OMA Consulting Protocol Review: OMACON-2019-2

5.Sample Pretreatment, Dilution and Analysis A preliminary sample pretreatment or dilution step is needed to perform the analysis of the sample. Liquid samples need to be pretreated before being analysed in the 0-200 mg/l range. To do so, add a capsule of charcoal activated in 50 ml of sample and cut it in half to speed up the mixing process. Shake until the active charcoal is homogeneously mixed with the milk sample and let it react for at least 30 minutes before analysing. Shake it occasionally. Eventually you might receive a pretreatment tube instead of a capsule. In that case, inject 5ml of milk sample inside the pretreatment tube, shake until the mixture is homogeneous and analyse the sample as usual. Activated charcoal (0-200 mg/l range)

Dilution (0-2 g/l range and 0-6 g/l range)

Samples (milk and other dairy products) in the 0-2 g/l and 0 -6 g/l ranges need to be diluted. To do so, mix 1 ml of sample with 9 ml of Measurement Solution and shake it to homogenize. Once the samples are prepared, they have to be analysed in a maximum of 2 hours and can be kept at ambient temperature.

General sample pretreatment

High viscous samples (greek yogurt, high protein yogurt, crème caramel or others) must be liquefy before analysing in order to be able to pipette them inside the measurement cuvette. Make use of an Ultra-turrax or a mincer. Occasionally, an extra step of heating is needed. For example, for spreadable or soft cheese, heat in a microwave at low power for a few seconds in order to melt it before analysing.

In case of high viscous samples, the electrodes must be cleaned with distilled water between analysis.

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