Studies on residual antibacterials in foods. IV. Simultaneous determination of penicillin G, penicillin V and ampicillin in milk by high-performance liquid chromatography

Determination of penicillin V potassium in pharmaceuticals and spiked human urine by chemiluminescence

A simple and selective method for penicillin V potassium (PVK) determination by chemiluminescence (CL) was developed. Oxidation of PVK by alkaline hydrogen peroxide produces CL, which is greatly enhanced by N, N-dimethyl formamide (DMF) and N-cetyl-N,N,N-trimethylammonium bromide (CTMAB). Optimum conditions were established using luminometry. There is a linear relationship between the chemiluminescent peak height and the amount of PVK within the range 0.5–129.5 mg L−1, with a detection limit of 0.2 mg L−1. The coefficient of variation was 1.2% for 40 mg L−1 PVK solution (n = 7). The method is very simple, has high sensitivity and good selectivity, and is usable for process control. It was successfully utilized for the determination of PVK in pharmaceuticals and spiked human urine.

[Simultaneous determination of five penicillins in muscle, liver and kidney from slaughtered animals using liquid chromatography coupled with electrospray ionization tandem mass spectrometry]

A simple and rapid method for the simultaneous determination of five penicillins (ampicillin, penicillin G, penicillin V, oxacillin and cloxacillin) in muscle, liver and kidney tissues using high-performance liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS/MS) was developed. Mass spectral acquisition was done in the negative ion mode by applying selected reaction monitoring (SRM). The five penicillins were extracted with water, and the extracted solution was cleaned up on a C18 cartridge. Phenethicillin was added as an internal standard, and the extract was diluted with water for injection into the LC-ESI-MS/MS. The recoveries of the five penicillins were in the range of 77.3-99.8% from muscle, liver and kidney fortified at 10-250 ng/g. The detection limits for ampicillin were 6 ng/g in muscle and kidney and 15 ng/g in liver. For penicillin G and penicillin V, the detection limits were 2 ng/g in muscle and kidney and 5 ng/g in liver. For oxacillin and cloxacillin, the detection limits were 4 ng/g in muscle and kidney and 10 ng/g in liver. Twenty-three muscle, fourteen liver and twenty-two kidney samples from the markets were analyzed by this method. No penicillins were detected in any sample.

Solid-phase extraction followed by liquid chromatography-mass spectrometry for trace determination of beta-lactam antibiotics in bovine milk

A confirmatory assay able to unambiguously identify and quantify 10 approved-for-use beta-lactam antibiotics in milk below stipulated U.S. and EU tolerance levels is presented. beta-Lactams are extracted from 10 mL of intact milk by a Carbograph 4 cartridge. After solvent removal, residue reconstitution, and filtration, a completely transparent and uncolored extract is injected into a liquid chromatography -mass spectrometry (LC-MS) instrument equipped with an electrospray (ES) ion source and a single quadrupole. During the chromatographic run, the ES/MS system is operated first in the positive-ion mode (PI) and then in the negative-ion (NI) mode. This is done to circumvent matrix interferences resulting in remarkable signal weakening of the last-eluted analytes, when detecting them as [M+H]+ adduct ions. MS data acquisition is performed by a time-scheduled three-ion selected ion monitoring program. At the 5 ng/mL level, recoveries of the beta-lactams are between 70 (nafcillin) and 108% (cephalin), with relative standard deviations ranging between 5 (oxacillin) and 11% (amoxicillin and ceftiofur). The response of the ES/MS detector is linearly related to injected amounts up to 500 ng, irrespective of the chemical characteristics of the beta-lactams and the acquisition mode selected (PI or NI modes). Limits of quantification, based on a minimal value of the signal-to-noise ratio of 10, were estimated to be within 0.4 (cephalin) and 3 ng/mL (dicloxacillin). Analyses of milk samples taken after intramammary application of amoxicillin showed that 1.2 ng/mL of this penicillin was still present 6 days after treatment. At this concentration level, the identification power of the method is not weakened, as signals of the three product ions of amoxicillin are still well distinguishable from the background noise.

Pulsed electrochemical detection of sulfur-containing antibiotics following high performance liquid chromatography

Pulsed electrochemical detection (PED) following reversed-phase chromatography has been applied to the direct detection of sulfur-containing antibiotics, specifically, penicillins, cephalosporins, and lincomycin. The compounds are detected sensitively and selectively without the need for derivatization. Integrated pulsed amperometric detection (IPAD) yields limits of detection lower than UV detection for these compounds. Detection limits using an optimized IPAD waveform are typically 10 ppb or less. The high selectivity of PED for thiocompounds reduces sample preparation. This work is applied to the determination of penicillin and related analogues in various pharmaceutical formulations/preparations, including a chicken feed.

Simultaneous determination of beta-lactam antibiotics in milk by ion-pair liquid chromatography

A simple and rapid ion-pairing liquid chromatographic method was developed for the simultaneous determination of five penicillins (PCs), ampicillin (AB-PC), benzylpenicillin (PC-G), Dicloxacillin (MDI-PC) and nafcillin (NF-PC) in milk. These PCs are most frequently used for the treatment of mastitis of cows. These antibiotics were extracted with acetonitrile from milk and cleaned up by solid-phase extraction with a C18 cartridge. PCs were separated on a Kaseisorb LC ODS-300-5 column with a mobile phase (1 ml/min) of acetonitrile-methanol-0.05 M potassium dihydrogenphosphate (20:10:80, v/v/v) mixture containing 5 mM of sodium 1-decanesulfonate adjusted to pH 3.5 and UV detection at 210 nm. The average recoveries of five PCs from milk fortified at 0.5 and 1.0 micrograms/ml (n = 5) were 79.8-89.4% with relative standard deviations ranging from 2.7 to 7.2% The detection limit of PCs in milk were 0.03-0.05 microgram/ml.

Multiresidue determination of beta-lactam antibiotics in milk and tissues with the aid of high-performance liquid chromatographic fractionation for clean up

Screening of milk shipments for beta-lactam antibiotic residues is mandatory in the USA and is widely used in other countries. Interpretation of positive screening test results has been difficult. Only six beta-lactam antibiotics are approved for use in food-producing animals in the USA but many others are used in other countries. A multiresidue procedure was developed for identification and quantitation of unknown beta-lactam antibiotics. The residues were extracted with acetonitrile and tetraethylammonium chloride. The extract was concentrated by evaporation and filtered. The concentrated extract was then loaded onto an HPLC column in 100% 0.01 M KH2PO4 and eluted with an acetonitrile gradient. Fractions corresponding to analytes of interest were collected and tested for antibiotics using rapid milk screening tests. Fractions testing positive were analyzed by HPLC. The identity of beta-lactams was confirmed by treating a replicate with beta-lactamase.

Assay for cephapirin and ampicillin in raw milk by high-performance liquid chromatography--integrated pulsed amperometric detection

The FDA has issued guidelines governing the use of antibiotics in cattle and routinely tests for the presence of antibiotics in milk. Unfortunately, these compounds are often difficult to detect by direct methods because they often lack a chromophore or fluorophore. Integrated pulsed amperometric detection (IPAD) following reversed-phase liquid chromatography is well-suited for this analysis because it is selective, sensitive, and direct; i.e., derivatization is not required. This work involves the development of a simple, rapid assay for the determination of beta-lactam antibiotic residues in milk using HPLC-IPAD, specifically, ampicillin and cephapirin. Since the analyst studied here are detectable by UV detection, a comparison between IPAD and UV detection will be made. Sample preparation schemes that involve the extraction of antibiotics of interest from the milk matrix and subsequent cleanup are an important aspect of this project. These procedures will be discussed in detail. In addition, analytical figures of merit and IPAD wave form optimization will be addressed.

Determination of isoxazolylpenicillins residues in milk by ion-pair reversed-phase high-performance liquid chromatography after precolumn derivatization

A high-performance liquid chromatographic method has been developed for the determination of isoxazolylpenicillins (oxacillin, cloxacillin and dicloxacillin) residues in milk. This method involves extraction of the penicillins from milk with phosphate buffer pH 8, deproteinization by acidification with sulfuric acid followed by cleanup and concentration on a C18 solid-phase extraction column and reaction with 1,2,4-triazole and mercury(II) chloride solution pH 9.0 at 65 degrees C. The derivatized compound is eluted on a C8 column with a mobile phase containing acetonitrile, methanol and phosphate buffer (pH 6.5, 0.1 mol l(-1)) loaded with sodium thiosulfate and ion-pairing tetrabutylammonium hydrogenosulphate. The detection limit of the method is 2 microg l(-1) for oxacillin, 3 microg l(-1) for cloxacillin and 5 microg l(-1) for dicloxacillin in milk and the three penicillins have been quantified down to 15 microg l(-1) in line with the EU criteria of the directive No. 93/256/EEC.

Determination of ampicillin residues in milk by ion-pair reversed phase high performance liquid chromatography after precolumn derivatization

A high performance liquid chromatography method has been developed for the determination of ampicillin residues in milk. The method involves extraction of ampicillin from milk with trichloroacetic acid solution followed by concentration on a conditioned C18 solid phase extraction column, acetylation with acetic anhydride in aqueous solution (pH 8.0) at ambient temperature for 3 min followed by reaction with 2 M 1, 2, 4-triazole and 10(-2) M mercury (II) chloride solution (pH 9.0) at 65 degrees C for 10 min. The resulting product is eluted on a C18 column with a mobile phase containing phosphate buffer (pH 6.5; 0.1 M), the ion-pairing agent tetrabutylammonium hydrogenosulphate, acetonitrile and methanol. The detection limit of the method is 3 ng ml-1 in milk.

Liquid chromatographic analysis of antibacterial drug residues in food products of animal origin

This paper reviews recent developments in the liquid chromatographic (LC) methods of analysis for the residues of antibiotics (aminoglycosides, chloramphenicol, sulfonamides, tetracyclines, macrolides, beta-lactams, etc.) in food products of animal origin. The review also covers clean-up procedures, such as, ultrafiltration, liquid-liquid partition, solid-phase extraction, immunoaffinity, and matrix solid-phase dispersion, for use as extraction, deproteination, and concentration steps. The LC methods offer considerable potential for rapid automated analysis, and some may be used as direct screening for residues in meat and milk.

High performance liquid chromatography of penicillins with penicillin-enhanced luminol chemiluminescence detection

A high performance liquid chromatographic method with chemiluminescence detection for the determination of penicillin G and ampicillin is reported. The method is based on the enhancement of the luminol chemiluminescence with beta-lactam antibiotics. The linear relationship was obtained between the peak height and the concentration of penicillin G or ampicillin up to 15 nmol per 20 microL injection. Detection limits were 1 nmol for penicillin G and 0.5 nmol for ampicillin with a signal-to-noise ratio of 2. Relative standard deviations for five replicate measurements of 4 nmol/injection each of penicillin G and ampicillin were 2.1 and 2.3%, respectively.

Chromatographic methods of analysis for penicillins in food-animal tissues and their significance in regulatory programs for residue reduction and avoidance

Chromatographic methods for penicillin analysis in animal tissues play a significant role in the regulation of the use of these drugs in livestock production. Regulatory agencies rely on data generated from these methods to establish withdrawal times and to determine whether presumptive positive tissue samples from slaughtered animals intended for human consumption contain violative levels of penicillins to necessitate regulatory action. The need to develop sensitive, accurate, and reliable methods to support regulatory programs is examined together with emerging techniques that could be taken advantage of to improve the sensitivity and usefulness of current chromatographic methods for tomorrow's regulatory agency.

Chromatographic analysis of antibiotic materials in food

The monitoring of food materials for antibiotic residues is an area of increasing concern and importance due to the potential impact on human health. Large-scale screening applications require methods that are rapid, accurate, provide low detection limits and are free from interference. The problem is further complicated by the wide range of chemical functionalities and modes of operation exhibited by the antibiotic materials of physiological significance in use today. As demonstrated, chromatographic methods provide many of the advantages necessary for screening applications. Judicious choice of sample preparation method, separation mode and detection strategy can provide significant immunity from problems associated with the food matrix. Gas chromatography can provide extremely high separation efficiencies, however, only a limited number of antibiotic compounds are inherently volatile enough for direct analysis by gas chromatography. Derivatization to enhance the volatility of the antibiotic is one approach to overcome this limitation. Among the methods available, reversed-phase high-performance liquid chromatography is used extensively for the analysis of many antibiotic systems as it does not require derivatization and it combines relatively high separation efficiencies with low detection limits. The diverse group of properties exhibited by the antibiotic materials in use today suggests that the choice of detection strategy is a key component in the successful development of an analysis technique. Derivatization of the antibiotic material is frequently used to add either a fluorogenic of chromogenic moiety to the antibiotic compound to enhance detection. Derivatization procedures suffer from several limitations which are problematic when making measurements in complicated food matrices. Among the different detection modes utilized for antibiotic analysis, polarimetric detection has the potential to provide extremely selective detection of most antibiotic materials, and this selective response can minimize many of the constraints placed upon the separation system by the sample matrix. Although many of the separation modes used for antibiotic analysis are well developed, separations based on capillary electrophoretic methods have much potential in the field of antibiotic analysis. Future investigations are needed to extend the generality of these techniques and expand their use into the field of food analysis.

Liquid chromatographic determination of amoxicillin concentrations in bovine plasma by using a tandem solid-phase extraction method

We report a means of determining amoxicillin in bovine plasma by liquid chromatography with UV detection at 235 nm. Purification and concentration of extracts were accomplished by a tandem solid-phase extraction procedure with two reversed-phase columns. Separation of amoxicillin from interferences was improved by the incorporation of a crown ether in the solvent systems used both for the solid-phase extraction and the final high-pressure liquid chromatography. Cefadroxil was added as an internal standard. The average recovery of amoxicillin from plasma (n = 23) was 78.2 +/- 3.0%, and the within-run and between-run coefficients of variation ranged from 1.8 to 7.0%. The detection limit was estimated at 0.1 microgram/ml. This method was used to determine amoxicillin in bovine plasma after intramuscular administration of the drug.

[Gas chromatographic method for the analysis of residues of seven penicillins in food of animal origin]

A capillary gas chromatographic method is described for the determination of residues of benzylpenicillin, phenoxymethylpanicillin, methicillin, oxacillin, cloxacillin, dicloxacillin and nafcillin in bovine muscle, liver, kidney, adipose tissue and milk. The samples are extracted with acetonitrile under slightly acidic conditions, the co-extracted water is separated with the addition of sodium chloride and dichloromethane and discarded. Clean-up is performed by liquid/liquid partitioning steps and anion exchange chromatography. The penicillin residues are methylated with diazomethane. After derivatization, only the extracts from liver and kidney needed further clean-up using cartridges with a polar diol sorbent. The gas chromatographic procedure is based on split/splitless injection, programmed temperature vaporization, separation on a methyl silicone fused silica column and nitrogen-specific thermionic detection. Internal standardization is used for quantification. The limits of detection for all penicillins are well below 3 microgram/kg in milk and all tissues. Recoveries of spiked samples at 3 and 10 micrograms/kg are in the range of 65-80% for milk and 50-70% for bovine tissues.

Determination of penicillin G in milk by high-performance liquid chromatography with automated liquid chromatographic cleanup

Specific confirmatory tests are needed to identify and quantify beta-lactam antibiotic residues detected in milk at levels of less than 10 parts per 10(9) (ppb) by screening tests. A liquid chromatographic method for penicillin G was developed using the liquid chromatography system for cleanup as well as analysis. Milk was deproteinized with two volumes of acetonitrile. The acetonitrile was extracted with hexane-methylene chloride (1:1) and the remaining water layer was concentrated by evaporation. The water layer (2 ml = 5 ml milk) was injected onto a Polymer Laboratories PLRP-S column using a WISP autosampler with the solvent, 0.01 M pH 7.0 phosphate buffer (A). Penicillin G was eluted with acetonitrile (B) gradient A-B (100:0) (0-3 min)-(40:60) (25 min). Penicillin G eluted as a narrow band in less than 0.5 min. A narrow fraction containing penicillin G was collected and rechromatographed on the same type of column at low pH (1.96). This effectively separated penicillin G from interferences. Recoveries were 92 +/- 9% with a sensitivity limit near 2 ppb. The approach used is applicable to determination of other beta-lactam antibiotics but specific conditions for analysis must be determined for each one. The cleanup procedure can be automated using an autosampler, gradient controller, and fraction collector.

Determination of benzylpenicillin in plasma and lymph at the ng ml-1 level by reversed-phase liquid chromatography in combination with digital subtraction chromatography technique

A method for the determination of benzylpenicillin (Pc-G) at very low levels in plasma and lymph is described. Detection at 325 nm of the mercuric mercaptide of benzylpenicillinic acid was made by liquid chromatography via a pre-column derivatization method. By using a digital subtraction chromatography technique, the bioanalytical method could be applied to different kinds of samples whether interfering peaks were present or not. Two different clean-up steps were used for two concentration ranges 0.1-100 micrograms and 1-1000 ng Pc-G ml-1; namely, precipitation of a 100-microliters sample with acetonitrile, or precipitation of a 1- or 2-ml sample followed by concentration via liquid-liquid extraction. The pre-column derivative of Pc-G was achieved using mercury(II)chloride in the presence of imidazole. The blank samples required for the digital subtraction chromatography technique were obtained by penicillinase treatment. Standard curves were made in the two concentration ranges. The relative standard deviation (RSD) at 5 ng Pc-G ml-1 plasma was 4.9% and at 5 micrograms Pc-G ml-1 lymph it was 2.8%. The stability of Pc-G, including the problems with non-sterile samples, was studied.

Penicillins and cephalosporins. Physicochemical properties and analysis in pharmaceutical and biological matrices

Penicillins and cephalosporins belong to the most prescribed antibiotics. Despite the relatively extended knowledge of these drugs, the qualitative and quantitative analysis of the compounds still gives rise to many problems. These difficulties are due to the chemical instability of the common beta-lactam nucleus, the minor differences in chemical structures between the analogues, and the complex and relatively fast degradation of the compounds in aqueous solutions. In this review a compilation of the physicochemical properties, the degradation routes and methods for analysis of these substances in biological and other matrices is presented.

Effect of the silica support of bonded reversed-phase columns on chromatography of some antibiotic compounds

Chromatographic behavior of three types of antibiotics was investigated on bonded C18 and polymeric reversed-phase columns. With penicillins with carboxylic acid functions only, retention and separations on the two types of columns were similar. beta-Lactam antibiotics with basic functions did not give as sharp peaks on the C18 column unless a silanol blocking agent, tetramethyl ammonium chloride (TMA) was added. In 0.01 M orthophosphoric acid-acetonitrile, tetracyclines were separated on the polymeric reversed-phase columns, but not on the C18 columns. With addition of TMA, results on C18 and polymeric reversed-phase columns were nearly identical. Addition of an ion pair also improved separations on the C18 columns, but not as much as TMA. Interaction with the silica support of C18 columns was used to separate tylosin from interferences in extracts of biological materials. The results demonstrate the importance of interactions with the silica support in chromatography of basic antibiotics on C18 packings. These interactions can be either beneficial or detrimental to separations, depending on the conditions used.