Oxytetracycline (OTC) residue in honey is detected using a portable analyzer designed to specifically target tetracycline (TC) drugs based on europium-sensitized luminescence (ESL). A 385 nm light emitting diode (LED) is used as the excitation source and a photomultiplier tube as the light detector. OTC is extracted from honey and cleaned up by solid phase extraction (SPE) using Strata X-WC weak cation exchange cartridges. To the eluate Eu(III) is added to form a Eu-TC chelate at pH 8.5. Efficient intrachelate energy transfer allows sensitive OTC detection at λex=385 nm and λem=610 nm. After a 25-µs time delay, the ESL signal is integrated over a 25-1000 µs interval. The signal intensity reveals a linear relationship (R2=0.972) to OTC concentrations in the 10-200 ng/g range. The limit-of-detection is 6.7 ng/g with an average 5.8% relative standard deviation. The background signal corresponds to ~10 ppb. This instrumentation and method combination enables field analysis that is especially useful for beekeeping industry.
A portable fluoroquinolone (FQ) analyzer is designed and prototyped based on terbium-sensitized luminescence (TSL). The excitation source is a 327-nm light emitting diode (LED) operated in pulsed mode; and the luminescence signal is detected by a photomultiplier tube (PMT). In comparison to a conventional xenon flashlamp, an LED is small, light, robust, and energy efficient. More importantly, its narrow emission bandwidth and low residual radiation reduce background signal. In pulse mode, an LED operates at a current 1-2 orders of magnitude lower than that of a xenon flashlamp, thus minimizing electromagnetic interference (EMI) to the detector circuitry. The PMT is gated to minimize its response to the light source. These measures lead to reduced background noise in time domain. To overcome pulse-to-pulse variation signal normalization is implemented based on individual pulse energy. Instrument operation and data processing are controlled by a computer running a custom LabVIEW program. Enrofloxacin (ENRO) is used as a model analyte to evaluate instrument performance. The integrated TSL intensity reveals a linear dependence up to 2 ppm. A 1.1-ppb limit of detection (LOD) is achieved with relative standard deviation (RSD) averaged at 5.1%. The background noise corresponds to ~5 ppb. At 19 lbs, this portable analyzer is field deployable for agriculture, environmental and clinical analyses.
Oxytetracycline (OTC) is extensively used in aquaculture worldwide for preventive and therapeutic purposes. Most of the drug, however, is discharged into the marine environment due to leaching from medicated feed and poor gastrointestinal (GI) absorption. Without exposure to sun light OTC has a long lifetime in the marine environment, therefore it is important to monitor and study its occurrence, distribution, fate and impact on the ecosystem. A portable tetracycline (TC) analyzer was developed in this laboratory for this purpose based on europium-sensitized luminescence. In this study, an assay method is developed for OTC analysis in water using this instrument. Water samples are filtered with glass wool; and solid phase extraction (SPE) is performed using Oasis HLB cartridges for OTC extraction and cleanup. Following reagent application, the samples are excited by 385 nm LED pulses; and time-resolved luminescence (TRL) is measured at 610 nm by a photomultiplier tube. A 0-3 ppm linear dynamic range (r2 = 0.9988) and a 0.021 ppb limit of detection were achieved with a typical <5% relative standard deviation.
Tetracycline (TC) is a significant class of antibiotic drugs in human and veterinary medicine. Its extensive use may lead to pollution in the marine environment and residues in foods of animal origin. To perform TC analysis in the field, a portable TC-specific analyzer was developed based on europium-sensitized luminescence. A 385 nm light emitting diode (LED) is used in pulsed mode as the light source to selectively excite TC. In comparison to a conventional xenon flashlamp, its narrower emission band and cleaner post-pulse extinction lead to reduced background and improved sensitivity. The time-resolved luminescence (TRL) signal is detected by a photomultiplier tube (PMT) that is gated to minimize its response to the LED pulse. The energy of individual LED pulses is monitored by a photodiode (PD) for signal normalization. Both instrument operation and data processing are controlled by a laptop computer running a custom LabVIEW program. The PD and the PMT signals are acquired at 4-μs time resolution and 12-bit amplitude resolution. The instrument performance is evaluated using oxytetracycline, a significant member of the TC antibiotics, as a target analyte. The analyzer achieves a 0-3 ppm linear dynamic range (r2 = 0.9988) and a 0.021-ppb limit of detection with a typical 5% relative standard deviation.
Evanescent field sensors provide unique analytical features. For fiber-optic fluorescence sensors the sensing zone geometry plays an important role in coupling excitation energy to the evanescent field and reciprocally collecting the fluorescence signal. In the past a tapered geometry was introduced to overcome V-number mismatch by mode conversion in the taper zone. It was later developed into a combination-taper profile to improve signal reproducibility. The spectroscopic throughput of fiber-optic evanescent-field sensors, however, is limited by the intrinsically small penetration depth and the small fiber format. In this study it was improved by dimension scale-up and cladding elimination using tapered waveguides fabricated from 6-mm quartz rods. Optimization of their profile was aided by fluorescence imaging, a technique that visually revealed the locations and intensity of the light coupled to evanescent field, as well as the light leaking to the bulk of the solution due to violation of conditions for total internal reflection. Based on this technique, a taper-cylinder profile was selected that provided the best performance among tested geometries in time-resolved luminescence. A 0.64 ppb limit of detection and a 0-500 ppb linear dynamic range (r2 = 0.9996) were achieved using tetracycline as a model analyte.
A rugged, filter-based fluorometer capable of time-resolved luminescence (TRL) measurements was designed, prototyped and tested for field applications. The instrument operation and data processing were controlled by a laptop computer running a custom LabVIEW program. A xenon flashlamp was used as the light source and a photomultiplier tube (PMT) as the photodetector. A gating technique was implemented to effectively overcome PMT saturation by intense xenon lamp flash so signal integrity was maintained even at very high gains, leading to improved sensitivity and reproducibility. The instrument was tested by TRL using tetracycline as a model analyte; and the signal was digitized at a 2-μs time resolution and a 12-bit amplitude resolution. Its performance was similar to or slightly better than that of a commercial fluorescence spectrophotometer. A 0-300 ppb linear dynamic range (r2 = 0.9996) and a 0.025-ppb limit of detection (LOD) were achieved with a ≤5% relative standard deviation.
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