Hyphenation of Sorbent Extraction and Solid-Matrix Time-Resolved Luminescence Using Tetracycline in Milk as a Model Analyte

Abstract

Hyphenation of sorbent extraction and solid-matrix time-resolved luminescence (TRL) was demonstrated using tetracycline (TC) in milk as a model analyte. The performance of a C18-impregnated silica layer was evaluated as both an extraction sorbent and a TRL substrate. To extract TC, a 10 x 6 mm glass-backed C18 layer was dipped into a 10 mL milk sample for 10 min followed by a 3-min water immersion for cleanup. The sorbent was then spotted with a TRL reagent solution at pH 9 that contained 5 mM europium nitrate and 5 mM EDTA. After a brief desiccation period, TRL was measured directly on the sorbent surface with a commercial fluorescence spectrophotometer. By eliminating the need to elute the analyte from the sorbent, organic solvent was not needed and sample preparation was greatly simplified. The integrated signal showed a linear dependence (R(2) = 0.9938) on TC concentration in the 0-3000 microg/L range. The same protocol was applicable to screening TC in fat-free, 2% low-fat, and whole milk at 300 microg/L, the US. regulatory tolerance level set by the Food and Drug Administration (FDA). This easy, fast, and low-cost screening method is friendly to the environment and particularly suitable for liquid samples.

Development and Validation of Europium-Sensitized Luminescence (ESL) Method for the Determination of Tetracycline Residues in Milk

“…Literature based on europium-sensitized fluorescence methods for tetracycline determination in milk is more scarce (Savage et al 1998;Gala et al 1997), and it includes only a few examples of solid-matrix time-resolved luminescence and stopped flow techniques; only recently has the method received renewed attention (Chen and Liu 2004;Traviesa-Alvarez et al 2007). …”

Time-Resolved Luminescence Screening of Antibiotics in Tissue Matrices without Centrifugation and Filtration: Spiked Recovery Studies

“…To improve efficiency, it can be integrated into the overall analytical scheme, for example, absorptiometry carried out directly on ion-exchange resin (1) or C18 surface (2) after extraction and enrichment. On the basis of this concept, we developed a methodology that combines sorbent extraction and solid-matrix TRL (SMTRL) using a small-format C18 layer that functions as a sorbent medium and a TRL matrix (3), demonstrated by a simple protocol to screen tetracycline in milk (4). With minor modifications its application can be extended from liquid to tissue matrices that cover broader food categories at a higher overall volume, demonstrated here by oxytetracycline (OTC) screening in catfish muscle.…”