AOAC Methods in Codex STAN 234 (Preliminary Methods Review)

972

CAJAN r:T AL.: J. ASSUC. OFF. ANAL. CH!iM. (VOL. 65, NO. 4, 19112)

Table 1. Tin Interference data from analy1ls" of spiked food samples"

Cadmium found, ppm

Lead found, ppm

200ppm Sn added

200ppm Sn added

No Sn addedc

Commodity

No Sn added "

Green beans

0.08 :I: 0.01

0 06 0.08 0.05 0.04 0.03 o.03 0.06 0.05 0 10 009 0.04 0.03

0.08 J: 0.01

0.06 0 06 0.07 0.06 0.08 0.10 0.10 0.12 013 0.11 0.14 0.15

Apple juice

0.03 ± 0.01

0.08 ± 0.01

Infant formula

0.04 :1: 0.01

0 08 :1: 0,01

0.05 ± 0.01

Fish (mackerel)

0.11 ± 0.01

0 08 ± 0.01

0 11 ± 0.01

c~real

0.03 ± 0.003

Baby beef

0.16 :I: O.Ql

• Results obtained by OPASV/HMOE. t> Spiked food samples are those also listed in Tables 7 and 8. "Mean :I: SD of 10 results.

Results and Discussion

reagent blanks, conservative estimates of thr quantitation limits of the method are 0.005 ppm cadmium and 0.010 ppm lead. However, each laboratory should determine its own quantitation limits and verify them frequently. Interferences Under certain conditions, tin will interfere in the ASV determinative step, depending or– sample preparation and electrolyte used (25,261 We found that adding sn+ 2 to the final cell so– lution produces a peak which interferes with thl cadmium peak. This interfering peak is due lo the formation of a Sn-tartaric acid comple~ which is reduced or oxidized at the same poten– tial as cadmium. However, tin is not detecte

Quantitatio11 Limit The lowest level of lead or cadmium that can be reliably quantitated in a food sample is pri– marily dependent on the levels of these elements ,rnd the precision of their measurement in the reagent blank. We have not yet lowered our reagent blank to the point at which instrumental noise is the primary limitation. Because the sample analytical responst' measurement is composed of both reagent and sample compo– nents, we must be assured that the sample re– sponse is significantly d ifferent from the reagent blank response. Therefore, our quantitation limit is defined as that amount of lead or cadmi– um which is S standard deviations (SDs) of the blank above the mean quantity of the respective analyte contributed by the reagent blank cell solution. Lower quantitation limits may bt' achit>ved with less concentrated reage nt blanks. The analysis of 12 reagent blanks during 4 analytical sessions yielded the following results (mean ± SD) by DPASV/ HMDE: 0.00042 ± 0.00046 µg cadmium and 0.0061 ± 0.0015 µg lead. The means plus 5 times their SDs equal 0.00272 µg cadmium and 0.0136 µg lead, which are the amounts of these elements in a sample cell which must be obtained before quantitation is consid– ered reliable. Subtraction of the mean reagent blanks from these results and calculation based on a 10 g sample and analysis of a 5 mL aliquot g ive quantitation limits of 0.0023 ppm cadmium and 0.0075 ppm lead. Because of possible vari– ations in the levels of cadmium and lead in the