⚗️ Orthophosphate and total phosphorus in water and wastewater — continuous flow analysis (CFA) with spectrophotometric detection, PN-EN ISO 15681-2

Physicochemistry PN-EN ISO 15681-2

Overview

WHAT THE STANDARD COVERS. The scope from the PKN catalogue card of the 2019-02 edition, quoted in full: "This document specifies continuous flow analysis (CFA) methods for the determination of the mass concentrations of orthophosphate in the range from 0.01 mg/l to 1.00 mg/l P, and of total phosphorus in the range from 0.10 mg/l to 10.0 mg/l P. The method includes the digestion of organic phosphorus compounds and the hydrolysis of inorganic polyphosphates, performed either manually as described in ISO 6878 and in references [4], [5] and [7], or with an integrated UV digestion and hydrolysis unit. This document is applicable to various types of water, such as ground water, water intended for human consumption, surface water, leachates and wastewater. The range of application can be changed by changing the operating conditions. The method is also applicable to the analysis of sea water by adapting the carrier and calibration solutions to the salinity of the samples, but taking into account changes in the sensitivity of the determination. Depending on the required range, the method can also be used for analysis with cuvettes from 10 mm to 50 mm. For extreme sensitivity, capillary flow cells (LCFC) with a length of 250 mm and 500 mm can also be used. However, the method is not validated for such applications. This may require changes in the sensitivity range and in the calibration solutions. Annex A gives examples of CFA systems. Annex B gives performance data from interlaboratory trials. Annex C gives information on the determination of orthophosphate and total phosphorus by CFA and tin(II) chloride reduction." (our translation of the Polish card text)

STATUS (state of the cards on 29 September 2026). The card of PN-EN ISO 15681-2:2019-02 (English version) carries no withdrawal note — the standard is CURRENT. Published 04-02-2019, 32 pages, PKN technical committee KT 121 (Water Quality — Chemical Testing — Inorganic Substances), ICS 13.060.50; "Introduces: EN ISO 15681-2:2018 [IDT], ISO 15681-2:2018 [IDT]"; "Supersedes: PN-EN ISO 15681-2:2006 - Polish version". The card of PN-EN ISO 15681-2:2006 (Polish version): heading "Withdrawn", published 28-02-2006, "Date of withdrawal: 04-02-2019", "Superseded by: PN-EN ISO 15681-2:2019-02 - English version"; its scope covered orthophosphate from 0.01 to 1.0 mg/l and total phosphorus from 0.1 to 10.0 mg/l. Part 1 of this standard (PN-EN ISO 15681-1, flow injection analysis FIA) does not appear in any accreditation scope in our copy.

REGULATION FOR WASTEWATER — REFERENCE METHODOLOGIES. Regulation of the Minister of Maritime Economy and Inland Navigation of 12 July 2019 on substances particularly harmful to the aquatic environment and the conditions to be met when discharging wastewater into waters or into the ground (…) (Journal of Laws 2019 item 1311), § 18: "In testing samples of wastewater and of rainwater or snowmelt water, the reference methodologies for sample analysis specified in Annex 12 to the regulation shall be applied." (our translation) Annex 12, item 27 "Total phosphorus": molecular absorption spectrophotometry with digestion before determination — PN-EN ISO 6878, inductively coupled plasma atomic emission spectrometry — PN-EN ISO 11885, inductively coupled plasma mass spectrometry — PN-EN ISO 17294-2. Flow analysis is not on this list for total phosphorus (for other parameters the annex does name it — e.g. CFA and FIA flow analysis according to PN-EN ISO 14402 for the phenol index, item 25). Whether a result according to PN-EN ISO 15681-2 can serve for the assessment of wastewater under § 18 — WE DO NOT DECIDE. The values against which total phosphorus in wastewater from municipal treatment plants is compared depend on the population equivalent: from 5 mg P/l to 1 mg P/l, for larger plants alternatively a minimum percentage reduction of 80 % (Annex 2, item 5).

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17 September 2026, read on 28 September 2026). All records of number 15681 with Part 2: 18 entries at 12 laboratories. Forms: "PN-EN ISO 15681-2:2019-02" — 16 entries at 10 laboratories; "PN-EN ISO 15681-2:2006" — AB 312 (withdrawn edition, PCA scope issue no. 25 of 15 June 2026); "PN-EN 15681-2:2019-02" without "ISO" — AB 075 (PCA scope issue no. 29 of 13 January 2026). Note on this last record: under the number PN-EN 15681-2 the PKN catalogue has a standard on glass in building ("Glass in building -- Basic alumino silicate glass products -- Part 2: Product standard", edition 2017-04) — the number alone without "ISO" therefore points to a different document. The "Laboratories" tab searches for records BEGINNING with "PN-EN ISO 15681-2" and will show 11 laboratories — checked with the tab query on the labcoda.pl production server on 29 September 2026: 11; AB 075 remains outside it. Current scopes on the PCA website (read on 29 September 2026): all entries stand in the valid issues, every numerical range from the copy appears in the current document and no entry is suspended.

WHAT LABORATORIES DETERMINE AND IN WHAT RANGES. Total phosphorus — eight laboratories (AB 075, AB 127, AB 188, AB 313, AB 418, AB 794, AB 805, AB 1448), orthophosphate or "phosphates" — eight (AB 085, AB 176, AB 177, AB 188, AB 312, AB 313, AB 418, AB 805); four have both determinations. Technique: at 11 laboratories "continuous flow analysis method (CFA) with spectrophotometric detection", at AB 075 — "flow analysis method (CFA) with spectrometric detection". Object: water and wastewater. Ranges for total phosphorus: lower from 0.010 mg/l (AB 075, AB 805) to 0.10 mg/l (AB 127, AB 313, AB 1448), upper from 10 mg/l (AB 127, AB 188 for water, AB 794) to 300 mg/l (AB 418); for orthophosphate and phosphates — from 0.005 mg/l of phosphate phosphorus and 0.015 mg/l PO₄ (both AB 805) to 900 mg/l PO₄ (AB 418). The card gives orthophosphate 0.01–1.00 mg/l P and total phosphorus 0.10–10.0 mg/l P for the standard, but notes that "the range of application can be changed by changing the operating conditions" — the upper limits of the laboratories (total phosphorus up to 300 mg/l, orthophosphate up to 900 mg/l PO₄) lie far outside the range on the card, and the lower limit for total phosphorus at AB 075 and AB 805 (0.010 mg/l) — ten times below it. Two laboratories (AB 418, AB 805) give the orthophosphate range as PO₄, the others without indicating the form — when comparing results from different laboratories it has to be checked whether the result is expressed as P or as PO₄.

ALONGSIDE THIS STANDARD. For total phosphorus in water and wastewater (207 laboratories in the copy; AB 005 and AB 1188 record it with the abbreviation "Pog") the most often cited standards are PN-EN ISO 6878 — 142 laboratories, PN-EN 14672 — 17, PN-EN ISO 11885 — 17 and this standard — 8; for orthophosphate and phosphates (130 laboratories) — PN-EN ISO 6878 — 82, PN-EN ISO 10304-1 — 37 and this standard — 8. This is the top of the list, not the full list: in the copy there are over 300 different document records for phosphorus, mostly in-house procedures and variants of the record of PN-EN ISO 6878.

WHAT WE DO NOT GIVE. We did not have the text of the standard — PKN sells it. We do not give the reagents and the colour reaction, the digestion conditions (the card names manual digestion as in ISO 6878 or integrated UV digestion with hydrolysis), the wavelength, the scheme of the CFA system (according to the card examples are in Annex A), the calibration curve or the precision (interlaboratory data are in Annex B according to the card — we did not have them).

Method principle

According to the card of the standard, orthophosphate and total phosphorus in water are determined by continuous flow analysis (CFA); for total phosphorus, organic phosphorus compounds are digested and inorganic polyphosphates hydrolysed — manually, by the method described in ISO 6878, or in an integrated UV digestion and hydrolysis unit. The card mentions cuvettes from 10 to 50 mm and — for extreme sensitivity — capillary flow cells of 250 and 500 mm (for which the method is not validated), and Annex C concerns a variant with tin(II) chloride reduction. Laboratories record spectrophotometric detection in their scopes (AB 075 — "spectrometric"). Range from the card: orthophosphate 0.01–1.00 mg/l P, total phosphorus 0.10–10.0 mg/l P. For wastewater the regulation names other standards as reference methodologies for total phosphorus (PN-EN ISO 6878, PN-EN ISO 11885, PN-EN ISO 17294-2). We DO NOT GIVE the reagents, digestion or measurement conditions — we did not have the text of the standard.

Applications

• According to the card: ground water, water intended for human consumption, surface water, leachates and wastewater; sea water after adapting the carrier and calibration solutions to the salinity of the samples
• Orthophosphate and total phosphorus in water and wastewater — in the accreditation scopes of 12 laboratories, all with CFA
• Wastewater: assessment of total phosphorus against values depending on the population equivalent (Journal of Laws 2019 item 1311, Annex 2, item 5) — the reference methodologies of Annex 12 do not include this standard

Key parameters

Standard

Standard number

PN-EN ISO 15681-2:2019-02 (wersja angielska)

Title (PL)

Jakość wody — Oznaczanie ortofosforanów oraz fosforu ogólnego za pomocą analizy przepływowej (FIA i CFA) — Część 2: Metoda ciągłej analizy przepływowej (CFA)

Title (EN)

Water quality — Determination of orthophosphate and total phosphorus contents by flow analysis (FIA and CFA) — Part 2: Method by continuous flow analysis (CFA)

Step-by-step procedure

1. Status and record of the standard

   PKN card: edition 2019-02 current, 2006 withdrawn on 04-02-2019 (state of the cards on 29 September 2026). In the scopes AB 312 still cites the 2006 edition, and AB 075 writes the number without "ISO".

2. Choice of determination

   Orthophosphate or total phosphorus — the latter after digestion of organic compounds and hydrolysis of polyphosphates (manually as in ISO 6878 or in an integrated UV unit). Record whether the result is expressed as P or as PO₄.

3. Flow measurement

   Determination in the CFA system; the range is adjusted by the operating conditions (card). Conditions, reagents and wavelength NOT GIVEN.

4. Result

   Concentration in mg/l; for wastewater — check whether the client needs a result by a reference methodology from Annex 12 of the regulation.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The safety data sheets of the reagents used for the colour reaction and digestion apply — their composition is NOT GIVEN, we did not have the text of the standard
• SUBSTANTIVE NOTE: for wastewater a result according to this standard is not a result of any of the reference methodologies listed for total phosphorus in Annex 12 of the regulation

Frequently asked questions