⚗️ Automatic determination of ammonium, the sum of nitrate and nitrite, nitrite, chloride, orthophosphate and silicate (photometrically) and sulfate (turbidimetrically) in water with a discrete analysis system — defined volumes of sample and reagent are mixed in a separate reaction vessel for each determination, incubated (e.g. 37 °C) and the absorbance measured at the appropriate wavelength (340–880 nm); samples filtered through 0.45 µm, calibration according to ISO 8466-1/-2, correction for inherent colour according to Annex A; procedures for the parameters in Annexes B–H, PN-EN ISO 15923-1

Physicochemistry PN-EN ISO 15923-1

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in two iTeh samples: SIST EN ISO 15923-1:2025 (English text) — title page of EN ISO 15923-1:2024, European foreword and endorsement notice, ISO title page, contents, ISO foreword and introduction — and ISO 15923-1:2013 (French version) — from the title page through Clauses 1–12 to the end of Annex A (correction for inherent colour) on page 6. Outside the samples remain Annexes B–H (procedures for ammonium, the sum of nitrate and nitrite by the hydrazine method, nitrite, chloride by the thiocyanate method, orthophosphate, sulfate by the turbidimetric method and silicate), Annex I (performance data) and the bibliography — we know only their titles from the contents.

ACCORDING TO THE TEXT OF EN ISO 15923-1:2024 AND ISO 15923-1:2013. The first ISO edition of 15.12.2013 was prepared by ISO/TC 147 “Water quality”, Subcommittee SC 2 “Physical, chemical and biochemical methods”; the text was taken over as EN ISO 15923-1:2024 by CEN/TC 230 “Water analysis” (secretariat DIN), CEN approved it on 05.08.2024 without modification, and national implementation was due by February 2025 at the latest. According to the introduction, many photometric determinations can be automated in a discrete analysis system: one instrument determines many parameters, and the parameters can be specified for each sample; working with small volumes requires less sample and reagent; samples beyond the measuring range can be diluted automatically or measured again with a different range; the field of application is water (in the English text of the introduction: ground, potable, surface, waste, eluates and boiler water). Scope (1, French version): automated spectrophotometric and turbidimetric methods with a discrete analysis system for the determination of ammonium, nitrate, nitrite, chloride, orthophosphate and silicate; field — ground, drinking, surface and boiler water and eluates. References (2): ISO 3696, ISO 5667-3, ISO 8466-1, ISO 8466-2. Principle (3): a discrete analysis system is an automated system for spectrophotometric and turbidimetric determinations; colour reactions take place in reaction vessels (which may be cuvettes) in an incubator; a new vessel is used for each determination; defined volumes of sample and reagent are pipetted into the vessels and mixed; after incubation the absorbance is measured at the wavelength applicable to the determination — the cuvettes are moved into the photometer or the solution is transferred to the photometer through a flow cell. Interferences (4): particles may cause clogging and interfere with the photometric measurement — filtration of all samples through a 0.45 µm membrane is recommended, except for total phosphate and Kjeldahl nitrogen digests (Annexes B and F); particles can also be removed by decanting, centrifuging or dialysis; the method is applicable to samples in the pH range 5–9 (most natural waters), outside this range pH correction may be needed; inherent colour and turbidity interfere (Annex A), and parameter-specific interferences are described in Annexes B–H; according to a note, inherent colour is compensated by measuring the sample absorbance before adding the colour reagent or with a compensation solution, whereas no proper procedure for turbidity correction can be given — the Lambert–Beer law does not apply to turbid solutions, and many colour reagents and coloured complexes adsorb on particles. Reagents (5): reagents for each parameter — in Annexes B–H; reagents of recognized analytical grade; thermally stable solid reagents are dried for at least 1 h at (105 ± 5) °C and kept in a desiccator; reagent volumes may be adjusted to local or instrument requirements; water of grade 1 according to ISO 3696. Apparatus (6): discrete analysis system — sample introduction (automatic or manual), sample vessels, reagent vessels (refrigerated or not), thermostated incubator (e.g. 37 °C), UV/VIS detector, e.g. spectrophotometer, for 340–880 nm, control and data processing unit, recording (e.g. computer with software). Sampling and sample preparation (7): clean vessels; turbidity and particles interfere with detection — samples are clarified by filtration through a 0.45 µm membrane (or decanting, centrifuging or dialysis), discarding the first 20–30 ml of filtrate to avoid contamination from the membrane; samples for total phosphate should not be filtered (Annex F); the sample is prepared and preserved according to Annexes B–H or ISO 5667-3; grade 1 water prepared like the sample is used as a blank; a control solution from an independent standard with a concentration similar to the samples is analysed as a sample at appropriate intervals — at least once every 20 samples is recommended. Calibration (8): a calibration function for each parameter is established initially and at appropriate intervals according to ISO 8466-1 or ISO 8466-2, with a series of standard solutions according to Annexes B–H including a zero solution; its validity is checked at regular intervals with a standard solution, at least at the end of the batch; if full calibration is not done daily, initial validity is checked with two solutions in the lower and upper third of the working range. Procedure (9): installation and calibration according to the standard and the manufacturer’s instructions; constant incubation temperature and time are essential for stable absorbance measurements — the times in Annexes B–H are recommendations and may vary with experience; the blank is measured according to Annex A; if the sample absorbance exceeds the highest calibration point, the sample is diluted or its intake reduced so that it falls into the upper half of the calibration range, and the analysis is repeated; the procedures of Annexes B–H may be modified for the instrument, range, sensitivity, concentrations or sample types. Calculation (10): mass concentration in µg/l or mg/l from the calibration curve and corrected absorbances according to ISO 8466-1 or -2, taking dilutions into account, usually automatically in the software. Expression of results (11): at most three significant figures; before reporting, the form is decided — ammonium, nitrate and nitrite as N or as the ion, orthophosphate as P or PO4, silicate as SiO4, SiO2 or Si; Table 1 gives conversion factors (e.g. N → NH4 × 1.286; N → NO3 × 4.427; N → NO2 × 3.285; P → PO4 × 3.066; Si → SiO2 × 2.139). Test report (12): reference to ISO 15923-1:2013, sample identification, date of analysis, results, deviations and circumstances that may have affected the result. Annex A (normative): inherent colour is corrected either with a sample blank (only when the reaction vessels are also cuvettes — measurement after adding the sample and reagents that change its colour, before the colour reagent, subtracted taking the volume ratio into account; standards are measured in the same way) or with a compensation solution (the same volumes without the colour-forming compound — water or a reagent without that compound instead of the colour reagent); turbidity generally cannot be corrected.

STATUS (as of 03.10.2026). The PKN search (query “PN-EN ISO 15923-1”, 03.10.2026) returns one result: PN-EN ISO 15923-1:2025-02 (English version, “Wprowadza: EN ISO 15923-1:2024 [IDT], ISO 15923-1:2013 [IDT]”) without a withdrawal note. In the iTeh catalogue (read on 03.10.2026) ISO 15923-1:2013 has the status “Published”, stage 90.93 (standard confirmed).

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 15923-1 appears in 20 records at 3 laboratories: AB 313 (8), AB 1651 (1), AB 1711 (11). In the current PCA documents (read on 03.10.2026, issues from 06.02.2026 to 09.09.2026) the number appears in 11 rows — 3 at AB 313, 3 at AB 1651 and 5 at AB 1711; one reference there often covers several characteristics in the same cell, so there are fewer rows with the number than records; 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). The database copy has only the phosphate item for AB 1651; the other two AB 1651 items with this number (chloride, sulfate, nitrite and ammonium in water, water intended for human consumption and wastewater, and an item in the flexible scope) are not in the database copy. Form “PN-EN ISO 15923-1:2025-02” (AB 313, AB 1651) and “ISO 15923-1:2013” (AB 1711). None of these items is suspended. The “Laboratories” tab (query “PN-EN ISO 15923-1”) shows 2 laboratories — AB 313 and AB 1651; AB 1711, which cites “ISO 15923-1:2013”, is under the query “ISO 15923-1” — checked with tab queries on the labcoda.pl production server on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). AB 313 (water and wastewater; for nitrate also swimming pool water): nitrate nitrogen (0.10–1000) mg/l and nitrate (0.45–4000) mg/l, silica (2.00–200) mg/l, chloride and sulfate (2.00–2000) mg/l, ammonium nitrogen (0.04–1000) mg/l and ammonium ion (0.05–1200) mg/l, nitrite nitrogen (0.01–50) mg/l and nitrite (0.03–150) mg/l, fluoride (0.10–100) mg/l, orthophosphate (0.40–400) mg/l — spectrophotometric method. AB 1651 (water, water intended for human consumption, wastewater): chloride (1.0–1000) mg/l, sulfate (10–1000) mg/l, nitrite (0.010–33.0) mg/l NO2- and nitrite nitrogen (0.003–10.0) mg/l, ammonium nitrogen (0.20–250) mg/l and ammonium ion (0.26–193) mg/l — spectrophotometric method; water and wastewater: phosphate (0.020–5.00) mg/l — colorimetric method; in addition the same characteristics as in the first item in a flexible accreditation scope. AB 1711: total phosphorus (0.05–200) mg/l (water, wastewater); sulfate (5.0–5000) mg/l and chloride (2.0–5000) mg/l (water, wastewater, drinking water); in wastewater nitrate nitrogen (0.50–500) mg/l, ammonium nitrogen (0.50–1000) mg/l, nitrite nitrogen (0.10–50.0) mg/l with conversions to ions; in water and drinking water silica (0.08–200) mg/l, phosphate phosphorus (0.01–100) mg/l, nitrate nitrogen (0.05–200) mg/l, ammonium nitrogen (0.04–200) mg/l, nitrite nitrogen (0.003–5.0) mg/l with conversions to ions — spectrophotometric method.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. At the sample: filtration through 0.45 µm discarding the first 20–30 ml of filtrate, but no filtration for total phosphorus (4, 7). At pH: the method is for pH 5–9, otherwise correction (4). At colour and turbidity: colour is corrected with a sample blank or a compensation solution, turbidity generally cannot be corrected (4, Annex A). At the range: a sample above the highest calibration point is diluted to the upper half of the range and measured again (9). At incubation: constant temperature and time determine the stability of absorbance (9). At control: a control solution at least once every 20 samples, a calibration check at least at the end of the batch (7, 8). At the result: at most three significant figures and an unambiguous form (N or ion, P or PO4) with the conversion factors of Table 1 (11). At the parameters: fluoride (AB 313) is not in the title or scope of the standard, and sulfate is determined turbidimetrically (introduction, Annex G).

WHAT WE DO NOT GIVE. We did not read the procedures, reagents, wavelengths, ranges and interferences for the individual parameters (Annexes B–H) or the performance data (Annex I).

Method principle

For each sample and each parameter the discrete analyser pipettes defined volumes of sample and reagent into a new reaction vessel, mixes and incubates at constant temperature (e.g. 37 °C), and then measures the absorbance at the wavelength appropriate to the determination (detector 340–880 nm); sulfate is determined turbidimetrically. The concentration is read from the calibration function established according to ISO 8466-1 or -2, after correction for the sample’s inherent colour (Annex A) and taking dilutions into account.

Applications

• Ground, drinking, surface and boiler water and eluates — ammonium, nitrate with nitrite, nitrite, chloride, orthophosphate, silicate, sulfate (1, introduction)
• Laboratories with large numbers of samples — many parameters in one instrument, small sample and reagent volumes, automatic dilution (introduction)
• Water, water intended for human consumption, swimming pool water and wastewater — nutrients, chloride, sulfate, silica — items in the accreditation scopes of 3 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN ISO 15923-1:2025-02

Title (PL)

Jakość wody — Oznaczanie wybranych parametrów za pomocą systemów analizy dyskretnej — Część 1: Amoniak, azotany, azotyny, chlorki, ortofosforany, siarczany i krzemiany z detekcją fotometryczną

Title (EN)

Water quality — Determination of selected parameters by discrete analysis systems — Part 1: Ammonium, nitrate, nitrite, chloride, orthophosphate, sulfate and silicate with photometric detection

Step-by-step procedure

1. Sample

   Clean vessels, filtration 0.45 µm (not for total phosphorus), preservation according to the annexes or ISO 5667-3 (7). PN-EN ISO 15923-1:2025-02 without a withdrawal note (03.10.2026).

2. Calibration

   Function according to ISO 8466-1/-2 for each parameter; validity checks within the batch (8).

3. Measurement

   Automatic dosing, incubation at constant temperature and time, absorbance; blank according to Annex A (9).

4. Dilution

   Sample above the range — dilution to the upper half of the range and repetition (9).

5. Result

   Concentration from the curve, taking dilutions into account; at most 3 significant figures, form (N, ion, P, PO4, SiO2) according to Table 1 (10, 11).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard does not address all safety issues — the user establishes health and safety practices in line with national regulations; tests should be carried out by suitably trained staff (warning)

Frequently asked questions