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APPLICATION NOTE
ICP-Mass Spectrometry
Authors
Lee Davidowski, Ph.D.
Zoe Grosser, Ph.D.
Laura Thompson
PerkinElmer, Inc.
710 Bridgeport Avenue
Shelton, CT USA
The Determination Introduction
Dietary supplements are regulated by the FDA under the general umbrella of foods,
of Metals in Dietary but with different regulations than conventional foods. Dietary supplements have been
Supplements defined by Congress as materials taken by mouth that include ingredients intended to
provide dietary supplementation. They can be found in various forms, including tablets,
powders, and liquids. They may consist of vitamins, minerals, herbs or other botanicals,
amino acids, and substances such as enzymes, organ tissues, glandulars, and metabolites.
Under the Dietary Supplement Health and Education Act of 1994 (DSHEA), the dietary
supplement manufacturer is responsible for ensuring that a dietary supplement is safe
before it is marketed. FDA is responsible for taking action against any unsafe dietary
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supplement product after it reaches the market.
One facet of ensuring a safe product is analysis of the final product before distribution. Although organic components often
form the majority of a supplement, metals may be found due to their inclusion in vitamin structures such as vitamin B-12
(cobalt) and minerals, such as selenium. They may also be added as a contaminant through natural products or in the manu-
facturing process. The measurement of toxic metals or metals intended to be present for quality and labeling confirmation
may be required. Analysis challenges include measurement at low concentrations in a variety of matrices. In this note we
will use inductively coupled plasma mass spectrometry (ICP-MS) to measure a variety of elements generally considered to
be hazardous to human health at low to medium concentrations. The four elements generally considered to be hazardous
and not necessary for nutrition are Pb, Cd, As, and Hg. The elements Se and Cr are often added at low concentrations for
nutritional purposes and were also included.
Experimental Arsenic analysis employed cell technology to remove the
Samples of a variety of commercially available protein supple- chloride interference, arising from natural chlorine content,
ments representing different types of matrices were selected salt added to a supplement material or hydrochloric acid used
and prepared in duplicate. Microwave digestion was used in sample preparation, which can degrade the detection limit.
™ This cell allows a gas to react with the sample and under con-
(Multiwave 3000, PerkinElmer, Inc. Shelton, CT USA) trolled conditions the interference is chemically separated
to obtain clear solutions. Six mL of nitric and 1 mL of hydro- from the analyte. Figure 1 shows how the dynamic reaction
™
chloric acid (GFS Chemical , Columbus, OH USA) were cell (DRC) operates in removing arsenic from the chloride
added to PTFE vessels with approximately 0.3 g of sample and interference by shifting the mass observed from 75 to 91.
the digestion program shown in Table 1 applied. The samples Detection limits are improved compared to other approaches
were then transferred and diluted to 50 mL with ASTM Type and the precision in varying matrices is more consistent. An
I water. The samples were fairly homogeneous and in a form instrument detection limit for arsenic measured in 1000 mg/L
that allowed a representative sample to be easily taken. If the NaCl was shown to be 2.3 ng/L, comparing favorably to
samples were chunky solids, grinding, blending or other pro- detection limits of 0.6-1.8 ng/L, measured in 1% nitric acid
cedures might be necessary to ensure a more homogeneous 3
sample to be measured. Preparing replicate samples will allow solution, using this technique.
us to evaluate if our homogeneity assumption is accurate.
Table 1. Microwave Digestion Program.
Step Power (W) Ramp (min) Hold (min) Fan
1 750 10:00 10:00 1
2 1200 10:00 10:00 1
3 0 15:00 3
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The ELAN DRC-e ICP-MS (PerkinElmer, Shelton, CT USA) Figure 1. Dynamic reaction cell (DRC ) operates with the PerkinElmer
was used for measurement. The instrumental conditions are ELAN ICP-MS to react and remove interferences or to move measurement
shown in Table 2. to masses where interferences are not present.
The mass for selenium measurement was chosen to avoid
Table 2. ICP-MS Instrumental Conditions. interference from calcium, common in dietary supplements.
Nebulizer Quartz Concentric Results and Discussion
Spray Chamber Quartz Cyclonic Methodology developed on the ICP-MS was tested through
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analysis of a NIST reference material NIST 1548a, Typical
RF Power 1500 W Diet. The sample was measured and carried through the same
digestion procedure along with the supplement materials.
Integration time 1000 ms (per analyte) Table 3 shows the results obtained for Typical Diet material.
Replicates 3 The results from duplicate sample preparations are in good
agreement with each other. Generally less than 20% relative
Reaction Gas for arsenic O = 0.6 mL/min percent difference is acceptable and these range from 2-13%.
2
The agreement with the certified value is within 10%, showing
91
RPq for arsenic as AsO 0.5 excellent agreement.
2
Table 3. Analysis Results, Typical Diet Reference Material (1548a).
1548a – 1 (mg/kg) 1548a – 2 (mg/kg) Average (mg/kg) Certified Value (mg/kg) % Rec
AsO 91 0.183 0.192 0.188 0.20 ±0.1 93.8
Cd 111 0.036 0.038 0.037 0.035 ±0.0015 106
Cr 52 0.135 0.118 0.127 -
Pb 208+207+206 0.045 0.046 0.046 0.044 ±0.009 104
Hg 202 < DL < DL
Se 82 0.231 0.251 0.241 0.245 ±0.028 98.4
Detection limits were estimated from the standard deviation of The results for the samples are shown in Table 5. The multi-
the blank solutions prepared using the same digestion procedure vitamin samples contain lead, arsenic and small amounts
and are shown in Table 4. of cadmium. These metals were not added intentionally as
nutritional components and may arise from contaminants in
Table 4. Estimated Detection Limits. other whole food ingredients added to the supplement. Dolan,
et. al., surveyed a variety of dietary supplement products and
2
mg/kg in supplement found many contain small amounts of Pb and Cd. As long as
the daily dosage was not large the total amount of these metals
AsO 91 0.17 ingested did not exceed the safe daily exposure limit.
Cd 111 0.0008 The protein powder and liquid supplement contained less of
the toxic elements, although the liquid supplement listed many
Cr 52 0.05 whole food components that might be a source of contaminants.
Pb 208 0.01 A post-digestion spike on the liquid supplement (1 ppb As,
Cd, Cr, Pb, and Se; 0.1 ppb Hg) showed good recoveries,
Hg 202 0.004 further supporting that both method and instrument were
operating as expected.
Se 82 0.10
Table 5. Sample Results (mg/kg).
As Cd Cr Pb Hg Se
Multivitamin Supplement 1 0.287 0.032 11.8 0.530 < DL 5.30
Multivitamin Supplement 2 0.280 0.027 9.97 0.432 < DL 5.01
Protein Powder 1 < DL 0.036 1.21 < DL < DL 0.700
Protein Powder 2 < DL 0.036 0.223 < DL < DL 0.181
Liquid Supplement < DL < DL 0.691 < DL < DL 0.854
Liquid Supplement Spike (% Rec) 89.6 80.0 104 89.1 79.0 83.1
3
Table 6 shows the agreement between the label claims of the
liquid supplement and the results obtained here for chromium
and selenium. The agreement between the values was good,
differing by only a few percent.
Table 6. Comparison with Label Claims.
Label Value Found Value This Work
0.676 mg/kg Cr 0.691 mg/kg
0.845 mg/kg Se 0.854 mg/kg
Conclusion
Measurement of trace toxic metals can help ensure dietary
supplement product safety. ICP-MS can be used to examine a
variety of metals at low concentrations. In this note, analysis
was used for four toxic metals and two nutritional elements
that can be toxic at higher concentrations. The suite of elements
can be easily expanded to include different elements as regula-
tory needs evolve or metal contamination is suspected. This
methodology can be applied to final products or to evaluate
possible contamination in starting materials.
References
1. U.S. FDA Website
http://www.cfsan.fda.gov/~dms/supplmnt.html
2. Dolan, Scott P., Nortrup, David A., Bolger, P. Michael, and
Capar, Stephen G., Analysis of Dietary Supplements for
Arsenic, Cadmium, Mercury, and Lead Using Inductively
Coupled Plasma Mass Spectrometry, J. Agric. Food Chem.
2003, 51, 1307-1312.
3. Ruth E. Wolf and Kenneth R Neubauer, Determination
of Arsenic in Chloride Matrices, PerkinElmer Application
Note D6357A, 2002.
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