Some factors affecting the concentration of available chlorine in commercial sources of sodium hypochlorite

To evaluate the availability, effect of storage, dilution and heating on some commercial sources of sodium hypochlorite (NaOCl).

All pharmacies in a Regional Health Authority were telephone surveyed to establish the proprietary and nonproprietary NaOCl products available, their cost and concentration. Ninety-six freshly produced bottles of a commercially available thin household bleach (J. Sainsbury's) were randomly stored in four different modes (full 1 L bottles in dark at room temperature, half-empty 1 L bottles under the same conditions, full 200 mL bottles under the same conditions, full 200 mL bottles stored at 37 degrees C) up to 6 months. The available chlorine in the bleach solutions was evaluated at specific time intervals (0, 1, 2 weeks, 1, 2, 3, 4, 6 months) using iodometric titration. Four brands of commercially available bleaches (J. Sainsbury's Thin Household Bleach, Tesco's Value Bleach, Tesco's Red Label Bleach, Safeway's Savers Bleach) were diluted (by 1 : 1, 1 : 2 or 1 : 3 dilution factors) and samples taken from each dilution for titration to test predictability. NaOCl solutions (5% w/w) were heated in covered or uncovered beakers up to 60-85 degrees C. Samples were taken from each beaker at time 0 and each h up to 4 h, for titration.

Of the 116 pharmacies, 33% could supply a proprietary product and 53% a nonproprietary product. In all, 78% were able to supply a NaOCl product. There was no significant difference (P < 0.05) in available chlorine at baseline between the different modes of storage. After storage at room temperature for 6 months, there were no significant differences (3% of original; P > 0.05) between the different modes of storage. When the storage temperature was 37 degrees C, however, there was a significant difference (38% of original; P < 0.01) at 6 months. Comparison of baseline with the concentrations of available chlorine at 6 months showed significant differences (P < 0.01) for all conditions. The available chlorine concentration in four brands of 'thin' supermarket bleaches could be predictably reduced according to the dilution factor. When 5% NaOCl was heated to 60-85 degrees C for up to 4 h, the available chlorine was increased to 6% in covered solutions and 9% in uncovered solutions.

Both proprietary and nonproprietary solutions of NaOCl should be relatively easily obtainable in the UK. Stored under appropriate conditions, commercially available thin bleaches and nonproprietary solutions of NaOCl may be diluted to obtain predictable concentrations. Heating solutions of NaOCl may cause unpredictable changes to the concentration, depending upon conditions.