Roybal Je

Confirmation of avermectin residues in food matrices with negative-ion atmospheric pressure chemical ionization liquid chromatography/mass spectrometry

A multi-residue LC/MS method has been developed to confirm avermectin drug residues in several food matrices. Ivermectin (IVR), doramectin (DOR), eprinomectin (EPR) and moxidectin (MOX) are confirmed using atmospheric pressure chemical ionization (APCI) with negative ion detection and selected ion monitoring of three to four ions for each compound. The drug residues are extracted from tissue or milk using previously published procedures. IVR and DOR are confirmed at 20 ppb levels in fortified salmon muscle; IVR is also confirmed in tissue from salmon dosed with the drug. Residues of DOR, IVR, and EPR are confirmed in fortified milk at the 20 ppb level and in fortified beef liver at 40 ppb. Residues of MOX can also be confirmed in these matrices, but at slightly higher levels (40-80 ppb).

Application of size-exclusion chromatography to the analysis of shrimp for sulfonamide residues

The determination of several sulfonamide residues from shrimp tissue using size-exclusion chromatography is presented. Shrimp tissue is extracted with ethyl acetate. The extracted solution is evaporated to dryness and the re-dissolved residue is applied to a chromatographic column containing Sephadex LH-20 gel. Cleanup is performed using this size-exclusion procedure. Determination is accomplished utilizing liquid chromatography. Elution of the sulfonamides from a phenyl column is performed with a methanol: acetic acid: counter-ion mobile phase. Recovery of sulfonamide residues from shrimp range from 70 to 100%.

1-(4-hydroxyphenyl)-, 1-(2,4-dihydroxyphenyl)- and 1-(2,5-dihydroxyphenyl-2-bromoethanones: new labels for determination of carboxylic acids by high-performance liquid chromatography with electrochemical and ultraviolet detection

A method is presented for the derivatization and determination of carboxylic acids by high-performance liquid chromatography with electrochemical and ultraviolet detection. The derivatizing reagents used in this study were synthesized, and their suitability was investigated for determination of drugs and metabolites with carboxylic acid groups. Quinoxaline-2-carboxylic, benzoic and salicylic acids each labeled with 1-(4-hydroxyphenyl)-, 1-(2,4-dihydroxyphenyl)- and 1-(2,5-dihydroxyphenyl)-2-bromoethanone were the principal esters studied; in addition, some antibiotics and their salts were also esterified. Conditions of derivatization are relatively mild at 60 degrees C for 60 min or less, and the reaction is 76% complete. The detection limits are as low as 1 pmol for some acids. Clean-up steps are not required to remove excess derivatizing reagent.