Gas chromatographic determination of carbonyl compounds in biological and oil samples by headspace single-drop microextraction with in-drop derivatisation

A suitable method for the gas chromatographic determination of 10 characteristic carbonyls in biological and oil samples based on the in-drop formation of hydrazones by using 2,4,6-trichlorophenylhydrazine (TCPH), has been developed. The derivatisation-extraction procedure was optimized separately for aqueous and oil samples with respect to the appropriate organic drop solvent, drop volume, in-drop TCPH concentration, sample stirring rate, temperature during single-drop microextraction (SDME), reaction time and headspace-to-sample volume ratio. The optimization showed differentiation of optimum values between the studied matrices. The limits of detection were found to range from 0.001 to 0.003 μg mL⁻¹ for the aqueous biological samples and from 0.06 to 0.20 μg mL⁻¹ for the oil samples. The limits of quantification were in the range of 0.003-0.010 μg mL⁻¹ and 0.020-0.059 μg mL⁻¹ for aqueous and oil samples, respectively. The overall relative standard deviations of the within-day repeatability and between-day reproducibility were <4.4% and <8.2% for the aqueous biological samples and <3.9% and <7.4% for the oxidized oil samples.     

Development, validation and application of a SDME/GC-FID methodology for the multiresidue determination of organophosphate and pyrethroid pesticides in water

A single-drop microextraction (SDME) procedure was developed for the analysis of organophosphorus and pyrethroid pesticides in water by gas chromatography (GC) with flame ionization detection (GC-FID). The significant parameters that affect SDME performance, such as the selection of microextraction solvent, solvent volume, extraction time, and stirring rate, were studied and optimized using a tool screening factorial design. The limits of detection (LODs) in water for the four investigated compounds were between 0.3 and 3.0 μg L⁻¹, with relative standard deviations ranging from 7.7 to 18.8%. Linear response data were obtained in the concentration range of 0.9-6.0 μg L⁻¹ (λ-cyhalothrin), 3.0-60.0 μg L⁻¹ (methyl parathion), 9.0-60.0 μg L⁻¹ (ethion), and 9.0-30.0 μg L⁻¹ (permethrin), with correlation coefficients ranging from 0.9337 to 0.9977. The relative recoveries for the spiked water ranged from 73.0 to 104%. Environmental water samples (n = 26) were successfully analyzed using the proposed method and methyl parathion presented concentration up to 2.74 μg L⁻¹. The SDME method, coupled with GC-FID analysis, provided good precision, accuracy, and reproducibility over a wide linear range. Other highlights of the method include its ease of use and its requirement of only small volumes of both organic solvent and sample.     

Tetradecyl(trihexyl)phosphonium chloride ionic liquid single-drop microextraction for electrothermal atomic absorption spectrometric determination of lead in water samples

A highly efficient single-drop microextraction (SDME) procedure using a low-cost room temperature ionic liquid (RTIL), i.e., tetradecyl(trihexyl)phosphonium chloride (CYPHOS^® IL 101), for Pb determination at trace levels in real water samples was developed. Lead was chelated with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) reagent and extracted into a 4 μL microdrop of CYPHOS^® IL 101. The RTIL drop was directly injected into the graphite furnace of the electrothermal atomic absorption spectrometer (ETAAS). Under optimal microextraction conditions, a preconcentration factor of 32 was achieved with only 1.5 mL of sample resulting in a phase-volume ratio of 375. The limit of detection (LOD) obtained was 3.2 ng L⁻¹ and the relative standard deviation (RSD) for 10 replicates at 0.5 μg L⁻¹ Pb²⁺ concentration level was 4.9%, calculated at peak heights. The calibration graph was linear from concentration levels near the detection limits up to at least 4.5 μg L⁻¹ with a correlation coefficient of 0.9996. The accuracy of the methodology was evaluated by analysis of a certified reference material (CRM). The method was successfully applied to the determination of Pb in tap, mineral, well and river water samples.     

Ion chromatography for rapid and sensitive determination of fluoride in milk after headspace single-drop microextraction with in situ generation of volatile hydrogen fluoride

In this article, we report a new method that involves headspace single-drop microextraction and ion chromatography for the preconcentration and determination of fluoride. The method lies in the in situ hydrogen fluoride generation and subsequent sequestration into an alkaline microdrop (15 μL) exposed to the headspace above the stirred aqueous sample. The NaF formed in the drop was then determined by ion chromatography. The influences of some crucial single-drop microextraction parameters such as the extraction temperature, extraction time, sample stirring speed, sulphuric acid concentration and ionic strength of the sample, on extraction efficiency were investigated. In the optimal condition, an enrichment factor of 97 was achieved in 15 min. The calibration working range was from 10 μg L⁻¹ to 2000 μg L⁻¹ (R² = 0.998), and the limit of detection (signal to noise ratio of 3) was 3.8 μg L⁻¹ of fluoride. Finally, the proposed method was successfully applied to the determination of fluoride in different milk samples. The recoveries of fluoride (at spiked concentrations of 200 μg L⁻¹ and 600 μg L⁻¹ into milk) in real samples ranged from 96.9% to 107.7%. Intra-day precision (N = 3) in terms of peak area, expressed as relative standard deviation, was found to be within the range of 0.24-1.02%.     

Dispersive liquid-liquid microextraction versus single-drop microextraction for the determination of several endocrine-disrupting phenols from seawaters

Two liquid-phase microextraction procedures: single-drop microextraction (SDME) and dispersive liquid-liquid microextraction (DLLME), have been developed for the determination of several endocrine-disrupting phenols (EDPs) in seawaters, in combination with high-performance liquid chromatography (HPLC) with UV detection. The EDPs studied were bisphenol-A, 4-cumylphenol, 4-tertbutylphenol, 4-octylphenol and 4-n-nonylphenol. The optimized SDME method used 2.5 μL of decanol suspended at the tip of a micro-syringe immersed in 5 mL of seawater sample, and 60 min for the extraction time. The performance of the SDME is characterized for average relative recoveries of 102 ± 11%, precision values (RSD) < 9.4% (spiked level of 50 ng mL⁻¹), and detection limits between 4 and 9 ng mL⁻¹. The optimized DLLME method used 150 μL of a mixture acetonitrile:decanol (ratio 15.7, v/v), which is quickly added to 5 mL of seawater sample, then subjected to vortex during 4 min and centrifuged at 2000 rpm for another 5 min. The performance of the DLLME is characterized for average relative recoveries of 98.7 ± 3.7%, precision values (RSD) < 7.2% (spiked level of 20 ng mL⁻¹), and detection limits between 0.2 and 1.6 ng mL⁻¹. The efficiencies of both methods have also been compared with spiked real seawater samples. The DLLME method has shown to be a more efficient approach for the determination of EDPs in seawater matrices, presenting enrichment factors ranging from 123 to 275, average relative recoveries of 110 ± 11%, and precision values (RSD) < 14%, when using a real seawaters (spiked level of 3.5 ng mL⁻¹).     

Determination of glyphosate and aminomethylphosphonic acid in natural water using the capillary electrophoresis combined with enrichment step

A previously elaborated capillary electrophoresis (CE) method used for the determination of glyphosate and aminomethylphosphonic acid (AMPA) was slightly modified in order to improve the sensitivity. However, detection limits attained (5 μg mL⁻¹ for glyphosate and 4 μg mL⁻¹ for AMPA) were still not satisfactory for analytical purposes, thus the addition of a preconcentration step before the CE analysis was proposed. AMBERLITE^®IRA-900, a strong anion-exchange resin, was used to preconcentrate both analytes in environmental aqueous samples. The experimental conditions optimised in a previous work were readapted, by decreasing the eluent concentration due to CE limitations. Satisfactory results were attained when spiked ultrapure water was applied, with recoveries from 84 to 87% for glyphosate (R.S.D. < 6%) and from 85 to 98% for AMPA (R.S.D. < 5%). Enrichment factors up to 65 were achieved with this system, allowing the determination of 85 ng mL⁻¹ of glyphosate and 60 ng mL⁻¹ of AMPA. The extraction efficiency varied when four different natural water samples of varying conductivity were applied. Especially the strong dependence on ion concentration in samples on AMPA recovery was found. For glyphosate, good recoveries (86-99%) were obtained for samples of low and medium conductivity (0-800 μS). The effect of sample salt content on extraction efficiency was studied and a linear relationship could be established for AMPA (r² = 0.996). An important improvement on recoveries was observed when lower volumes of sample were treated.A HPLC method with UV-vis detection and pre-column derivatisation with p-toluensulphonyl chloride was compared to the CE method. No significant differences in results were found when t- and F-statistical tests were applied.     

Microwave-assisted headspace single-drop microextration of chlorobenzenes from water samples

A one-step and in-situ sample preparation method used for quantifying chlorobenzene compounds in water samples has been developed, coupling microwave and headspace single-drop microextraction (MW-HS-SDME). The chlorobenzenes in water samples were extracted directly onto an ionic liquid single-drop in headspace mode under the aid of microwave radiation. For optimization, a Plackett-Burman screening design was initially used, followed by a mixed-level factorial design. The factors considered were: drop volume, aqueous sample volume, stirring speed, ionic strength, extraction time, ionic liquid type, microwave power and length of the Y-shaped glass-tube. The optimum experimental conditions found from this statistical evaluation were: a 5 μL microdrop of 1-hexyl-3-methylimidazolium hexafluorophosphate exposed for 20 min to the headspace of a 30 mL aqueous sample, irradiated by microwaves at 200 W and placed in a 50 mL spherical flask connected to a 25 cm Y-shaped glass-tube. Under the optimised experimental conditions, the response of a high performance liquid chromatographic system was found to be linear over the range studied and with correlation coefficients ranging between 0.9995 and 0.9999. The method showed a good level of repeatability, with relative standard deviations varying between 2.3 and 8.3% (n = 5). Detection limits were found in the low μg L⁻¹ range varying between 0.016 and 0.039 μg L⁻¹. Overall, the performance of the proposed method demonstrated the favourable effect of microwave sample irradiation upon HS-SDME. Finally, recovery studies from different types of environmental water samples revealed that matrix had little effect upon extraction.     

Development of on-line single-drop micro-extraction sequential injection system for electrothermal atomic absorption spectrometric determination of trace metals

A novel automatic sequential injection (SI) single-drop micro-extraction (SDME) system is proposed as versatile approach for on-line metal preconcentration and/or separation. Coupled to electrothermal atomic absorption spectrometry (ETAAS) the potentials of this SI scheme are demonstrated for trace cadmium determination in water samples. A non-charged complex of cadmium with ammonium diethyldithiophosphate (DDPA) was produced and extracted on-line into a 60 μL micro-drop of di-isobutyl ketone (DIBK). The extraction procedure was performed into a newly designed flow-through extraction cell coupled on a sequential injection manifold. As the complex Cd(II)-DDPA flowed continuously around the micro-droplet, the analyte was extracting into the solvent micro-drop. All the critical parameters were optimized and offered good performance characteristics and high preconcentration ratios. For 600 s micro-extraction time, the enhancement factor was 10 and the sampling frequency was 6 h⁻¹. The detection limit was 0.01 μg L⁻¹ and the precision (RSD at 0.1 μg L⁻¹ of cadmium) was 3.9%. The proposed method was evaluated by analyzing certified reference material.     

On-line continuous flow ultrasonic extraction coupled with high performance liquid chromatographic separation for determination of the flavonoids from root of Scutellaria baicalensis Georgi

An on-line method, based on coupling dynamic ultrasonic extraction (DUE), continuously sampling the suspension of sample and solvent, high performance liquid chromatographic separation with diode array detection, has been developed for the determination of the flavonoids, including baicalin, baicalein and wogonin, from the root of Scutellaria baicalensis Georgi. Variables influencing the DUE were evaluated by orthogonal test. The extraction yields of baicalin, baicalein and wogonin in the roots of S. baicalensis Georgi obtained from five different cultivated areas are 73.8–131.5 μg mg⁻¹ (RSD ≤ 6.24%), 6.8–15.9 μg mg⁻¹ (RSD ≤ 5.36%) and 4.4–14.3 μg mg⁻¹ (RSD ≤ 5.30%), respectively. The limits of detection for baicalin, baicalein and wogonin are 0.30, 0.37 and 0.41 μg mL⁻¹, respectively. Linearity is from 0.55 to 109 μg mL⁻¹ for baicalin, from 0.51 to 105 μg mL⁻¹ for baicalein and from 0.53 to 102 μg mL⁻¹ for wogonin. Compared with off-line continuous flow-DUE, the proposed method would be more convenient for the determination of the analytes and the rapid optimization of the extraction process. The extraction yields of flavonoids obtained by the proposed method are comparable with those obtained by dynamic microwave assisted extraction, static ultrasonic extraction and reflux extraction. The result indicated that the proposed method is suitable to determine the active components in Chinese herbal medicine.     

Determination of organochlorine pesticides in complex matrices by single-drop microextraction coupled to gas chromatography-mass spectrometry

A rapid and simple single-drop microextraction method (SDME) has been used to preconcentrate eighteen organochlorine pesticides (OCPs) from water samples with a complex matrix. Exposing two microlitre toluene drop to an aqueous sample contaminated with OCPs proved an excellent preconcentration method prior to analysis by gas chromatography-mass spectrometry (GC-MS). A Plackett-Burman design was used for screening and a central composite design for optimizing the significant variables in order to evaluate several possibly influential and/or interacting factors. The studied variables were drop volume, aqueous sample volume, agitation speed, ionic strength and extraction time. The optimum experimental conditions of the proposed SDME method were: 2 μL toluene microdrop exposed for 37 min to 10 mL of the aqueous sample containing 0% w/v NaCl and stirred at 380 rpm.The calculated calibration curves gave high-level linearity for all target analytes with correlation coefficients ranging between 0.9991 and 0.9999. The repeatability of the proposed method, expressed as relative standard deviation, varied between 5.9 and 9.9% (n = 8). The detection limits were in the range of 0.022-0.101 μg L⁻¹ using GC-MS with selective ion monitoring. The LOD values obtained are able to detect these OCPs in aqueous matrices as required by EPA Method 625. Analysis of spiked effluent wastewater samples revealed that the matrix had no effect on extraction for eleven of the analytes but exerted notable effect for the other analytes.     

Coupling chemiluminescence with capillary electrophoresis to analyze single human red blood cells

In this paper, we describe a new method for determination of hemoglobin of single red blood cells by coupling chemiluminescence with capillary electrophoresis (CL-CE). The chemiluminescent detection is based on the catalytic effects of hemoglobin on the luminol-hydrogen peroxide reaction. The conditions of chemiluminescent reaction and capillary electrophoresis were investigated. Hemoglobin in human blood samples was detected with the present method, the linear range from 1.7 μg mL⁻¹ to 6.8 μg mL⁻¹ was tested, and the correlation coefficient of 0.997 and low detection limit of 0.17 μg mL⁻¹ (approximately 2.2 pg, S/N = 3) were obtained. Cell injection procedure was improved, and the method was successfully used to determine hemoglobin of single red blood cells and the statistical result of the average content of hemoglobin in 26 human red blood cells was 23.6 pg. Compared to other current methods, CE with CL system is simple, sensitive and will become an attractive alternative method for single cell analysis.     

Capillary electrophoretic determination of ammonia using headspace single-drop microextraction

A new method involving headspace single-drop microextraction (SDME) and capillary electrophoresis (CE) is developed for the preconcentration and determination of ammonia (as dissolved NH₃ and ammonium ion). An aqueous microdrop (5 μL) containing 1 mmol/L H₃PO₄ and 0.5 mmol/L KH₂PO₄ (as internal standard) was used as the acceptor phase. Common experimental parameters (sample and acceptor phase pH, extraction temperature, extraction time) affecting the extraction efficiency were investigated. Proposed SDME-CE method provided about 14-fold enrichment in about 20 min. The calibration curve was linear for concentrations of NH₄⁺ in the range from 5 to 100 μmol/L (R² = 0.996). The LOD (S / N = 3) was estimated to be 1.5 μmol/L of NH₄⁺. Such detection sensitivity is high enough for ammonia determination in common environmental and biological samples. Finally, headspace SDME was applied to determine ammonia in human blood, seawater and milk samples with spiked recoveries in the range of 96-107%.     

An amperometric method for the detection of amitrole, glyphosate and its aminomethyl-phosphonic acid metabolite in environmental waters using passive samplers

The herbicides amitrole and glyphosate, and its metabolite aminomethyl-phosphonic acid (AMPA), in water samples have been directly analysed by high-performance liquid chromatography using an electrochemical (EC) detector. Limits of detection of 0.3 μg mL⁻¹ for glyphosate, 0.05 μg mL⁻¹ for AMPA and 0.03 μg mL⁻¹ for amitrole were comparable to those obtained by other authors using EC and also by liquid chromatography coupled to mass spectrometry, but the latter method requires derivatisation and pre-concentration of the sample whereas EC methods show similar sensitivity without the need of any derivatisation. The method was specifically designed to analyse extracts from passive samplers used for monitoring of polar herbicide residues in waters. To this purpose, three types of Empore^® disks were tested for their ability to adsorb and desorb these ionic, polar analytes. A procedure for their extraction from the membranes and reducing the interferences from other substances present in natural waters (i.e. humic acids) is described. The method is simple, does not require sophisticated equipment and is valid for the analysis and monitoring of herbicides residues using passive samplers.     

Sensitive quantitative determination of oxymatrine and matrine in rat plasma by capillary electrophoresis with stacking induced by moving reaction boundary

A quantitative method of capillary electrophoresis with sample stacking induced by moving reaction boundary (MRB) was developed for sensitive determination of oxymatrine (OMT) and matrine (MT) in rat plasma. The experimental conditions were optimized firstly. Below are the optimized experimental conditions: 20 mM sodium formate solution (HCOONa, adjusted to pH 10.70 by ammonia) as sample solution, 3 min 14 mbar sample injection, 40 mM formic buffer (HCOOH-HCOONa, pH 2.60) as stacking buffer, 7 min 14 mbar injection of stacking buffer, 100 mM HCOOH-HCOONa (pH 4.80) as separation buffer, 73 cm capillary (effective length 64 cm), 21 kV voltage, 210 nm wavelength. Under the optimized conditions, higher than 60-fold sensitivity improvement of the stacking was simply achieved as compared with capillary zone electrophoresis, and the detectable limits obtained for OMT and MT were 0.26 and 0.19 μg mL⁻¹, respectively. Then, numerous demonstrations were carefully performed for the methodological validations of OMT and MT in rate plasma, including high specificity of method, good linearity (r = 0.9993 for OMT, r = 0.9991 for MT), fair wide linear concentration range (1.30-65.00 μg mL⁻¹ for OMT, 0.84-42.00 μg mL⁻¹ for MT), low limit of detection (1.03 μg mL⁻¹ for OMT, 0.38 μg mL⁻¹ for MT), less than 5% intra- and inter-day variance value, and higher than 96% recovery of OMT and MT in plasma. The developed method could be used for the trace analyses of OMT and MT in plasma and was finally used for the investigation on pharmacokinetic study of OMT in rat plasma.     

Simultaneous determination of salbutamol sulphate, bromhexine hydrochloride and etofylline in pharmaceutical formulations with the use of four rapid derivative spectrophotometric methods

Four simple, rapid, accurate, precise, reliable and economical spectrophotometric methods have been proposed for simultaneous determination of salbutamol sulphate (SS), bromhexine hydrochloride (BH) and etofylline (ET) in pure and commercial formulations without any prior separation or purification. They were first derivative zero crossing spectrophotometry (method 1), simultaneous equation method (method 2), derivative ratio spectra zero crossing method (method 3) and double divisor ratio spectra derivative method (method 4). The ranges for SS, BH and ET were found to be 1-35 μg mL⁻¹, 4-40 μg mL⁻¹ and 5-80 μg mL⁻¹. For methods 1 and 2, the values of limit of detection (LOD) were 0.2314 μg mL⁻¹, 0.4865 μg mL⁻¹ and 0.2766 μg mL⁻¹ and the values of limit of quantitation (LOQ) were 0.7712 μg mL⁻¹, 1.6217 μg mL⁻¹ and 0.9221 μg mL⁻¹ for SS, BH and ET, respectively. For method 3, LOD values were 0.3297 μg mL⁻¹, 0.2784 μg mL⁻¹ and 0.7906 μg mL⁻¹ and LOQ values were 0.9325 μg mL⁻¹, 0.9282 μg mL⁻¹ and 2.6352 μg mL⁻¹ for SS, BH and ET, respectively. For method 4, LOD values were 0.3161 μg mL⁻¹, 0.2495 μg mL⁻¹ and 0.2064 μg mL⁻¹ and LOQ values were 0.9869 μg mL⁻¹, 0.8317 μg mL⁻¹ and 0.6879 μg mL⁻¹ for SS, BH and ET. The precision values were less then 2% R.S.D. for all four methods. The common excipients and additives did not interfere in their determinations. The results obtained by the proposed methods have been statistically compared by means of Student t-test and by the variance ratio F-test.     

Separation and determination of benzene, toluene, ethylbenzene and o-xylene compounds in water using directly suspended droplet microextraction coupled with gas chromatography-flame ionization detector

The directly suspended droplet microextraction (DSDME) technique coupled with the capillary gas chromatography-flame ionization detector (GC-FID) was used to determine BTEX compounds in aqueous samples. The effective parameters such as organic solvent, extraction time, microdroplet volume, salt effect and stirring speed were optimized. The performance of the proposed technique was evaluated for the determination of BTEX compounds in natural water samples. Under the optimal conditions the enrichment factors ranged from 142.68 to 312.13, linear range; 0.01-20 μg mL⁻¹, limits of detection; 0.8-7 ng mL⁻¹ for most analytes. Relative standard deviations for 0.2 μg mL⁻¹ of BTEX in water were in the range 1.81-2.47% (n = 5). The relative recoveries of BTEX from surface water at spiking level of 0.2 μg mL⁻¹ were in the range of 89.87-98.62%.     

Chromogenic platform based on recombinant Drosophila melanogaster acetylcholinesterase for visible unidirectional assay of organophosphate and carbamate insecticide residues

In this study we propose a chromogenic platform for rapid analysis of organophosphate (OP) and carbamate (CM) insecticide residues, based on recombinant Drosophila melanogaster acetylcholinesterase (R-DmAChE) as enzyme and indoxyl acetate as substrate. The visible chromogenic strip had the advantages identical to those of commonly used lateral flow assays (LFAs) with utmost simplicity in sample loading and result observation. After optimization, depending on the color intensity (CI) values, the well-established assay has the capabilities of both qualitative measurement via naked eyes and quantitative analysis by colorimetric reader with the desirable IC₅₀ values against the tested six insecticides (0.06 μg mL⁻¹ of carbofuran, 0.28 μg mL⁻¹ of methomyl, 0.03 μg mL⁻¹ of dichlorvos, 31.6 μg mL⁻¹ of methamidophos, 2.0 μg mL⁻¹ of monocrotophos, 6.3 μg mL⁻¹ of omethoate). Acceptable matrix effects and satisfactory detection performance were confirmed by in-parallel LC–MS/MS analysis in different vegetable varieties at various spiked levels of 10⁻³ to 10¹ μg g⁻¹. Overall, the testified suitability and applicability of this novel platform meet the requirements for practical use in food safety management and environmental monitoring, especially in the developing world.     

Optimization of experimental parameters in single-drop microextraction-gas chromatography-mass spectrometry for the determination of periodate by the Malaprade reaction, and its application to ethylene glycol

The aim of present work was to optimize the experimental parameters in single drop microextraction under solution immersion (SDME) and headspace (HS-SDME) extraction modes for the determination of periodate using guaifenesine [3-(2′-methoxyphenoxy)-1,2-propane diol] and norephedrine (phenylpropanolamine) as new and alternative reagents for the Malaprade reaction. The reactions were complete within 5 min resulting in the formation of 2-(2′-methoxyphenoxy)-acetaldehyde and benzaldehyde, respectively. SDME/HS-SDME of oxidation products with 2 μl of anisole or 1 μl of toluene, respectively, has permitted the determination of periodate at μg l⁻¹ concentration levels. The results indicated that HS-SDME (range 0.01-10 mg l⁻¹, r² = 0.9990; limit of detection 1.55 μg l⁻¹) was more sensitive than SDME (range 0.05-50 mg l⁻¹, r² = 0.9984; limit of detection 3.42 μg l⁻¹), and was inexpensive, rapid and convenient. Tolerance of excess of iodate has permitted the application of this method in the determination of ethylene glycol in motor oil; the average recovery on spiked sample was 98.6% with R.S.D. of 4.2%.     

Cold vapor generation interface for mercury speciation coupling capillary electrophoresis with electrothermal quartz tube furnace atomic absorption spectrometry: Determination of mercury and methylmercury

A novel on-line coupled capillary electrophoresis (CE) cold vapor generation (CVG) with electrothermal quartz tube furnace atomic absorption spectrometry (EQTF-AAS) system for mercury speciation has been developed. The mercury species (inorganic mercury and methylmercury) were completely separated by CE in a 80 cm length × 100 μm i.d. fused-silica capillary at 20 kV and using a buffer of 100 mM boric acid and 10% (v/v) methanol (pH 8.30). The effects of the inner diameter of quartz tube, the acidity of HCl, the NaBH₄ concentration and N₂ flow rate on Hg signal intensity were investigated. Speciation of mercury was highlighted using CE-CVG-EQTF-AAS. The detection limits of methylmercury and mercury were 0.035 and 0.027 μg mL⁻¹, respectively. The precisions (RSDs) of peak height for six replicate injections of a mixture of 10 μg mL⁻¹ (as Hg) were better than 4%. The interface was used for speciation analysis of mercury in dry goldfish muscle.     

Simple and commercial readily-available approach for the direct use of ionic liquid-based single-drop microextraction prior to gas chromatography: Determination of chlorobenzenes in real water samples as model analytical application

A simple and commercial readily-available approach that enables the direct use of ionic liquid (IL)-based single-drop microextraction (SDME) prior to gas chromatography (GC) is presented. The approach is based on thermal desorption (TD) of the analytes from the IL droplet to the GC system, by using a robust and commercially-available thermodesorption system. For this purpose, a two-glass-tube concentrically disposed system was designed. The inner tube is a laboratory-cut Pyrex tube (20 mm length) that houses the ionic liquid droplet from the SDME process, and the outer tube is a commercially-available TD glass tube (187 mm length) commonly employed for stir-bar sorptive extractions (SBSE). In this way, the proposed device prevents IL from entering the GC system, as this could dirty the inlet or even block the column. The determination of 10 chlorobenzenes in water samples by GC coupled with mass spectrometric (MS) detection has been chosen as model analytical application, showing the feasibility of the proposed approach. The SDME process consists of a 5 μL droplet of 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) suspended in the headspace (HS) of a 10 mL stirred sample. After extracting for 37 min at room temperature, the IL droplet is directly placed into the small inner tube, which is placed into the TD tube. The whole device is placed inside the TD unit, where desorption of the analytes is performed at 240 °C for 5 min with a helium flow rate of 100 mL min⁻¹. The analytical figures of merit of the proposed IL-(HS)-SDME-TD-GC–MS approach are very suitable for the determination of chlorobenzenes at ultratrace levels, with relative standard deviation values ranging between 2% and 17%, and limits of detection ranging between 1 and 4 ng L⁻¹, showing the potential offered by the IL-based SDME process with GC.