High-performance liquid chromatography method for the simultaneous determination of sulfamethoxazole and trimethoprim in bovine milk using an on-line clean-up column

Europium chelate-anionic exchange functionalized covalent organic frameworks for the sensing of aristolochic acid a in humans and sulfamethoxazole/trimethoprim in surface water

The application of covalent organic frameworks (COFs) in fluorescence detection is of great interest. Herein, we have synthesized the ionic covalent organic framework TGH⁺·PD: Eu(TTA)₄ with the characteristic emission of lanthanides by a straightforward ion-exchange method. This is the first time that aristolochic acid A (AA), a key biomarker for absorption and metabolism in the body for early diagnosis of diseases, has been detected by using COF as a fluorescent probe, which exhibits a good linear correlation with the AA concentration over a range from 5.0 to 1000 μM with a detection limit of 0.0808 μM. In addition, the selective response to sulfamethoxazole (SMZ)/trimethoprim (TMP) is achieved by varying the excitation wavelength with detection lines of 30.2 nM and 2.898 μM, respectively. It is worth mentioning that BNPP has been developed for the accurate determination of SMZ in uncertain samples. In a word, the prepared TGH⁺·PD: Eu(TTA)₄-based sensor can be used for the quantitative detection of AA and SMZ/TMP, separately, effectively extending the application of COFs in the field of fluorescence sensing.

Rapid electrochemical recognition of trimethoprim in human urine samples using new modified electrodes (CPE/Ag/Au NPs) analysing tunable electrode properties: experimental and theoretical studies

Pharmaceutical effluents are a serious environmental issue, which require to be treated by a suitable technique; thus, the electrochemical process is actively considered as a viable method for the treatment. In this work, new carbon paste electrodes (CPEs) were fabricated by compressing gold and silver nanoparticles (NPs), namely, CPE/Ag NPs, CPE/Au NPs, and CPE/Ag/Au NPs and then completely characterized by different analytical methods. The performance of the electrodes was studied after determining their surface area (×10^-6 cm²) as 4.17, 5.05, 5.27, and 5.12, producing high anodic currents for K₄[Fe(CN)₆] compared to the commercial electrode. This agrees with the results of impedance study, where the electron transfer rate constants (k_app, ×10^-3 cm s^-1) were determined to be 28.7, 42.6, 41.0, and 101.4 for CPE, CPE/Ag NPs, CPE/Au NPs, and CPE/Ag/Au NPs, respectively, through the Bode plot-phase shifts. This is consistent with the charge transfer resistance (R_CT, Ω), resulting as 171 for CPE/Ag/Au NPs < 395 for CPE/Ag NPs < 427 for CPE/Au NPs and < 742 for CPE. Therefore, these electrodes were employed to detect trimethoprim (TMP) since metallic NPs contribute good crystallinity, stability, conduciveness, and surface plasmon resonance to the CPE, convalescing the sensitivity; comprehensively, they were applied for its detection in real water and human urine samples, and the limit of detection (LOD) was as low as 0.026, 0.032, and 0.026 μmol L^-1 for CPE/Ag NPs, CPE/Au NPs, and CPE/Ag/Au NPs, respectively. In contrast, unmodified CPE was unable to detect TMP due to the lack of efficiency. The developed technique shows excellent electrochemical recovery of 92.3 and 97.1% in the urine sample. Density functional theory (DFT) was used to explain the impact of the metallic center in graphite through density of states (DOS).

Rapid screening of mycotoxins in liquid milk and milk powder by automated size-exclusion SPE-UPLC-MS/MS and quantification of matrix effects over the whole chromatographic run

An automated, size-exclusion solid phase extraction (SPE)-UPLC-MS/MS protocol without pre-treatment of samples was developed to screen for four mycotoxins (OTA, ZEN, AFB1, and AFM1) in liquid milk and milk powder. Firstly, a mixed macropore-silica gel cartridge was established as a size-exclusion SPE column. The proposed methodology could be a candidate in green analytical chemistry because it saves on manpower and organic solvent. Permanent post-column infusion of mycotoxin standards was used to quantify matrix effects throughout the chromatographic run. Matrix-matched calibration could effectively compensate for matrix effects, which may be caused by liquid milk or milk powder matrix. Recovery of the four mycotoxins in fortified liquid milk was in the range 89-120% and RSD 2-9%. The LOD for the four mycotoxins in liquid milk and milk powder were 0.05-2 ng L(-1) and 0.25-10 ng kg(-1), respectively. The LOQ for the four mycotoxins in liquid milk and milk powder were 0.1-5 ng L(-1) and 0.5-25 ng kg(-1), respectively.

Automated Online Solid-Phase Extraction Coupled with Sequential Injection-HPLC-EC System for the Determination of Sulfonamides in Shrimp

The use of fully automated online solid-phase extraction (SPE) coupled with sequential injection analysis, high-performance liquid chromatography (HPLC), and electrochemical detection (EC) for the separation and determination of sulfonamides has been developed. A homemade microcolumn SPE system coupled with sequential injection analysis (SIA) was used to automate the sample cleanup and extraction of sulfonamides. The optimal flow rate of sample loading and elution was found to be 10 μL/s, and optimal elution time of zone was 20–24 s. Under the optimal conditions, a linear relationship between peak area and sulfonamide concentrations was obtained in the range of 0.01–8.0 μg mL−1. Detection limits for seven sulfonamides were between 1.2 ng mL−1and 11.2 ng mL−1. The proposed method has been applied for the determination of sulfonamides in shrimp. Recoveries in the range of 84–107% and relative standard deviations (RSDs) below 6.5% for intraday and 13% for inter-day were received for three concentration levels of spiking. The results showed that the present method was simple, rapid, accurate and highly sensitive for the determination of sulfonamides.

The pivotal role of mass spectrometry in determining the presence of chemical contaminants in food raw materials

During recent years, a rising interest from consumers and various governmental organizations towards the quality of food has continuously been observed. Human intervention across the different stages of the food supply chain can lead to the presence of several types of chemical contaminants in food-based products. On a normal daily consumption basis, some of these chemicals are not harmful; however, for those that present a risk to consumers, legislation rules were established to specify tolerance levels or in some cases the total forbiddance of these specific contaminants. Hence, the use of appropriate analytical tools is recommended to properly identify chemical contaminants. In that context, mass spectrometry (MS)-based techniques coupled or not to chromatography offer a vast panel of features such as sensitivity, selectivity, quantification at trace levels, and/or structural elucidation. Because of the complexity of food-based matrices, sample preparation is a crucial step before final detection. In the present manuscript, we review the contribution and the potentialities of MS-based techniques to ensure the absence of chemical contaminants in food-based products.

Method validation and determinations of levofloxacin, metronidazole and sulfamethoxazole in an aqueous pharmaceutical, urine and blood plasma samples using quantitative nuclear magnetic resonance spectrometry

Selective, rapid and accurate quantitative proton nuclear magnetic resonance (qHNMR) method for the determination of levofloxacin, metronidazole benzoate and sulfamethoxazole in aqueous solutions was developed and validated. The method was successfully applied to the determinations of the drugs and their admixtures in pharmaceutical, urine and plasma samples. Maleic acid and sodium malate were used as internal standards. Effect of temperature on spectral measurements was evaluated. Linear dynamic ranges of 0.50-68.00, 0.13-11.30 and 0.24-21.00 mg per 0.60 mL solution were obtained for levofloxacin, metronidazole benzoate and sulfamethoxazole, respectively. Average recovery % in the range of 96.00-104.20 ± (0.17-2.91) was obtained for drugs in pure, pharmaceutical, plasma and urine samples. Inter and intra-day analyses gave average recoveries % in the ranges 96.10-98.40 ± (1.68-2.81) and 96.00-104.20 ± (0.17-2.91), respectively. Instrumental detection limits ≤0.03 mg per 0.6 mL were obtained for the three drugs. Developed method has demonstrated high performance characteristics for analyzing investigated drugs and their admixtures. Student t-test at 95% confidence level revealed insignificant bias between the real and measured contents of investigated drugs in pure, pharmaceutical, urine and plasma samples and its admixtures. Application of the statistical F-test revealed insignificant differences in precisions between the developed method and arbitrary selected reference methods.

Generation of broad specificity antibodies for sulfonamide antibiotics and development of an enzyme-linked immunosorbent assay (ELISA) for the analysis of milk samples

Immunoreagents appropriately produced to detect a wide range of sulfonamide antibiotic congeners have been used to develop a highly sensitive enzyme-linked immunosorbent assay (ELISA). The selectivity has been achieved by combining antibodies raised against 5-[6-(4-aminobenzenesulfonylamino)pyridin-3-yl]-2-methylpentanoic acid (SA1), covalently coupled to horseshoe crab hemocyanin (HCH), and 5-[4-(amino)phenylsulfonamide]-5-oxopentanoic acid (SA2), coupled to ovalbumin (OVA), on an indirect ELISA format. The immunizing hapten has been designed to address selectivity against the common aminobenzenesulfonylamino moieties, using theoretical calculations and molecular modeling tools. Hapten SA1 has been synthesized in four steps from methyl 5-(4-amino-3-pyridinyl)-2-methyl-4-pentenoate through a Heck reaction, under Jeffery conditions, to avoid introduction of additional epitopes in the linker. The microplate immunoassay developed is able to reach the necessary detectability for the determination of the sulfonamide antibiotics most frequently used in the veterinary field, in compliance with the EC Regulation 2377/90. As an example, the IC(50) and LOD values accomplished for sulfapyridine are 2.86 +/- 0.24 and 0.13 +/- 0.03 microg L(-1), respectively. Studies performed with different types of milk samples demonstrate that direct and accurate measurements can be performed in this type of matrix without any previous sample cleanup method.

Simultaneous quantification of sulfamethoxazole and trimethoprim in whole egg samples by column-switching high-performance liquid chromatography using restricted access media column for on-line sample clean-up

This work reports the application of restricted access media (RAM) column, in a multidimensional configuration, for simultaneous analysis of sulfamethoxazole (SMX) and trimethoprim (TMP) in whole eggs with ultraviolet detection. The proteins were partially precipitated by adding 0.5 mL of acetonitrile into 1.0 mL of blended egg followed by centrifugation. The supernatant was injected (250 microL) directly into the multidimensional system. At the first dimension, a restricted access medium (RAM) bovine serum albumin (BSA) octadecyl column (100 mm x 46 mm I.D., Luna silica, 10 microm particle size and 100 A pore size), was used for extraction and concentration of the analytes and at second dimension, an octadecyl column (150 mm x 46 mm I.D., Luna silica, 10 microm particle size and 100 A pore size), for analysis. The developed method showed good selectivity, accuracy and precision for quantification of these different compounds in eggs, and the limits of quantification were 80 ng/mL, for both compounds. The validated method is reliable and sensitive for monitoring residues in whole eggs samples and thus, to determine withdraw period for laying hens using veterinary medicine having SMX-TMP combination.

Sample preparation methods in the analysis of pesticide residues in baby food with subsequent chromatographic determination

Pesticides are widely utilized at various stages of cultivation and during postharvest storage to protect plants against a range of pests and/or to provide quality preservation. Reliable confirmatory methods are required to monitor pesticide residues in baby foods and to ensure the safety of baby food supply. This review covers methods in which pesticide residues have been determined in baby food by the use of a wide range of chromatographic techniques after various sample preparation steps. The main attention is paid to the evaluation and improvement of sample extraction and clean-up methods (liquid extraction, solid-phase extraction (SPE), dispersive SPE (DSPE), microextraction procedures, matrix solid-phase dispersion (MSPD) and supercritical fluid extraction (SFE)) considering low concentration levels of pesticide residues in baby food resulting from stringent European Union (EU) legislation. Instrumental aspects together with the matrix effects significantly contributing to the most important parameters considered in pesticide residues analysis of baby food--limits of detection (LODs) and limits of quantification (LOQs) were included within the scope of this overview. Paper involves also monitoring studies.

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 and simultaneous determination of sulfamethoxazole and trimethoprim in human plasma by high-performance liquid chromatography

A simple and reproducible high-performance liquid chromatographic method was developed for simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) in human plasma. The method entailed injection of the samples after deproteination with perchloric acid and subsequent neutralizing. Primidone was used as internal standard. Chromatography was performed on a C(18) column (250 mm x 4.6 mm, 5 microm) under isocratic elution with 50 mM aqueous sodium dihydrogen phosphate-acetonitrile-triethylamine (100:25:0.5, v/v), pH 5.9. Detection was made at 240 nm and analyses were run at a flow-rate of 1.5 ml/min at a temperature of 35 degrees C. The recovery was 83.4, 88.5 and 98.2% for TMP, SMX and internal standard, respectively. The precision of the method was 2.6-9.8% over the concentration range of 0.125-2 microg/ml for TMP and 0.39-50 microg/ml for SMX. The limit of quantification (LOQ) in plasma was 0.125 and 0.39 microg/ml for TMP and SMX, respectively. The method was used for a bioequivalence study.

Development of restricted-access media supports and their application to the direct analysis of biological fluid samples via high-performance liquid chromatography

A quick overview of published methods for analyzing compounds in complex biological samples reveals that the most difficult step is the clean-up or extraction of a required compound from the matrix. The strategy required to analyze exogenous compounds in biological fluids depends greatly upon the nature of the compound and upon the biomatrix. Coupled-column separation using restricted-access media as the first dimension in order to exclude macromolecules and retain micromolecules has been successfully used for a number of biological fluids. This paper presents the history of the development of restricted-access media supports and of their application to the direct injection of biological fluid samples in high-performance liquid chromatography.

High-throughput screening for multi-class veterinary drug residues in animal muscle using liquid chromatography/tandem mass spectrometry with on-line solid-phase extraction

A rapid qualitative method using on-line column-switching liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed and validated for screening 13 target veterinary drugs: four macrolides - erythromycin A, josamycin (leucomycin A3), kitasamycin (leucomycin A5), and tylosin A; six (fluoro)quinolones - ciprofloxacin, danofloxacin, enrofloxacin, flumequine, oxolinic acid, and sarafloxacin; and lincomycin, virginiamycin M1, and trimethoprim in different animal muscles. Clindamycin, norfloxacin, nalidixic acid, oleandomycin, ormetoprim, and roxithromycin were used as the internal standards. After simple deproteination and analyte extraction of muscle samples using acetonitrile, the supernatant was subjected to on-line cleanup and direct analysis by LC/MS/MS. On-line cleanup with an extraction cartridge packed with hydrophilic-hydrophobic polymer sorbent followed by fast LC using a short C18 column resulted in a total analysis cycle of 6 min for 19 drugs. This screening method considerably reduced the time and the cost for the quantitative and confirmatory analyses. The application of a control point approach was also introduced and explained.