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Lead (Pb) by isotope dilution ICPMS for CA Prop. 65 in antacids, supplements, and raw materials

Introduction

Interest in trace amounts of lead (Pb) in calcium based antacids and food supplements is fueled by California Prop 65 because it limits the exposure to lead to 0.5 ug/day  Now testing has expanded from calcium based products to practically all types of food supplements and herbal products. Lead is a concern in products containing amino acids, ferrous fumarate, magnesium, aluminum, and many other food grade materials. 

 Our test method involves addition of an isotope dilution standard, dissolution or digestion of the product in nitric acid, and analysis of the lead isotopes using ICPMS. To date, the procedure has been validated on more than 20 products from various manufacturers according to the California Attorney General’s (CA AG) specifications. The use of an isotope dilution technique makes the method exceedingly robust across a wide variety of challenging sample types. Below is a table showing the CA AG specifications for validation and our typical results using the isotope dilution ICPMS method. As you can see, the method has excellent performance characteristics.

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CA AG Specifications

Typical WCAS Results
Calibration: . .
multipoint regression fit (R2) >0.98 >0.9999
verification (NIST SRM1640) 93-107% 95-105%
continuing standard 94-106% 98-102%
Detection Limit: . .
instrument  limit (ug/L)

1

 0.05
LOD in solids (ug/g) . 0.01-0.03
LOD in liquids (ug/g) . 0.001-0.003
Reference Material: .. .
NIST SRM 1486, Bone Meal 80-120% 95-105%
Precision: .. .
1 aliquot, N=10 (RSD) <15% <3%
6 aliquots (RSD) <25% <6% a
Accuracy: . .
% Recovery of Spikes at 0.05, 1.0, and 3.0 ug/g 80-120% 94-106% b
Ruggedness: . .
6 aliquots X 2 analysts/instruments <25% <10% a

a dependent on product homogeneity
b dependent on sample background concentration

 

Comparison of GFAA and ICPMS

Early in the method development process, a comparison of these two techniques was performed.  A comparison of values for samples by both techniques appears in the graph below. The average difference between the values from GFAA and ICPMS is less than 20%. GFAA in some cases gave values that were much lower than ICPMS. 

We believe this is due to a sample matrix effect, because for some samples low spike recoveries have also been observed for GFAA.   GFAA and ICPMS both give acceptable values for most samples, however both the detection limits and the precision of the results are much better by ICPMS than by GFAA. There are generally more problems by GFAA with complex supplements causing interferences.  For a quotation......

An Update (Jan 2002)

This method has been successfully applied to the following types of samples:

  • Aluminum Hydroxide products
  • Ascorbic Acid
  • Biological Samples: urine, blood, etc.
  • Bismuth Subsalicylate products
  • Boron Aspartate
  • Calcium Carbonate, Lactate, Gluconate, Phosphate, and Pyruvate products
  • Collagen
  • Foods (Supplement Bars and Drinks, Rice, Spinach, Fruit Juice, Gum, etc.)
  • Ferrous Fumarate, Lactate, and Sulfate
  • Glucosamine
  • Herbal Products (Ginseng, Alfalfa, Godenseal, Boswellen, Cassia Nomame, Citrus Aurantium, Dong Quai, Echinaccea, Garcinia Cambogia, Ginko, Green Tea, St. John's Wort, Cordyceps, etc.)
  • Kaolin products
  • Magnesium Hydroxide products
  • Oyster Shell
  • Potassium Chloride
  • Sugars (dextrose, sucrose, etc.)
  • Talc
  • Zinc Stearate, Gluconate, and Oxide products

 

An Update (Dec 2006)
FAPAS Proficiency Test 0781

In October 2006, FAPAS conducted  Proficiency Test 0781 concerning lead (Pb) in chilli powder.  FAPAS is part of the Central Science Laboratory, an executive agency of the UK Government Department for Environment, Food and Rural Affairs (Defra).  This was an international study with samples sent to 31 recipients in 19 countries.  Of these, 26 participants (84%) were able to return results within the required time frame (~1 month).

As described above, Pb is an environmental health concern and regulated under CA Prop 65.  Imported chilli powder and Mexican candy containing chilli powder has been a particular concern.  Therefore WCAS voluntarily participated in the study.

As expected, our result (105 ug/kg) was well within acceptable criteria 116 ± 25.6 (mean ± sd).  However, 31% of the test results were unacceptable, |z| > 2.

 In analyzing the study results and the methods used by the laboratories, we noted the following:

(1) 46% of the labs said they used an accredited method, most GFAA based upon AOAC procedures.  58% of these labs reported unacceptable results

(2) All the labs using ICP-OES or flame AA and 56% of the labs using GFAA reported unacceptable results

(3) 38% of the labs reported using ICP-MS, and all of their results were acceptable.

You know where we're going with this.  As anyone can see, ICPMS gives the most reliable results, and this is due to it's superior sensitivity and lack of interferences.

For a quotation......

 

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9240 Santa Fe Springs Rd
Santa Fe Springs, CA 90670
562.948.2225   Fax 562.948.5850 info400@exova.com

Exova

Formerly West Coast Analytical Service (WCAS) and Bodycote Testing Group