ABSTRACT
This study reviews the effect of different gamma radiation doses (1, 3, 5, 10 and 20 kGy) on the degradation of chlorfenvinphos, diazinon, dimethoate, and profenofos at different concentrations (0.5, 1.0, and 5 µg/mL) in aqueous solutions (deionized, tap, and groundwater). The role of initial concentration, measured total dissolved solids and pH on degradation was investigated. The degradation of the four tested organophosphates due to gamma irradiation was determined using LC-MS/MS. The radiolytic degradation products were studied using the scan mode of GC-MS/MS. The radiation chemical yield, dose constant, D0.5, and D0.9 were calculated to evaluate degradation efficiency for each compound. All pesticides are completely eliminated, despite water type, at low concentration levels of 0.5 and 1 µg/mL. At concentration level 5 µg/mL, gamma irradiation could completely remove pesticides concentration in de-ionized water, but the binding effect of total dissolved solids decreased degradation efficiency of some organophosphates such as diazinon. The D0.9 of 5 µg/mL concentration of chlorfenvinphos, diazinon, dimethoate, and profenofos in de-ionized water were 6.6, 8.7, 11.0, and 17.6 respectively. Also, Gamma irradiating of an agriculture wastewater sample resulted in the removal of carbaryl, carbosulfan, and diazinon at 6 kGy dose.
ABSTRACT
This paper reports a practical approach for the stability testing of 37 veterinary drugs in stock standard solutions stored at -20°C for 1-3 years and the study of expiry date extension of 7 expired reference standard materials stored at 4°C. Stored stock solutions were compared versus freshly prepared stock solutions and concentrations determined using LC-MS/MS. The validity of expired reference materials was tested by new valid reference materials. LC-MS/MS method and parameters were optimised to get the maximum signal stability of the analytes. Statistical analysis was developed and performed to evaluate the stability results according to the acceptability criteria of 10% set by the European Commission guidance document SANTE/11813/2017. The stability of most of the stock solutions of the following veterinary drug families: ß-agonists, illegal dyes, inhibitors, macrolides, penicillins, quinolones, sulfonamides and tetracyclines ranged from 12 to 36 months. ß-Agonist compounds have the maximum stability period of 36 months while penicillin's stock solution in methanol showed the least stability. The results of testing the expiry date extension of reference standard materials demonstrated that there was no any deterioration of all tested compounds after manufacturer expiry date by 4-7 years.
