Natural deep eutectic solvent for the simultaneous derivatization and microextraction of isoniazid from human plasma.

BACKGROUND: Personalized medicine is a rapidly revolving field that offers new opportunities for tailoring disease treatment to individual patients. The main idea behind this approach is to carefully select safe and effective medications and treatment plant based on each patient's unique pharmacokinetic profile. Isoniazid is a first-line anti-tuberculosis drug that has interindividual variability in its metabolic processing, leading to significant differences in plasma concentrations among patients receiving equivalent doses. This variability necessitates the creation of individualized treatment regimens as part of personalized medicine to achieve more effective therapy. RESULTS: In this work, a deep eutectic solvent-based liquid-liquid microextraction approach for the separation and determination of isoniazid in human plasma by high-performance liquid chromatography with UV-Vis detection was developed for the first time. A new natural deep eutectic solvent based on thymol as a hydrogen bond donor and 4-methoxybenzaldehyde as a hydrogen bond acceptor was proposed as the extraction solvent. The developed microextraction procedure assumed two simultaneous processes during the mixing of the sample and extraction solvent: the derivatization of the polar analyte in the presence of 4-methoxybenzaldehyde (component of the natural deep eutectic solvent) with the formation of a hydrophobic Schiff base (1); mass transfer of the Schiff base from the sample phase to the extraction solvent phase (2). Under optimal conditions, the limits of detection and quantification were 20 and 60 µg L-1, respectively. The RSD value was <10 %, the extraction recovery was 95 %. SIGNIFICANCE: In this work, the possibility of isoniazid derivatization in the natural deep eutectic solvent phase with the formation of the Schiff base was presented for the first time. The approach provided the separation and preconcentration of polar isoniazid without the use of expensive derivatization agents and solid-phase extraction cartridges. The formation of the Schiff base was confirmed by mass spectrometry.

Supramolecular solvents based on hydrophobic natural deep eutectic solvents and primary amines for preconcentration and determination of enrofloxacin in milk.

In this work, coacervation in primary amines solutions with hydrophobic natural deep eutectic solvents based on terpenoids and carboxylic acids was demonstrated for the first time. A liquid-phase microextraction approach was developed based on supramolecular solvent formation with primary amine acting as amphiphile and hydrophobic deep eutectic solvent making up mixed vesicles and serving as coacervation agent. Such supramolecular solvents could be used to separate wide range of substances from different aqueous media, such as food products, biological liquids and wastewaters. It is important that both hydrophobic and ionic interactions with supramolecular aggregates take place ensuring synergetic effect and better extraction ability, which is significant in separating relatively polar analytes. Different primary amines and deep eutectic solvents were investigated for liquid-phase microextraction of proof-of-concept amphoteric analyte (enrofloxacin, widely used veterinary fluoroquinolone antibiotic) and its determination by high-performance liquid chromatography with fluorescence detection using Shimadzu LC-20 Prominence chromatograph and RF-20A fluorescence detector. It was found that the supramolecular solvent based on 1-nonylamine, formed after addition of a deep eutectic solvent based on menthol and hexanoic acid (molar ratio of 1:1), provided maximum extraction recovery (85 %) and maximum enrichment factor (34). To characterize the extraction system, the composition of the phases was investigated, and cryo-transmission electron microscopy images were obtained. Vesicular aggregates were observed in the supramolecular solvent. The extraction mechanism was proposed in terms of formation of mixed aggregates to capture the analyte. Limit of detection was found to be 7 µg kg-1, while linear range of 20-250 µg kg-1 was established. Relative standard deviation values were lower than 7 %. Relative bias did not exceed 12 %.

Primary alcohol-induced coacervation in alkyl polyglucoside micellar solution for supramolecular solvent-based microextraction and chromatographic determination of phthalates in baby food.

This study reports for the first time the phenomenon of supramolecular solvent formation based on alkyl polyglucoside as an amphiphile and primary alcohol as a coacervation agent. The physical properties (density, kinematic viscosity, phase diagram for ternary system) of the supramolecular solvent were investigated, and a mechanism for its formation was proposed. A green and simple microextraction procedure for preconcentration and determination of phthalates in baby foods packaged in plastic packaging was developed as proof-of-concept example. The microextraction procedure assumed separation of analytes from solid phase sample in micellar solution of decyl glucoside and in situ formation of supramolecular solvent for analytes preconcentration after addition of n-heptanol. The determination of phthalates in obtained extracts was implemented by high-performance liquid chromatography with UV-Vis detection. The limits of detection, calculated from a blank test based on 3σ, were determined to be 10 µg kg-1 for dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, and di-n-octyl phthalate. The developed procedure did not require filtration of sample suspension, and assumed the use of green and biodegradable substances for the supramolecular solvent formation across a wide pH range.

In situ formation of natural deep eutectic solvent on membrane after fat hydrolysis for lindane isomers determination in peanut paste.

In this work a sample pretreatment approach assumed liquid-liquid microextraction based on the in situ formation of a hydrophobic natural deep eutectic solvent on a hydrophobic membrane impregnated with natural terpenoid was developed. The procedure included alkaline hydrolysis of a food sample containing fat to form fatty acids, which acted as precursors for the in situ formation of the deep eutectic solvent with natural terpenoid. Two processes were observed on the membrane surface: in situ formation of the hydrophobic deep eutectic solvent and liquid-liquid microextraction of the target analytes. After microextraction, the membrane containing the analytes was easily removed from the sample solution. The developed approach was applied to the separation and preconcentration of hydrophobic organochlorine pesticides (ɑ-hexachlorocyclohexane and γ-hexachlorocyclohexane) from a hydrophobic sample matrix (peanut paste), followed by their determination by gas chromatography with electron capture detection. Under optimal conditions, the limits of detection and quantification for both analytes were 0.3 and 1.0 µg kg-1, respectively. The procedure allowed the separation of fat-soluble analytes from a complex sample matrix with a high content of fat. The extraction recoveries were in the range of 93-95 %.

Layered double hydroxide nanoparticles for a smartphone digital image colorimetry-based determination of fluoride ions in water, milk and dental products.

A novel smartphone digital image colorimetry-based approach was developed for fluoride ion determination, using layered double hydroxide (LDH) nanoparticles (Mg2Al(OH)7) as sorbents for analyte preconcentration and as a source of a central metal ion for a colored complex formation. A cotton rotating disk provided effective retention of the LDH nanoparticles during solid-phase microextraction and elution, excluding time-consuming centrifugation process. In the proposed procedure, the nanoparticles acted as aluminum ion source for alizarin complexone-Al3+-F- complex formation. An image of Eppendorf tube, containing the colored complex solution was obtained by a smartphone and converted, using the RGB model for fluoride ion determination. The procedure had a linear range of 0.20-20 mg L-1 with a limit of detection of 0.06 mg L-1. The developed procedure provided effective fluoride separation from various matrices for its determination by a smartphone without additional sample pretreatment.

Fast and ecofriendly triple sulfonamides mixture utilization using UV irradiation and spherical SnO2 nanoparticles with controllable parameters and antibacterial activity.

One of the solutions for the growing problem of water purification is photocatalytic degradation of the pollutants. Semiconductor nanoparticles are widely under study as a promising photocatalyst for this purpose. However, there is still lack of understanding of the relation between properties of nanoparticles, in their turn related with synthesis conditions, and photocatalytic efficiency, as well as of the other factors influencing the process. For the first time, a possibility to regulate photocatalytic activity of SnO2 nanoparticles under UV light via regulation of structural parameters is shown. A method for obtaining spherical nanoparticles with different parameters was developed. Obtained nanoparticles were fully characterized. Special attention was paid to the study of oxygen vacancies. With the help of quantum computational methods, it was shown, that the concentration of vacancies is around 1 per 32 tin atoms. Obtained data on oxygen vacancies were further used for the evaluation of pollutant-nanoparticle surface interaction to get closer to the calculations of real systems. On the example of methylene blue, it was shown that the greater is the amount of oxygen vacancies and the lower the amount of defects, the higher photocatalytic activity. The obtained dependence is confirmed by the fact that the photoresponse increases with a decrease of amount of defects in the sample. Degradation kinetics of sulfonamides mixture was studied, and its dependence on active complex formation was shown based on the quantum chemical calculation data. Degradation of antibiotics in water from Neva River reached more than 95% in 35 min, which indicates that developed photocatalyst efficiency is not affected by pollutants contained in open water in the centre of the metropolis. It was shown, that the use of nanoparticles allows to speed up the process of bacteria destruction under UV light, which indicates the antibacterial activity of obtained nanoparticles.

Primary amine citrate-based supramolecular designer solvent: Preconcentration of ochratoxin A for determination in foods by liquid chromatography.

BACKGROUND: Supramolecular solvents are nanostructured liquids that are separated from colloidal solutions of amphiphilic compounds as a result of self-assembly of amphiphiles and coacervation under changing conditions. They are considered to be designer solvents as their properties can be tailored to a specific analytical task by controlling the conditions of their formation (amphiphile, coacervation inducer, medium, concentration of components). The discovery of new extraction systems based on supramolecular solvents and their application to relevant analytical tasks are of great importance for the advancement of environmentally-friendly sample preparation. RESULTS: A novel green liquid-phase microextraction approach involving in situ formation of 1-octylamine citrate followed by preconcentration of ochratoxin A from aqueous extract of food sample in supramolecular solvent droplets was developed. The extraction system was carefully characterized. The density of the solvent allowed it to be to retrieved from the extraction system by its solidification. The alkaline nature of the obtained extract allowed the use of acetic acid for its dissolution instead of more toxic organic solvents followed by high-performance liquid chromatography with fluorometric detection. An excellent extraction recovery of 99 % and a satisfactory enrichment factor of 8.3 were achieved. The limit of detection was 0.5 µg kg-1, while the calibration plot was linear over the range of 1.5-50 µg kg-1. Cereal and roasted coffee bean samples were successfully analyzed with a relative bias less than 20 %. SIGNIFICANCE: In the present work, a phenomenon of supramolecular solvent formation based on primary amine citrate was presented for the first time. Tetrabutylammonium bromide was investigated as a coacervation agent in an extraction system, and possible interactions responsible for its ability to induce phase separation in a micellar solution of primary amine citrate were described. The critical micelle concentration of 1-octylamine citrate in aqueous solution of tetrabutylammonium bromide was firstly determined.

Three-component deep eutectic solvent-based microextraction approach for biodiesel quality control: Determination of water and metals.

Biodiesel is an important alternative fuel produced by blending biofuels with petroleum diesel. Biofuel production is usually carried out by catalytic interesterification of animal fats or vegetable oils, followed by the removal of by-products and catalysts through washing with water. Residual amounts of water and catalysts can accelerate fuel biodegradation and contribute to the corrosion of metal surfaces. Considering the need to control the quality of biodiesel fuel, a simple and environmentally friendly analytical approach was first developed for the determination of water and metals (sodium, potassium, magnesium, calcium as catalysts, and iron, copper, tin, zinc, lead as feedstock elements) using a deep eutectic solvent. The technique involved microextraction of analytes from biodiesel into a new three-component deep eutectic solvent (choline chloride, lactic acid, and cobalt chloride) using a laboratory vortex, followed by impregnating the filter paper with the obtained extract to determine the analytes. The colorimetric determination of water is based on a change in the color of the deep eutectic solvent, which goes from blue to pink due to the formation of cobalt aqua complexes. The detection of water on the filter paper was carried out using a conventional scanner. The content of metals on the filter paper was determined by X-ray fluorescence spectrometry. Under optimal conditions, the detection limit was 100 mg kg-1 for water and 0.03-3 mg kg-1 for metals. The technique enabled multicomponent analysis to be carried out without the use of dangerous Karl Fischer reagents (for water determination) and microwave mineralization of samples (for elemental analysis). The enrichment factor ranged from 290 to 330, and the RSD was less than 15%.

Deep eutectic solvents with low viscosity for automation of liquid-phase microextraction based on lab-in-syringe system: Separation of Sudan dyes.

In the work limitations of deep eutectic solvents in the flow-based analysis are discussed. Deep eutectic solvents based on terpenes and fatty acids with low viscosity were studied as extraction solvents for liquid-liquid microextraction into a lab-in-syringe system for the first time. As a result an automated deep eutectic solvent-based microextraction approach was proposed. The procedure involved aspiration of deep eutectic solvent (based on terpene and fatty acid) and aqueous sample solution followed by phases mixing by a magnetic stirrer inside a syringe of flow system. After phase separation the extract phase was transferred from the syringe into a vial followed by analysis by a high-performance liquid chromatography with diode-array detection. The determination of Sudan I, Sudan II and Sudan III in chili-based sauces was considered as an analytical task. The mass-transfer intensification performed by the magnetic stirring inside the syringe allowed to perform fast (2 min) and efficient (extraction recoveries 87-95%) extraction. The limits of detection, calculated from a blank test based on 3σ, were from 0.003 to 0.005 mg kg-1, RSD was <9%. The microextraction procedure did not involve the use of hazardous organic solvents, only 100 µL of natural deep eutectic solvent was required for dyes preconcentration.

Liquid-liquid microextraction with hydrophobic deep eutectic solvent followed by magnetic phase separation for preconcentration of antibiotics.

This study describes a miniaturized approach for liquid-liquid microextraction based on mass transfer into low volume of deep eutectic solvent and magnetic phase separation, using specially produced magnetic chromium dioxide nanoparticles with a hydrophobic surface layer of fatty acids. The nanoparticles modified with fatty acid helped to recover low volumes of viscous hydrophobic deep eutectic solvent-based extract reproducibly and easily (up to 10 µL) in a microextraction procedure with the application of magnetic forces. It was demonstrated that the collector properties depend on nanoparticles' surface and magnetic characteristics. The developed approach was implemented for the separation and preconcentration of trace fluoroquinolone antibiotics from environmental waters prior to their determination by high-performance liquid chromatography with fluorometric detection as a model analytical task. The limits of detection, calculated from a blank test based on 3σ, were 0.01 µg L-1 for ofloxacin, 0.02 µg L-1 for lomefloxacin and fleroxacin, and 0.04 µg L-1 for norfloxacin. The procedure provides significant solvent reduction and high enrichment factors. The approach is green, which is proved by the analytical eco-scale assessment tool with the total score equal to 85 out of 100.

Stir membrane liquid-phase microextraction based on milk fats hydrolysis and deep eutectic solvent formation: Determination of bisphenols.

In this paper, a stir membrane liquid-phase microextraction approach based on milk fats hydrolysis and in situ deep eutectic solvent formation was developed for the first time. The approach was applied to clean-up and preconcentrate bisphenols from milk samples. The procedure assumed alkaline hydrolysis of samples fats to obtain water-soluble salts of fatty acids that acted as precursors for the deep eutectic solvent formation. A stir membrane disk impregnated with menthol was placed into the sample solution. The formation of microdroplets of the hydrophobic fatty acids was observed under sample acidification. Collection of the extract phase on the disk was based on deep eutectic solvent formation. Under optimal conditions, the RSD was < 6 %, limits of detection for bisphenols were 0.3-0.5 µg kg-1. The extraction recoveries were in the range of 95-97 %, which indicated the excellent capability of the developed approach to extract hydrophobic analytes from complex matrices.

Alkyl polyglucoside-based supramolecular solvent formation in liquid-phase microextraction.

The phenomenon of alkyl polyglucoside-based supramolecular solvent formation in the presence of alkyl carboxylic acid acted as coacervation agent was described for the first time. Various alkyl polyglucosides and carboxylic acids were studied as the amphiphiles and coacervation agents, respectively. A possible mechanism of the new supramolecular solvent formation was presented. The physico-chemical properties of the developed alkyl polyglucoside-based supramolecular solvents were investigated. The green liquid-phase microextraction approach with the use of alkyl polyglucoside-based supramolecular solvent was developed and applied to epinephrine (hormone and biomarker for the diagnosis of adrenal glands neoplastic diseases) separation and preconcentration from human urine samples prior to its chromatographic determination. Caprylyl/capryl glucoside was found to be the most effective supramolecular solvent precursor for microextraction of the epinephrine (extraction recovery 95%). The microliter amount of the heptanoic acid was required to induce coacervation process and phase separation. The reduced fluidity of alkyl polyglucoside-based supramolecular solvent under cooling was used to simplify the collection of the extract phase by decantation. The green supramolecular solvent obtained was less viscous then known nonionic surfactant-based solvents and as result more compatible with the high-performance liquid chromatography with fluorometric detection.

An effervescence-assisted dispersive liquid-liquid microextraction based on three-component deep eutectic solvent for the determination of fluoroquinolones in foods.

An effervescence-assisted dispersive liquid-liquid microextraction approach using three-component deep eutectic solvent based on short-chain and medium-chain carboxylic acids and terpenoid was developed for the first time. The microextraction procedure was applied to the determination of fluoroquinolone antibiotics in foods (milk and shrimp samples) by high-performance liquid chromatography with fluorometric detection. In this microextraction procedure three-component deep eutectic solvent acted as a proton donor agent and an extractant. The carbon dioxide bubbles caused by the fast reaction between precursor of deep eutectic solvent (short-chain carboxylic acid) and effervescent agent (sodium carbonate) promoted the dispersion of the extractant in an aqueous sample phase. Various carboxylic acids were studied as hydrogen bond donors for the formation of deep eutectic solvents and proton donor agents for the generation of CO2 bubbles. Two natural terpenoids (menthol and thymol) were studied as the hydrogen bond acceptors for the formation of three-component solvent. The extraction system based on heptanoic acid and thymol (1:2, mol/mol) containing formic acid (proton donor for generating CO2 bubbles) provided maximum extraction recovery (86-99%) and a higher extraction efficiency of analytes compared to their extraction into individual hydrophobic precursors of the system. The LODs, calculated from the blank tests based on 3σ, were varied from 0.03 to 0.06 µg L-1 and from 0.3 to 0.6 µg kg-1 for fluoroquinolone antibiotics in milk and shrimp samples, respectively. The proposed approach provided effective dispersion of extractant speeding up the extraction process and fast separation of phases without any external energy assistance.

The strategy for organic dye and antibiotic photocatalytic removal for water remediation in an example of Co-SnO2 nanoparticles.

A challenging problem to create an efficient photocatalyst suitable for industrial water remediation, aiming to remove cyclic organic compounds attracts increasing attention. The current study aimed to clarify a few "dark spots" in the field, namely to find out if it is possible to make an efficient photocatalyst activated with visible light by using a simple and cheap strategy and what are the key factor impacting its efficiency. In this work, a new procedure to obtain spherical nanoparticles with the same average size but different amounts of oxygen vacancies and defects and dopant concentrations was developed. The approach based on hydrothermal treatment was suggested to obtain rod-shaped nanoparticles. The systematic study of photocatalytic behavior on the example of oxytetracycline and methylene blue degradation under visible light of widely available LED lamp was performed. Based on chemical and computational experiments the main factor affecting the process efficiency was determined.

Deep Eutectic Solvents or Eutectic Mixtures? Characterization of Tetrabutylammonium Bromide and Nonanoic Acid Mixtures.

Deep eutectic solvents have quickly attracted the attention of researchers because they better meet the requirements of green chemistry and thus have the potential to replace conventional hazardous organic solvents in some areas. To better understand the nature of these mixtures, as well as expand the possibilities of their use in different industries, a detailed examination of their physical properties, such as density, viscosity, the nature of the interactions between their constituents, the phase diagrams, depression of their melting point, and interpretation of these results is necessary. In this work, the mixtures of tetrabutylammonium bromide (TBAB) and nonanoic acid (NA) in different molar ratios are theoretically and experimentally investigated by applying a phase diagram constructed on the basis of differential scanning calorimetry measurements and COSMO-RS model. Spectral properties are investigated based on Fourier transform infrared spectroscopy and density functional theory. The observed eutectic point indicates the formation of a DES in the TBAB-NA system in a 1:2 molar ratio. This is due to the presence of hydrogen bonds between the carboxyl group from the NA molecule and the bromine atom from the TBAB molecule. Other eutectic mixtures are most likely the solutions of TBAB in NA, in which hydrogen bonds predominate between acid molecules.

A surfactant-mediated microextraction of synthetic dyes from solid-phase food samples into the primary amine-based supramolecular solvent.

An effective and simple surfactant-mediated microextraction of synthetic dyes from solid-phase food samples into the primary amine-based supramolecular solvents is presented for the first time. The developed procedure involved two stages: (i) an isolation of dyes from a solid-phase food sample into a micellar solution of the primary amine; (ii) a preconcentration of the extracted dyes into the supramolecular solvent phase generated from the obtained micellar solution under a coacervation process. The microextraction procedure was applied for the determination of synthetic dyes in confectionery, dried fruits, and spices samples. The supramolecular solvent formed from aqueous micelle aggregates of 1-octylamine due to coacervation induced by thymol provided maximum extraction recovery values for synthetic dyes. In the proposed two-stage extraction procedure the micellar solution of primary amine was a media for analytes isolation from solid-phase and their followed preconcentration.

Deep eutectic solvents based on carboxylic acids for metals separation from plant samples: Elemental analysis by ICP-OES.

Deep eutectic solvents based on choline chloride, carboxylic acids, urea, and polyols were investigated for separation of 14 metals from plant samples. It was found that carboxylic acid as precursor of DES played key-role for effective metals separation. It was established that the solvent synthesized from choline chloride and malic acid provided highest extraction recovery (from 73 to 88%). Mixing and heating the solvent and sample for 30 min at a temperature of 70 °C provided effective separation of metals from plant sample. The developed procedure is not required a microwave digestion of samples. After separation the solvent phase containing analytes was dissolved in aqueous phase and analyzed. The developed procedure was applied to elemental analysis of plant tobacco and lettuce samples by inductively coupled plasma optical emission spectroscopy. Limits of detection calculated as three times the signal-to-noise ratio were in the range from 0.2 to 17 mg kg-1.

Hydrolysis of triglycerides in milk to provide fatty acids as precursors in the formation of deep eutectic solvent for extraction of polycyclic aromatic hydrocarbons.

A microextraction pretreatment for powdered milk analysis, relying on the formation of a natural deep eutectic solvent is proposed. It relies on the in situ hydrolysis of milk fats (triglycerides) which yields fatty acids as precursors in the formation of the natural deep eutectic solvent. As a proof-of-concept, the innovation was applied to the determination of thirteen polycyclic aromatic hydrocarbons in powdered milk samples by HPLC with fluorometric detection. The alkaline hydrolysis of milk triglycerides minimized sample matrices interference through removal of proteins and fats, and led to formation of natural deep eutectic solvent precursors (fatty acids) directly from the sample components. Addition of only one precursor (terpenoid) was then required. Menthol and thymol (natural terpenoids) were investigated as deep eutectic solvent precursors for microextraction of polycyclic aromatic hydrocarbons. Under the selected experimental conditions, limits of detection were estimated within the 0.002-0.09 µg kg-1 range. The innovation provided satisfactory (70-91%) extraction of hydrophobic analytes from complex powdered milk matrices containing hydrophobic components (triglycerides) without the need for hazardous organic solvents. The RSD values were <5.2%.

Reversed-phase dispersive liquid-liquid microextraction based on decomposition of deep eutectic solvent for the determination of lead and cadmium in vegetable oil.

In this work, a reversed-phase dispersive liquid-liquid microextraction procedure based on the decomposition of deep eutectic solvent was suggested for the first time. The procedure was utilized for fast and simple separation of lead and cadmium from vegetable oil samples. The procedure assumed mixing of oil sample and DES based on menthol, formic acid and water. Water as component of DES promoted its decomposition in sample matrix resulting menthol dissolution in the sample phase and dispersion of aqueous formic acid solution. In this procedure menthol acted as a dispersive solvent during DES decomposition for dispersion of aqueous formic acid solution. The metals were determined by the square-wave anodic stripping voltammetry. The limits of detection, were 0.01 µg kg-1 for lead and 0.006 µg kg-1 for cadmium. The RSD was less then 6% for both analytes. The enrichment factor was 36 and 39 for lead and cadmium, respectively.

Automated liquid-liquid microextraction and determination of sulfonamides in urine samples based on Schiff bases formation in natural deep eutectic solvent media.

In this work, an automated liquid-liquid microextraction procedure for the determination of sulfonamides (sulfamethoxazole, sulfamethazine and sulfapyridine) in urine samples using natural deep eutectic solvent is presented for the first time. The mechanism for extraction of sulfonamides was based on the formation of colored Schiff bases in the presence of vanillin, which acted as a derivatization reagent and precursor of natural deep eutectic solvent (an extractant). In this procedure, thymol was used as both media for Schiff bases formation and as a second precursor of the natural deep eutectic solvent. The formation of the Schiff bases was confirmed by mass spectrometry. A Lab-In-Syringe concept was applied for the automation of the microextraction procedure. The procedure involved mixing the sample and natural deep eutectic solvent into a syringe of a flow system, formation and microextraction of colored Schiff base followed by UV-Vis detection. Under optimal automated conditions the limits of detection, calculated from a blank test based on 3s (sigma) were 0.06, 0.1, and 0.06 mg L-1 for sulfapyridine, sulfamethoxazole and sulfamethazine. The proposed automated procedure permitted the routine determination of one drug (sulfamethoxazole, sulfamethazine or sulfapyridine) in urine samples to be achieved in less than 10 min.