Direct analysis of six antibiotics in wastewater samples using rapid high-performance liquid chromatography coupled with diode array detector: A chemometric study towards green analytical chemistry

Direct injection liquid chromatography-tandem mass spectrometry as a sensitive and high-throughput method for the quantitative surveillance of antimicrobials in wastewater

Environmental antimicrobial pollution and antimicrobial resistance pose a threat to environmental and human health. Wastewater analysis has been identified as a promising tool for antimicrobial monitoring and the back-estimation of antimicrobial consumption, but current pretreatment methods are tedious and complicated, limiting their scope for high-throughput analysis. A sensitive direct injection method for the quantification of 109 antimicrobials and their metabolites in wastewater samples was developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The method was validated for both wastewater influent and effluent in terms of specificity, calibration range, matrix effect, filtration loss, accuracy, precision, limit of detection (LOD), and limit of quantification (LOQ). Most analytes achieved calibration of R2 > 0.99, and the calibration range was from 0.0002 to 150 μg L-1. Recoveries ranged consistently between ~50 % and ~100 % and losses were attributed to sample filtration. Method LOQs were determined as low as 0.0003 μg L-1, and acceptable accuracy (75 %-125 %) and precision (within 25 %) were achieved for >90 % of the analytes. The method was subsequently further assessed using wastewater of raw influent and treated effluent collected from 6 Australian wastewater treatment plants in 2021. In total, 37 analytes were detected in influent and 22 in effluent. Most of them could be quantified at concentrations ranging from 0.0053 to 160 μg L-1, with benzalkonium chloride-C12, amoxicilloic acid, and cephalexin detected at the highest concentrations. The current study provides a straightforward analytical method for antimicrobial monitoring in wastewater with a fast and simple pretreatment procedure.

Liquid chromatography on a centrifugal platform for separation and collection of water-soluble dyes

A reversed-phase chromatographic process is developed on a centrifugal platform to separate and collect water-soluble dyes from a mixture. A separation column filled with C18-reversed phase silica gel was used to separate the components from a mixture and the eluate was collected by a series of collecting chambers. The purified components can then be identified and extracted from the collecting chambers. The effects of the silica gel's particle size (7-10, 20-45, and 46-63 µm) and the platform's rotational speed (1000, 1500, 2000 RPM) on the separation and collection efficiency were investigated. Experimental results showed that dye separation could be well performed in the column with smaller-sized silica gels (7-10 µm) under a low rotational speed (1000 RPM). However, for the eluate collection, the high eluent flowrate and long processing time resulted in a convective band-broadening problem in the collecting chambers, which affected the recovery ratio of the dyes. Experimental results showed that the convective band broadening effect can be reduced by reducing the flowrate, shortening the collecting time, and switching the eluent to a different composition. The best recovery ratio of the dyes in the current design can be achieved by using the column with a powder size distribution of 46-63 µm and operating at the rotational speed of 1500 RPM. This platform can process a sample volume of 1 μL and the processing time is about 30 min. Since the only instrument used is a motor, the complete chromatographic process, from separation to fraction collection, can be carried out on a centrifugal platform at a low cost.

Green Multiplex Chromatographic Determination of Nine Penicillin Antibiotics Residues in Industrial Air Dust and Wastewater Environmental Samples

Determination of penicillin residues in different industrial effluents including wastewater and air samples is important to prevent exposure to residual amounts of penicillin and the development of antibiotic resistance. A green high performance liquid chromatography (HPLC) method coupled with diode array detection has been developed and validated for multiplex determination of nine penicillin antibiotics in the industrial air dust and wastewater environmental samples of penicillin facility in addition to the monitoring of facility surface cleaning. Separation was performed on C18 column with gradient elution of methanol and phosphate buffer (pH 4) at a flow rate of 1.5 mL min-1 and ultra violet (UV) detection at 220 nm. Low limits of detection were achieved (0.1-0.3 μg mL-1) indicating good sensitivity of the proposed. The method was applied for ensuring the efficiency of cleaning validation after worst-case selection. Recovery studies of the studied penicillins from fortified stainless steel and polycarbonate surfaces and swabs were between 91.91 and 100.22% with relative standard deviation 0.11-1.79%. The presence of any of the studied penicillins in wastewater samples from penicillin plant drainage was checked. Also, total air dust concentration (mg m-3) and % of penicillin active material residues in air dust were calculated from the area of the exposed group in suspension, tablet and vial production lines. The proposed method can be recommended for routine analysis of air and wastewater environmental samples for the detection of penicillin antibiotics at low levels as well as monitoring of facility surface cleaning with high accuracy and precision.

Heterogeneous Photocatalysis of Metronidazole in Aquatic Samples

Metronidazole (MET) is a commonly detected contaminant in the environment. The compound is classified as poorly biodegradable and highly soluble in water. Heterogeneous photocatalysis is the most promoted water purification method due to the possibility of using sunlight and small amounts of a catalyst needed for the process. The aim of this study was to select conditions for photocatalytic removal of metronidazole from aquatic samples. The effect of catalyst type, mass, and irradiance intensity on the efficiency of metronidazole removal was determined. For this purpose, TiO₂, ZnO, ZrO₂, WO₃, PbS, and their mixtures in a mass ratio of 1:1 were used. In this study, the transformation products formed were identified, and the mineralization degree of compound was determined. The efficiency of metronidazole removal depending on the type of catalyst was in the range of 50-95%. The highest MET conversion (95%) combined with a high degree of mineralization (70.3%) was obtained by using a mixture of 12.5 g TiO₂-P25 + PbS (1:1; v/v) and running the process for 60 min at an irradiance of 1000 W m^-2. Four MET degradation products were identified by untargeted analysis, formed by the rearrangement of the metronidazole and the C-C bond breaking.

Eco-Friendly Pharmaceutical Analysis of Rifaximin in Tablets by HPLC-MS and Microbiological Turbidimetry

Rifaximin, an antimicrobial used for the treatment of various diseases, lacks analytical methods in official compendia for evaluation of the final product. This paper presents an eco-friendly protocol for rifaximin tablets by high performance liquid chromatography coupled with mass spectrometry (HPLC-MS). The method was completely validated according to the International Conference on Harmonization guidelines and developed following the concept of Quality by Design. The separation was achieved using a C18 column, purified water +0.1% glacial acetic acid and ethyl alcohol, 52:48 (v/v), as mobile phase, 0.9 mL min-1 at 290 nm and ambient room temperature. Mass spectral analyses were performed using electrospray ionization (ESI) ion source and ion trap mass analyzer. The method was linear over the concentration range of 5-50 μg mL-1. The sample was subjected to acidic, basic, neutral, oxidative and photolytic degradation. Degradation products did not interfere in the quantification of the rifaximin, so the method can be considered indicative of stability. Degradation products were also evaluated individually by microbiological method using Escherichia coli. The validated method could be used promisingly as green analytical strategies for detection and quantification of rifaximin in tablets.

Evaluation and Optimization of Antibiotics Resistance Profile against Clostridium perfringens from Buffalo and Cattle in Pakistan

Clostridium perfringens is a serious threat to successful bovine farming. It causes severe damage to the buffalo and cattle health causing a drastic reduction in milk and meat production. In Pakistan, C. perfringens is a constant threat, and for its management, antibiotics are mostly used. Most bovine farmers use a single antibiotic to suppress the bacterial infection which in turn, increases the antimicrobial resistance (AMR) against the particular antibiotic. To reduce the resistance, the administration of multiple antibiotics in their standard doses at different times can be a possible remedy to manage the AMR and reduce their viability. This study aims to evaluate the effect of 11 commonly used antibiotics at their standard concentrations for inhibiting 33 strains of C. perfringens from five districts of Punjab province in Pakistan. Based on the zone of inhibition, ciprofloxacin, ampicillin, and cefotaxime (CAC) at their standard concentrations effectively inhibited the bacterium. These antibiotics showed appropriate significance statistically, i.e., correlation, Chi-square test, and cluster analysis. Optimization of these antibiotics using response surface methodology (RSM) revealed that the selected antibiotics from medium to high range not only reduce the bacterial propagation but also their population up to a considerable extent. Hence, the health of milk- and meat-producing large animals could be improved, which will be cost-effective and less harmful to the animal, human health, and the environment. Moreover, optimized administration of the selected antibiotics would reduce the impact of drug-resistant superbugs.

High-throughput multi-residue quantification of contaminants of emerging concern in wastewaters enabled using direct injection liquid chromatography-tandem mass spectrometry

A rapid quantitative method for 135 contaminants of emerging concern (CECs) in untreated wastewater enabled with direct injection liquid chromatography-tandem mass spectrometry is presented. All compounds were analysed within 5 min on a short biphenyl cartridge using only 10 μL of filtered sample per injection. Up to 76 compounds were monitored simultaneously during the gradient (including mostly two transitions per compound and stable isotope-labelled analogues) while yielding >10 data points per peak. Evaluation of seven solid phase extraction sorbents showed no advantage for wastewater matrix removal. Excellent linearity, range, accuracy and precision was achieved for most compounds. Matrix effects were <11 % and detection limits were <30 ng L^-1 on average. Application to untreated wastewater samples from three wastewater treatment works in the UK, USA and Mexico, enabled quantification of 56 compounds. Banned and EU 'watch-list' substances are critically discussed, including pesticides, macrolide antibiotics, diclofenac, illicit drugs as well as multiple pharmaceuticals and biocides. This high-throughput method sets a new standard for the speedy and confident determination of over a hundred CECs in wastewater at the part-per-trillion level, as demonstrated by performing over 260 injections per day.

Spectroscopic techniques combined with chemometrics for fast on-site characterization of suspected illegal antimicrobials

The threats of substandard and falsified (SF) antimicrobials, posed to public health, include serious adverse drug effects, treatment failures and even development of antimicrobial resistance. Next to these issues, it has no doubt that efficient methods for on-site screening are required to avoid that SF antimicrobials reach the patient or even infiltrate the legal supply chain. This study aims to develop a fast on-site screening method for SF antimicrobials using spectroscopic techniques (mid infrared, benchtop near infrared, portable near infrared and Raman spectroscopy) combined with chemometrics. 58 real-life illegal antimicrobials (claiming 18 different antimicrobials and one beta-lactamase inhibitor) confiscated by the Belgian Federal Agency for Medicines and Health Products (FAMHP) and 14 genuine antimicrobials were analyzed and used to build and validate models. Two types of models were developed and validated using supervised chemometric tools. One was used for the identification of the active pharmaceutical ingredients (APIs) by applying partial least squares-discriminant analysis (PLS-DA) and another one was used for the detection of non-compliant (overdosed or underdosed) samples by applying PLS-DA, k-nearest neighbors (k-NN) and soft independent modelling by class analogy (SIMCA). The best model capable of identifying amoxicillin and clavulanic acid (co-amoxiclav), azithromycin, co-trimoxazole and amoxicillin was based on the mid-infrared spectra with a correct classification rate (ccr) of 100%. The optimal model capable of detecting non-compliant samples within the combined group of amoxicillin and co-amoxiclav via SIMCA showed a ccr for the test set of 88% (7/8) using mid infrared or benchtop near infrared spectroscopy. The best model for detecting non-compliant samples within the group of amoxicillin via SIMCA was obtained using mid-infrared or Raman spectra, resulting in a ccr of 80% for the test set (4/5) and a ccr for calibration of 100%. For the group of co-amoxiclav, the optimal models showed a ccr of 100% for the detection of non-compliant samples by applying mid-infrared, benchtop near infrared or portable near infrared spectroscopy. Taken together, the obtained models, hyphenating spectroscopic techniques and chemometrics, enable to easily identify suspected SF antimicrobials and to differentiate non-compliant samples from compliant ones.

Rapid and simultaneous determination of three fluoroquinolones in animal-derived foods using excitation-emission matrix fluorescence coupled with second-order calibration method

The matter of fluoroquinolone residues in various foods still arouses wide public concern nowadays. In the present work, the strategy of excitation-emission matrix (EEM) fluorescence data coupled with second-order calibration method based on alternating normalization-weighted error (ANWE) algorithm was used to determine ofloxacin, lomefloxacin and ciprofloxacin in milk powder, milk and beef. Owning the unique "second-order advantage", the ANWE-assisted analytical method was proved to successfully and eco-friendly resolve the overlapped fluorescence spectra of multi-component in complex food matrixes without tedious pretreatment steps and sophisticated high-cost instrumentations. The feasibility of the proposed method was validated by experiments. The average spiked recoveries of three fluoroquinolones range from 82.6% to 110.5% with relative standard deviations lower than 7.4%, and the limits of detection range from 0.18 and 2.41 ng mL^-1. For further evaluation, analytical figures of merit such as sensitivity and selectivity, as well as the RSDs of intra-day (≦10.6%) and inter-day (≦9.4%) were calculated. The satisfactory analytical results demonstrated that the proposed strategy could be a competitive alternative for simple, rapid and simultaneous determination of multiple fluoroquinolones in animal-derived food samples.

Rapid, simultaneous and interference-free determination of three rhodamine dyes illegally added into chilli samples using excitation-emission matrix fluorescence coupled with second-order calibration method

In this study, a smart and green analytical method based on the second-order calibration algorithm coupled with excitation-emission matrix (EEM) fluorescence was developed for the determination of rhodamine dyes illegally added into chilli samples. The proposed method not only has the advantage of high sensitivity over the traditional fluorescence method but also fully displays the "second-order advantage". Pure signals of analytes were successfully extracted from severely interferential EEMs profiles via using alternating trilinear decomposition (ATLD) algorithm even in the presence of common fluorescence problems such as scattering, peak overlaps and unknown interferences. It is worth noting that the unknown interferents can denote different kinds of backgrounds, not only refer to a constant background. In addition, the method using interpolation method could avoid the information loss of analytes of interest. The use of "mathematical separation" instead of complicated "chemical or physical separation" strategy can be more effective and environmentally friendly. A series of statistical parameters including figures of merit and RSDs of intra- (≤1.9%) and inter-day (≤6.6%) were calculated to validate the accuracy of the proposed method. Furthermore, the authoritative method of HPLC-FLD was adopted to verify the qualitative and quantitative results of the proposed method. Compared with the two methods, it also showed that the ATLD-EEMs method has the advantages of accuracy, rapidness, simplicity and green, which is expected to be developed as an attractive alternative method for simultaneous and interference-free determination of rhodamine dyes illegally added into complex matrices.

Synthesis and Evaluation of a Molecularly Imprinted Polymer for the Determination of Metronidazole in Water Samples

A molecularly imprinted polymer was developed and evaluated for selective determination of metronidazole (MNZ) in wastewater. This was achieved by using sodium methacrylate as monomer, toluene as porogen, ethylene glycol dimethacrylate as crosslinker, azobisisobutyronitrile as initiator and metronidazole as template molecule to generate the selectivity of the polymer for the compound, as well as non-imprinted polymers were synthesized. Two different polymerization approaches were used, bulk and emulsion and the polymers obtained by emulsion presented higher retention percentages the MIP 2-M presented the higher retention (83%). The performed method, was validated in fortified water, showing linearity from 10 up to 1000 ng/mL; limit of detection and quantification for compound were between 3 and 10 ng/mL, respectively. Finally, the method was applied in samples of a wastewater treatment plant in the city of San Luis Potosí, México, and the concentrations of MNZ in these samples were 84.1-114 ng/mL.

Effects of the antioxidant moieties of dissolved organic matter on triplet-sensitized phototransformation processes: Implications for the photochemical modeling of sulfadiazine

Previous studies have shown that the photodegradation of some pollutants, induced by the excited triplet states of chromophoric dissolved organic matter (³CDOM*), can be inhibited by back-reduction processes carried out by phenolic antioxidants occurring in dissolved organic matter (DOM). Here, for the first time to our knowledge, we included such an inhibition effect into a photochemical model and applied the model predictions to sulfadiazine (SDZ), a sulfonamide antibiotic that occurs in surface waters in two forms, neutral HSDZ and anionic SDZ^- (pK_a = 6.5). The input parameters of the photochemical model were obtained by means of dedicated experiments, which showed that the inhibition effect was more marked for SDZ^- than for HSDZ. Compared to the behavior of 2,4,6-trimethylphenol, which does not undergo antioxidant inhibition when irradiated in natural water samples, the back-reduction effect on the degradation of SDZ was proportional to the electron-donating capacity of the DOM. According to the model results, direct photolysis and OH reaction would account for the majority of both HSDZ and SDZ^- photodegradation in waters having low dissolved organic carbon (DOC < 1 mgC L^-1). With higher DOC values (>3-4 mgC L^-1) and despite the back-reduction processes, the ³CDOM* reactions are expected to account for the majority of HSDZ phototransformation. In the case of SDZ^- at high DOC, most of the photodegradation would be accounted for by direct photolysis. The relative importance of the triplet-sensitized phototransformation of both SDZ^- and (most importantly) HSDZ is expected to increase with increasing DOC, even in the presence of back reduction. An increase in water pH, favoring the occurrence of SDZ^- with respect to HSDZ, would enhance direct photolysis at the expense of triplet sensitization. SDZ should be fairly photolabile under summertime sunlight, with predicted half-lives ranging from a few days to a couple of months depending on water conditions.

Occurrence of enrofloxacin in overflows from animal lot and residential sewage lagoons and a receiving-stream

Enrofloxacin (ENRO), a fluoroquinolone, was quantified in overflows from an animal lot and residential sewage lagoons and in a receiving-stream (Gans Creek). The concentrations of ENRO in samples was determined by high-performance liquid chromatography - tandem mass spectrometry. In total, ninety samples including duplicates were analyzed during several monthly sampling campaigns. The samples collected represented the residential sewage lagoon overflow (RLO), animal lot lagoon overflow (ALLO), the combined overflows (RLO and ALLO), and Gans Creek (upstream, midstream and downstream positions). The frequency of detection of ENRO was 90% for RLO and 100% for both ALLO and Gans Creek. The highest concentration of ENRO (0.44 μg/L) was found in ALLO sample collected during high precipitation. ENRO levels found in RLO samples ranged from < LOQ to 259 ng/L and the highest value observed also coincided with high flow. The levels of ENRO found in Gans Creek ranged from 17-216 ng/L. A preliminary ecotoxicological assessment was conducted through calculation of the risk quotients (RQs) for organisms based on the ratio of the measured environmental concentrations in this study to the predicted-no-effect-concentrations (acute and chronic effect) data. From the RQs, high risks were observed for Microcystis aeruginosa (cyanobacteria; RQ = 4.4); Anabaena flosaquae (cyanobacteria; RQ = 1.3); and Lemna minor (aquatic vascular plant; RQ = 2.0). The long-term effects of mixtures of PHCs on Gans Creek watershed are probable.

A road map for multi-way calibration models

A road map is proposed for the selection of a multi-way calibration model according to the data properties.