الفهرس 
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Abstract
Diquat (1,1’-ethylene-2,2’-bipyridylium dication) is a quaternary ammonium herbicide with fast acting and broad spectrum contact activity. It is widely used in Egypt as pre-harvest desiccants to facilitate mechanical harvest of potato. Unfortunately, the residues of diquat can’t be determined easily by the commonly used multi residue methods due to its high polarity and basic characters. Therefore, a rapid and accurate method for the analysis diquat residues in potato is needed in order to monitor the handled foods in local markets and to prevent the rejection cases when exported due to high levels of the residues. Considering the previous background, the present work aimed to develop, optimize, evaluate and validate such method. The developed method complies with the national and international MRLs of diquat in potato.
The obtained results could be summarized as follows:
1- A reversed phase liquid chromatography method for the determination of diquat was developed. The chromatographic separation is done under a temperature of 40°C with 2 μL injection volume. Diquat is separated using iso-crataic elution of 10% 50 mM ammonium acetate in deionized water with 0.1% formic acid as eluent A and 90% acetonitrile as eluent B at 0.6 mL/min flow rate on a Kinetex C18 column.
2- MS/MS detection was executed using electrospray ionization in the positive ion mode with the multiple reaction monitoring (MRM) mode. The precursor ion was 183 m/z which could be either the dehydrogenated molecular ion radical [M+•−H] or the deprotonated molecule [M2+−H+]. The product ions used in the method were 157 m/z and 130 m/z.
3- Different sample preparation parameters (pH modifier type, sample size effect, and elevated temperature effect) have been tested and optimized. The final conditions involve the usage of 10 mL acetonitrile on 5 g of potato sample under elevated temperature and basic conditions using ammonium hydroxide. Phase separation was achieved by shaking the extract with magnesium sulfate and sodium chloride.
4- The procedure was validated on potato in accordance with the method validation criteria stated in the document SANTE/11945/2015. The precision and trueness of the method were determined from recovery experiments on five replicates of spiked blank potato samples at 0.01, 0.05 and 0.1 mg/kg. The range of the obtained recoveries was from 74 to 110% and their RSD% was less than 5% for all the concentrations.