🧪 TOC, DOC, total bound nitrogen (TNb) and dissolved bound nitrogen (DNb) after catalytic combustion — PN-EN ISO 20236

Physicochemistry PN-EN ISO 20236

Overview

SCOPE FROM THE PKN CARD (PN-EN ISO 20236:2025-05): a method for the determination of total organic carbon (TOC; Polish OWO), dissolved organic carbon (DOC; RWO), total bound nitrogen (TNb) and dissolved bound nitrogen (DNb) in the form of free ammonia, ammonium, nitrite, nitrate and organic compounds capable of conversion to nitrogen oxides. Cyanide, cyanate and particles of elemental carbon (soot), if present in the sample, may be determined together with the organic carbon. Dissolved gaseous nitrogen (N2) is not determined. The method can be applied to water intended for human consumption, raw water, groundwater, surface water, seawater, wastewater and leachates — for TOC and DOC ≥ 1 mg/l and for TNb and DNb ≥ 1 mg/l. The upper range is limited by the instrument (e.g. the injection volume); higher concentrations are determined after dilution. Note to the scope: the method can in principle be applied to total carbon (TC; OW) and total inorganic carbon (TIC; OWN) — Annex A.

WHAT "TOTAL BOUND NITROGEN" MEANS. TNb is NOT the sum of all forms of nitrogen: it follows from the scope that it covers ammonium, nitrite, nitrate and organic nitrogen — the nitrogen that is converted into nitrogen oxides under the combustion conditions. Molecular nitrogen dissolved in water is not determined. The difference between "total" and "dissolved" (TNb/DNb, TOC/DOC) results from the sample preparation: the dissolved form is determined in a filtered sample — we do not give the filtration method from this standard. WHERE AN ERROR HIDES BEHIND A SEEMINGLY CORRECT RESULT: cyanide, cyanate and soot enter the TOC result. In industrial wastewater with these components, the "organic carbon" therefore contains carbon that is not organic.

WHAT THE 2022 EDITION DID NOT COVER — AND WHERE IT CAME FROM. The card of the edition PN-EN ISO 20236:2022-04 (withdrawn on 13-05-2025) still gave two sentences: that for samples with volatile organic compounds (e.g. industrial wastewater) another method is applied (Annex A) and that the method is not suitable for volatile or purgeable organic carbon. Why they are not in the scope on the card of the 2025 edition — we do not know: the text of the scope on this card breaks off mid-sentence ("Oznaczanie stężeń…" [determination of concentrations…]). The 2022 edition replaced PN-EN 12260:2004 — an earlier standard for bound nitrogen (English-language and German-language versions).

STATUS AND EDITIONS (state of the PKN cards on 25.09.2026). PN-EN ISO 20236:2025-05 — English-language version, publication 13-05-2025, 32 pages, KT 122 Water Quality — Chemical Testing — Organic Substances; it implements EN ISO 20236:2024 and ISO 20236:2024 [IDT]; it replaces PN-EN ISO 20236:2022-04. The card has no "Withdrawn" header. There is no Polish-language version. COMPARISON WITH PN-EN 1484 (a separate entry in this database on TOC): PN-EN 1484:1999 in the Polish-language version, current according to the card (25.09.2026), gives guidelines for determining TOC and DOC in the range from 0.3 mg/l to 1000 mg/l. PN-EN ISO 20236 starts from 1 mg/l, but adds bound nitrogen from the same sample to carbon. In five entries of the scopes the two standards stand together.

HOW ACCREDITATION SCOPES CITE THE STANDARD. Measurement of 25.09.2026 on the database of PL accreditation scopes (1310 laboratories with entries): 23 entries at 15 laboratories. Forms: "PN-EN ISO 20236:2025-05" (18), "PN-EN ISO 20236:2022-04" (2 — a withdrawn edition), "PN-EN ISO 20236:2025-04" (1 — there is no such edition in the catalogue), "PN EN- ISO 20236:2025-05 M" (1). Object: water and wastewater (also drinking water and rainwater); two entries concern soils, aggregates, sediments and waste — an aqueous extract (eluate) is determined there. NITROGEN, NOT CARBON: the methodology in 11 entries is "Stężenie azotu ogólnego" [total nitrogen concentration], in addition total bound nitrogen, dissolved nitrogen and DNb (1 each), and one entry calculates "Stężenie azotu Kjeldahla (z obliczeń)" [Kjeldahl nitrogen concentration (calculated)] from the result. Carbon — DOC/RWO (4), TOC/OWO (2), total carbon TC (1). Technique: high-temperature combustion with chemiluminescence detection (nitrogen, 12 + 2 as "metoda chemiluminescencyjna" [chemiluminescence method]) or with IR detection (carbon). A DECLARED RANGE EXTENDING LOWER THAN THE STANDARD: several entries give a lower limit of 0.50 mg/l (e.g. "(0,50 – 3000) mg/l", "(0,50 – 150) mg/l"), while the scope of the standard starts from 1 mg/l. This may be the result of validation in the laboratory, but for results below 1 mg/l it is worth checking what this limit is based on.

THE KEY OF THE "LABORATORIES" TAB: "PN-EN ISO 20236" — 14 laboratories and 22 entries, without any foreign entries; it will not show one laboratory (AB 1095) with the notation "PN EN- ISO 20236:2025-05 M".

WHAT WE DO NOT GIVE. We did not have the text of the standard — neither the 2024 edition nor the 2018 one. Everything about the method comes from the PKN cards. WE DO NOT GIVE the combustion temperature, the type of catalyst, the way inorganic carbon is removed, the preparation and preservation of samples, the calibration or precision data.

Method principle

The water sample is injected into a furnace with a catalyst bed, in which at high temperature and in an oxidising atmosphere organic compounds are converted to carbon dioxide and nitrogen compounds (other than N2) to nitrogen oxides. CO2 is measured with an infrared detector, nitrogen oxides with a chemiluminescence detector. To obtain organic carbon, inorganic carbon must be eliminated; the dissolved form (DOC, DNb) is the result for a filtered sample. WE DO NOT GIVE the details of the combustion conditions — we did not have the text of the standard.

Applications

• Total nitrogen in wastewater and waters — control of treatment plants and wastewater discharges
• TOC and DOC in drinking water, surface water, groundwater and seawater
• Landfill leachates
• Eluates from soils, sediments and waste — in the accreditation scopes

Key parameters

Standard

Standard number

PN-EN ISO 20236:2025-05 (wersja angielska; wprowadza EN ISO 20236:2024 [IDT], ISO 20236:2024 [IDT])

Title (PL)

Jakość wody — Oznaczanie ogólnego węgla organicznego (OWO), rozpuszczonego węgla organicznego (RWO), ogólnego azotu związanego (TNb) oraz rozpuszczonego azotu związanego (DNb) po wysokotemperaturowym katalitycznym spalaniu utleniającym

Title (EN)

Water quality — Determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb) and dissolved bound nitrogen (DNb) after high temperature catalytic oxidative combustion

Step-by-step procedure

1. Choice of quantity

   Establish whether the total form (unfiltered sample) or the dissolved form (after filtration) is determined, and whether carbon, nitrogen or both.

2. Checking the range

   Expected concentrations ≥ 1 mg/l; dilute samples with a concentration above the instrument range.

3. Combustion and detection

   High-temperature catalytic oxidative combustion; CO2 measured in the infrared, nitrogen oxides by chemiluminescence. WE DO NOT GIVE the conditions.

4. Assessment of the sample composition

   For wastewater with cyanide, cyanate or soot, remember that they enter the TOC result.

5. Report

   State the edition of the standard (2025-05) and whether the result concerns the total or the dissolved form.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Analyser furnace at high temperature — do not open during operation
• Oxygen or synthetic air cylinders — fastening, fittings free of grease
• Wastewater samples — biological hazard, gloves and goggles

Frequently asked questions