Influence of solvent and storage conditions on the stability of acaricide standard stock solutions

The stability of bromopropylate, coumaphos, amitraz and chlordimeform stock solutions in methanol and in n-hexane and the incidence of storage conditions have been studied using GC-MS. It has been found that the initial concentrations have a progressive depletion from the starting time, this fact is more important when methanolic solutions are stored at room temperature. Several degradation products have been detected and identified, their concentration has been rising during storage time. A lifetime for the stock solutions should be established on the basis of their diminishing concentration percentages in order to avoid further errors in quantitative analysis, below the limit the solutions should be changed for new ones.