Overview
ISO 2121:1972 specifies a gravimetric method for determining the volatile water content of liquid chlorine for industrial use. The procedure targets the water fraction that volatilizes with chlorine during gasification and is applicable to products with water content greater than 0.0005 % (m/m) (5 ppm). The standard describes sampling by gasification, absorption of water in tared absorbers, elimination and absorption of gaseous chlorine, and gravimetric determination of moisture by mass difference.
Key Topics and Requirements
- Scope: Measurement of volatile water in industrial liquid chlorine; not suitable for samples stored in corrodible bottles (risk of hygroscopic ferric chloride contamination).
- Detection limit: Applicable for water content > 5 ppm (0.0005 % m/m).
- Principle:
- Gasify an accurately metered sample of liquid chlorine.
- Pass the gas through tared absorbers containing either phosphorus pentoxide (P2O5) or magnesium perchlorate (Mg(ClO4)2) to absorb volatile water.
- Flush the absorbers with dry air or nitrogen heated to about 80 °C to remove gaseous chlorine and other volatile impurities.
- Absorb the outgoing chlorine in a tared bottle containing sodium hydroxide solution (approx. 200 g/L or ~5 N).
- Determine water mass by reweighing absorbers and calculating the mass difference.
- Apparatus and reagents: Tared absorber tubes (T1, T2, T3), flacon with NaOH (2 L), flowmeter/manometer to control ~25 L/h chlorine flow (~100 L total sample), barboteur with iodized starch for absorption check, U-tube filters, and chlorine-resistant tubing and greases.
- Quality control:
- Use three absorber tubes to monitor breakthrough (T1 primary; T2/T3 guards).
- Results expressed in g/kg with two-decimal precision.
- Annex: Procedure to check hydration level of magnesium perchlorate dessicant by calorimetric dissolution (sample, Dewar, temperature rise vs. calibration curve).
Applications
- Quality control and acceptance testing for suppliers and users of industrial liquid chlorine.
- Moisture determination for chlorine used in water treatment, chemical synthesis, bleaching, and disinfection processes where moisture affects reactivity, corrosion, or downstream processes.
- Analytical laboratories performing routine chlorine product testing and compliance verification.
Who should use this standard
- Analytical chemists and QA/QC laboratories in chlorine production, chemical manufacturing, and water treatment sectors.
- Transport and storage operators responsible for product specification and quality certificates.
- Health, safety and regulatory personnel overseeing safe handling and testing of chlorine consignments.
Safety & Practical Notes
- Chlorine is a vesicant and irritant; workplace concentration must remain below 1 ppm (3 mg/m³). Use appropriate PPE, ventilation, and trained personnel.
- Avoid analyzing samples from corrodible containers to prevent biased moisture results.
Related standards
- Refer to other ISO standards on gas sampling, industrial gas analysis, and chlorine handling for complementary guidance (sampling practice, safety, and instrumentation).