Chloride ions in aqueous extracts of soils, when free of interfering particulates, can be measured by ICPAES, if the instrument can operate at a wavelength of 134.72 nm. Spectroflame™ ICP is one that can meet this criterion.
Reagent Water Blank
As for Method 3A1.
Chloride Primary Standard
1 mL contains 2 mg of Cl.
Prepare as for 5A2a.
Chloride Working Standards
Prepare as for 5A2a to achieve solutions equivalent to soil concentrations of (as required) 10.0, 25.0, 50.0, 125, 250, 375, 500, 750, 1000 and 1250 mg Cl/kg of air-dry soil.
Prepare 1:5 soil/water suspensions as described in Method 3A1. Filter a suitable aliquot for same-day analysis using a ≤0.45 μm pre-washed membrane.
Set up the ICPAES instrument according to the manufacturer’s instructions. Specifications may change over time but for a Cl– wavelength of 134.724 nm, instrument settings are likely to be: plasma power = 1200 W; nebuliser pressure = ≈55 psi; nebuliser flow rate = ≈0.9 L/min; auxiliary flow = ≈1.15 L/min; coolant flow = ≈15 L/min.
Equilibrate the system at constant temperature for ≈15–20 min or until stable performance is achieved. Make other instrumental adjustments in accord with expected Cl– concentration and calibrate the instrument with an appropriate selection of working standard solutions.
Analyse the reagent water blank, appropriate calibration solutions and unknown clarified or filtered soil extracts and calculate Cl– concentrations as described in Method 5A2a.
Report water-soluble Cl– (mg Cl/kg) on an air-dry basis.