Ultrasound-assisted matrix solid phase dispersive extraction for the simultaneous analysis of ß-lactams (four penicillins and eight cephalosporins) in milk by high performance liquid chromatography with photodiode array detection.

The application of ultrasound-assisted matrix solid phase dispersive extraction for the confirmatory analysis of 12 ß-lactam antibiotics in milk by high performance liquid chromatography with photodiode array detection has been proposed herein. Four penicillins (cloxacillin, dicloxacillin, oxacillin, and amoxicillin) and eight cephalosporins (cefaclor, cefadroxil, ceftiofur, cefuroxime, cefoperazone, cefazolin, cephalexin, and cefotaxime) are effectively extracted using a mixed sorbent of Quick Easy Cheap Effective Rugged Safe technique and OASIS HLB providing a matrix free from any endogenous interference. Examined analytes were well resolved on an Inertsil ODS-3 analytical column with a mobile phase of CH(3)COONH(4) (0.05 M) and acetonitrile delivered under a gradient program. 1,7-Dimethyl-xanthine was used as internal standard. The method was validated meeting the European Legislation determining linearity, selectivity, stability, decision limit, detection capability, accuracy, precision, and ruggedness according to the Youden approach. Recoveries of all antibiotics rated from 85.0 to 115.7%, while RSD values were <12.7%. Finally, the method was successfully applied to milk samples purchased from local market.

Development and validation according to European Union Decision 2002/657/EC of an HPLC-DAD method for milk multi-residue analysis of penicillins and amphenicols based on dispersive extraction by QuEChERS in MSPD format.

A precise and reliable method for milk residue analysis regarding five penicillins and three amphenicols by HPLC-diode array detection has been developed herein. The chromatographic separation was performed using a mobile phase of CH3 COONH4 (0.05 M) and ACN delivered by gradient program on a Kinetex(™) -C18 core-shell, 2.6 µm column, starting at a volume ratio of 95:5 and ending at 60:40 after 17 min, remaining stable for 3 more min. A modified matrix solid phase dispersion procedure was applied for the extraction and clean-up procedure of antibiotics using a mixture of Strata by Phenomenex and QuEChERS as a sorbent. The method was validated at the respective 0.5× MRL, MRL and 1.5 ×MRL level for each compound. Results were quantitated against the internal standard paracetamol (2 ng/µL) according to the matrix-matched approach. The method was validated in line with the EC guidelines as cited in the Decision 2002/657/EC. The within-laboratory reproducibility, expressed as a RSD, never exceeded 16%. All decision limit (CCα) values lay in the range between 35.2 and 56.3 µg/kg and the corresponding results for detection capability (CCß) were 39.9 and 61.9 µg/kg. Ruggedness was estimated according to the Youden approach.

An overview of the use of monoliths in sample preparation and analysis of milk.

Monolithic columns with a unique structure possess some exceptional characteristics, which make them an excellent tool in the hands of analytical chemists, not only for separation but also for sample preparation. Their much higher external porosity compared to conventional particle-packed columns results in higher permeability and low-pressure drop with higher separation efficiency. Till now, monolithic columns have been applied to the analysis of different analytical matrices: pharmaceuticals, biofluids, food matrices, environmental samples, biochemical species, proteomics, etc. Since they offer a great potential for the separation of complex mixtures, it can be expected that the interest in applying these columns will increase. As long as more experience is gained with monolithic column technology, the emergence of applications is expected to continue. The need of reduction in organic solvent consumption also justifies this trend, in the frame of environmentally friendly methods. More and more applications using monolithic columns arise. In the future, monolithic columns are expected to prevail especially in the field of miniaturization and in chip-based nano-LC systems. In this review, we try to summarize any attempt that has been reported in the analysis of a sample of great complexity like milk using the technology of the monoliths.

On the use of Kinetex(™) -C(18) core-shell 2.6 µm stationary phase to the multiclass determination of antibiotics.

Fast and accurate analysis is a prerequisite in all analytical fields especially in food, biological, pharmaceutical, and environmental samples. The new trend of ultra performance liquid chromatography (LC) has the main drawback of expensive instrumentation, which can't be easily found in low-budget analytical laboratories. The evolution of core shell technology has contributed to this direction, since ultra high efficiency can be achieved on common LC instrument platforms. Herein the novel core shell analytical column, KINETEX (™) 2.6 µm, (150 mm × 4.6 mm) was comparatively studied against two conventional reversed-phase silica-based and one monolithic column. Eight antimicrobial agents representing two different classes: penicillins and amphenicols, were separated using a typical 400 bar high performance liquid chromatography (HPLC) equipment. Comparison of column performance was carried out by calculation of the number of theoretical plates N, the tailing factor T(f) , the relative retention time RRT, the retention factor k, the resolution factor R(s) , and the precision of the retention time and peak area. Optimal chromatographic conditions were used to validate the method. Its applicability was proven by the analysis of veterinary drug formulations. The examined antibiotics were well resolved within 17 min. Limit of quantitation values were 25.9 ng for amoxicillin, 14.1 ng for ampicillin, 41.6 ng for thiamphenicol, 9.6 ng for oxacillin, 23.5 ng for florfenicol, 26.7 for cloxacillin, 23.5 ng for chloramphenicol and 42.3 ng for dicloxacillin for 20 µL injection volume. The developed method can be easily and readily transferred to any laboratory.

Application of ultrasound-assisted matrix solid-phase dispersion extraction to the HPLC confirmatory determination of cephalosporin residues in milk.

Ultrasound-assisted matrix solid-phase dispersion (MSPD) was applied to isolate eight cephalosporins (cefadroxil, cefaclor, cephalexin, cefotaxime, cefazolin, cefuroxime, cefoperazone and ceftiofur) from milk. Multi-residue analysis was subsequently performed by HPLC-diode array detection. Extraction yield by matrix solid-phase dispersion using Nexus sorbent was higher than various investigated SPE protocols. Three analytical columns, two conventional silica based and one monolithic, were compared based on resolution, peak shape and retention time. The optimum method using Chromolith RP-18e (100×4.6 mm) achieved separation in less than 16 min. Method validation was performed according to the European Union Decision 2002/657/EC, determining linearity, selectivity, stability, decision limit, detection capability, accuracy and precision. RSD values observed were lower than 15.3%. Recovery rates of examined antimicrobials from milk ranged from 93.8 to 101.9% for cefadroxil, from 94.7 to 103.6% for cefaclor, from 93.4 to 106.6% for cephalexine, from 104.1 to 115.3% for cefotaxime, from 97.1 to 105.6% for cefazolin, from 97.4 to 108.6% for cefuroxime, from 98.8 to 103.4% for cefoperazone and from 95.5 to 103.6% for ceftiofur. Correlation coefficients ranged from 0.9926 to 0.9999. CC(b) values were in the range from 103.5 to 112.3 µg/kg for analytes with a maximum residue limit of 100 µg/kg and from 54.4 to 56.3 µg/kg for those with a maximum residue limit of 50 µg/kg.