Fluorimetric assay of tetracycline mixtures

Polyethyleneimine capped bimetallic Au/Pt nanoclusters are a viable fluorescent probe for specific recognition of chlortetracycline among other tetracycline antibiotics

A highly selective method has been developed for the fluorometric determination of chlortetracycline (CTC) among other tetracycline antibiotics (TCs). It is making use of fluorescent Au/Pt nanoclusters (NCs) capped with polyethyleneimine (Au/PtNCs@PEI). The nanoprobe, with a green emission peaking at 512 nm, was synthesized by an environmentally friendly hydrothermal method. The capped NCs have a large Stokes shift (∼150 nm), are insensitive to extreme pH values and high ionic strength, and are excellently photostable under UV irradiation. In the presence of CTC, the fluorescence of the capped NCs is quenched due to aggregation. The effect is also found for tetracycline, oxytetracycline and doxycycline. This shows that sensitive but non-selective detection of such TCs is possible. However, CTC is specifically complexed by Al(III) ions, and this generates a strong fluorescence peaking at 520 nm even though the fluorescence of the capped NCs is fully quenched. Obviously, the effects are caused by CTC only, and this enables CTC to be specifically recognized by an "on-off-on" strategy. Fluorescence increases linearly in the 0.5 to 10 μM CTC concentration range, and the limit of detection is 0.35 μM. The method was successfully applied to the determination of CTC in (spiked) milk, and the recoveries suggest that this fluorescent probe is an effective tool for detecting CTC in foodstuff. Graphical abstract Schematic illustration and photographic images of the luminescence quenching response of Au/Pt nanoclusters (Au/PtNCs) toward chlortetracycline (CTC) (from on to off), and then the recovery upon Al³⁺ addition (from off to on).

Microscopic determination of tetracycline based on aluminum-sensitized fluorescence of a self-ordered ring formed by a sessile droplet on glass slide support

A fluorescent microscopic determination of trace amount of tetracycline is reported based on the aluminum-sensitized fluorescence effect of a self-ordered ring formed by a sessile droplet on glass slide support. Since the evaporative loss of the solvent from the edge wedge of the droplet that is spotted on a hydrophobic-treated glass slide, an outward capillary flow of the interior solvent of the droplet occurs. The resulted outward capillary flow then carries the solute to the perimeter of the droplet spot where the solute accumulates to form a fluorescent self-ordered ring (SOR). Depending on the spotted volume of the aluminum-tetracycline chelate solution, different size of SOR with the outer diameter (o.d.) less than 1.1mm and the ring belt width less than 21.6 microm can be obtained. Data analysis for the imaged SOR by using a digitalized CCD camera showed that the chelate molecule across the fluorescent SOR belt section follows a Gaussian distribution, and the maximum fluorescent intensity (I(max)) was found to be proportional to tetracycline content. When a 0.1 microl droplet was spotted on the solid surface, tetracycline in the range of 7.5-800.0 fmol (or 7.9 x 10(-8) to 800.0 x 10(-8)moll (-1)) can be detected, and the limit of detection can reach 0.8 fmol (or 7.9 x 10(-9) moll (-1)). With present method, the contents of tetracycline in capsule, tablet, urine and fresh milk were satisfactorily detected with the recoveries of 97.0-106.5% and RSD of 1.2-4.2%, correspondingly.

Rapid determination of tetracycline in milk by FT-MIR and FT-NIR spectroscopy

The feasibility of measuring tetracycline at the ppb levels in milk was investigated by Fourier transform mid-infrared (FT-MIR) and Fourier transform near-infrared (FT-NIR) spectroscopic techniques. Milk samples spiked with different concentrations of tetracycline were scanned using FT-MIR and FT-NIR spectroscopy. Suitable spectral wave number regions were selected for principal least square (PLS) regression models development. Prediction errors were high when the calibration model was developed using the wide range of tetracycline concentrations (4 to 2000 ppb) in milk. Maximum correlation coefficient (R2) value of about 0.89 was obtained for the validation models developed using different concentration ranges. Prediction errors were high for FT-NIR method. Results indicated that FT-MIR spectroscopy could be used for rapid detection of tetracycline hydrochloride residues in milk.

Determination of tetracycline and its major degradation products by liquid chromatography with fluorescence detection

A liquid chromatographic method of tetracycline and its major degradation products on a C8-reversed phase column with acidic mobile phase and fluorescence detection is described. The quantification limit, measured as the amount of sample that gave a signal ten times the peak-to-peak noise of the baseline, was: 0.25 ng for tetracycline (TC) and epitetracycline (ETC), 25 ng for and 4-epianhydrotetracycline (EATC) and 50 ng for anhydrotetracycline (ATC) of injected standard. By means of this liquid chromatography (LC) assay TC, ETC, EATC and ATC as main degradation products of tetracycline, can be separated and determined with good sensitivity and specificity within 15 min.

Application of the computerized compensation method and the orthogonal functions method to correct for irrelevant interference in spectrofluorometry

The computerized compensation method and the orthogonal functions method were applied to correct for the presence of interferences in spectrofluorometric analysis. The methods were demonstrated by the determination of tetracycline (TC) and anhydrotetracycline (ATC) in combination. The calibration graphs were linear in the concentration range 0.02-0.12 mg/100 ml of either TC or ATC.

Effect of surfactant on tetracycline absorption across everted rat intestine

Absorption of tetracycline hydrochloride (500 micrograms/ml) from oxygenated modified Krebs buffer in randomized everted rat jejunal segments was determined alone and in the presence of calcium, polysorbate 80, and calcium plus polysorbate 80. Surfactant increased absorption of tetracycline in the presence and absence of calcium, with 0.01% (w/v) polysorbate 80 increasing transfer to the greatest extent of the concentrations examined(0.005, 0.01, 0.05, 0.1, and 1%); tetracycline hydrochloride + 12.5 mM CaCl2, 143 +/- 45 micrograms/ml; tetracycline hydrochloride + polysorbate 80, 389 +/- 18 micrograms/ml; tetracycline hydrochloride + 12.5 mM CaCl2 + polysorbate 80, 255 +/- 31 micrograms/ml. On the premise that the effective surfactant concentration is similar to the critical micelle concentration, an absorption mechanism based on micellar solubilization is postulated.

Rapid fluorimetric assay of minocycline in plasma or serum: comparison with microbiological assay

1. Plasma concentrations of minocycline were assayed by measuring the fluorescence emission of an aluminum-minocycline chelate in a spectrofluorimeter. 2. The assay gives reproducible results over the concentration range 0.05-5.0 mug ml-1, and compared favourably with results achieved using a conventional large plate agar diffusion microbiological assay in a double-blind comparison of the two methods. 3. Fluorimetric assay of minocycline in plasma was found to correlate closely with antibiotic activity (r = 0.95). The method is easy and economical to perform, results being obtained in 1 h.