⚗️ Determination of selected volatile organic compounds in water — an exact volume of unfiltered sample is sealed gastight in a headspace vial, heated until equilibrium between the water and the gas phase, and a measured volume of the gas phase is determined by gas chromatography with mass spectrometric detection; 54 compounds from Table 1 (among them trihalomethanes, tri- and tetrachloroethene, 1,2-dichloroethane, benzene, toluene, ethylbenzene, xylenes, trichlorobenzenes, MTBE, ETBE, TAME, vinyl chloride), from 0.1 µg/l, with internal standard and salt addition, PN-EN ISO 20595

Physicochemistry PN-EN ISO 20595

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in two iTeh samples: SIST EN ISO 20595:2023 (English text) — title page and European foreword of EN ISO 20595:2022, contents, ISO foreword and introduction — and ISO 20595:2018 (English text) — from the title page through Clauses 1–7 to Clause 8 (sampling) on page 6. Outside the samples remain the procedure (9, including blank control and identification of compounds), calibration (10), evaluation (11), expression of results (12), test report (13) and Annexes A–D (example column, vial and septum; example internal standards; example headspace and GC conditions; performance data).

ACCORDING TO THE TEXT OF ISO 20595:2018 AND EN ISO 20595:2022. The first ISO edition (2018-01) was prepared by ISO/TC 147 “Water quality”, Subcommittee SC 2 “Physical, chemical and biochemical methods”; the text was taken over as EN ISO 20595:2022 by CEN/TC 230 “Water analysis” (secretariat DIN), CEN approved it on 19.09.2022 without modification, and national implementation was due by March 2023 at the latest. According to the introduction, various methods are available for highly volatile organic compounds in water, and this document specifies GC-MS with the static headspace technique. Scope (1): determination of selected volatile organic compounds in water (Table 1) — among others volatile halogenated hydrocarbons and gasoline components (BTXE, TAME, MTBE and ETBE) — in drinking water, groundwater, surface water and treated waste water at mass concentrations > 0.1 µg/l; the lower application range depends on the compound, the blank value and the matrix; applicability to further volatile compounds is not excluded but is checked in individual cases. Table 1 (name, formula, CAS, EC number, molar mass) — 54 compounds, among them: allyl chloride, benzene, biphenyl, bromodichloromethane, chlorobenzene, chloroprene, 2-, 3- and 4-chlorotoluene, dibromochloromethane, 1,2-dibromoethane, 1,2-, 1,3- and 1,4-dichlorobenzene, dichlorodiisopropyl ether, 1,1- and 1,2-dichloroethane, 1,1-, cis- and trans-1,2-dichloroethene, dichloromethane, 1,2-dichloropropane, cis- and trans-1,3-dichloropropene, 2,3-dichloropropene, TAME, ethylbenzene, ETBE, hexachlorobutadiene, hexachloroethane, cumene, MTBE, naphthalene, n-propylbenzene, 1,1,1,2-tetrachloroethane, tetrachloroethene, tetrachloromethane, toluene, bromoform, 1,2,3-, 1,2,4- and 1,3,5-trichlorobenzene, 1,1,1- and 1,1,2-trichloroethane, trichloroethene, chloroform, 1,1,2-trichlorotrifluoroethane, 1,2,4- and 1,3,5-trimethylbenzene, styrene, vinyl chloride and o-, m- and p-xylene; according to footnotes, allyl chloride and vinyl chloride do not have long-term stability, and m- and p-xylene can coelute. References (2): ISO 3696 and ISO 5667-3, -4, -5, -6, -10, -11. Terms (3): none. Principle (4): an exact volume of unfiltered water sample is sealed gastight in a headspace vial and heated; after equilibrium is established between the compounds dissolved in the water and those in the gas phase above it, an exact gas volume is taken and determined by gas chromatography with mass spectrometric detection. Interferences (5): a sample with several liquid phases is analysed by another method; some compounds in Table 1 are solvents frequently used in laboratories — their vapours in laboratory air can lead to overestimates, so regular blank examinations are indispensable; matrix effects (different recoveries and response factors than in standards) are reduced by adding salt, which also increases sensitivity — sodium sulfate and sodium chloride have proven effective, though interferences can occur depending on the salt; some compounds may decompose while equilibrium forms at e.g. 80 °C — 1,1,2,2-tetrachloroethane decomposes to trichloroethene, overestimating trichloroethene; according to a note, the decomposition can be prevented by acidifying the water in the vial with H2SO4 to pH < 2 and using Na2SO4 as salt, but the acid greatly shortens column and injector life; interferences from the injection system and inadequate separation are rectified with expert help and according to the instrument manuals, and system performance is checked regularly (e.g. with solutions of known composition); performance data from a 2013 interlaboratory trial are in Annex D. Reagents (6): purity “for analysis” or “for residue analysis”; water of grade 1 according to ISO 3696 without interfering blanks; high-purity operating gases for GC and MS (e.g. helium at least 99.996 %); salts — sodium sulfate, sodium chloride; solvents — e.g. methanol or dimethylformamide; reference compounds of defined purity; internal standards (examples in Annex B); stock solutions e.g. 100 µg/ml of each compound in methanol, stored at not more than 6 °C in the dark, stable at least 12 months; intermediate dilutions 0.05–5 µg/ml in methanol (e.g. 5–500 µl of stock in a 10 ml flask), stable at least 6 months; internal standard solution e.g. 1 µg/ml each in methanol; aqueous calibration solutions — e.g. 10 ml of water in a 20 ml vial, 10 µl of spiking solution and 10 µl of internal standard solution directly into the water, immediate capping and shaking; salt is added before the water — close to saturation is recommended (e.g. 3 g NaCl or 4 g Na2SO4 per 10 ml); solutions can also be added through the septum (septum quality checked with blanks); a constant spiking volume is recommended; when prepared in flasks — stirring at least 10 s without forming a vortex; sodium thiosulfate pentahydrate (according to a note, ascorbic acid can also neutralize chlorine if validated). Apparatus (7): equipment and glass in contact with the sample free of the analytes and residues; sample bottles, e.g. narrow-necked flat-bottomed with glass stoppers, preferably brown glass, e.g. 250 ml or less; drying cabinet; gas chromatograph with mass spectrometer and headspace sampler; capillary columns e.g. medium-polar phase, inner diameter ≤ 0.32 mm, length about 30–60 m, film 1–3 µm (phase ratio > 300); PTFE-encased stirring bar; microlitre syringes 10–1000 µl; headspace vials e.g. 20 ml; volumetric flasks 10, 50, 100 ml; pipettes. Sampling (8): according to ISO 5667-3, -4, -5, -6, -10 and -11; the bottle is filled completely, flow must be laminar because turbulence causes losses; to water likely to contain chlorine sodium thiosulfate is added to about 80–100 mg/l; the bottle is not pre-rinsed with sample (more suspended matter and loss of stabilizing reagents); equipment of glass or stainless steel, not plastics (blanks and adsorption losses); no interfering compounds may enter the sample and no losses may occur.

STATUS (as of 03.10.2026). The PKN search (query “PN-EN ISO 20595”, 03.10.2026) returns one result: PN-EN ISO 20595:2023-02 (English version, “Wprowadza: EN ISO 20595:2022 [IDT], ISO 20595:2018 [IDT]”) without a withdrawal note. In the iTeh catalogue (read on 03.10.2026) EN ISO 20595:2022 has the status “Published”, and ISO 20595:2018 — “Published”, stage 90.92 (to be revised) since 09.03.2026.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read on 03.10.2026). The number 20595 appears in 5 records at 3 laboratories: AB 377 (2), AB 379 (2), AB 487. In the current PCA documents (read on 03.10.2026, issues from 25.11.2025 to 28.04.2026) the number appears in 5 rows — 2 each at AB 377 and AB 379 and 1 at AB 487; in each of the three documents the number of page markers equals the number of PDF pages, without repetitions; a search of all 1291 PCA documents downloaded from BIP on 03.10.2026 found no laboratories outside the database copy (17 laboratories in the register have no link to a scope document on BIP). Form at all: “PN-EN ISO 20595:2023-02”. None of these items is suspended. The “Laboratories” tab (query “PN-EN ISO 20595”) shows all 3 laboratories — checked with a tab query on the labcoda.pl production server on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). AB 377 — water and water intended for human consumption: chloroform, bromodichloromethane, bromoform, dibromochloromethane (1.00–150.00) µg/l; trichloroethene, tetrachloroethene, 1,2-dichloroethane, tetrachloromethane (0.50–40.00) µg/l; benzene, toluene, ethylbenzene, o-xylene, 1,3,5-, 1,2,4- and 1,2,3-trichlorobenzene (0.20–6.00) µg/l; m,p-xylene (0.40–12.00) µg/l; calculated sums of THM, tri- and tetrachloroethene and trichlorobenzenes; swimming pool water — four trihalomethanes (0.0010–0.1500) mg/l. AB 379 — water and drinking water: benzene (0.20–4.5) µg/l, trichloroethene and tetrachloroethene (1.0–20) µg/l with their sum, 1,2-dichloroethane (0.80–13.5) µg/l; water, drinking water and swimming pool water: chloroform (3.2–130), bromodichloromethane, dibromochloromethane, bromoform (3.0–130) µg/l with THM sum. AB 487 — drinking water: vinyl chloride (0.10–2.0) µg/l. Technique: HS-GC-MS at all.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. At the laboratory: solvent vapours in the air overestimate results — regular blanks (5.2). At decomposition: 1,1,2,2-tetrachloroethane decomposes in the vial to trichloroethene and raises its result (5.4). At the sample: full bottle, laminar flow, no pre-rinsing with sample, no plastic equipment, thiosulfate for chlorinated water (8). At the matrix: salt close to saturation, the same in samples and standards (5.3, 6.8.4). At unstable compounds: vinyl chloride and allyl chloride lack long-term stability, and m- and p-xylene coelute (Table 1) — AB 377 reports m,p-xylene together. At the range: the method applies from > 0.1 µg/l, the lower limit depending on compound, blank and matrix (1). At the water matrix: only treated waste water, and a multi-phase sample — another method (1, 5.1).

WHAT WE DO NOT GIVE. We did not read the headspace and GC conditions, blank control, identification, calibration and calculation (9–12, Annexes A–C) or the performance data (Annex D). We do not give permissible concentrations of these compounds in water.

Method principle

An exact volume of unfiltered water sample (e.g. 10 ml, with salt close to saturation and an internal standard) is sealed gastight in a headspace vial (e.g. 20 ml) and heated until equilibrium is established between the compounds dissolved in the water and the gas phase above it. A measured volume of the gas phase is introduced by the sampler into the gas chromatograph, and the compounds are separated on a capillary column and detected by mass spectrometry, with calibration by aqueous standard solutions prepared in the same way as the samples.

Applications

• Drinking water, groundwater, surface water and treated waste water — 54 volatile compounds from Table 1 from 0.1 µg/l (1)
• Volatile halogenated hydrocarbons (trihalomethanes, tri- and tetrachloroethene, dichloroethanes, vinyl chloride) and gasoline components (BTEX, MTBE, ETBE, TAME) (1, Table 1)
• Water, water intended for human consumption and swimming pool water — trihalomethanes, BTEX, chloroethenes, trichlorobenzenes, vinyl chloride — items in the accreditation scopes of 3 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN ISO 20595:2023-02

Title (PL)

Jakość wody — Oznaczanie w wodzie wybranych związków organicznych o wysokiej lotności — Metoda wykorzystująca chromatografię gazową i spektrometrię mas oraz technikę statycznego headspace (HS-GC-MS)

Title (EN)

Water quality — Determination of selected highly volatile organic compounds in water — Method using gas chromatography and mass spectrometry by static headspace technique (HS-GC-MS)

Step-by-step procedure

1. Sampling

   ISO 5667; full glass bottle, laminar flow, thiosulfate with chlorine (8). PN-EN ISO 20595:2023-02 without a withdrawal note (03.10.2026).

2. Vial preparation

   Salt, exact volume of unfiltered sample, internal standard, immediate capping (4, 6.8.4).

3. Headspace equilibrium

   Heating to equilibrium; watch for decomposition of 1,1,2,2-tetrachloroethane (4, 5.4).

4. GC-MS

   Injection of a measured gas-phase volume, separation on a capillary column, MS detection (4, 7.4).

5. Control

   Regular blanks and system checks with solutions of known composition (5.2, 5.5); calibration according to Clause 10 (not read).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Some analytes (e.g. benzene, vinyl chloride) are hazardous substances — standard solutions in a fume hood
• Sulfuric acid for acidifying vials — eye and hand protection (5.4, note)

Frequently asked questions