BS ISO 20647:2015 pdf download – Infant formula and adult nutritionals — Determination of total iodine — Inductively coupled plasma mass spectrometry (ICP-MS)
For the standard reference material, accurately weigh approximately 0,5 g of NIST SRM 1849a reference material into a 50 ml tube (4.1) or 1 g into a 100 ml tube (4.1). For ready-to-feed (RTF) material, accurately weigh approximately 1 g of the RTF test sample into a 50 ml tube (4.1) or 2 g into a 100 ml tube (4.1). The remaining RTF material should be transferred to a sealed, brown polypropylene container and held at refrigerated conditions between 2 °C to 8 °C. The solutions should be discarded after five days. For the blank, designate at least one 50 ml tube (4.1) or a 100 ml tube (4.1) digestion vessel as the digest blank. The digestion blank(s) should be treated in the same manner as the samples. Proceed to 5.3.
5.3 Addition of reagents Add 10 ml of purified water to each 50 ml tube or 20 ml to each 100 ml tube. Add 5 ml of KOH solution (3.10.2) if the material was weighed into a 50 ml tube or add 10 ml of KOH solution (3.10.2) if the material was weighed into a 100 ml tube. Seal the vessels and swirl or use a vortex apparatus to mix. Avoid inverting as this may allow the sample to adhere to the inner walls of the vessel above the level of digestion solution. Proceed to 5.4 or to 5.5.
5.4 Oven digestion Digest the samples in an oven (4.2) set to maintain 105 °C ± 5 °C until the dissolution of iodine is complete, approximately 1 h.
The digestion vessels may either be tightened completely or loosened slightly while in the oven. Carefully swirl by hand each digestion vessel at approximately halfway through the digestion/extraction procedure. After removal of the samples from the oven, add 1 ml of stabilizer concentrate (3.10.3) to the 50 ml tube or add 2 ml if the material was weighed into a 100 ml tube. Allow the samples to cool to room temperature. Alternatively, allow samples to cool to room temperature first and then add the stabilizer concentrate. If 50 ml or 100 ml vessels were used for digestion, bring the samples to a final volume of 50 ml or 100 ml respectively with purified water. Cap all vessels and then invert a minimum of three times to mix thoroughly.
5.5 Open vessel microwave digestion Place the digestion vessels into the carousel of the open-vessel microwave digestion unit. If less than the maximum capacity is to be digested, distribute the vessels evenly throughout the carousel. Digest the samples in the microwave until the dissolution of iodine is complete. See Table 5 for suggested open- vessel microwave digestion parameters. Using AOAC method iodine 2012.15  the parameters in Table 5, with the corresponding number of vessels, produced acceptable results for NIST SRM 1849a material for infant and adult nutritional formula. The microwave used was a CEM MARS 5 4) or a CEM MARS 6 4) .
The vessel caps should be loosened slightly (from fully tightened) during the digestion procedure. Alternatively, instead of just loosening the caps, drill small holes (approximately 3 mm) in the caps. In this way the caps can be tightened, but venting (thus the ‘open’ vessel) can occur.
The caps may be reused after acid washing. After removal of samples from the microwave digestion unit, add 1 ml of stabilizer concentrate (3.10.3) to the 50 ml tube samples or add 2 ml if the material was weighed into a 100 ml tube. Allow the samples to cool to room temperature.
NOTE Alternatively, allow samples to cool to room temperature first, and then add the stabilizer concentrate. If 50 ml or 100 ml vessels were used for digestion, bring the samples to a final volume of 50 ml or 100 ml respectively with purified water. Cap all vessels and then invert a minimum of three times to mix thoroughly.
5.6 Sample filtering
Filter each sample solution by filling a disposable syringe with the digested sample solution, attach a 1 µm membrane filter, then filter an adequate amount (e.g. at least 5 ml) into an appropriate vessel (e.g. 15 ml polypropylene centrifuge tube or autosampler vial) to be used for analysis. Samples may be difficult to filter. Use of multiple filter membranes may be required. To ease filtration, allow the inverted sample digestates to rest for a period of time (e.g. 1 h) before filtering. Digested sample solutions may be stored at ambient temperature. Samples may be stored at ambient temperature indefinitely, as long as the results for the applicable digest blank(s) and/or control sample(s) are acceptable when analysed.
5.7 Sample dilution Aliquot 5 ml of each sample’s filtrate into an appropriate volumetric vessel and then bring to a final volume of 10 ml with diluent (3.10.5). Analyse all samples diluted 5 ml to 10 ml.
The following parameters were applied satisfactorily when using an ICP-MS from Perkin Elmer, ELAN DRC II: — Mode: Standard (STD); — Gas: Argon (≥99,998 %, high purity); — Rinse: 0,1 % Triton/1 % NH 4 OH in purified water;