Does sodium lauryl sulfate concentration vary with time?

When performing skin irritation tests with sodium lauryl sulfate (SLS), the quality of the test solution is of major importance for the reproducibilit y and comparability of the results. The influence of 4 different storage pa rameters (concentration, duration, temperature, material of the storage via ls) on the stability of aqueous SLS solutions was investigated under non-st erile conditions. SLS solutions at 5 different concentrations (0.001%. 0.01 %, 0.1%o. 0.5%, 1%) were analysed by mobile phase ion chromatography. Analy ses were performed after a storage time of 3 h, 1 week, and 4 weeks. Storag e was carried out at different temperatures: -18 degrees C, 6 degrees C, an d 23 degrees C. The storage containers were of 2 different materials (glass and polypropylene). After a storage of 1 week, no decrease in SLS concentr ation was observed, regardless of the chosen conditions. After 3 weeks at 6 degrees C and 23 degrees C, the SLS concentration was found to be signific antly decreased for the 2 lowest concentrations (0.001% and 0.01%). At high er concentrations and lower temperatures, no decrease in SLS concentration had occurred. In parallel to the loss of SLS, contamination with bacteria w as found in the solutions, especially at the 2 lowest concentrations. Bacte rial growth was not observed at higher concentrations. The possibility of b iodegradation of SLS has to be taken into account, especially when dealing with low concentrations of SLS.