Confirmation of patulin and 5-hydroxymethylfurfural in apple juice by gas chromatography/mass spectrometry

A gas chromatographic/mass spectrometric (GC/MS) method was developed for the confirmation of patulin and 5-hydroxymethylfurfural (HMF) extracted from apple juice. The extraction is based on the official AOAC method for liquid chromatographic analysis. Juice extracts are quickly and easily derivatized with bis(trimethylsilyl)trifluoracetamide under mild conditions, and the trimethylsilyl ethers of the analytes are stable for at least several hours. The analytes are determined by GC/MS using an electron-impact source and selected ion monitoring of characteristic ions. For both analytes, the interassay differences between base-peak ratios for samples and standards were all <7.1% (absolute). The presence of patulin was confirmed at fortification levels of about 30-400 microg/L and naturally occurring levels of about 80-400 microg/L. The presence of HMF was also confirmed at levels < or = 2 mg/L. The proposed mass spectral fragmentation pathways of the analytes are presented.

Simultaneous determination of residues of chloramphenicol, florfenicol, florfenicol amine, and thiamphenicol in shrimp tissue by gas chromatography with electron capture detection

A gas chromatographic (GC) method is presented for determining residues of chloramphenicol (CAP), florfenicol (FF), florfenicol amine (FFa), and thiamphenicol (TAP) in shrimp tissues, with meta-nitrochloramphenicol (mCAP) as the internal standard. The composited shrimp is extracted with basic ethyl acetate, followed by an acetonitrile-basic ethyl acetate mixture. This extract is centrifuged, filtered, evaporated, and reconstituted in water; the reconstituted extract is acidified, defatted with hexane, and passed through a propylsulfonic acid (PRS) and C18 solid-phase extraction (SPE) system. The C18 SPE column is eluted with methanol, and the PRS SPE column is eluted with basic MeOH plus counter ion. The combined eluates are evaporated, reconstituted in acetonitrile, and derivatized with Sylon BFT. After derivatization, the addition of toluene directly to the sample, followed by the addition of basic water, quenches the derivatization process. After centrifugation, the organic layer is carefully removed, and the analytes are determined by GC with electron capture detection. Shrimp tissues were fortified with fenicols (i.e., CAP, FF, FFa, and TAP) at 5, 10, 20, 40, and 80 ng/mL. Overall recoveries were 88, 101, 91, and 84% with overall interassay (between-day) variabilities (i.e., relative standard deviations) of 5.3, 9.4, 12.8, and 7.4% for CAP, FF, FFa, and TAP, respectively. The method detection limits were calculated as 0.7, 1.4, 2.4, and 1.3 ng/g (ppb) for CAP, FF, FFa, and TAP, respectively, based on a 10 g sample. The quantitation limit as determined empirically by this method is the lower limit of the standard curve, which is about 5 ng/g (ppb) for each analyte.

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).

Determination of ivermectin in salmon muscle tissue by liquid chromatography with fluorescence detection

A liquid chromatographic method was developed for determination of ivermectin B1a (IVR) extracted from raw fortified and incurred Atlantic salmon muscle tissues. The method was also used to determine fortified doramectin (DOR) in Atlantic salmon. Tissue extract was applied to C8 solid-phase extraction (SPE) column, followed by a silica SPE column. Residues in the eluate were treated with trifluoroacetic anhydride and methylimidazole to dehydrate the IVR molecule and form an aromatic fluorescent moiety with a trifluoroacetic ester. This product was subsequently treated with ammonium acetate in methanol to cleave the ester and convert the functional group back to a stable alcohol form. The analytes were determined by fluorescence with excitation at 272 nm and emission at 465 nm. A C18 Hypersil column was used for analysis with a mobile phase of acetonitrile-water (90 + 10, v/v) and an oven temperature of 65 degrees C. IVR and DOR were determined at 5 fortification levels (1, 5, 10, 20, and 40 ppb). Intra-assay absolute recoveries ranged from 75 to 89% for IVR and from 73 to 85% for DOR. Relative standard deviations (RSDs) were < 7% in all cases. The limit of detection (3 x baseline noise) was 0.25 ppb extracted from tissue. Incurred tissues had an average concentration of 32 ppb, with an RSD of 3%.

Particle beam liquid chromatography-mass spectrometry of triphenylmethane dyes: application to confirmation of malachite green in incurred catfish tissue

Eight triphenylmethane dyes (malachite green, leucomalachite green, gentian violet, leucogentian violet, brilliant green, pentamethyl gentian violet, N',N'-tetramethyl gentian violet and N',N"-tetramethyl gentian violet) have been characterized by particle beam liquid chromatography-mass spectrometry. The electron ionization spectra obtained of these dyes by this technique exhibit similar fragmentation, with the formation of phenyl and substituted phenyl radicals, and loss of alkyl groups from the amines. It was observed that the six cationic dyes are reduced in the mass spectrometer source to form the corresponding leuco compounds. This technique was evaluated for the confirmation of malachite green and leucomalachite green in incurred catfish (Ictalurus punctatus) muscle tissue.

Determination of flunixin in milk by liquid chromatography with confirmation by gas chromatography/mass spectrometry and selected ion monitoring

A liquid chromatographic (LC) method was developed for the determination of flunixin (FNX) in raw bovine milk. The milk was acidified and mixed with silica gel, and the mixture was packed into a chromatographic column. The column was defatted with water-saturated dichloromethane-hexane (30 + 70, v/v), and the analyte was eluted with EtOAc. The EtOAc extract was washed with water at pH 3.5, the water was discarded, and the EtOAc layer was then extracted with 0.1M NaOH. The aqueous layer was drained, passed through a primed C18 solid-phase extraction (SPE) column, and eluted with EtOAc. The EtOAc layer was dried under N2, taken up in a solution of MeOH-(5 mM tetrabutylammonium [TBA]-H2PO4 + 2 mM NaOH) (50 + 50), sonicated, and filtered. FNX was determined by LC using a C18 column (ODS Hypersil), a mobile phase mixture of 58% A (MeOH) and 42% B (5 mM TBA-H2PO4 + 2 mM NaOH), and a diode-array ultraviolet detector at 285 nm. FNX was determined in raw milk at 5 spiking levels (5, 10, 20, 40, and 80 ng drug/mL milk). Absolute recoveries ranged from 69.6 to 74.4%, and relative standard deviations ranged from 1.1 to 6.9%. The limit of quantitation was 1.7 ng drug/mL milk. A lactating cow was dosed intravenously (2.2 mg/kg) with flunixin meglumine (Banamine) to generate incurred milk residues. FNX residues ranged from 7.34 ng/mL at 16 h postdose to 1.74 ng/mL at 24 h postdose. Both levels were obtained with additional beta-glucuronidase treatment (almost no incurred drug was detected at these low levels without the enzyme treatment).(ABSTRACT TRUNCATED AT 250 WORDS)

Simultaneous determination of nitrofurazone, nitrofurantoin, and furazolidone in channel catfish (Ictalurus punctatus) muscle tissue by liquid chromatography

A liquid chromatographic (LC) method was developed for the simultaneous determination of nitrofurazone (NFZ), nitrofurantoin (NFT), and furazolidone (FZD) in catfish muscle tissue. The drugs were extracted from the tissue with acetonitrile, and the lipids were removed from the extract with hexane. The acetonitrile extract was evaporated by rotary evaporation, and the resultant drug residues were dissolved with LC mobile phase. The mixture was sonicated, centrifuged, and filtered. The drugs were determined by using LC with a C18 reversed-phase (ODS Hypersil) column, a mobile phase of acetonitrile-1% aqueous acetic acid (25 + 75), and a photodiode array ultraviolet detector at 375 nm. NFZ, NFT, and FZD were each determined in catfish tissue at 5 fortification levels (80, 40, 20, 10, and 5 ng drug/g tissue). Average recoveries of each of the 3 drugs at each level ranged from 70.7 to 101.5%, and relative standard deviations ranged from 2.2 to 18.6%. The limit of detection of each drug was approximately 1 ng drug/g tissue, and the limit of quantitation was 5 ng drug/g tissue. In the second part of the study, the method was used to determine nitrofuran residues incurred in catfish tissue. Live channel catfish were intravascularly doses (10 mg/kg body wt) with NFZ to generate drug-incurred fish muscle tissue. Incurred NFZ levels exceeded 400 ng drug/g tissue at 2 h after dosing but decreased rapidly to approximately 1 ng drug/g tissue by 8 h after dosing, as determined by this method.

Simultaneous determination of nitrofurazone and furazolidone in shrimp (Penaeus vannamei) muscle tissue by liquid chromatography with UV detection

A liquid chromatographic (LC) method was developed for the simultaneous determination of nitrofurazone (NFZ) and furazolidone (FZD) in shrimp muscle tissue. The drugs are extracted from the tissue with acetonitrile, and the lipids and lipophilic pigments are removed from the extract with hexane. The remaining acetonitrile extract is evaporated by rotary evaporation, and the resultant residues are dissolved with LC-grade water, applied to a preconditioned C18 solid-phase extraction column, and eluted with acetonitrile. The acetonitrile eluant is then dried under nitrogen, and the resultant drug residues are dissolved with mobile phase and filtered. The drugs are determined by LC by using a C18 reversed-phase (octyldecylsilyl Hypersil) column, a mobile phase of acetonitrile--1% aqueous acetic acid (25 + 75, v/v), and a photodiode array UV detector at 375 nm. NFZ and FZD were determined in shrimp tissue at each of 5 spiking levels (64, 32, 16, 8, and 4 ng drug/g tissue). Absolute recoveries ranged from 70.6 to 78.4%, and relative standard deviations ranged from 4.0 to 13.6%. The limit of detection of pure standard of each drug was approximately the equivalent of 1 ng drug/g tissue, and the limit of determination in a sample was 4 ng drug/g tissue.