⚗️ Determination of dissolved iodide, thiocyanate, thiosulfate, sulfite and chromate in water by ion chromatography — separation on a low-capacity anion exchanger, conductivity detection (with or without suppressor), UV or amperometric detection; working ranges from 0,05 to 50 mg/l, PN-EN ISO 10304-3

Physicochemistry PN-EN ISO 10304-3

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN ISO 10304-3:2001 (Polish version), in full (our translation): “Three chemical-physical methods for the determination of five anions in water by ion chromatography are specified. The ions are separated by liquid chromatography using a separating column, followed by measurement with a detector. Three different types of detection are given”. We read the text of the standard in the sample of ISO 10304-3:1997 (first edition, 1997-08-15; the Polish standard adopts it without changes) from the cover to 4.2.2 with Figures 2 and 3, i.e. up to the requirements for the separator column in the procedure for iodide, thiocyanate and thiosulfate. We do not have the rest of Clause 4 (interferences 4.3, sampling and sample pretreatment 4.4, procedure 4.5, calculation 4.6, expression of results 4.7, test report 4.8), the whole of Clause 5 (sulfite), the whole of Clause 6 (chromate), the precision (Clause 7) or Annexes A (interlaboratory trials) and B (bibliography) — we know them only from the table of contents.

ACCORDING TO THE TEXT OF ISO 10304-3:1997 (foreword, introduction, Clauses 1–4.2.2, table of contents). The standard was prepared by ISO/TC 147 “Water quality”, subcommittee SC 2 “Physical, chemical and biochemical methods”. The ISO 10304 series has the common title “Determination of dissolved anions by liquid chromatography of ions”; Part 1 covers fluoride, chloride, bromide, nitrate, nitrite, orthophosphate and sulfate in water with low contamination, Part 2 bromide, chloride, nitrate, nitrite, orthophosphate and sulfate in waste water, Part 3 chromate, iodide, sulfite, thiocyanate and thiosulfate. The introduction lists the minimum requirements for the system: column resolution for the anion to be determined not below R = 1,3; detection by conductivity measurement (with or without suppressor), spectrometric UV/VIS measurement (direct or indirect) or direct amperometric detection; working ranges according to Table 1; calibration and determination of the linear working range according to ISO 8466-1; validity check of the calibration function, replicate determinations if necessary. Scope (1): iodide, thiocyanate and thiosulfate — Clause 4; sulfite — Clause 5; chromate — Clause 6; an appropriate pretreatment of the sample (e.g. dilution) and a conductivity (CD), UV or amperometric (AD) detector make the ranges of Table 1 feasible. Table 1: chromate 0,05–50 mg/l, UV 365 nm; iodide 0,1–50 mg/l, CD or UV 205–236 nm, AD approx. 0,7–1,1 V; sulfite 0,1–50 mg/l with CD and 0,5–50 mg/l with UV 205–220 nm; thiocyanate 0,1–50 mg/l, CD or UV 205–220 nm, AD approx. 0,7–1,1 V; thiosulfate 0,1–50 mg/l, CD or UV 205–220 nm, AD approx. 0,7–1,1 V; footnote: the working range is restricted by the exchange capacity of the columns — if necessary the sample is diluted into the working range. References (2): ISO 5667-1, -2 and -3 (sampling, preservation and handling of water samples), ISO 8466-1 (statistical evaluation of the linear calibration function), ISO 10304-1:1992 and ISO 10304-2:1995. Principle (3): separation on a column with a low-capacity anion exchanger, eluent usually aqueous solutions of salts of weak monobasic and dibasic acids; the addition of organic agents (e.g. 4-hydroxybenzonitrile) or organic solvents speeds up the elution and reduces tailing, especially of the strongly polarizable iodide, thiocyanate and thiosulfate; with a conductivity detector the eluent must have a sufficiently low conductivity, so the detector is often combined with a suppressor (cation exchanger) that reduces the conductivity of the eluent and transforms the sample ions into their respective acids; the UV detector measures absorption directly or — for anions transparent in the UV — the decrease of the background absorption of a UV-absorbing eluent (indirect measurement, wavelength depending on the eluent composition); the amperometric detector measures the oxidation current of the anions, and the required voltage depends on the pH of the eluent; the concentration is determined by calibration of the overall procedure, in particular cases by standard addition. Reagents for Clause 4 (4.1): analytical grade, weighing to 1 % of the nominal mass; water with a conductivity below 0,01 mS/m, free of particles larger than 0,45 µm (an increase in conductivity due to carbon dioxide uptake does not interfere); eluents are chosen for the column and detector according to the column manufacturer’s instructions, and the compositions given are examples; eluents are degassed, protected against renewed gas pick-up (e.g. by helium superposition), stored in the dark and renewed every 2–3 days. Example eluent for the suppressor technique: concentrate of 36 g sodium carbonate and 36,1 g sodium hydrogen carbonate in 1000 ml (0,34 mol/l Na₂CO₃ and 0,43 mol/l NaHCO₃, stable for months at 4–6 °C); eluent — 50 ml of concentrate and 750 mg of 4-hydroxybenzonitrile to 5000 ml (0,0034 mol/l Na₂CO₃, 0,0043 mol/l NaHCO₃, 0,0013 mol/l 4-hydroxybenzonitrile). Examples of eluents without suppressor (salt concentration usually 0,0005–0,01 mol/l): concentrate of 4,485 g phthalic acid and 100 ml acetonitrile in 1000 ml, adjusted to pH 4 with tris(hydroxymethyl)aminomethane (0,027 mol/l), eluent 100 ml of concentrate to 1000 ml (0,0027 mol/l, approx. 1 % acetonitrile, pH 4,0–4,5); borate/gluconate concentrate (16 g sodium gluconate, 18 g boric acid, 25 g disodium tetraborate, 250 ml glycerol in 1000 ml), eluent 23,5 ml of concentrate and 120 ml acetonitrile to 1000 ml (pH 8,3–8,7); a pH outside these intervals can increase retention times or reduce the resolution below R = 1,3. Stock solutions 1000 mg/l (Table 2): sodium iodide 1,1812 g/l after drying for 3 h at 103–106 °C, potassium thiocyanate 1,6732 g/l after drying for 1 h at 103–106 °C, sodium thiosulfate pentahydrate 2,2134 g/l without drying, with titre adjustment necessary before use; stable for several months at 4–6 °C in polyethylene bottles (commercial solutions may be used). Mixed standard solutions in polyethylene vessels, always the same vessels for the same anions and concentrations: I — 100 mg/l of each anion (about one week at 4–6 °C), II — 10 mg/l (only 1–2 days, even at 4–6 °C). Calibration solutions: 5 to 10 solutions covering the expected range as evenly as possible, e.g. 1–10 mg/l (1–10 ml of solution I to 100 ml) with 0,1 ml of 0,1 mol/l sodium hydroxide (or 0,1 ml of eluent concentrate); blank — water with the same addition. Apparatus (4.2): ion chromatograph — eluent reservoir, HPLC pump, injection system with sample loop (e.g. 50 µl), precolumn, separator column, conductivity detector (with or without suppressor), UV detector (e.g. spectrophotometer 190–400 nm) or amperometric detector, recording device. Column requirement (4.2.2): only columns giving baseline-resolved separation of all injected ions (e.g. iodide, thiocyanate and thiosulfate at 1 mg/l each) may be used; at higher concentrations the resolution to the nearest interfering peak shall not fall below R = 1,3 (the sample does not contain equation (1)); the elution sequence and retention times depend on the column and the eluent (Figure 2).

STATUS (catalogue cards as of 03.10.2026). The card of PN-EN ISO 10304-3:2001 (Polish version, published 23-07-2001, 27 pages, price group N) has no “Withdrawn” header: Health, Environment and Medicine Sector, KT 121 Water Quality — Chemical Testing — Inorganic Substances, ICS 13.060.50, “Introduces: EN ISO 10304-3:1997 [IDT], ISO 10304-3:1997 [IDT]”. The PKN search engine (query “PN-EN ISO 10304-3”, 03.10.2026) shows only this edition. ISO document: according to the iTeh catalogue (read 03.10.2026), ISO 10304-3:1997 has the status “Published”, stage 90.93 — standard confirmed in the systematic review; there is no newer ISO edition.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 03.10.2026). The number 10304-3 appears in 16 records at 9 laboratories: AB 005, AB 213, AB 300, AB 418, AB 550, AB 688, AB 713, AB 883, AB 1095. In the current scopes on the PCA website (read 03.10.2026, issues from 16.12.2025 to 22.09.2026) all of them give “PN-EN ISO 10304-3:2001”. The “Laboratories” tab (“PN-EN ISO 10304-3”) shows 8 of them — all except AB 005, which has this standard in one item together with PN-EN ISO 10304-1, written second; checked with the tab query on the production server labcoda.pl on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA scopes). Sulfite — 7 laboratories: AB 213 (0,50–150 mg/l), AB 300 (0,10–1000 mg/l), AB 418 (0,50–2000 mg/l), AB 550 (water and waste water 0,5–50,0 mg/l; in addition aqueous extracts of construction raw materials and materials, ashes, dusts and sands together with PN-EN 12457-2 and PN-EN 12457-4: 0,5–50,0 mg/l and 5,0–500 mg/kg), AB 688 (0,10–20 mg/l), AB 713 (0,050–10,0 mg/l), AB 883 (water 0,025–25 mg/l, waste water 0,50–25 mg/l). Iodide — 5 laboratories: AB 005 (0,30–250 mg/l), AB 213 (0,25–50 mg/l), AB 300 (0,30–1000 mg/l), AB 418 (0,25–50 mg/l), AB 1095 (0,10–50 mg/l). Thiocyanate — 5 laboratories: AB 005 (0,50–100 mg/l), AB 213 (0,50–150 mg/l), AB 300 (0,10–1000 mg/l), AB 418 (0,50–200 mg/l), AB 1095 (0,10–50 mg/l). Chromium(VI) — 1 laboratory: AB 418 (0,010–20,0 mg/l), with spectrophotometric detection (IC-UV/Vis). None of the 9 laboratories lists thiosulfate. Matrices: water, water intended for human consumption, waste water; the technique is most often “ion chromatography with conductivity detection (IC-CD)”.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Resolution: a column that separates the anions at 1 mg/l may merge the peak of the analyte with a neighbouring one at higher concentrations — the criterion R ≥ 1,3 applies to chromatograms of samples and standards at higher concentrations, not only to the column test (4.2.2). Eluent: a pH of the phthalate eluent outside 4,0–4,5 or of the borate/gluconate eluent outside 8,3–8,7 can increase retention or reduce resolution below 1,3 (footnotes 3 and 4); 4-hydroxybenzonitrile, which speeds up elution, can interfere with UV detection of iodide, thiocyanate and thiosulfate (footnote 1, reference to 4.3.4). Standards: the 10 mg/l solution is stable only 1–2 days, and thiosulfate requires titre adjustment before use — an old standard lowers the calibration and thus raises the sample result (4.1.17, 4.1.18). Range: Table 1 ends at 50 mg/l and is limited by the column capacity — the higher ranges in PCA scopes (up to 1000 and 2000 mg/l) require dilution of the sample; on the other hand several ranges in PCA scopes start below the lower limits of Table 1 (sulfite from 0,025 mg/l at AB 883 and from 0,050 mg/l at AB 713 versus 0,1 mg/l with CD; chromium(VI) from 0,010 mg/l at AB 418 versus 0,05 mg/l) — the part of the standard we read says nothing about this. Sulfite and chromate: the determination most often accredited under this standard (sulfite) and chromate have their own Clauses 5 and 6, whose text we do not have — the conditions of Clause 4 described here apply to iodide, thiocyanate and thiosulfate.

WHAT WE DO NOT GIVE. We do not have 4.3–4.8, Clauses 5–7 or the annexes: interferences and their removal, preservation and pretreatment of samples (including samples with sulfite, which oxidizes easily), the measurement procedure, the resolution equation (1), calculations, eluents and reagents for sulfite and chromate, detection conditions for chromate other than the 365 nm wavelength from Table 1, and precision values — so we give none of these values.

Method principle

Dissolved anions are separated on a column with a low-capacity anion exchanger, eluted with an aqueous solution of salts of weak acids (e.g. sodium carbonate and hydrogen carbonate, phthalate or borate with gluconate), and detected with a conductivity detector (with or without suppressor), a UV detector (directly or indirectly) or an amperometric detector; the concentration of each anion is determined by calibration of the overall procedure, in particular cases by standard addition.

Applications

• Water, water intended for human consumption and waste water — sulfite (7 laboratories), iodide and thiocyanate (5 laboratories each) in PCA scopes
• Chromium(VI) as chromate in water and waste water — UV detection at 365 nm (Table 1); one laboratory in PCA scopes
• Aqueous extracts of construction materials, ashes and dusts (together with PN-EN 12457-2 and -4) — sulfite in mg/l and mg/kg; one laboratory
• Thiosulfate — within the scope of the standard (Clause 4), not found in Polish accreditation scopes

Key parameters

Standard

Standard number

PN-EN ISO 10304-3:2001

Title (PL)

Jakość wody — Oznaczanie rozpuszczonych anionów za pomocą cieczowej chromatografii jonowej — Część 3: Oznaczanie chromianów, jodków, siarczynów, tiocyjanków i tiosiarczanów

Title (EN)

Water quality — Determination of dissolved anions by liquid chromatography of ions — Part 3: Determination of chromate, iodide, sulfite, thiocyanate and thiosulfate

Step-by-step procedure

1. Choice of procedure

   Iodide, thiocyanate and thiosulfate — Clause 4; sulfite — Clause 5; chromate — Clause 6 (we do not have the text of Clauses 5 and 6). PN-EN ISO 10304-3:2001 current (PKN catalogue card as of 03.10.2026).

2. Eluent

   Choose for the column and detector according to the column manufacturer (e.g. carbonate/hydrogen carbonate with suppressor, or phthalate or borate/gluconate without suppressor); degas, protect against gas, store in the dark, renew every 2–3 days.

3. Column check

   Baseline separation of a 1 mg/l standard of each anion; at higher concentrations resolution to the nearest interfering peak at least R = 1,3.

4. Calibration

   5–10 calibration solutions evenly over the expected range (e.g. 1–10 mg/l from the 100 mg/l mixed standard), each with 0,1 ml of 0,1 mol/l NaOH; blank with the same addition; linearity according to ISO 8466-1.

5. Measurement and result

   Dilute the sample into the range of Table 1 if necessary; measurement, calculation and expression of results according to 4.5–4.7 (we do not have the text).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Chromates (chromium(VI)) are carcinogenic — standards and samples with chromium(VI) require gloves and handling as hazardous waste; the part of the standard we read contains no separate warnings
• Acetonitrile and methanol are flammable and toxic — prepare eluents with solvents in a fume hood

Frequently asked questions