ISO 20596-2-2021 pdf free download – Water quality — Determination of cyclic volatile methylsiloxanes in water — Method using liquid-liquid extraction with gas chromatography-mass spectrometry (GC-MS).
4 Principle
4.1 Principle of preservation and extraction
The siloxane compounds (D4), (D5), and (D6) are relatively volatile and have low solubility in water thus making accurate quantification in aqueous matrices challenging. Low density polyethylene (LDPE) is added to samples to prevent volatilization of the cVMS through a partial physical barrier between the water and headspace and a matrix to which the cVMS may adsorb. Hexane is then used to extract the dissolved and sorbed fractions of cVMS. The hexane extracts are then analysed by GC-MS (Annex A).
5 Interferences
5.1 Interferences with sampling and processing Silicones, including D4, D5, and D6 are widely used in industrial applications as well as personal care products such as conditioner, hand lotion, sunscreens, and cosmetics (not all inclusive). Persons involved with the collection and analysis of samples should refrain from using siloxane containing products to limit potential contamination of the sample. Additionally, the users should refrain from using collection devices, sampling containers, laboratory equipment or consumables which may contain silicones/siloxanes. Sample contact surfaces should be suitably rinsed with acetone or hexane and subsequently dried in a clean area of the laboratory to remove any contamination.
5.2 Interferences with GC-MS Silicones are also commonly found in parts and consumables associated with gas chromatography including septa for the vials and inlet. Commonly used types of GC columns are polydimethylsiloxane based which when exposed to moisture or when heated may generate cVMS and in such a way can contribute to background. Thus, the use of non-polydimethylsiloxane-based GC columns is highly recommended, in particular when analysing sub-ppb concentrations. Autosampler vial septa should be silicone free or at a minimum coated with polytetrafluoroethylene on the side exposed to the sample.
The inlet septum should be replaced with a Merlin MicroSeal™ 1) to reduce background contamination from this source. In addition, any solvents should be dried prior to injection into the GC or care should be taken to use a solvent in which water is only soluble in the mg/l levels.
5.3 Interferences determination In order to determine the integrity of the sampling, preparation and instrumental analysis of the samples, it is recommended to prepare quality control (QC) samples. An example of QC samples consists of a series of blanks and spikes to identify potential sources of contamination or loss during the life cycle of the samples.
6 Reagents
It is recommended to verify the absence (or presence of only negligible amounts) or absence of cVMS from solvents being utilized.
6.1 Water, grade 1, as defined in ISO 3696.
6.2 Hexane, C 6 H 14 n-hexane or mixture of isomers, determined to be suitably free of cVMS.
6.3 Tetrahydrofuran, C 4 H 8 O.
6.4 Calibration stock solutions.
6.4.1 Reference substances
See Table 1.
— Octamethylcyclotetrasiloxane;
— Decamethylcyclopentasiloxane;
— Dodecamethylcyclohexasiloxane.
6.4.2 Calibration stock solution 1
Weigh 30 mg of each of the listed standards into a 25 ml volumetric flask and fill to volume with hexane (6.2). The concentration of this solution is approximately 1 200 µg/ml.
6.4.3 Calibration stock solution 2
Dilute calibration stock solution 1 (6.4.2) with hexane (6.2) in a ratio of 1:250. The concentration of this solution is approximately 4 800 ng/ml.
6.4.4 Calibration stock solution 3
Dilute calibration stock solution 2 (6.4.3) with hexane (6.2) in a ratio of 1:100. The concentration of this solution is approximately 48 ng/ml.ISO 20596-2 pdf download.