomplished by the technique of flame atomic absorption spectroscopy (FAAS). FAAS has the advantages of lower initial cost, low cost per analysis, and requires less operator training than many other trace elemental techniques. The objective of this work is to demonstrate the applicability of FAAS using the PerkinElmer® PinAAcle™ 900T to accomplish this task. Seven elements are determined in two commercially available multi-mineral tablets, a NIST® Standard Reference Material, and a commercial reference material which simulates a mixed food diet. Experimental Instrumentation The PinAAcle 900T flame and longitudinal Zeeman furnace atomic absorption spectrometer controlled by WinLab32™ for AA software, running under Microsoft® Windows® 7, was used for all analyses (PerkinElmer, Inc., Shelton, CT). A high-sensitivity nebulizer (Part No. N3160112) with a spacer was employed. Single-element Lumina™ hollow cathode lamps (HCLs) were used and the instrumental operating conditions for each element in this application are shown in Table 1. A four-second integration time and three replicates were used for all elements. approximately one hour and warmed, not to boiling, on a hot plate. Deionized water was then added to the volumetric mark after removal of the magnetic stir bar. The sample digestion solution was then filtered through Whatman® 46 paper (passes < 8 micron) to remove waxy undissolved material, presumably from the tablet’s coating. The filtrate was then analyzed, after appropriate dilution, against singleelement aqueous standards (PerkinElmer Pure) for elemental quantitation. A Certified Reference Material Mixed Food Diet (CRM-MFD) (High Purity Standards, Charleston, SC) was prepared by dissolution, following the manufacturer’s instructions, to an appropriate concentration for individual elements. All tablets also contained about 2 mg/tablet of silicon, much of which may have remained undissolved. For an accurate measurement of the silicon, HF (trace metal grade) and plastic volumetric flasks should be employed for the dissolution. For calcium and magnesium determinations, La(NO3)2 (reagent grade) was added to all standards, blank and samples to a concentration level of 0.2% to remove chemical inferences from other matrix elements. For potassium determinations, CsCl (reagent grade) was added to all test solutions to a concentration level of 0.2% as an ionization buffer. Figure 1. PinAAcle 900T atomic absorption spectrometer. Results Sample and Standard Preparation One NIST® SRM 3280 Multi-vitamin/Multi-mineral Tablet and two over the counter multi-vitamin/multi-mineral tablets were coarsely ground. Nominally, 0.75 g were weighed out and rinsed into a 1000 mL volumetric flask containing about 20 mL of ASTM® Type I deionized water (>16MΩ • cm). Four mL of HCl (trace metal grade), two mL of HNO3 (trace metal grade), and a magnetic stirring bar were then added to the flask. This sample digestion solution was stirred for All elements showed acceptable calibration criteria. The results obtained for the FAAS analyses of the multi-vitamin/ multi-mineral tablets are shown in Table 2. The values are corrected for laboratory sample dissolution steps and dilutions. The commercial tablets were calculated and reported in mg/ tablet as this was the unit shown and guaranteed on each label. All elements were found to be within the certified range for the NIST® 3280 tablet. Both commercial tablets showed good correlation to labeled quantity guaranteed by the manufacturer. Table 1. PinAAcle 900T Instrumental Parameters. 2 Element Parameter Ca Mg K Fe Zn Cu Mn Wavelength (nm) 422.7 285.2 766.5 248.3 213.9 324.8 279.5 Slit Width (nm) 0.7 0.7 0.7 0.2 0.7 0.7 0.2 Oxidant Flow (L/min) 10 10 10 10 10 8.7 10 C2H2 Flow (L/min) 2.5 2.5 2.5 2.2 2.5 2.0 2.5 Working Range (mg/L) 5 1 4 4 1 4 2 HCL Part Nos. N3050114 N3050144 N3050139 N3050126 N3050191 N3050121 N3050145 Standard Part Nos. N9303763 N9300179 N9303779 N9303771 N9300178 N9300183 N9303783 Table 2. Corrected FAAS results for one certified reference material and two commercial multi-vitamin/multi-mineral samples. Element NIST® 3280 (mg/g) Certified Found Commercial Tablet 1 (mg/Tab) SD Label Found SD Commercial Tablet 2 (mg/Tab) Label Found SD Ca 110.7 107 0.8 162 163 0.6 200 211 0.6 Mg 67.8 69.1 0.2 100 107 0.4 100 109 0.4 K 53.1 53.8 0.3 80 83.8 0.4 80 90.7 0.4 Fe 12.35 12.9 0.05 18 19.1 0.08 n/a 0.23 0.006 Zn 10.15 10.1 0.02 15 15.5 0.04 15 15.2 0.03 Cu 1.4 1.42 0.01 2 2.19 0.01 2 2.04 0.01 Mn 1.44 1.48 0.01 2 1.91 0.01 2 2.04 0.01 The results for the FAAS analysis of the Certified Reference Material – Mixed Food Diet from High Purity Standards – are given in Table 3. All elements were found to be within 5% of the certified value, showing excellent agreement with the reference material. Table 3. Mixed Food Diet CRM results using aqueous standards and FAAS on a PinAAcle 900T. CRM-MFD (mg/L) Element Certified Found SD Ca 40 39.8 0.2 Mg 12 11.8 0.03 K 160 159 0.005 Fe 0.8 0.802 0.005 Zn 0.3 0.290 0.001 Cu 0.06 0.061 0.001 Mn 0.2 0.191 0.003 Conclusions The mineral content of multi-vitamin/multi-mineral tablets must be determined in order to ensure the quality of commercial dietary supplements. This method demonstrates the ability of the PinAAcle 900T flame atomic absorption system to accurately measure minerals in both commercial tablets and food simulation diets. It is an efficacious method that allows for cost effectiveness and ease of use, with less operator training than other analytical methods. The PinAAcle 900H (Flame and Deuterium Furnace) and PinAAcle 900F (Flame only) spectrometers can also be used for this application. 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