🌿 Determination of sulfate in groundwater, drinking water and wastewater by continuous flow analysis (CFA) — after removal of Ca, Mg, Fe and Al on a cation exchange column, sulfate reacts in acid medium with barium chloride (BaSO4), the excess barium is bound in alkaline medium to methylthymol blue, and the absorbance of the unbound dye is measured in a flow detector at 460 ± 10 nm; range 30–300 mg/l SO4 (other ranges covering exactly one decade), at least 5 calibration solutions, addition of 6 mg/l sulfate for linearity in the lower part of the curve; ISO 22743 with corrigendum Cor 1:2007

Environment ISO 22743

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in the iTeh sample of ISO 22743:2006 (first edition, English text): contents, foreword, introduction, Clauses 1–5 and Clause 6 up to 6.1.2 — the sample ends on page 3. We also read the whole corrigendum ISO 22743:2006/Cor 1:2007 (in the sample SIST ISO 22743:2010/Cor 1:2010). We do not read the rest of the apparatus (6), sampling and sample pretreatment (7), procedure (8), calculation (9), expression of results (10), test report (11) or Annexes A (example of a CFA system) and B (precision and accuracy); we know the titles from the contents.

ACCORDING TO THE TEXT OF ISO 22743:2006. The standard was prepared by ISO/TC 147 “Water quality”, Subcommittee SC 2 “Physical, chemical and biochemical methods”. Introduction: flow analysis methods automate wet chemical procedures and are particularly suitable for many analytes in large sample series at high frequency; analysis can be performed by flow injection (FIA) or continuous flow (CFA) — in both the sample is introduced automatically into a manifold where it reacts with reagents, and the product is measured in a flow detector; sample preparation may be integrated in the manifold; this standard describes CFA only; tests are to be carried out by suitably trained staff. Scope (1): determination of sulfate by CFA in various waters (e.g. groundwater, drinking water, wastewater); for SO4 mass concentrations from 30 to 300 mg/l; other ranges are applicable provided they cover exactly one decade of concentration (e.g. 100–1000 mg/l). References (2): ISO 3696, ISO 5667-3, ISO 8466-1, ISO 8466-2. Interferences (3): calcium, magnesium, iron and aluminium ions give a negative bias — reduced by treatment with a cation exchanger; sulfide, sulfite, phosphate and tannic acids may give a positive bias, but concentrations causing measurable interference are usually not found in real samples. Principle (4): sulfate reacts in acid solution with barium chloride to form barium sulfate; the excess barium chloride reacts in alkaline solution with methylthymol blue to form a chelate; the absorbance of the free, non-chelated methylthymol blue is measured at 460 ± 10 nm in a flow-through detector; calcium, magnesium, iron and aluminium are removed on an ion exchange column before the reaction with barium. Reagents (5): analytical grade reagents with a check of the blank; grade 1 water according to ISO 3696; barium chloride dihydrate, concentrated HCl 12 mol/l, methylthymol blue, surfactant (polyoxyethylene-23-lauryl ether, 30 %), NaOH, tetrasodium EDTA, ammonium chloride, ammonia 25 %, ethanol 96 %, sodium sulfate dried for 2 h at 105 °C, cation exchange resin (e.g. DOWEX 50W-X8, 0,3–0,8 mm, H+ form); barium chloride solution — 917 ± 1 mg BaCl2·2H2O in 1 l (stable for one month at 2–6 °C); HCl 1 mol/l (82 ml concentrated acid in 1 l); methylthymol blue solution — 160 ± 1 mg in 50 ml barium chloride solution, 4 ml hydrochloric acid, 360 ml ethanol, to 1 l, 1 ml surfactant (stable for one week at 2–6 °C); buffered Na4-EDTA solution pH 10,5 (6,75 g NH4Cl and 40,0 g Na4-EDTA, 57 ml ammonia, to 1 l); NaOH 0,25 mol/l; sulfate stock solution 3000 mg/l (4436 ± 1 mg Na2SO4 in 1 l); sulfate spiking solution 6 mg/l (2,00 ml stock in 1 l, 1 ml surfactant) — note: it is added for better linearity in the lower part of the calibration curve, without it this part is not linear, and the amount may be slightly changed depending on the sulfate in the blank and the quality of the dye; at least five calibration solutions from the stock solution — Table 1: 1–10 ml to 100 ml gives 30–300 mg/l in steps of 30 mg/l. Apparatus (6, beginning): CFA system (Figure A.1) — including a sampler for reproducible sample introduction and reagent containers. Corrigendum Cor 1:2007 (published 15.08.2007) changes 5.15: 4 ml of diluted hydrochloric acid (5.14, 1 mol/l), not concentrated (5.3), is added to the methylthymol blue solution.

STATUS (as of 03.10.2026). In the PKN search (term “22743”, 03.10.2026) there is no result — the standard has not been adopted as a Polish Standard, and laboratories cite the ISO document. In the iTeh catalogue (read 03.10.2026) ISO 22743:2006 has the status “Published”, stage 90.93 (international standard confirmed), published 06.04.2006; corrigendum ISO 22743:2006/Cor 1:2007 — “Published”, published 15.08.2007; the Slovenian adoption SIST ISO 22743:2010 — “Published”.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read 03.10.2026). The number 22743 appears in 3 records at 2 laboratories: AB 313 (2), AB 418 (1). In the current PCA documents (read 03.10.2026; AB 418 issue No. 37 of 26.01.2026, AB 313 issue No. 43 of 08.07.2026) the number appears in 3 lines at the same 2 laboratories (2 and 1); in each document the number of page markers equals the number of PDF pages, without repetitions; a search of all PCA documents downloaded from the BIP on 03.10.2026 found no laboratories outside the database copy. Form “ISO 22743:2006” at both, without the corrigendum; at AB 313 in the waste item together with “PN-EN12457-4:2006”. None of these items is suspended. The “Laboratories” tab (term “ISO 22743”) shows both laboratories — checked by a tab query on the labcoda.pl production server on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). All items: CFA with spectrophotometric detection. AB 418: water, wastewater — sulfate(VI) concentration (5,0–10 000) mg/l. AB 313: water, wastewater — (5,00–10 000) mg/l; waste with specified codes and waste according to DAB-11 (e.g. waste from waste treatment, sewage sludge, plastics) — in the eluate according to PN-EN 12457-4 (5,00–10 000) mg/l and (50,0–100 000) mg/kg, marked “1,2” = tests for the regulated area covered by the regulations on the admission of waste to landfills and on underground waste repositories.

WHERE AN APPARENTLY CORRECT RESULT IS EASY TO GET. With the range: the standard covers 30–300 mg/l or another range exactly one decade wide (1); the PCA items give (5,0–10 000) mg/l, i.e. more than three decades — how they are covered (working ranges, dilutions) lies in the part of the standard outside the sample and in the laboratory’s documentation, and the range entry alone does not show it. With the lower part of the curve: without the 6 mg/l sulfate addition the lower part of the calibration is not linear (5.19, note); the references include ISO 8466-1 (linear calibration function) and ISO 8466-2 (non-linear second-order function) (2). With interferences: Ca, Mg, Fe and Al lower the result, which the cation exchange column limits (3, 4) — the efficiency of the column determines the result in samples rich in these cations; sulfides, sulfites, phosphates and tannins may raise it (3). With the reagent: according to corrigendum Cor 1:2007, 1 mol/l hydrochloric acid, not concentrated, is added to the methylthymol blue solution — a laboratory working to the text without the corrigendum prepares a different reagent; the PCA designation does not indicate the corrigendum. With stability: the methylthymol blue solution is stable for one week, barium chloride for one month, at 2–6 °C (5.13, 5.15). With eluates: a result in mg/kg of waste requires conversion from the eluate according to the leaching standard, not according to ISO 22743.

WHAT WE DO NOT GIVE. We do not quote the configuration of the flow system, preparation of the ion exchange column, sample storage, the measurement procedure, formulae, precision and accuracy data — they lie outside the sample. We do not summarize PN-EN 12457-4 or ISO 8466 in this entry. We do not give limit values for sulfate in water, wastewater or eluates.

Method principle

In a continuous flow analysis system the water sample passes through a cation exchange column, which removes calcium, magnesium, iron and aluminium. Sulfate reacts in acid medium with dosed barium chloride to form barium sulfate; the excess barium binds methylthymol blue in alkaline medium as a chelate. The absorbance of the unbound dye, measured at 460 ± 10 nm in a flow detector, increases with the sulfate concentration, which is read from the calibration.

Applications

• Sulfate in groundwater, drinking water and wastewater, 30–300 mg/l or another single decade of concentration (1)
• Large sample series at high analysis frequency (introduction)
• Water, wastewater and waste eluates — 3 items in the accreditation scopes of 2 laboratories in PCA

Key parameters

Standard

Standard number

ISO 22743:2006

Title (PL)

Jakość wody — Oznaczanie siarczanów — Metoda ciągłej analizy przepływowej (CFA)

Title (EN)

Water quality — Determination of sulfates — Method by continuous flow analysis (CFA)

Step-by-step procedure

1. Reagents

   Prepared with corrigendum Cor 1:2007 in 5.15; reagent blank check (5). ISO 22743:2006 — no PN, “Published”, stage 90.93 (03.10.2026).

2. Calibration

   ≥ 5 solutions within one decade of concentration, with sulfate addition (5.19, 5.20).

3. Samples

   Sampling and preservation according to ISO 5667-3 (2; Clause 7 outside the sample).

4. CFA measurement

   Cation exchanger, reaction with BaCl2 and methylthymol blue, absorbance at 460 nm (4; Clause 8 outside the sample).

5. Result

   SO4 concentration in mg/l from calibration (9–10 outside the sample).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard does not address all safety problems; tests are carried out by trained staff (warning)
• Barium chloride is toxic; concentrated hydrochloric acid, ammonia and sodium hydroxide are corrosive (5.2, 5.3, 5.6, 5.9)

Frequently asked questions