ISO 20596-2:2021 pdf download – Water quality — Determination of cyclic volatile methylsiloxanes in water — Part 2: Method using liquid-liquid extraction with gas chromatography-mass spectrometry (GC-MS).
3? Terms? and? definitions No terms and definitions are listed in this document. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at http:// www .iso .org ./ obp — IEC Electropedia: available at http:// www .electropedia .org/ 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.
6.5 Spiking stock solutions 6.5.1 Spiking stock solution 1 Dilute calibration stock solution 1 (6.4.2) with tetrahydrofuran (6.3) in a ratio of 1:100. The concentration of this solution is approximately 12 µg/ml. 6.5.2 Spiking stock solution 2 Dilute spiking stock solution 1 (6.5.1) with tetrahydrofuran (6.3) in a ratio of 1:50. The concentration of this solution is approximately 240 ng/ml. 6.6 Internal standard working solution 6.6.1 Individual internal standards 13 C-labelled cVMS. Typical products available from suppliers are: — 13 C-D4, such as 2,4,6,8- 13 C 4 -octamethylcyclotetrasiloxane; or — 2,2,4,4,6,6,8,8- 13 C 8 -octamethylcyclotetrasiloxane; — 13 C-D5, such as 2,4,6,8,10- 13 C 5 -decamethylcyclopentasiloxane; or — or 2,2,4,4,6,6,8,8,10,10- 13 C 10 -decamethylcyclopentasiloxane; — 13 C-D6, such as 2,4,6,8,10,12- 13 C 6 -dodecamethylcyclohexasiloxane. 6.6.2 Internal standard stock solution 1 Weigh 10 mg of the appropriate internal standard (6.6.1) into a 100 ml volumetric flask and fill to volume with hexane (6.2). The concentration of this solution is approximately 100 µg/ml. 6.6.3 Internal standard stock solution 2 Dilute internal standard stock solution 1 (6.6.2) with hexane (6.2) in a ratio of 1:100. The concentration of this solution is approximately 1 000 ng/ml. 6.6.4 Internal standard working solution Dilute internal standard stock solution 2 (6.6.3) with hexane (6.2) in a ratio of 1:250. The concentration of this solution is approximately 4 ng/ml.