A 5-kg time-resolved luminescence photometer with multiple excitation sources

Authors: Chen, Guoying

Submitted to: Journal of Applied Spectroscopy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2011
Publication Date: 3/1/2012
Citation: Chen, G. 2012. A 5-kg time-resolved luminescence photometer with multiple excitation sources. Journal of Applied Spectroscopy. 66(33):341-346.

Interpretive Summary: A terbium-sensitized luminescence (TSL) method was developed to screen presence of residues of four fluoroquinolones (FQ) registered in goat milk in the European Union (EU): enrofloxacin, ciprofloxacin, flumequine, and danofloxacin. After extraction and cleanup, TSL was measured using a portable fluorometer. Flumequine was designated to set the screening criterion; other FQ drugs can also be effectively screened because of their higher signals at their maximum residue limits. The potential of this work is to reduce a large sample pool to a small fraction, and subject only those presumptive positives to confirmation. Excellent sensitivity of our portable instrument enabled screening at rigorous EU regulation for FQ drugs at 30-100 parts per billion in milk. Satisfactory results were obtained on 48 blind samples. The method and instrumentation are both field deployable to facilitate field testing on dairy farms, and hence to promote timely decision making and food safety.

Technical Abstract: A portable fluorometer was developed to detect food contaminants and environmental pollutants including, in particular, two classes of antibiotics: tetracyclines and fluoroquinolones. Time resolution was implemented to take advantage of lanthanide-sensitized luminescence. Excitation sources included UV light emitting diodes with reduced background noise, and a continuous xenon flashlamp with flexibility to excite any target fluorophore. The detector, a photomultiplier tube module, was gated to reject time-domain interferences. Analytical performance was evaluated using danofloxacin as a model analyte. Luminescence signal was reasonably linear (R2=0.998) in four decades (0.2–2000 ng/mL) with background noise equivalent to 1.93 ng/mL. Relative standard deviations were less than 1% and less than 5% beyond and below 2 ng/mL. The limit of detection (LOD) was 1.99 ng/mL. Weighing less than 5 kg, this analyzer is deployable for in-situ analysis.