⚗️ Dissolved anions in water (Br⁻, Cl⁻, F⁻, NO₃⁻, NO₂⁻, PO₄³⁻, SO₄²⁻) — ion chromatography with conductometric detection

Physicochemistry PN-EN ISO 10304-1

Overview

ISO 10304-1:2007 specifies a method for determining dissolved bromide, chloride, fluoride, nitrate, nitrite, orthophosphate and sulfate in water — drinking water, groundwater, surface water, wastewater, leachate and sea water — by liquid chromatography of ions. The lower limit of application is 0.05 mg/l for bromide and nitrite and 0.1 mg/l for chloride, fluoride, nitrate, orthophosphate and sulfate; it depends on the matrix and on the interferences. The working range can be extended to lower concentrations (e.g. 0.01 mg/l) after suitable preparation of the sample (trace-analysis conditions, preliminary concentration) or with a UV detector for bromide, nitrate and nitrite. Interferences: aliphatic organic acids (mono- and dicarboxylic) may interfere with the separation; sulfite gives high sulfate results through autoxidation (the sample can be brought to pH 10 and formaldehyde added); metals (alkaline earth, transition and heavy metals) are removed on special cation exchangers (a cartridge in the H or Na form; the H form may cause losses of fluoride and nitrite). The 2019 regulation (Dz.U. 2019 poz. 1311 [Journal of Laws 2019, item 1311]) names PN-EN ISO 10304-1 as the reference method for fluoride, chloride, nitrate and sulfate in wastewater, among others.

In Poland it is in force as PN-EN ISO 10304-1:2009 (English version; it replaced PN-EN ISO 10304-1:2001). In laboratory practice (the PWr textbook "Chemia wody" [Water chemistry]) the range of determination depends on the chromatograph, the column, the detector and the loop — for example fluoride 0.01–10, chloride 0.1–100, nitrite 0.05–20, orthophosphate 0.1–20, bromide 0.05–20, nitrate 0.1–50, sulfate 0.1–200 mg/dm³; an example system: an IonPac AS9-HC column (4 × 250 mm) with an AG9-HC guard column, a 25 µl loop, an eluent of 9 mmol/l Na₂CO₃ and a CO₂ suppressor; the results are reported to three significant figures (two for low concentrations), and conversions such as NO₃⁻ → N-NO₃ use the factor 0.2259 and PO₄³⁻ → P-PO₄ the factor 0.3261.

Method principle

The sample is prepared beforehand in order to remove solid particles and, if necessary, sulfite and metal ions. The anions are separated by liquid chromatography on an anion-exchange resin (the stationary phase) with aqueous solutions of the salts of weak mono- and dibasic acids as eluents for isocratic or gradient elution (e.g. a carbonate, hydrogen carbonate or hydroxide eluent). Detection is carried out with a conductometric detector (CD); since the eluent has to have a sufficiently low conductivity, the CD is usually combined with a suppressor (a cation exchanger), which lowers the conductivity of the eluent and converts the ions being determined into the corresponding acids. A UV detector is not required, but it can be used for bromide, nitrate and nitrite (λ = 200–215 nm) when greater sensitivity is needed or where there are matrix interferences. The resolution R between the peak of the anion being determined and the nearest peak must not be less than 1.3. Calibration is carried out in accordance with ISO 8466-1 or ISO 8466-2 (in particular cases with extended ranges, e.g. two decades of concentration); control experiments on the validity of the calibration function are necessary, and where there are matrix interferences — the standard addition method. An example eluent: a concentrate of 28.6 g of Na₂CO₃ and 8.4 g of NaHCO₃ in 1000 ml (0.27 mol/l and 0.1 mol/l; stable for several months at 2–8 °C), 20 ml of which is diluted to 2000 ml (0.0027 mol/l Na₂CO₃ and 0.001 mol/l NaHCO₃); the water for the eluents is degassed, and the eluents are freshly prepared every 3 days. Stock solutions of 1000 mg/l of each anion are available commercially or are prepared from salts dried at (105 ± 5) °C (NaBr 1.2877 g/6 h, NaCl 1.6484 g/2 h, NaF 2.2100 g/1 h, NaNO₃ 1.3707 g/24 h, NaNO₂ 1.4998 g/1 h, KH₂PO₄ 1.4330 g/1 h, Na₂SO₄ 1.4786 g/1 h); a mixed standard solution of 10 mg/l (1.0 ml of each stock solution made up to 100 ml) is stable for a week in the dark at 2–8 °C in polyethylene bottles; 5 to 10 calibration solutions are spread evenly over the working range (e.g. 0.05–0.5 mg/l from portions of 100–1000 µl into 20 ml flasks) and are prepared on the day of use.

Applications

• Drinking water, groundwater and surface water — simultaneous determination of 7 anions from a single injection
• Wastewater and leachate — fluoride, chloride, nitrate, sulfate (the reference method under Dz.U. 2019 poz. 1311)
• Sea water and saline waters (after dilution within the capacity of the column)
• Trace analysis of bromide, nitrate and nitrite with UV detection or after preliminary concentration (down to about 0.01 mg/l)
• High-throughput laboratories — autosampler, calibration according to ISO 8466

Key parameters

Standard

Standard number

PN-EN ISO 10304-1:2009 (ISO 10304-1:2007)

Title (PL)

Jakość wody — Oznaczanie rozpuszczonych anionów za pomocą chromatografii jonowej — Część 1: Oznaczanie bromków, chlorków, fluorków, azotanów, azotynów, fosforanów i siarczanów

Title (EN)

Water quality — Determination of dissolved anions by liquid chromatography of ions — Part 1: Determination of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate

Step-by-step procedure

1. Sampling and preparation of the sample

   Take the sample into clean bottles intended for IC (not cleaned with acids or alkaline detergents); filter it through a 0.45 µm membrane filter, discarding the first part of the filtrate; store at 4–6 °C. If necessary remove the metals on a cation exchanger and stabilise the sulfite (pH 10, formaldehyde).

2. Eluent

   Prepare the eluent from degassed water (e.g. from the carbonate/hydrogen carbonate concentrate, 20 ml → 2000 ml) or as recommended by the column supplier; replace it after 3 days.

3. Calibration

   From the stock solutions of 1000 mg/l prepare a mixed standard of 10 mg/l and 5 to 10 calibration solutions spread evenly over the working range (e.g. 0.05–0.5 mg/l); establish the retention times and the calibration function in accordance with ISO 8466-1/-2.

4. Check of the separation

   Check on the chromatograms of the standards and the samples that the resolution R between the anion and the nearest peak is at least 1.3 and that interfering anions do not overlap with the ones being determined.

5. Analysis

   Inject the sample (loop of e.g. 0.02 ml or an autosampler); record the signal of the conductometric detector after the suppressor (and the UV signal, if used). Run a blank with grade 1 water and control experiments on the validity of the calibration; where there are matrix interferences use the standard addition method; repeat the determination if necessary.

6. Calculation and result

   Read the concentrations from the peak-area (peak-height) versus concentration relationship; report them in mg/l to three significant figures (two for low values); convert if necessary (e.g. NO₃⁻ → N-NO₃ × 0.2259; PO₄³⁻ → P-PO₄ × 0.3261).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Alkaline eluents (NaOH/KOH) and the acids used to regenerate the suppressor — goggles and gloves
• Formaldehyde (stabilisation of sulfite) — work in a fume hood
• The HPLC system is under pressure — check the tubing and the fittings before starting it

Frequently asked questions