BS/EN 17298-2019 pdf download.Animal feeding stuffs — Methods of sampling and analysis — Determination of benzoic and sorbic acid by High Performance Liquid Chromatography (HPLC).
4 Principle
The sample is extracted with a mixture of sodium acetate buffer and methanol. The extract is filtered or centrifuged and — if necessary — diluted. The amount of organic acids extracted from the sample is determined with high-performance liquid chromatography (HPLC), applying a RP 18 column, in conjunction with diode array detection (DAD) or ultraviolet detection (UV). The quantification is carried out by an external calibration.
WARNING — The use of this European Standard can involve hazardous materials, operations and equipment. This standard does not purport to address all the safety problems associated with its use. It is the responsibility of the user of this European Standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
5 Reagents
5.1 Water, grade 2 in accordance with EN ISO 3696.
5.2 Benzoic acid, pa., minimum 99 % purity.
5.3 Sorbic acid, pa., minimum 99 % purity.
5.4 Acetic acid, p.a., w = 100 %.
5.5 Methanol, gradient grade, w  99,8 %.
5.6 Sodium acetate trihydrate, p.a.
5.7 Sodium acetate solution, c = I mol/l.
Dissolve 13,6 g sodium acetate trihydrate (5.6) with approximately 80 ml water (5.1) in a 100 ml volumetric flask, mix and fill up to the mark with water (5.1).
The maximum storage time is 3 months at room temperature.
5.8 Acetic acid solution, c = I mol/1.
Dissolve 6,00 g acetic acid (5.4) with approximately 80 ml water (5.1) in a 100 ml volumetric flask, mix
and fill up to the mark with water (5.1).
The maximum storage time is 3 months at room temperature.
5.9 Acetate buffer, c = 0,1 mol/l.
Mix 50,0 ml sodium acetate solution (5.7) and 50,0 ml acetic acid solution (5.8) in a 1 000 ml volumetric flask and add approximately 700 ml water (5.1). Adjust the pH with acetic acid solution (5.8) to 4,6. Fill up to the mark with water (5.1).
The maximum storage time is 6 months at room temperature.
NOTE A pH of 4,6 is the best range for an optimal HPLC separation regarding the referred conditions,
5.10 HPLC Mobile phase
Mix acetate buffer (5.9) and methanol (5.5) in proportion of 75:25 (v/v) by means of graduated cylinder. Filter for HPLC use.
The maximum storage time is 6 months at room temperature.
5.11 Extraction solution
Mix acetate huller (5.9) and methanol (5.5) in proportion of 60:40 (v/v) by means of graduated cylinder.
The maximum storage time is 6 months at room temperature.
5.12 Standard stock solution, app. 500 mg/I.
Weigh 125 mg benzoic acid (5.2) and 125 mg sorbic acid (5.3) into the same 250 ml volunwtric flask Dissolve with approximately 150 ml extraction solution (5.11). dissolve 5 mm in an ultrasonic bath and fill to the mark with extraction solution (5.11).
The maximum storage time is 2 months at 4 °C
NOTE 1 The shelf life of the stock solution is limited because of esterification reactions.
NOTE 2 If available, single acid standard solutions with adequate and required specifications can be used.
7 Sampling
It is important that the labporatory receives a sample which is truly representative and has not been damaged or changed during transport or storage.
Sampling is not part of the method specified in this document A recommended sampling method is given in EN ISO 6497 131.
Store the sample in such a way that deterioration and change in its composition are prevented.
8 Preparation of test sample
Prepare the test sample in accordance with EN ISO 6498.
Grinding (si mm) shall be done in such conditions that the substance is not appreciably heated. The whole ground product is placed in a flask made of e.g. polypropylene, which can be stoppered and stored in such way to prevent any change in composition.
Before any weighing is carried out for the analysis, the whole test sample shall be thoroughly mixed for reasons of homogeneity.
9 Procedure
9.1 General
An overview of the procedure is given in Annex A.
9.2 Extraction
Accurately weigh 5,00 g ± 10 mg of prepared sample into a 250 ml conical flask Add 100 ml extraction solution (5.11). mix well and dissolve the sample for 30 mm in an ultrasonic bath (6.3).
NOTE 1 It Is important to avoid temperature above 50 C because of evaporation of extraction solution.
NOTE 2 For highly concentrated homogenous samples (premixtures). the sample weight can be reduced because of the limited solubility of sorbic acid.
Allow the particles to settle. Filter through folded filter (6.8), discarding the first 3 ml of the filtrate, and collect the rest. Alternatively centrifuge the sample extract for 3 mm (appr. 5 000 x g).
Dilute the filtered/centrifuged solution with extraction solution (5.11) to a final concentration according to the working range of the calibration (5- 100 rig/mI) — see below for a dilution example.
Before HPLC analysis filter through a 0,45 gtm membrane filter (6.7) discarding the first drops of the filtrate and collect the rest.BS/EN 17298-2019 pdf download.