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Title:   Author  item
                                            Chen, Guoyingitem
                                            Liu, Linshu
  Submitted to: Journal of Agricultural and Food Chemistry
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 8/10/2004
                                    Publication  Date: 10/20/2004
                                    Citation: Chen, G., Liu, L.S. 2004. Hyphenation of c18 sorbent extraction and solid-matrix time-resolved luminescence using tetracycline in milk as a model analyte. J. Agri. Food Chem. 52. pp. 7199-7205.Interpretive Summary: The presence of drug and chemical residues in food is a health concern.  Elaborate extraction, clean-up and enrichment are typically needed to isolate and concentrate trace amount of residues from biological or environmental matrices.  This sample preparation usually costs more time and effort than the detection itself.  To improve sensitivity and throughput a new method was developed that hyphenates sorptive extraction and time-resolved luminescence (TRL). A thin coating of silica on glass was used to perform these two functions and to detect tetracycline in milk.  The method successfully screened presence of tetracycline at the US. regulatory tolerance level of 300 ug/L with high throughput rate, low operation cost and no need of organic solvents.  This semiquantitative method can be used to screen antibiotics in foods and pollutants in environmental samples, and is especially suitable for liquid samples, such as milk.
                                Technical Abstract: A new analytical approach was proposed that hyphenated sorptive extraction and time-resolved luminescence (TRL).  Tetracycline (TC) in milk was used as a model analyte to evaluate the performance of C18-bonded silica coating as both an extraction medium and a TRL matrix.  Sample preparation was greatly simplified without using organic solvents.  TC was first extracted from milk onto a 10 x 6 mm C18 coating in a 10-min immersion, followed by a 3-min water wash clean-up.  The membrane was then spotted with a pH 9 TRL reagent solution that contained europium and EDTA.  After desiccation TRL was measured directly on the coating surface with a commercial fluorescence spectrophotometer.  The integrated signal showed a linear dependence (R(2)= 0.9938) on TC concentration in the 0-3000 ug/L range.  The recovery was in the 63-65% range, and the limit of detection was 14 ug/L.  This semiqualitative method applied equally well to screening TC in skim, 2% and whole milk at 300 ug/L, the tolerance level set by the Food and Drug Administration (FDA).  With high sensitivity and low cost this method is particularly suitable for high-throughput screening of liquid samples.


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