In order to find the proper reduction method of the impurities produced by alliinase activity in Allium crops (garlic, onion, shallot and welsh onion etc.), the new analytical method for pesticide residues using HPLC/UVD(DAD) were investigated.
The impurities, containing organic sulfur compounds with double bond and unpaired electrons, have influenced HPLC/UVD determination as chromophores.
In this experiment, the more effective analytical method were investigated with removal of interferences originated by Allium crops.
Firstly, pH change and temperature control were introduced to remove the intereference.
Before homogenizing the sample, strong acid (pH 2) and strong alkali (pH 12) were added to the sample and were found 81.1% and 68.4% of removal effects, respectively. In this process some pesticides were decomposed by strong acidic and alkalic condition.
Then, it was found that the frozen sample (at -20℃) also removal efficiency of 68.7% ~ 76.1% in Welsh onion and 66.8% ~ 77.8% in shallot, respectively.
Therefore, mixing with dryice to sample were selected for the proper method to keep low temperature during analysis. Mixing ratio of 0.5 ~ 1.0 (dryice/sample, w/w) was shown to reliable result for removal of impurities.
Using dryice it was achieved 87.2% of removal efficiency in shallot, and the efficiency was getting decreased by time course, 48.1% in 2 hrs later.
Recovery were satisfied in 70%～120% of analytical guideline in almost pesticides. Among 70 pesticides, 9 of them were affected by impurities and showed over 130% recovery level such as boscalid, teflubenzuron, acetamiprid etc.
Even those Pesticides also showed 90%～120% recovery removing the matrix effect by UPLC/MS analysis
Comparing with existing pesticide residue method, The new improved method was shown the high removal efficiency in Welsh onion of 93.7%, shallot of 87.2%, garlic of 46.3% and onion of 66.5%