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.     

Development of a validated liquid chromatographic method for the quality control of Prunellae Spica: Determination of triterpenic acids

A simple and rapid reversed-phase HPLC-UV method was developed for the determination of triterpenic acids in the crude extract of Prunellae Spica. Five triterpenic acids were extracted and isolated from P. Spica as marker compounds for use in the quality control of herbal medicines. Various solvent extraction techniques were evaluated, and the greatest efficiency was observed with sonication in 100% ethanol. Elemental compositions of the five marker compounds were determined by high-resolution mass spectroscopy. The dynamic range of the HPLC-UV method depended on the specific analyte, and acceptable quantitation was obtained between 10 and 250 μg mL⁻¹ for oleanolic acid, between 10 and 300 μg mL⁻¹ for ursolic acid, between 3 and 75 μg mL⁻¹ for 2α,3α,24-trihydroxyolean-12en-28oic acid, between 5 and 100 μg mL⁻¹ for euscaphic acid, and between 5 and 100 μg mL⁻¹ for 2α,3α-dihydroxyurs-12en-28oic acid. The method was deemed satisfactory by inter- and intra-day validation and exhibited both high accuracy and precision (relative standard deviation <9.4%). Overall limits of quantitation and detection were approximately 0.5-2.5 μg mL⁻¹ at a signal-to-noise ratio (S/N) of 3 and were about 3.0-10.0 μg mL⁻¹ at a S/N of 10. In addition, principal component analysis (PCA) was performed on the analytical data of 15 different P. Spica samples in order to classify samples collected from different regions.     

Investigation on enhanced chemiluminescence reaction systems with bis(hydrogenperiodato) argentate(III) complex anion for fluoroquinolones synthetic antibiotics

A novel chemiluminescence (CL) reaction system with bis(hydrogenperiodato) argentate(III) complex anion (Ag(III) complex, [Ag(HIO₆)₂]⁵⁻), for the first time, is developed for the determination of lomefloxacin (LMFX), enrofloxacin (ENLX) and pefloxacin (PFLX). The possible CL emission mechanism was discussed by comparing the fluorescence emission with CL spectra. The CL conditions of [Ag(HIO₆)₂]⁵⁻-H₂SO₄-LMFX/ENLX/PFLX systems were investigated and optimized. Under the optimized experimental conditions, the CL intensity is proportional to the concentration of the drugs in the range 0.2994-36.80 × 10⁻⁷ g mL⁻¹ for LMFX, 4.00-30.0 × 10⁻⁷ g mL⁻¹ for ENLX and 1.54-27.64 × 10⁻⁷ g mL⁻¹ for PFLX. The limit of detection (s/n = 3) was 9.1 × 10⁻⁹ g mL⁻¹ for LMFX, 3.1 × 10⁻⁹ g mL⁻¹ for ENLX and 4.4 × 10⁻⁹ g mL⁻¹ for PFLX. The recovery of LMFX, ENLX and PELX from the spiked pharmaceutical preparations was in the range of 92.3-105% with the RSDs of 0.5-2.7%. For urine, serum and milk samples the recoveries of the three drugs were in the range of 85.1-107% for LMFX with the RSDs of 2.3-3.4%. 80.2-112% for ENLX with the RSDs of 1.4-2.8%, and 87.8-114% for PFLX with the RSDs of 1.6-2.7%. The proposed method was applied successfully to the determination of these compounds in real samples.     

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.     

Flow injection chemiluminescence determination of nitrofurazone in pharmaceutical preparations and biological fluids based on oxidation by singlet oxygen generated in N-bromosuccinimide-hydrogen peroxide reaction

A simple flow injection chemiluminescence (FI-CL) method was proposed for the determination of nitrofurazone. Strong CL signal was generated during the reaction of nitrofurazone with H₂O₂ and N-bromosuccinimide (NBS) in alkaline condition. The CL signal was proportional to the nitrofurazone concentration in the range 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ g mL⁻¹. The detection limit was 2 × 10⁻⁸ g mL⁻¹ nitrofurazone and the relative standard deviation was less than 4% (6.0 × 10⁻⁶ g mL⁻¹ nitrofurazone, n = 11). The proposed method was successfully applied to the determination of nitrofurazone in compound furacillin nasal drops, human plasma and urine samples. The CL reaction mechanism was also discussed briefly. Singlet oxygen generated in the reaction between H₂O₂ and NBS was suggested to be participated in the CL reaction.     

A reversed-phase high performance liquid chromatography coupled with resonance Rayleigh scattering detection for the determination of four tetracycline antibiotics

A new reversed-phase high performance liquid chromatography with resonance Rayleigh scattering detection (HPLC-RRS) was developed for simultaneous separation and determination of four tetracycline antibiotics (TCs). A good chromatographic separation among the compounds was achieved using a Synergi Fusion-RP column (150 mm × 4.6 mm; 4 μm) and a mobile phase consisting of methanol-acetonitrile-oxalic acid (5 mM) at the flow rate of 0.8 mL min⁻¹. Column temperature was 30 °C. The RRS signal was detected at λ_ex = λ_em = 370 nm. The recoveries of sample added standard ranged from 95.3% to 103.5%, and the relative standard deviation was below 2.79%. A detection limit of 2.12-5.12 μg mL⁻¹ was reached and a linear range was found between peak height and concentration in the range of 10.36-518.0 μg mL⁻¹ for oxytetracycline (OTC), 12.11-605.5 μg mL⁻¹ for tetracycline (TC), 11.79-589.5 μg mL⁻¹ for chlortetracycline (CTC) and 10.32-516.0 μg mL⁻¹ for doxycycline (DC). The linear regression coefficients were all above 0.999. The method has been applied successfully to the determination of OTC, TC, CTC, DC in pharmaceutical formulations and in honey. The method was simple, rapid and showed a better linear relation and high repeatability.     

Monolithic silica spin column extraction and simultaneous derivatization of amphetamines and 3,4-methylenedioxyamphetamines in human urine for gas chromatographic-mass spectrometric detection

A simple, sensitive, and specific method with gas chromatography-mass spectrometry was developed for simultaneous extraction and derivatization of amphetamines (APs) and 3,4-methylenedioxyamphetamines (MDAs) in human urine by using a monolithic silica spin column. All the procedures, such as sample loading, washing, and elution were performed by centrifugation. APs and MDAs in urine were adsorbed on the monolithic silica and derivatized with propyl chloroformate in the column. Methamphetamine-d₅ was used as an internal standard. The linear ranges were 0.01-5.0 μg mL⁻¹ for methamphetamine (MA) and 3,4-methylenedioxymethamphetamine (MDMA) and 0.02-5.0 μg mL⁻¹ for amphetamine (AP) and 3,4-methylenedioxyamphetamine (MDA) (coefficient of correlation ≧0.995). The recovery of APs and MDAs in urine was 84-94%, and the relative standard deviation of the intra- and interday reproducibility for urine samples containing 0.1, 1.0, and 4.0 μg mL⁻¹ of APs and MDAs ranged from 1.4% to 13.6%. The lowest detection limit (signal-to-noise ratio ≧ 3) in urine was 5 ng mL⁻¹ for MA and MDMA and 10 ng mL⁻¹ for AP and MDA. The proposed method can be used to perform simultaneous extraction and derivatization on spin columns that have been loaded with a small quantity of solvent by using centrifugation.     

Interdigitated array microelectrode based impedance immunosensor for detection of avian influenza virus H5N1

Continuous outbreaks of avian influenza (AI) in recent years with increasing threat to animals and human health have warranted the urgent need for rapid detection of pathogenic AI viruses. In this study, an impedance immunosensor based on an interdigitated array (IDA) microelectrode was developed as a new application for sensitive, specific and rapid detection of avian influenza virus H5N1. Polyclonal antibodies against AI virus H5N1 surface antigen HA (Hemagglutinin) were oriented on the gold microelectrode surface through protein A. Target H5N1 viruses were then captured by the immobilized antibody, resulting in a change in the impedance of the IDA microelectrode surface. Red blood cells (RBCs) were used as biolabels for further amplification of the binding reaction of the antibody-antigen (virus). The binding of target AI H5N1 onto the antibody-modified IDA microelectrode surface was further confirmed by atomic force microscopy. The impedance immunosensor could detect the target AI H5N1 virus at a titer higher than 10³ EID₅₀/ml (EID₅₀: 50% Egg Infective Dose) within 2 h. The response of the antibody-antigen (virus) interaction was shown to be virus titer-dependent, and a linear range for the titer of H5N1 virus was found between 10³ and 10⁷ EID₅₀/ml. Equivalent circuit analysis indicated that the electron transfer resistance of the redox probe [Fe(CN)₆]^3−/4− and the double layer capacitance were responsible for the impedance change due to the protein A modification, antibody immobilization, BSA (bovine serum albumin) blocking, H5N1 viruses binding and RBCs amplification. No significant interference was observed from non-target RNA viruses such as Newcastle disease virus and Infectious Bronchitis disease virus. (The H5N1 used in the study was inactivated virus.)     

Flow injection chemiluminescence determination of naproxen based on KMnO4-Na2SO3 reaction in neutral aqueous medium

A simple, rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of naproxen. It was found that strong CL signal was generated when naproxen was mixed with KMnO₄ and Na₂SO₃ in neutral aqueous medium. Under the optimum experimental conditions, the CL intensity was linearly related to the concentration of naproxen from 4.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g mL⁻¹ (r = 0.9993). The detection limit was 2 × 10⁻⁹ g mL⁻¹ naproxen, the relative standard deviation for 1.0 × 10⁻⁷ g mL⁻¹ naproxen solution was 1.5% (n = 11) and the sampling frequency was 120 h⁻¹. The method was applied to the determination of naproxen in pharmaceutical preparation with satisfactory results. The mechanism of CL reaction was discussed briefly.     

Determination of indole-3-acetic acid and indole-3-butyric acid in mung bean sprouts using high performance liquid chromatography with immobilized Ru(bpy)3-KMnO4 chemiluminescence detection

A novel method for determination of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) in an extract from mung bean sprouts using high performance liquid chromatography (HPLC) with chemiluminescence (CL) detection is described. The method is based on the CL reaction of auxin (indole-3-acetic acid and indole-3-butyric acid) with acidic potassium permanganate (KMnO₄) and tris(2,2′-bipyridyl)ruthenium(II), which was immobilized on the cationic ion-exchange resin. The chromatographic separation was performed on a Nucleosil RP-C18 column (i.d.: 250 mm × 4.6 mm, particle size: 5 μm, pore size: 100) with an isocratic mobile phase consisting of methanol-water-acetic acid (45:55:1, v/v/v). At a flow rate of 1.0 mL min⁻¹, the total run time was 20 min. Under the optimal conditions, the linear ranges were 5.0 × 10⁻⁸ to 5.0 × 10⁻⁶ g mL⁻¹ and 5.0 × 10⁻⁷ to 1.0 × 10⁻⁵ g mL⁻¹ for IAA and IBA, respectively. The detection limits were 2.0 × 10⁻⁸ g mL⁻¹ and 2.0 × 10⁻⁷ g mL⁻¹ for IAA and IBA, respectively. The relative standard deviation (RSD) of intra-day were 3.1% and 2.3% (n = 11) for 2 × 10⁻⁶ g mL⁻¹ IAA and 2 × 10⁻⁶ g mL⁻¹ IBA; The relative standard deviations of inter-day precision were 6.9% and 4.9% for 2 × 10⁻⁶ g mL⁻¹ IAA and 2 × 10⁻⁶ g mL⁻¹ IBA. The proposed method had been successfully applied to the determination of auxin in mung bean sprouts.     

Flame atomic absorption spectrometry for the determination of trace amount of rhodium after separation and preconcentration onto modified multiwalled carbon nanotubes as a new solid sorbent

The present article reports on the application of modified multiwalled carbon nanotubes (MMWCNTs) as a new, easily prepared and stable solid sorbent for the preconcentration of trace rhodium ion in aqueous solution. Rhodium ions were complexed with 1-(2-pyridylazo)-2-naphthol (PAN) in the pH range of 3.2-4.7 and then the formed Rh-PAN complex was adsorbed on the oxidized MWCNTs. The adsorbed complex was eluted from MWCNTs sorbent with 5.0 mL of N,N-dimethylformamide (DMF). The rhodium in eluted solution was determined by flame atomic absorption spectrometry (FAAS). Linear range for the determination of rhodium was maintained between 0.16 ng mL⁻¹ and 25.0 μg mL⁻¹ in initial solution. Relative standard deviation for the 10 replicated determination of 4.0 μg mL⁻¹ of rhodium was ±0.97%. Detection limit was 0.010 ng mL⁻¹ in initial solution (3S_bl, n = 10) and preconcentration factor was 120. Sensitivity for 1% absorbance of rhodium (III) was 0.112 μg mL⁻¹. The sorption capacity of oxidized MWCNTs for Rh (III) was 6.6 mg g⁻¹. The effects of the experimental parameters, including the sample pH, flow rates of sample and eluent solution, eluent type, breakthrough volume and interference ions were studied for the preconcentration of Rh³⁺. The proposed method was successfully applied to the extraction and determination of rhodium in different samples.     

Ligandless-dispersive liquid-liquid microextraction of trace amount of copper ions

In the present work, a new ligandless-dispersive liquid-liquid microextraction (LL-DLLME) method has been developed for preconcentration trace amounts of copper as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach 1,2-dicholorobenzene and ethanol were used as extraction and dispersive solvents, respectively. Some factors influencing on the extraction efficiency of copper and its subsequent determination were studied and optimized, such as the extraction and dispersive solvent type and volume, pH of sample solution, extraction time and salting out effect. Under the optimal conditions, the calibration curve was linear in the range of 1.0 ng mL⁻¹-0.6 μg mL⁻¹ of copper with R² = 0.9985. Detection limit was 0.5 ng mL⁻¹ in original solution (3S_b/m) and the relative standard deviation for seven replicate determination of 0.2 μg mL⁻¹ copper was ±1.4%. The proposed method has been applied for determination of copper in standard and water samples with satisfactory results.     

A novel application of immobilization on membranes for the separation and spectrofluorimetric quantification of amiloride and furosemide in pharmaceutical samples

A new, simple and highly sensitive method for spectrofluorimetric determination of amiloride (AMI) and furosemide (FUR) in pharmaceuticals is presented. The proposed method is based on the separation of AMI from FUR by solid-phase extraction using a nylon membrane, followed by spectrofluorimetric determination of both drugs, on the solid surface and the filtered aqueous solution, respectively. AMI shows low native fluorescence, but its separation-preconcentration by immobilization (solid-phase extraction) on nylon membrane surface provides a considerable enhancement in fluorescence intensity. The fluorescence determination is carried out at λ_ex = 237, λ_em = 415 nm for FUR; and λ_ex = 365, λ_em = 406 nm for AMI. The calibration graphs are linear in the range 3.20 × 10⁻⁴ to 0.8 μg mL⁻¹and 1.33 × 10⁻³ to 4.0 μg mL⁻¹, for AMI and FUR, respectively, with a detection limit of 9.62 × 10⁻⁵ and 4.01 × 10⁻⁴ μg mL⁻¹ (S/N = 3). The commonly found excipients in commercial pharmaceutical formulations do not interfere. The developed method is successfully applied to the determination of both drugs in pharmaceutical formulations.     

Development of enzyme-linked immunosorbent assays for the detection of deacetoxycephalosporin C and isopenicillin N synthase activity

Although there are a number of existing assays for monitoring the activity of both isopenicillin N synthase (IPNS) and deacetoxycephalosporin C synthase (DAOCS), none have demonstrated the qualities required for screening a mutant library. Hence, enzyme-linked immunosorbent assays (ELISAs) for IPNS and DAOCS were developed based on the detection of the catalytic turnover products isopenicillin N and cephalexin/phenylacetyl-7-aminodeacetoxycephalosporanic acid (G-7-ADCA), respectively. These assays are relatively fast compared to existing assays, such as the hole-plate bioassay, and are amenable with high-throughput screening. Both the IPNS and DAOCS-ELISAs were optimised for use with crude protein extracts rather than purified protein, thereby eliminating any additional time required for purification. The ELISA developed for the detection of cephalexin had an IC₅₀ value of 154 ± 9 ng mL⁻¹ and LOD of 7.2 ± 2.2 ng mL⁻¹ under conditions required for the assay. Good recoveries and correlation was observed for spiked samples when the concentration of crude protein was kept below 1 mg mL⁻¹. The DAOCS-ELISA was found to have increased sensitivity compared to the hole-plate bioassay (10.3 μg mL⁻¹). The IPNS-ELISA did not significantly increase the sensitivity (approximately 5 μg mL⁻¹) compared to that of the hole-plate bioassay (16 μg mL⁻¹) for isopenicillin N. The minimum amount of crude protein extract required for producing detectable amounts of product for both assays was below 0.5% of the maximum amount of protein that the assay could contain without any effect on the ELISA. This suggests that when screening a mutant library, mutants producing low amounts of the product could still be detected using these assays.     

Simultaneous chemiluminescence determination of promazine and fluphenazine using support vector regression

In this work, chemiluminescence (CL) behaviors of two selected phenothiazines, namely promazine and fluphenazine hydrochloride, were investigated for their simultaneous determination using oxidation of Ru(bipy)₃²⁺ by Ce⁴⁺ ions in acidic media. This method is based on the kinetic distinction of the CL reactions of fluphenazine and promazine with Ru(bipy)₃²⁺ and Ce⁴⁺ system in a sulfuric acid medium. Least square support vector regression models were constructed for relating concentrations of both compounds to their CL profiles. The parameters of the model consisting of σ² and γ were optimized using all possible combinations of σ² and γ to select the model with the minimum root mean square cross validation. Under optimized conditions, the univariate calibration curve was linear over the concentration ranges of 0.4-30.0 μg mL⁻¹ and 0.07-5.0 μg mL⁻¹ with detection limits of 0.1 μg mL⁻¹ and 0.04 μg mL⁻¹ for promazine and fluphenazine, respectively. The influence of potential interfering substances on the determination of promazine and fluphenazine were studied. The proposed method was used for simultaneous determination of both compounds in synthetic mixtures and in spiked human plasma.     

Improved porous silicon microarray based prostate specific antigen immunoassay by optimized surface density of the capture antibody

Enriching the surface density of immobilized capture antibodies enhances the detection signal of antibody sandwich microarrays. In this study, we improved the detection sensitivity of our previously developed P-Si (porous silicon) antibody microarray by optimizing concentrations of the capturing antibody. We investigated immunoassays using a P-Si microarray at three different capture antibody (PSA – prostate specific antigen) concentrations, analyzing the influence of the antibody density on the assay detection sensitivity. The LOD (limit of detection) for PSA was 2.5 ng mL⁻¹, 80 pg mL⁻¹, and 800 fg mL⁻¹ when arraying the PSA antibody, H117 at the concentration 15 μg mL⁻¹, 35 μg mL⁻¹, and 154 μg mL⁻¹, respectively. We further investigated PSA spiked into human female serum in the range of 800 fg mL⁻¹ to 500 ng mL⁻¹. The microarray showed a LOD of 800 fg mL⁻¹ and a dynamic range of 800 fg mL⁻¹ to 80 ng mL⁻¹ in serum spiked samples.     

Facile, sensitive and selective fluorescence turn-on detection of HSA/BSA in aqueous solution utilizing 2,4-dihydroxyl-3-iodo salicylaldehyde azine

A novel fluorescence turn-on detection method of human serum albumin (HSA) and bovine serum albumin (BSA) in aqueous solution is investigated using 2,4-dihydroxyl-3-iodo salicylaldehyde azine (DISA). Upon the addition of DISA to HSA/BSA solution, a fluorescence turn-on effect at 529 nm can be observed with a large stokes shift of ∼129 nm based on hydrophobic binding-mode between protein and dye. Under the optimal condition, the linear ranges of fluorescence intensity for HSA and BSA are 0.1-30 μg mL⁻¹ with the relative correlation coefficient of R² = 0.991 (n = 10) and 0.3-50 μg mL⁻¹ with R² = 0.997 (n = 10); and the detection limits for HSA and BSA based on IUPAC (C_DL = 3S_b/m) are 20 ng mL⁻¹ and 50 ng mL⁻¹, respectively.     

High extraction efficiency for polar aromatic compounds in natural water samples using multiwalled carbon nanotubes/Nafion solid-phase microextraction coating

A novel solid-phase microextraction (SPME) fiber coated with multiwalled carbon nanotubes (MWCNTs)/Nafion was developed and applied for the extraction of polar aromatic compounds (PACs) in natural water samples. The characteristics and the application of this fiber were investigated. Electron microscope photographs indicated that the MWCNTs/Nafion coating with average thickness of 12.5 μm was homogeneous and porous. The MWCNTs/Nafion coated fiber exhibited higher extraction efficiency towards polar aromatic compounds compared to an 85 μm commercial PA fiber. SPME experimental conditions, such as fiber coating, extraction time, stirring rate, desorption temperature and desorption time, were optimized in order to improve the extraction efficiency. The calibration curves were linear from 0.01 to 10 μg mL⁻¹ for five PACs studied except p-nitroaniline (from 0.005 to 10 μg mL⁻¹) and m-cresol (from 0.001 to 10 μg mL⁻¹), and detection limits were within the range of 0.03–0.57 ng mL⁻¹. Single fiber and fiber-to-fiber reproducibility were less than 7.5 (n = 7) and 10.0% (n = 5), respectively. The recovery of the PACs spiked in natural water samples at 1 μg mL⁻¹ ranged from 83.3 to 106.0%.     

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%.     

A novel microchip based on indium tin oxide coated glass for contactless conductivity detection

A microfluidic chip manufactured from glass substrate and indium tin oxide (ITO) coated glass use for contactless conductivity detection was developed. The detecting electrodes were fabricated by screen-printing and chemical etching methods using an ITO-coated glass wafer. Then, the glass substrate containing separation channels was bonded with the bare side of the processed ITO-coated glass, thus producing an electrophoresis chip integrated with contactless conductivity detector. The prepared microchip displayed considerable stability and reproducibility. Sensitive response was obtained at optimal conditions (including the gap between electrodes, excitation frequency, and excitation voltage). The feasibility of this microfluidic device was examined by detection of inorganic ions, and further demonstrated by the quantification of aminopyrine and caffeine in a compound pharmaceutical. The two ingredients can be completely separated within 1 min. The detection limits were 8 μg mL⁻¹ and 3 μg mL⁻¹, respectively; with the correlation coefficient of 0.996-0.998 in the linear range from 10 μg mL⁻¹ to 800 μg mL⁻¹. The results have showed that the present method is sensitive, reliable and fast.