💧 Sulphates in water by the turbidimetric method according to PN-C-04566-10 — standard withdrawn, and two different names of the technique in the scopes

Physicochemistry PN-79/C-04566

Overview

STATUS (state of the PKN card on 23.09.2026). PN-C-04566-10:1979 — Polish version — is WITHDRAWN. Publication date 23-11-1979, WITHDRAWAL DATE 07-07-2015, number of pages 2, technical body KT 121 (Water Quality — Chemical Testing — Inorganic Substances), ICS 13.060.50. The card contains no "Replaced by" row — the standard was withdrawn without a successor being indicated.

WHAT LABORATORIES CITE (measurement on the database of scopes, reading of 23.09.2026): 24 entries at 22 laboratories across all forms of notation; 22 entries at 20 laboratories when matching by the BEGINNING of the notation in the old scheme ("PN-79/C-04566") — this is the number the "Laboratories" tab shows. We also checked that the shortened prefix does not pull in other parts of the series: all notations beginning with "PN-79/C-04566" concern part 10.

TWO NAMES OF THE TECHNIQUE FOR ONE STANDARD. Thirteen entries declare "Metoda turbidymetryczna" [turbidimetric method], nine — "Metoda spektrofotometryczna" [spectrophotometric method]. The title of the standard speaks of the TURBIDIMETRIC method. The difference is not purely verbal: turbidimetry measures the attenuation of a light beam by a suspension (here: of barium sulphate precipitated from the sample), while spectrophotometry measures the absorption of light by a solution. The measurement is often made on the same instrument, and this is where the interchangeable naming comes from, but the measured quantity is different. WE DO NOT SETTLE whether these nine laboratories carry out the measurement differently from how the standard describes it — we did not have the text of the standard; we note the discrepancy because the reader of a report sees one of the two names in it.

MATRICES. "Woda, Woda do spożycia przez ludzi" [water, water intended for human consumption] (8 entries), "Woda do spożycia przez ludzi" [water intended for human consumption] (5), "Woda, woda do spożycia przez ludzi" (3), singly "Woda Ścieki" [water, waste water]. Although the title of the standard says "Water and waste water", in the accreditation scopes it stands almost exclusively next to drinking water.

MEASURING RANGES: (1.00 – 300) mg/l, (1.0 – 300) mg/l, (2.5 – 250) mg/l — five entries, (2.50 – 100.00) mg/l, (2.5 – 50) mg/l, (6 – 1000) mg/l, (10 – 500) mg/l.

AGAINST WHAT THESE NUMBERS APPLY. The parametric value for sulphates in water intended for human consumption is 250 mg/l (item 9 of the list of indicator parameters in the regulation of the Minister of Health of 22 May 2026 on the quality of water intended for human consumption — Journal of Laws 2026 item 748, in force since 24 June 2026; this regulation repealed the previous one from 2017). The same regulation sets TWO NUMERICAL REQUIREMENTS for the method: the limit of quantification is to be 30 % of the parametric value or less — i.e. for sulphates not more than 75 mg/l — and the measurement uncertainty not more than 15 % of the parametric value. The lower limits declared by laboratories (1–10 mg/l) meet this with a wide margin; what is decisive is rather whether the UPPER limit reaches above 250 mg/l: with a range ending at 100 mg/l, a result around the parametric value requires dilution of the sample.

WHAT WE DO NOT GIVE. We did not have the text of the standard. We DO NOT GIVE the composition of the precipitating reagent, the way of stabilising the barium sulphate suspension, the measurement time after precipitation or the wavelength. The standard has two pages, so the description that a laboratory uses today comes largely from its own procedure.

Method principle

Sulphates are precipitated from the sample as barium sulphate, and the resulting suspension is measured optically — the more sulphates, the stronger the attenuation of the light beam. The standard calls this the turbidimetric method. The result is read from a calibration curve prepared from solutions of known sulphate concentration. WE DO NOT DESCRIBE THE DETAILS OF EXECUTION — the composition of the reagents, the way of stabilising the suspension, the measurement time: we did not have the text of the standard.

Applications

• Determination of sulphates in water intended for human consumption
• Checking water against the parametric value of 250 mg/l
• Reading an accreditation scope in which a standard withdrawn in 2015 stands next to sulphates
• Distinguishing the declared technique: turbidimetry versus spectrophotometry with the same reference document

Key parameters

Standard

Standard number

PN-C-04566-10:1979 (wersja polska)

Title (PL)

Woda i ścieki — Badania zawartości siarki i jej związków — Oznaczanie siarczanów metodą turbidymetryczną

Step-by-step procedure

1. Checking which document stands in the scope

   PN-C-04566-10:1979, most often written in the scopes as PN-79/C-04566.10, has been withdrawn since 07-07-2015 and has no successor indicated on the card.

2. Checking which technique the laboratory has declared

   With the same standard, the scopes sometimes say "turbidimetric method", sometimes "spectrophotometric method". When ordering a test, it is worth knowing which name the laboratory will write in the report.

3. Precipitating barium sulphate

   Add the reagent with barium ions to the sample and stir in the way established in the procedure. The repeatability of stirring decides the size of the particles of the suspension, and therefore the result. We do not give the details of the standard — we did not have its text.

4. Measuring the suspension

   Measure the attenuation of the light beam by the suspension at the time established in the procedure, against a calibration curve prepared under the same conditions.

5. Checking whether the result is within the range

   With a result above the upper limit of the range, dilute the sample and repeat the determination. Several laboratories have an upper limit below the parametric value of 250 mg/l — there dilution is the rule, not the exception.

6. Relating to the parametric value

   Compare with the value of 250 mg/l for water intended for human consumption (Journal of Laws 2026 item 748). At the same time check the requirements for the method: limit of quantification not more than 75 mg/l and measurement uncertainty not more than 15 % of the parametric value.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard has been withdrawn since 07-07-2015 and has no successor on the card — citing its number alone does not say where today's description of the method comes from
• Two names of the technique for one reference document are not an editorial trifle: turbidimetry measures a suspension, spectrophotometry a solution, and only the name is visible in the report
• A range ending below the parametric value of 250 mg/l means that a result around this value is obtained by dilution — and dilution introduces its own uncertainty, limited by the regulation to 15 % of the parametric value
• A result read from an extended calibration curve above the upper limit of the range looks correct and is not correct — with a suspension the relationship ceases to be linear sooner than with a solution
• The regulation on the quality of drinking water changed in 2026 — a procedure citing the 2017 act cites a repealed regulation

Frequently asked questions