BS EN ISO 19036-2019 pdf download.Microbiology of the food chain – Estimation of measurement uncertainty for quantitative determinations. 5.2.2.2.4 Preparation of laboratory sample In order to minimize matrix uncertainty contributions, the laboratory sample or the test sample, in cases where the laboratory sample is too big to homogenize, should be made as homogeneous as possible. Laboratory samples that comprise the following should be mixed well prior to drawing test portions: — non-viscous liquids and powders (e.g. milk, coconut milk, dried milk); — minced/finely chopped solids or suspensions/emulsions (e.g. minced meat, mechanically separated meat, sausage meat, crushed meat, whipped cream, dairy ice cream, soya cream). Prior to drawing test portions, other laboratory samples or test samples should be mixed using an appropriate homogenization procedure. For possibilities suited to each type of sample material, see Iso 6887 (all parts). 5.2.2.2.5 Test portions Take at least two test portions from each laboratory (or test) sample to allow repeated measurements. 5.2.2.2.6 Initial suspension, artificial contamination (If needed) and conditions of analysis If artificial contamination is required, perform it in the initial suspension. Detailed procedures for the preparation of artificially inoculated food are described in ISO 16140-3. Perform the analyses on each test portion as in routine testing (e.g. preparation of one series of decimal dilutions, inoculation of one or two plates per dilution). The measurement conditions A and B for the two test portions (see Figure 2. or Annex A if more than two test portions are examined) should differ in as many ways as possible. Ideally, include as many variations in all relevant sources of technical uncertainty (see 5.1) as could be encountered from one day to another within the laboratory. These will typically include, but not be limited to, batches of culture media, reagents and membrane filters, vortex or other mixer, pH meter, incubators, time of analysis, etc. If possible, the two test portions should be tested by at least two different technicians. As the contamination of the food sample is rarely stable in food chain microbiology, the measurement repetitions should be done within a short period of time on a single day. Repetitions may be performed on more than one day only if contamination levels can he shown to he stable. The pattern of variation should not be the same for all laboratory (test) samples. For example, if sample 1 is tested by technician A using media batch B on day...
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