Highly sensitive detection of sulfadimidine in water and dairy products by means of an evanescent wave optical biosensor

An integrated biosensor for sensitive and automatic detection of sulfadimidine in aqueous samples based on an immunoassay and evanescent wave fluorescence excitation.

High-throughput quantitation of seven sulfonamide residues in dairy milk using laser diode thermal desorption-negative mode atmospheric pressure chemical ionization tandem mass spectrometry

Sulfonamides are antibiotic compounds widely used in the dairy industry. Their presence in diary milk poses a risk to public health and may also contribute to the spread of antibiotic resistance in bacteria. Sulfonamide residues in dairy milk were quantified by tandem mass spectrometry (MS/MS) using a novel ionization source based on laser diode thermal desorption-negative mode atmospheric pressure chemical ionization (LDTD-APCI(-)). Seven sulfonamides spiked in milk were extracted with acetonitrile, which yielded high recoveries (77.5-101.5%). Calibration curves in the matrix showed good linearity (0.9977 >or= R(2) >or= 0.9658) over the dynamic range (1.6-500 microg L(-1)), and limits of quantitation were between 2 and 14 microg L(-1), lower than or of the same magnitude as maximum residue criteria set by several regulatory agencies (10-100 ng L(-1)). In addition, the run time using the LDTD-MS/MS system was 30 s per sample, as compared to actual methods running from 7 to 84 min for the same sulfonamide residue compounds, which gave the method the high screening throughput capacity necessary for monitoring milk production.

Optimization of analytical conditions and validation of a fluorescence method for the determination of sulfadiazine in milk

This paper describes optimization and validation of a method for sulfadiazine determination in milk samples based on sulfadiazine derivatization with fluorescamine followed by excitation-emission (fluorescence) measurement. For both the optimization and the validation, a comparison between zero-order and first-order signals has been made, showing the advantages of using first-order signals. In the optimization the effects of the temperature of the derivatization reaction, the amount of fluorescamine and the derivatization time on the instrumental signal (maximum intensity or the net analyte signal) are studied by a factorial experimental design, with the optimal values of these factors which give the highest signal being 22 degrees C for the reaction temperature, 50 microl fluorescamine and 20 min of derivatization time. The validation of the method under the optimal experimental conditions shows that the analytical method is fit-for-purpose, with values of the capability of detection (CCbeta) of 4.3 microg l(-1) at a sulfadiazine concentration of zero and with probabilities of a false positive and a false negative of 5%. Around the permitted limit (established for the sulfonamides at 100 microg l(-1)), CCbeta is 112 microg l(-1). The precision, as the intermediate reproducibility, was established as 1.2 and 3.3 microg l(-1) around 0 and 100 microg l(-1), respectively. In the application to milk samples spiked with sulfadiazine a mean recovery of around 90% was obtained with a standard deviation of about 8% (14 samples of different concentrations).

Rapid determination of sulfonamides in milk samples using fluorescence spectroscopy and class modeling with n-way partial least squares

In this paper, a methodology to evaluate the probability of false non-compliance and false compliance for screening methods, which give first or second-order multivariate signals is proposed. For this task 120 samples of 6 different kinds of milk have been measured by excitation-emission fluorescence. The samples have been spiked with different amounts of three sulfonamides (sulfadiazine, sulfamerazine and sulfamethazine). These substances have been classified in group B1 (veterinary medicines and contaminants) of annex I of Directive 96/23/EC. The European Union (Commission Regulation EC no. 281/96) has set the maximum residue level (MRL) of total sulfonamides at 100 microg kg(-1) in muscle, liver, kidney and milk. The work shows that excitation-emission fluorescence together with the partial least squares class modeling (PLS-CM) procedure may be a suitable and cheap screening method for the total amount of sulfonamides in milk. Three models, PLS-CM, have been built, for the emission and excitation spectra (first-order signals) and for the excitation-emission matrices (second-order signals). In all the cases it reaches probabilities of false compliance below 5% as required by Decision 2002/657/EC. With the same flourescence signals, the total quantity of sulfonamide was calibrated using 2-PLS, 3-PLS and PARAFAC regressions. Using this quantitative approach, the capability of detection, CCbeta, around the MRL has been estimated between 114.3 and 115.1 microg kg(-1) for a probability of false non-compliance and false compliance equal to 5%.

Analysis of sulphonamide residues in edible animal products: A review

The methods of analysis for sulphonamide residues in edible animal products are reviewed. Sulphonamides are widely used for therapeutic and prophylactic purposes in both humans and animals, sometimes as growth promoters as additives in animal feed. As a result of their widespread use, there is concern about whether the levels used of these drugs can generate serious problems in human health, e.g., allergic or toxic reactions. Several methods for the determination of sulphonamides have been reported in the literature and this review considers high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC/MS), gas chromatography (GC), thin-layer chromatography (TLC), high-performance capillary electrophoresis (HPCE), enzyme-linked immunosorbant assay (ELISA), biosensor immunoassay (BIA) and microbiological methods. Specific aspects of analysing sulphonamides, such as sample handling, chromatographic conditions and detection methods are discussed. Methods for drug residue monitoring should be accurate, simple, economical in both time and cost, and capable of detecting residues below the maximum residue limits (MRL). The current sulphonamide detection technologies are based on chromatographic methods or bacteriological growth inhibition. The instrumental methods such as HPLC and GC are both sensitive and specific, but are laborious and expensive. Because of the labour-intensive processes, only a few cases of GC methods applied to residue analysis have been published. These methods are suitable for confirmation but not for screening of large numbers of samples. Microbiological methods do not require highly specialized and expensive equipment. They also use highly homogeneous cell populations for testing and thus result in better assay precision. Although HPCE has powerful separation ability, the precision is poor and the instrument still needs to be improved. To date, this technique has not been widely applied to routine analysis. Currently, TLC has been almost replaced by other instrumental analysis. A rapid, sensitive and specific assay is required to detect positive samples in routine analysis, which can then be confirmed for the presence of sulphonamides by HPLC. Immunochemical methods such as ELISA can be simple, rapid and cost-effective, with enough sensitivity and specificity to detect small molecules. This review can be considered as a basis for further research aimed at identifying the most efficient approaches.

Screening and analytical confirmation of sulfonamide residues in milk by capillary electrophoresis-mass spectrometry

A new methodology is proposed to automate the monitoring of sulfonamide residues in milk samples. It combines a screening unit for the total amount of sulfonamide with capillary electrophoresis-mass spectrometry (CE-MS) equipment for processing the samples containing a detectable level of sulfonamide. The screening unit consists of continuous-flow system (CFS) to precipitate the proteins connected on-line to the CE-MS equipment, in which a common characteristic ion of all sulfonamides was monitored with the MS detector by flushing the sample through the capillary. The confirmatory method is based on the purification and preconcentration of sulfonamides in a CFS unit and posterior analysis by CE-MS. The sample treatment unit was also on-line connected to the CE-MS equipment. In order to increase sensitivity, the flow rate of the sheath liquid was diminished from 0.5 to 0.2 microL.min(-1) by increasing the content in water from 0 to 50% and the formic acid from 0.5 to 1.5% in this liquid and by applying an overimposed pressure of 5 mbar during the electrophoretic separation. The method allowed the analysis of 30 samples per hour.