Paragraph 3 Preparation of the sample for analysis
Samples must be prepared in such a way that the amounts weighed out, as provided for in the methods of analysis, are homogeneous and representative of the final sample.
All the necessary operations must be performed in such a way as to avoid, as far as possible, any change in, or contamination of, the sample. Grinding, mixing and sieving should be carried out as quickly as possible, with minimal exposure of the sample to air and light. Overgrinding is to be avoided. Mills and grinders likely to heat the sample appreciably should not be used. Nevertheless, where some loss or gain of moisture is unavoidable, allowance should be made for such changes (see sub-paragraph (d) below). Manual grinding is recommended for feeding stuffs which are particularly sensitive to heat. Care should also be taken to ensure that the apparatus itself is not a source of contamination by trace elements.
If the final sample as received consists of unopened packages or containers then, immediately prior to the preparation of the sample for analysis, all the contents shall be thoroughly mixed together.
If the sample is appreciably moist, or if for any reason the preparation cannot be carried out without significant changes in the moisture content of the sample, determine the moisture content before and after preparation, using the method specified in columns 2 and 3 of Annex I to Part II of this Schedule, appearing opposite to the reference to “Moisture” in column 1 of that Annex.
When a microscopial examination for the presence of undesirable substances is required then, in the absence of good reason to the contrary–
the sample should be crushed and ground only to such an extent as facilitates the examination, and
grinding to pass 1 mm should not be used where it could lead to difficulties in identifying the undesirable substances listed in Schedule 5 of the Feeding Stuffs Regulations 1995f1.
Procedure
Mix the sample thoroughly either mechanically or manually. Divide the sample into two equal portions (the quartering method should be used where applicable). Preliminary crushing and/or grinding may be necessary, if the sample is in a coarse condition, to facilitate division. Keep one of the portions in a suitable container, i.e. non-corrodible, clean and dry and fitted with an air-tight stopper, and prepare the other portion or a representative part of it, of at least 100 g, as indicated below.
Feeding stuffs which can be ground as such
Unless otherwise specified in the method of analysis concerned, sieve the whole sample through a sieve having apertures of 1 mm squaref2f3, in accordance with recommendation ISO R565, after grinding, if necessary.
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Mix the sieved sample and collect it in a suitable container, i.e. non-corrodible, clean and dry and fitted with an air-tight stopper. Mix again, immediately before weighing out the amounts for analysis.
Feeding stuffs which can be ground only after drying
Unless otherwise specified in the method of analysis concerned, dry the sample to reduce its moisture content to a level of 8–12%, in accordance with the preliminary drying procedure specified in point 4.3 of the method referred to in sub-paragraph (d) above, until grinding enables the sample to be passed wholly through a sieve having apertures of 1 mm square. Then proceed as indicated in sub-paragraph (f)(i) above.
Liquid or semi-liquid feeding stuffs
Collect the sample in a suitable container, i.e. non-corrodible, clean and dry and fitted with an air-tight stopper. Mix thoroughly immediately before weighing out the amount for analysis.
Other feeding stuffs
A sample which cannot be prepared according to any of the above procedures should be treated by any other procedure which ensures that the amounts weighted out for analysis are homogeneous and representative of the final sample.
Storage of samples
Samples must be stored at such a temperature as will cause no compositional changes. A sample intended for the analysis of vitamins, or substances which are particularly sensitive to light, should be placed in a brown glass container.