Biomedical subjects

A R Long

Publications and source records attributed to A R Long.

48 records · Page 3Linked to original sources

PubMedDate not supplied

Gas chromatographic determination of chloramphenicol residues in shrimp: interlaboratory study.

An interlaboratory study of a gas chromatographic method for determining chloramphenicol (CAP) residues in shrimp was conducted. An internal standard (Istd), the meta isomer of CAP, was added to the shrimp, and the treated shrimp were homogenized with ethyl acetate. The ethyl acetate extract was defatted with hexane, and the CAP was partitioned into ethyl acetate from an aqueous salt solution. The ethyl acetate was evaporated, and the dried residue was treated with Sylon, a trimethylsilyl derivatizing agent, to yield the trimethylsilyl derivative of CAP. A portion of the solution containing the derivative was injected into a gas chromatograph equipped with an electron capture detector. Levels of fortified and incurred CAP were calculated from the peak area ratio of standard CAP to Istd. Recoveries of CAP from tissue directly fortified at 5 ppb were 102% (within-laboratory relative standard deviation [RSDr] = 5.6%), 104% (RSDr = 5.5%), and 108% (RSDr = 6.3%) from Laboratories 1, 2, and 3, respectively. Incurred-CAP residues at 5 and 10 ppb levels were also determined, with the following results: Laboratory 1: composite A, 4.56 ppb (RSDr = 14.0%); composite B, 8.38 ppb (RSDr = 11.6%); Laboratory 2: composite A, 4.17 ppb (RSDr = 12.5%); composite B, 8.90 ppb (RSDr = 5.60%); Laboratory 3: composite A, 4.66 ppb (RSDr = 14.9%); composite B, 11.0 ppb (RSDr = 11.8%).

Animals↗

PubMedDate not supplied

Preparation of milk samples for immunoassay and liquid chromatographic screening using matrix solid-phase dispersion.

The use of drugs to maintain the health and maximize the output of dairy cattle has made the monitoring of milk for such agents essential. Screening tests based on immunological, microbial inhibition, and bacterial receptor assays have been developed for the detection of violative levels of therapeutic substances. However, such assays are not infallible, and false positive or negative results can occur when contaminants bind receptors or compete for the binding of the target residues. Such effects may arise from dietary sources, diseases, or other variables. Thus, a violation by such a test is not definitive until further confirmation is obtained. Our laboratory has developed extraction procedures for several drugs used in dairy production. Our method uses matrix solid-phase dispersion (MSPD) to isolate drugs away from contaminants and to eliminate many possible interferences. MSPD can also be used to enhance the specificity of such assays by fractionating various classes of drugs that may cross-react. Similarly, such methods may be used for liquid chromatographic screening and confirmation of a suspect sample.

Animals↗

PubMedDate not supplied

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.

Animals↗

PubMedDate not supplied

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.

Animals↗

PubMedDate not supplied

Simultaneous determination of xylazine and its major metabolite, 2,6-dimethylaniline, in bovine and swine kidney by liquid chromatography.

A liquid chromatographic (LC) method is described for the simultaneous determination of xylazine (XY) and its major metabolite, 2,6-dimethylaniline (2,6-DMA), in bovine and swine kidney in the 25-100 ppb range. XY and 2,6-DMA are extracted from kidney with chloroform, followed by cleanup on an acidic Celite 545 column. A mu Bondapak phenyl column is used for LC separation with UV determination at 225 nm. The mobile phase is a mixture of acetonitrile, water, sodium acetate, and acetic acid. Mean recoveries from bovine kidney were 78.3% for XY, with a standard deviation (SD) of 7.45 and a coefficient of variation (CV) of 9.51%, and 87.2% for 2,6-DMA, with an SD of 8.38 and a CV of 9.61%. Mean recoveries from swine kidney were 80.8% for XY, with an SD of 5.92 and a CV of 7.33%, and 86.7% for 2,6-DMA, with an SD of 6.16 and a CV of 7.10%.

Aniline Compounds↗

PubMedDate not supplied

Determination and confirmation of identities of flumequine and nalidixic, oxolinic, and piromidic acids in salmon and shrimp.

A previously published liquid chromatographic (LC) method for determining residues of flumequine (FLU) and nalidixic (NAL), oxolinic (OXO), and piromidic (PIR) acids in catfish tissue was applied to salmon and shrimp muscle. Identities of all 4 residues in salmon and shrimp were confirmed by gas chromatography/mass spectrometry (GC/MS). The tissue is homogenized with acetone, the acetone extract is defatted with hexane, and the quinolones are extracted into chloroform. The extract is further purified by first partitioning into base and then back-extracting from a solution acidified to pH 6.0. Analytes are determined by LC with simultaneous UV and fluorescence detection. Muscle tissue was fortified with each quinolone at 5, 10, 20, 40, and 80 ng/g. Average recoveries and relative standard deviations (RSDs) for salmon, which represent an average of the 5 levels for each analyte, ranged from 75.9 to 90.8% and from 2.25 to 6.40%, respectively. Average recoveries and RSDs for shrimp ranged from 81.3 to 91.2% and from 7.34 to 10.7%, respectively. Identities of OXO, FLU, NAL, and PIR were confirmed in extracts of salmon and shrimp tissue fortified at 10 ng/g by determination of decarboxylated quinolones by GC/MS. Four diagnostic ions were monitored for OXO, FLU, and PIR, and 5 ions were monitored for NAL. All ion relative abundances were within 10% of those calculated for standard decarboxylated quinolones. Optimum conditions for decarboxylation and GC/MS confirmation are given.

Animals↗

PubMedDate not supplied

Determination of methylene blue in channel catfish (Ictalurus punctatus) tissue by liquid chromatography with visible detection.

Methylene blue (MB) is a thiazine dye that, although not regulated for use with edible fish, may sometimes be used as a chemotherapeutic agent in the aquaculture industry. A liquid chromatographic (LC) method was developed for the determination of MB in fish muscle. MB was extracted from catfish tissue with an acetonitrile-acetate buffer solution containing hydroxylamine and toluenesulfonic acid, partitioned into methylene chloride, and cleaned up on alumina and carboxylic acid solid-phase extraction cartridges. MB concentrations were determined by LC with visible detection at 660-665 nm. Recoveries of MB from catfish fortified at 10-50 ng/g were 75-90% (RSDs, 5-12%). Leucomethylene blue also can be recovered from catfish tissue as the MB colored form at low levels with similar recoveries. Analysis of catfish exposed to MB in a bath treatment at 5 ppm MB for 1 h recovered 10-20 ppb of the drug in the muscle tissue. The low tissue concentration suggests poor absorption of this drug compared with other antifungal dyes that tend to concentrate and remain in fish tissue at high levels.

Absorption↗

PubMedDate not supplied

Zero control reference materials for infant formula methods development.

A zero control reference material (ZRM) for milk and soy-based infant formula was manufactured and characterized. The ZRM was free of retinyl palmitate and all-rac-alpha-tocopheryl acetate. The composition was similar to commercially available infant formula. The ZRM provides a valuable tool to ascertain method performance.

Animals↗

PubMedDate not supplied

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%.

Animals↗

PubMedDate not supplied

Liquid chromatographic method for analysis of All-rac-alpha-tocopheryl acetate and retinyl palmitate in soy-based infant formula using a zero-control reference material (ZRM) as a method development tool.

A liquid chromatographic method is described for analysis of all-rac-alpha-tocopheryl acetate, tocopherols, and retinyl palmitate in soy-based infant formula. The vitamins are extracted in isopropyl alcohol and hexane--ethyl acetate without saponification and quantitated by normal-phase chromatography with fluorescence detection. All-rac-alpha-tocopheryl acetate and retinyl palmitate are quantitated isocratically with mobile phases of 0.5% (v/v) and 0.125% (v/v) isopropyl alcohol in hexane, respectively. Recoveries from zero control reference material soy-based formula averaged 97.2% (n = 25) for retinyl palmitate and 100% (n = 25) for all-rac-alpha-tocopheryl acetate. Coefficients of variation ranged from 1.21 to 2.86% for retinyl palmitate and from 1.49 to 5.16% for all-rac-alpha-tocopheryl acetate. The method provides a rapid, specific, and easily controlled assay for analysis of vitamin A and vitamin E in fortified infant formula. Additionally, the method eliminates use of chlorinated solvents.

Anticarcinogenic Agents↗

PubMedDate not supplied

Liquid chromatographic method for analysis of all-rac-alpha-tocopheryl acetate and retinyl palmitate in milk-based infant formula using matrix solid-phase dispersion.

A liquid chromatographic method is described for analysis of all-rac-alpha-tocopheryl acetate, tocopherols, and retinyl palmitate in milk-based infant formula. The vitamins are extracted from infant formula without saponification by matrix solid-phase dispersion and quantitated by normal-phase chromatography with fluorescence detection. Retinyl palmitate and vitamin E are quantitated isocratically with mobile phases of 0.125% (v/v) and 0.5% (v/v) isopropyl alcohol in hexane, respectively. Results were similar to the certified and non-certified ranges for all-rac-alpha-tocopheryl acetate, retinyl palmitate, and tocopherols in the infant formula standard reference material (SRM) 1846. Results also compared favorably with the label declaration on a retail infant formula. Recoveries were determined on an analyte-fortified zero control reference material for milk-based infant formula and averaged 96.8% (n = 30) for retinyl palmitate and 91.5% (n = 25) for all-rac-alpha-tocopheryl acetate. Examination of 5 concentrations for each analyte gave results that were linear (r = 0.999) over the concentration examined, with coefficients of variation ranging from 1.02 to 5.86%. The method provides a rapid, specific, and easily controlled assay for analysis of retinyl palmitate and vitamin E in fortified infant formula. Additionally, the method minimizes solvent use by using only 14 mL solvent per extraction.

Animals↗

PubMedDate not supplied

Liquid chromatographic determination of flumequine, nalidixic acid, oxolinic acid, and piromidic acid residues in catfish (Ictalurus punctatus).

A peer-verified, liquid chromatographic (LC) method for simultaneous determination of residues of flumequine (FLU), nalidixic acid (NAL), oxolinic acid (OXO), and piromidic acid (PIR) in catfish muscle is presented. Sample workup involves homogenizing tissue with acetone, defatting with hexane, and extracting quinolones into chloroform. Sample is purified further by partitioning into base and then subsequently back-extracting into chloroform after acidifying the aqueous phase. After solvent is evaporated, the residue is diluted with mobile phase, and analytes are introduced into an LC system where separations are made with a 5 microns, reversed-phase polymer column and an isocratic, buffered acetonitrile-tetrahydrofuran mobile phase. Determinations are made by UV detection at 280 nm for PIR and by fluorescence detection (excitation at 325 excitation and emission at 365 nm) for the other 3 analytes. Each quinolone was used to fortify catfish muscle at 5, 10, 20, 40, and 80 ng/g. The following recoveries and relative standard deviation (RSD) values represent an average of the 5 levels for each analyte: FLU, 79.7% (RSD = 5.7%); OXO, 80.8% (RSD = 6.3%); PIR, 75.0% (RSD = 5.9%); and NAL, 87.1% (RSD = 10%). Assay of 5 levels (base incurred catfish, plus 4 dilutions with control catfish) of catfish muscle incurred with the 4 quinolones gave the following averages: FLU: base, 198 ng/g (RSD = 2.3%); dilutions, 98.0 ng/g (RSD = 4.2%), 61.6 ng/g (RSD = 4.4%), 21.6 ng/g (RSD = 2.8%), 9.24 ng/g (RSD = 8.7%); OXO, base, 257 ng/g (RSD = 6.9%); dilutions, 146 ng/g (RSD = 5.5%), 95.0 ng/g (RSD = 4.1%), 30.7 ng/g (RSD = 3.8%), 13.7 ng/g (RSD = 4.6%); PIR, base, 22.1 ng/g (RSD = 4.2%); dilutions, 13.7% ng/g (RSD = 6.7%), 6.49 ng/g (RSD = 15%), 2.65 ng/g (RSD = 15%); and NAL, base, 75.1 ng/g (RSD = 3.8%); dilutions, 42.3 ng/g (RSD = 5.1%), 24.1 ng/g (RSD = 6.3%), 8.59 ng/g (RSD = 4.8%). A second multiresidue analysis of the 4 quinolones was performed by an outside analyst. Average recoveries from catfish fortified at 5, 10, 20, and 40 ng/g were FLU, 75.9% (RSD = 4.0%); OXO, 84.0% (RSD = 5.5%); NAL, 85.6% (RSD = 8.9%); and PIR, 66.2% (RSD = 8.7%).

Animals↗