BS ISO 23637:2021 pdf download – Cereals — Determination of cadmium content by graphite furnace atomic absorption spectrometry with diluted nitric acid extraction
This document specifies a method for the determination of cadmium (Cd) in cereals.
It is applicable to rice, brown rice, wheat and maize by graphite furnace atomic absorption spectrometry (GFAAS) after extraction with diluted nitric acid (HNO 3 ). The limit of quantification is 0,002 mg/kg; it is approximate and dependent on the sample matrix as well as on the instrument conditions.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 No terms and definitions are listed in this document.
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4 Principle
Cadmium (Cd) is extracted from the cereals using diluted nitric acid and then determined by graphite furnace atomic absorption spectrometry (GFAAS).
5 Reagents and solution
During the analysis, unless otherwise stated, use only reagents of recognized analytical purity and only water of grade 1 in accordance with ISO 3696.
5.1 Nitric acid (HNO 3 ), not less than 65 % (mass fraction) of approximately ρ(HNO 3 ) = 1,4 g/ml.
5.2 Nitric acid solution (0,5 %, volume fraction), mix 0,5 volume parts of HNO 3 (5.1) and 100 ml volume parts of water.
5.3 Nitric acid solution (50 %, volume fraction), mix HNO 3 (5.1) and water in equal volume.
5.4 Palladium nitrate hydrate (Pd(NO 3 ) 2 , 99,9 % purity).
7.3 Preparation of the test samples Grind the laboratory sample using a grinding mill (6.1) until it passes through the sieve (6.6) and mix thoroughly. The particle size of the maize and its milling products should be less than 0,25 mm. The particle size of other cereal varieties should be less than 0,40 mm.
7.4 Extraction
7.4.1 General Weigh 0,200 g ± 0,001 g (m) of the sample flour into a 10 ml plastic centrifuge tube, and add 5,0 ml of diluted nitric acid (5.2). Close the centrifuge tube tightly and mix the content thoroughly to make sure that there are no remaining lumps. Afterwards, the extract is centrifuged at 3 000 r/min for 5 min, or let it stand for 5 min to get a supernatant for further determination.
7.4.2 Reagent blank Prepare a blank solution in the same manner as the sample by transferring 5,0 ml of diluted nitric acid (5.2) into a 10 ml plastic centrifuge tube and following the same procedure as for the sample. In cases of high cadmium concentration, take into consideration the further dilution with diluted nitric acid (5.2)
7.5 Sample analysis
7.5.1 General Inspect the graphite furnace, the sample uptake system and the autosampler injector for any problems that can affect instrument performance. If necessary, clean the system and replace the graphite tube and/or platform. 7.5.2 Operating conditions Cadmium is determined at 228,8 nm. An exemplary furnace programme is given in Table 1. Prior to the use of this method, the instrument operating conditions shall be optimized. The analyst should follow the instructions provided by the manufacturer while using the reference conditions as a guide.
7.5.3 Calibration graph
Prepare a calibration graph at the beginning of the analysis,Inject at least four calibration solutions of different suitable concentrations (see 5.6.3). Plot the absorbance (peak height or peak area) of the cadmium calibration solutions (5.6.3) against the cadmium concentrations. Ensure that the linearity check is carried out [2] .
7.5.4 Determination The spectrum absorptions are obtained by detecting supernatant samples injected into the graphite furnace. The concentration of cadmium is determined from the regression equation by interpolating the spectrum absorption.
7.5.5? Application? of? matrix-modifier If there is an obvious background absorption peak, 100 mg/l of Pd(NO 3 ) 2 solution(5.5) can be used as matrix-modified. Adding 5 μl of the Pd(NO 3 ) 2 solution (5.5) while injecting will eliminate the matrix interference during calibration curve plotting and the measuring of samples.