Short‐term storage stability of Na OC l solutions when combined with Dual Rinse HEDP

Aim To assess the stability of Na OC l solutions when combined with a novel product for clinical use, Dual Rinse HEDP , which contains etidronate (1‐hydroxyethane 1,1‐diphosphonate). Methodology Mixtures of Na OC l solutions with Dual Rinse HEDP were prepared so that they initially contained 5.0%, 2.5% or 1.0% Na OC l and always 9.0% of dissolved Dual Rinse HEDP powder per total weight. Na OC l solutions alone were used as controls. The stability of these solutions over 8 h was assessed in transparent borosilicate glass bottles at ambient temperature (23 °C). Subsequently, the effects of heating (60 °C) or storing the solutions at 5 °C were studied in polypropylene syringes. Na OC l concentrations were measured by iodometric titration, that is free available chlorine contents. Experiments were performed in triplicate. Results In the glass bottles at 23 °C, the 5.0% Na OC l/9.0% Dual Rinse HEDP solution lost 20% of the available chlorine after 1 h, whilst the corresponding 2.5% Na OC l and 1.0% Na OC l solutions retained this relative amount of available chlorine for 2 and 4 h, respectively. Results obtained in the glass bottles were similar to those achieved in the syringes. Heating of the Na OC l/Dual Rinse HEDP mixtures had a detrimental effect on available chlorine, with a complete loss after 1 h. In contrast, storing the Na OC l/Dual Rinse HEDP mixtures in a refrigerator at 5 °C kept the available chlorine high for 7 h, with the expected loss after a further hour of storage at 23 °C. Conclusions Initial Na OC l concentration and temperature both affected short‐term storage stability of combined solutions containing Dual Rinse HEDP .