Evaluation of an automated and integrated flow-through immunoanalysis system for the rapid determination of cephalexin in raw milk

In the present work, an evaluation of an automated flow-through amperometri c immunoanalysis system for the quantitation of the antibiotic drug cephale xin (Ce) in milk is described. The detection limit of the method was calcul ated as 1 mug/l (S/N = 3), while the quantitation limit being 3 mug/l, well below the EU regulation mandated limit of 0.1 mg/kg for cephalexin in milk . Spiked mills samples with increased concentrations of cephalexin were inv estigated as blind coded duplicate samples. Total 20 milk samples spiked wi th cephalexin between 3 and 30 mug/l were analyzed leading to a good correl ation referred to the spiked values. The samples could be detected with a m ean recovery of 97 +/- 23%, indicating a good agreement with the spiked con centration. The precision and repeatability was determined using spiked sam ples with four different concentrations which were investigated on four dif ferent days. A mean within-day variation of 6.9% and a mean between-day var iation of 10.9% were obtained. Correct classifications were achieved in fal se negative and false positive studies when the cut-off values were set at 2.0 and 3.7 mug/l, respectively, further proving the detection and quantifi cation capabilities of the method. The method was specific for cephalexin a nd free of interferences from other cephalosporins and penicillins at conce ntrations up to at least 1000 mug/l. Milk matrix properties in terms of bac teriological quality, somatic cell content, and pH have no significant effe cts on the determination. The effect of the milk fat was eliminated by a si mple-defatting step. For the investigation of samples with concentrations h igher than 30 mug/l, a dilution step for the sample would be required. In a ddition, 17 natural contaminated milk samples of cephalexin-treated cows we re also analyzed and the results obtained were confirmed by an enzyme-linke d immunosorbent assay (ELISA) method. This intra-laboratory study demonstra ted that the proposed method is suitable for the rapid and reliable determi nation of cephalexin in raw milk samples. (C) 2001 Elsevier Science B.V All rights reserved.