Spreeta-based biosensor immunoassays to detect fraudulent adulteration in milk and milk powder

Biacore biosensors (Biacore AB, Uppsala, Sweden) have proven to be robust analytical tools for the automated immunochemical detection of different adulterants and contaminants in milk and milk powder. However, the significant cost of the instruments is a disincentive for their wide application in food control laboratories. Therefore, a low-cost alternative optical biosensor (Spreeta, Texas Instruments, Attleboro, MA) was built into an affordable liquid handling system. Using this prototype biosensor, an inhibition immunoassay for bovine K-casein was evaluated for the detection of cow's milk in ewe's and goat's milk and for the detection of bovine rennet whey powder in milk powder. Comparable sensitivities were obtained for both adulterants in the Spreeta-based prototype biosensor and a Biacore 3000 instrument. The limit of detection for cow's milk was 0.17% (v/v) and bovine rennet whey powder could be detected in milk powder above 1% (w/w). The Spreeta sensor was also useful in the control of fraudulent water additions to milk, simply by measuring differences in the bulk response.     

Determination of free clindamycin,flucloxacillin or tedizolid in plasma: Pay attention to physiological conditions when using ultrafiltration

Pharmacokinetic/pharmacodynamic indices of anti-infective drugs should be referenced to free drug concentrations. In the present study, clindamycin, flucloxacillin and tedizolid have been determined in human plasma by HPLC–UV. The drugs were separated isocratically within 3–6 min on a C₁₈ column using mixtures of phosphate buffer–acetonitrile of pH 7.1–7.2. Sample treatment for the determination of total drug concentrations in plasma included extraction/back-extraction (clindamycin) or protein precipitation (flucloxacillin, tedizolid). The free drug concentrations were determined after ultrafiltration. An ultrafiltration device with a membrane consisting of regenerated cellulose proved to be suitable for all drugs. Maintaining a physiological pH was crucial for clindamycin, whereas maintaining body temperature was essential for tedizolid. The methods were applied to the analysis of total and free drug concentrations in clinical samples and were sufficiently sensitive for pharmacokinetic studies and therapeutic drug monitoring.