Developmental toxicity of benzotriazole in the protochordate Ciona intestinalis (Chordata, Ascidiae)

Benzotriazoles (BT) are applied as anticorrosive and de-icing agents and have been detected in a variety of aquatic ecosystems and municipal wastewater effluents. We have assessed the developmental effects of benzotriazole (CAS number 95-14-7) to the marine invertebrate Ciona intestinalis (Chordata, Ascidiae). At 15 ± 1 °C, the 24 h No-Observed Effect Concentration (NOEC) and Lowest Observed Effect Concentration (LOEC) values based on embryo morphological development were 100 and >100 mg L⁻¹, respectively (nominal concentration under static conditions). After 48 h, the NOEC and LOEC values were 10 and 32 mg L⁻¹, respectively. Light and electron microscopy studies on benzotriazole-exposed larva indicated that the primary target cells were the extra-embryonic test cells, which are known to play a significant apoptotic role during ascidian metamorphosis. The visible decline of test cells in benzotriazole-exposed larvae raises the possibility that the compound interferes with the regulation of embryo development in protochordates such as C. intestinalis. Further research is warranted to assess the potential longer term sublethal impacts of benzotriazole in aquatic organisms.     

The Fed-Batch Production of a Thermophilic 2-Deoxyribose-5-Phosphate Aldolase (DERA) in <Emphasis Type="Italic">Escherichia coli</Emphasis> by Exponential Feeding Strategy Control

2-Deoxyribose-5-phosphate aldolase (DERA) catalyzes a sequential aldol reaction useful in synthetic chemistry. In this work, the effect of a feeding strategy on the production of a thermophilic DERA was investigated in fed-batch cultures of recombinant Escherichia coli BL21 (pET303-DERA008). The predetermined specific growth rate (μ _set) was evaluated at 0.20, 0.15, and 0.10 h⁻¹, respectively. The DERA concentration and volumetric productivity were associated with μ _set. The cells synthesized the enzyme most efficiently at μ _set = 0.15 h⁻¹. The maximum enzyme concentration (5.12 g/L) and total volumetric productivity (0.256 g L⁻¹ h⁻¹) obtained were over 10 and five times higher than that from traditional batch cultures. Furthermore, the acetate concentration remained at a relatively low level, less than 0.4 g/L, under this condition which would not inhibit cell growth and target protein expression. Thus, a specific growth rate control strategy has been successfully applied to induce fed-batch cultures for the maximal production of the thermophilic 2-deoxyribose-5-phosphate aldolase.     

Determination of cyanide in blood by electrospray ionization tandem mass spectrometry after direct injection of dicyanogold

An electrospray ionization tandem mass spectrometric (ESI-MS-MS) method has been developed for the determination of cyanide (CN^–) in blood. Five microliters of blood was hemolyzed with 50 μL of water, then 5 μL of 1 M tetramethylammonium hydroxide solution was added to raise the pH of the hemolysate and to liberate CN^– from methemoglobin. CN^– was then reacted with NaAuCl₄ to produce dicyanogold, Au(CN)₂^–, that was extracted with 75 μL of methyl isobutyl ketone. Ten microliters of the extract was injected directly into an ESI-MS-MS instrument and quantification of CN^– was performed by selected reaction monitoring of the product ion CN^– at m/z 26, derived from the precursor ion Au(CN)₂^– at m/z 249. CN^– could be measured in the quantification range of 2.60 to 260 μg/L with the limit of detection at 0.56 μg/L in blood. This method was applied to the analysis of clinical samples and the concentrations of CN^– in the blood were as follows: 7.13 ± 2.41 μg/L for six healthy non-smokers, 3.08 ± 1.12 μg/L for six CO gas victims, 730 ± 867 μg for 21 house fire victims, and 3,030 ± 97 μg/L for a victim who ingested NaCN. The increase of CN^– in the blood of a victim who ingested NaN₃ was confirmed using MS-MS for the first time, and the concentrations of CN^– in the blood, gastric content and urine were 78.5 ± 5.5, 11.8 ± 0.5, and 11.4 ± 0.8 μg/L, respectively.     

On-line ionic imprinted polymer selective solid-phase extraction of nickel and lead from seawater and their determination by inductively coupled plasma-optical emission spectrometry

Nickel(II) and lead(II) ionic imprinted 8-hydroxyquinoline polymers were synthesized by a precipitation polymerization technique and were used as selective solid phase extraction supports for the determination of nickel and lead in seawater by flow injection solid phase extraction on-line inductively coupled plasma-optical emission spectrometry. An optimum loading flow rate of 2.25 mL min⁻¹ for 2 min and an elution flow rate of 2.25 mL min⁻¹ for 1 min gave an enrichment factor of 15 for nickel. However, a low dynamic capacity and/or rate for adsorption and desorption was found for lead ionic imprinted polymer and a flow rate of 3.00 mL min⁻¹ for 4-min loading and a flow rate of 2.25 mL min⁻¹ for 1-min elution gave a enrichment factor of 5. The limit of detection was 0.33 μg L⁻¹ for nickel and 1.88 μg L⁻¹ for lead, with a precision (n = 11) of 8% (2.37 μg Ni L⁻¹) for nickel and 11% (8.38 μg Pb L⁻¹) for lead. Accuracy was also assessed by analyzing SLEW-3 (estuarine water) and TM-24 (lake water) certified reference materials, and the values determined were in good agreement with the certified concentrations.     

Variable Volume Fed-Batch Fermentation for Nisin Production by <Emphasis Type="Italic">Lactococcus lactis</Emphasis> subsp<Emphasis Type="Italic">. lactis W28</Emphasis>

A feeding technology that was suitable for improving the nisin production by Lactococcus lactis subsp. lactis W28 was established. The effects of initial sucrose concentration (ISC) in the fermentation broth, feeding time, and feeding rate on the fermentation were studied. It was observed that a fed-batch culture (ISC = 10 g l⁻¹) with 100 ml sucrose solution (190 g l⁻¹) being evenly fed (9–10 ml h⁻¹) into the fermenter after 3-h fermentation gave the best performance in terms of biomass and nisin yield. Under these conditions, the total biomass and the total nisin yield were approximately 23% and 51% higher than those in batch fermentation, respectively. When the sucrose concentration was controlled at 5–10 g l⁻¹ in variable volume intermittent fed-batch fermentation (VVIF) with ISC = 10 g l⁻¹, the total biomass and the total nisin yield were 29% and 60% above those in batch fermentation, respectively. The VVIF proved to be effective to eliminate the substrate inhibition by maintaining sucrose at appropriate levels. It is also easy to be scaled up, since various parameters involved in industrial production were taken into account.     

Simultaneous determination of catechol and hydroquinone based on poly (diallyldimethylammonium chloride) functionalized graphene-modified glassy carbon electrode

Simultaneous determination of catechol (CC) and hydroquinone (HQ) were investigated by voltammetry based on glassy carbon electrode (GCE) modified by poly (diallyldimethylammonium chloride) (PDDA) functionalized graphene (PDDA-G). The modified electrode showed excellent sensitivity and selectivity properties for the two dihydroxybenzene isomers. In 0.1 mol/L phosphate buffer solution (PBS, pH 7.0), the oxidation peak potential difference between CC and HQ was 108 mV, and the peaks on the PDDA-G/GCE were three times as high as the ones on graphene-modified glass carbon electrode. Under optimized conditions, the PDDA-G/GCE showed wide linear behaviors in the range of 1 × 10⁻⁶−4 × 10⁻⁴ mol/L for CC and 1 × 10⁻⁶−5 × 10⁻⁴ mol/L for HQ, with the detection limits 2.0 × 10⁻⁷ mol/L for CC and 2.5 × 10⁻⁷ mol/L for HQ (S/N = 3) in mixture, respectively. Some kinetic parameters, such as the electron transfer number (n), charge transfer coefficient (α), and the apparent heterogeneous electron transfer rate constant (k _s), were calculated. The proposed method was applied to simultaneous determine CC and HQ in real water samples of Yellow River with satisfactory results.     

A Rapid Spectrophotometric Method to Resolve Ternary Mixtures of Propyphenazone, Caffeine, and Acetaminophen in Tablets

Summary.  A simple and rapid derivative spectrophotometric assay procedure is described for the analysis of caffeine (1), acetaminophen (2), and propyphenazone (3) in tablet formulations. The concentration range of application is 5.0–25.0 μg·cm⁻³ for 2 and 3 and 1.0–5.0 μg·cm⁻³ for 1. The method involves the extraction of the drugs from tablets with 0.1 N H₂SO₄, filtration, appropriate dilution, and measurement of the fourth derivative absorbance values at zero crossing wavelengths of 230.0, 263.2, and 256.6 nm for 1, 2, and 3. As a reference method, a reversed phase HPLC procedure was developed. Commercially available tablets were analyzed; statistical comparison of the results with those obtained from the reference method showed good agreement. The derivative spectrophotometric method has the advantage of being simple, rapid, inexpensive, and easy to perform. Received April 18, 2001. Accepted (revised) June 5, 2001     

First results on Fe solid-phase extraction from coastal seawater using anatase TiO2 nano-particles

This paper describes the application of TiO₂ nano-particles (anatase form) for the solid-phase extraction of iron from coastal seawater samples. We investigated the adsorption processes by infra-red spectroscopy. We compared in batch and on-(mini)column extraction approaches (0.1 and 0.05 g TiO₂ per sample, respectively), combined to external calibration and detection by inductively coupled plasma mass spectrometry at medium mass resolution. Globally, this titania phase was slightly more efficient with seawater than with ultra-pure water, although between pH 2 and pH 7, the Fe retention efficiency progressed more in ultra-pure water than in seawater (6.9 versus 4.8 times improvement). Different reaction schemes are proposed between Fe(III) species and the two main categories of titania sites at pH 2 (adsorption of [FeL _x ]^{(3 − x)+} via possibly the mediation of chlorides) and at pH 7 (adsorption of [Fe(OH)₂]⁺ and precipitation of [Fe(OH)₃]⁰). Under optimised conditions, the inlet system was pre-cleaned by pumping 6% HCl for ∼2 h, and the column was conditioned by aspirating ultra-pure water (1.7 g min⁻¹) and 0.05% ammonia (0.6 g min⁻¹) for 1 min. Then 3 g seawater sample was loaded at the same flow rate while being mixed on-line with 0.05% ammonia at 0.6 g min⁻¹ to adjust the pH to 7. The iron retained on the oxide powder was then eluted with 3 g 6% HCl (<0.002% residual salinity in the separated samples). The overall procedural blank was 220 ± 46 (2 s, n = 16) ng Fe kg⁻¹ (the titania was renewed in the column every 20 samples, with 2-min rinsing in between samples with 6% HCl at 1.5 g min⁻¹). The recovery estimated from the Canadian certified reference material CASS-2 was 69.5 ± 7.6% (2 s, n = 4). Typically, the relative combined uncertainty (k = 2) estimated for the measurement of ∼1 μg Fe kg⁻¹ (0.45 μm filtered and acidified to pH 1.5) of seawater was ∼12%. We applied our method to a similar sample, from the coastal region of the North Sea. The agreement well within stated uncertainties of our result with the value obtained independently by isotope dilution mass spectrometry further validated our method.     

Accurate quantification of mercapturic acids of styrene (PHEMAs) in human urine with direct sample injection using automated column-switching high-performance liquid chromatography coupled with tandem mass spectrometry

Styrene is one of the most important industrial chemicals, with an enormously high production volume worldwide. The urinary mercapturic acids of its metabolite styrene-7,8-oxide, namely N-acetyl-S-(2-hydroxy-1-phenylethyl)-l-cysteine (PHEMA 1) and N-acetyl-S-(2-hydroxy-2-phenylethyl)-l-cysteine (PHEMA 2), are specific biomarkers for the determination of individual internal exposure to this highly reactive intermediate of styrene. We have developed and validated a fast, specific and very sensitive method for the accurate determination of the sum of phenylhydroxyethyl mercapturic acids (PHEMAs) in human urine with an automated multidimensional liquid chromatography–tandem mass spectrometry method using ¹³C₆-labelled PHEMAs as internal standards. Analytes were stripped from the urinary matrix by online extraction on a restricted access material, transferred to the analytical column and subsequently determined by tandem mass spectrometry. The limit of quantification (LOQ) for the sum of PHEMAs was 0.3 μg/L urine and allowed us to quantify the background exposure of the (smoking) general population. Precision within series and between series ranged from 1.5 to 6.8% at three concentrations ranging from 3 to 30 μg/L urine; the mean accuracy was between 104 and 110%. We applied the method to spot urine samples from 40 subjects of the general population with no known occupational exposure to styrene. The median levels (range) for the sum of PHEMAs in urine of non-smokers (n = 22) were less than 0.3 μg/L (less than 0.3 to 1.1 μg/L), whereas in urine of smokers (n = 18), the median levels were 0.46 μg/L (less than 0.3 to 2.8 μg/L). Smokers showed a significantly higher excretion of the sum of PHEMAs (p = 0.02). Owing to its automation and high sensitivity, our method is well suited for application in occupational or environmental studies.     

Diamond paste-based electrodes for the determination of sildenafil citrate (Viagra)

Three types of monocrystalline diamond: natural diamond 1 μm, synthetic diamond 50 μm (synthetic-1), and synthetic diamond 1 μm (synthetic-2) were used for the design of diamond paste electrodes for the determination of sildenafil citrate (Viagra) using square wave voltammetry. The linear concentration ranges recorded for sildenafil citrate when natural diamond, synthetic-1, and synthetic-2 based electrodes were used were between 10⁻¹² and 10⁻⁸, 10⁻¹² and 10⁻⁹, and 10⁻¹¹ and 10⁻⁹ mol/L, respectively. Low detection limits which lie between 0.1 and 1 pmol/L proves the sensitivity of the electrodes. It was found that sildenafil citrate yielded a peak at about +0.175 ± 0.025 V (versus Ag/AgCl) for all the electrodes. Sildenafil citrate was determined with high reliability from its pharmaceutical formulation.     

A hydrophilic interaction ultraperformance liquid chromatography (HILIC–UPLC) method for genomic DNA methylation assessment by UV detection

A hydrophilic interaction chromatography-based method, in combination with 1.7 μm ethylene bridged hybrid particle packed column (100 mm × 2.1 mm I.D.) and ultraperformance liquid chromatography, has been developed to measure cytosine (C) and methylcytosine (mC) in order to evaluate the extent of DNA methylation. Separation of cytosine and methylcytosine was achieved with good resolution and in fairly short times (5.5 min) by using isocratic elution with a mixture of 97:3 (v/v) acetonitrile/10 mM ammonium acetate as a mobile phase. The determination coefficients of C and mC were high (R ² > 0.999) within the range tested. The %RSD for intraday and interday were respectively 2.2% and 2.5% for C and 3.5% and 3.8% for mC. The limit of detection was 0.52 μM (0.52 fmol on-column) both for C and mC while the limit of quantification was 1.72 μM (1.72 fmol on-column) both for C and mC. The smallest amount of purified DNA that yielded a measurable level of C and mC was 10 μg. On the whole, this method is simple, rapid, sensitive, and precise.     

Electrocatalytic oxidation of aspirin and acetaminophen on a cobalt hydroxide nanoparticles modified glassy carbon electrode

The electrocatalytic oxidation of aspirin and acetaminophen on nanoparticles of cobalt hydroxide electrodeposited on the surface of a glassy carbon electrode in alkaline solution was investigated. The process of oxidation and the kinetics have been investigated using cyclic voltammetry, chronoamperometry, and steady-state polarization measurements. Voltammetric studies have indicated that in the presence of drugs, the anodic peak current of low valence cobalt species increases, followed by a decrease in the corresponding cathodic current. This indicates that drugs are oxidized on the redox mediator which is immobilized on the electrode surface via an electrocatalytic mechanism. With the use of Laviron’s equation, the values of anodic and cathodic electron-transfer coefficients and charge-transfer rate constant for the immobilized redox species were determined as α _s,a = 0.72, α _s,c = 0.30, and k _s = 0.22 s⁻¹. The rate constant, the electron transfer coefficient, and the diffusion coefficient involved in the electrocatalytic oxidation of drugs were reported. It was shown that by using the modified electrode, aspirin and acetaminophen can be determined by amperometric technique with detection limits of 1.88 × 10⁻⁶ and 1.83 × 10⁻⁶ M, respectively. By analyzing the content of acetaminophen and aspirin in bulk forms using chronoamperometric and amperometric techniques, the analytical utility of the modified electrode was achieved. The method was also proven to be valid for analyzing these drugs in urine samples.     

Inhibition of Pro-inflammatory Secreted Phospholipase A2 by Extracts from <Emphasis Type="Italic">Cynara cardunculus L</Emphasis>.

The aim of the present work was to evaluate the anti-inflammatory properties of Cynara cardunculus L. (Asteraceae) during its growth using various solvents such as n-hexane, dichloromethane, acetone, and methanol for air-dried leaves and stems. The anti-inflammatory activities of crude extracts were evaluated by measuring the inhibition potency of mammalian non-pancreatic phospholipases A2 (hG-IIA). The methanol and acetone extracts of leaves harvested in February exhibit potent inhibition of hG-IIA (IC₅₀ = 50 and 70 μg/ml, respectively). However, the acetone extract of stems harvested in December inhibits the hG-IIA with a lower IC₅₀ around 130 μg/ml. Fractionation on silica gel and hydrophobic gel of the methanol extract of leaves harvested in February increases the inhibitory effect, and the IC₅₀ reached 10 μg/ml.     

Electrochemical behaviors of metol on ionic-liquid-modified carbon paste electrode and its analytical application

The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (k _s) as 4.02 × 10⁻³ s⁻¹, and the diffusion coefficient (D) as 6.35 × 10⁻⁵ cm²/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10⁻⁶ ∼ 1.0 × 10⁻³ mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10⁻⁶ mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions.     

Fluctuation in the ergosterol and deoxynivalenol content in barley and malt during malting process

This paper describes determination of the deoxynivalenol and ergosterol in samples from different varieties of barley and, consequently, malt produced from this barley. In total, 20 samples of barley and 20 samples of barley malt were analyzed. The alkaline hydrolysis with consequent extraction into hexane was applied to obtain the ergosterol from cereals. Extraction to acetonitrile/water and subsequent solid-phase extraction (SPE) were used for deoxynivalenol. The determination of the samples was performed on high-performance liquid chromatography using UV detection (ergosterol) and mass spectrometric detection (deoxynivalenol). The influence of the malting process on the production of two compounds of interest was assessed from obtained results. Ergosterol concentration ranged 0.88–15.87 mg/kg in barley and 2.63–34.96 mg/kg in malt, where its content increased to 95% compared to samples before malting. The malting process was observed as having a significant effect on ergosterol concentration (P = 0.07). The maximum concentration of deoxynivalenol was found to be 641 μg/kg in barley and 499 μg/kg in malt. Its concentration was lower than the legislative limit for unprocessed cereals (1,250 μg/kg). The statistic effect of the malting process on deoxynivalenol production was not found. Linear correlation between ergosterol and deoxynivalenol content was found to be very low (barley R = 0.02, malt R = 0.01). The results revealed that it is not possible to consider the ergosterol content as the indicator of deoxynivalenol contamination of naturally molded samples.     

Quantitative determination of Phakellistatin 13, a new cyclic heptapeptide,in rat plasma by liquid chromatography/tandem mass spectrometry: application to a pharmacokinetic study

A sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, followed by a 96-well protein precipitation, has been developed and fully validated for the determination of Phakellistatin 13 (PK13), a new cyclic heptapeptide isolated from the sponge Phakellia fusca Thiele, in rat plasma. After protein precipitation of the plasma samples (50 μL) in a 96-well plate by methanol (200 μL) containing the internal standard Pseudostellarin B (20 ng/mL), the plate was vortex mixed for 3 min. Following filtration for 5 min, the filtrate was directly injected into the LC-MS/MS system. The analytes were separated on an XB-C18 analytical column (5 μm, 50 mm × 4.6 mm i.d.) using an eluent of methanol–water (85:15, v/v) and detected by electrospray ionization mass spectrometry in the negative multiple reaction monitoring mode with a chromatographic run time of 5.0 min. The method was sensitive with a lower limit of quantification (LLOQ) of 0.1 ng/mL, with good linearity (r > 0.999) over the quantitation range of 0.1–5 ng/mL. The validation results demonstrated that this method was significantly specific, accurate, precise, and was successfully applied in measuring levels of PK13 in rat plasma following intravenous administration of 20, 50, and 100 μg/kg of peptide in rats, respectively, which was suitable for the preclinical pharmacokinetic studies on PK13.     

Development of a sequential injection–square wave voltammetry method for determination of paraquat in water samples employing the hanging mercury drop electrode

This work describes the development and optimization of a sequential injection method to automate the determination of paraquat by square-wave voltammetry employing a hanging mercury drop electrode. Automation by sequential injection enhanced the sampling throughput, improving the sensitivity and precision of the measurements as a consequence of the highly reproducible and efficient conditions of mass transport of the analyte toward the electrode surface. For instance, 212 analyses can be made per hour if the sample/standard solution is prepared off-line and the sequential injection system is used just to inject the solution towards the flow cell. In-line sample conditioning reduces the sampling frequency to 44 h⁻¹. Experiments were performed in 0.10 M NaCl, which was the carrier solution, using a frequency of 200 Hz, a pulse height of 25 mV, a potential step of 2 mV, and a flow rate of 100 μL s⁻¹. For a concentration range between 0.010 and 0.25 mg L⁻¹, the current (i _p, μA) read at the potential corresponding to the peak maximum fitted the following linear equation with the paraquat concentration (mg L⁻¹): i _p = (−20.5 ± 0.3)C _paraquat − (0.02 ± 0.03). The limits of detection and quantification were 2.0 and 7.0 μg L⁻¹, respectively. The accuracy of the method was evaluated by recovery studies using spiked water samples that were also analyzed by molecular absorption spectrophotometry after reduction of paraquat with sodium dithionite in an alkaline medium. No evidence of statistically significant differences between the two methods was observed at the 95% confidence level.     

Optimization on fabrication and performance of A-site-deficient La0.58Sr0.4Co0.2Fe0.8O3-δ cathode for SOFC

A-site-deficient perovskite cathode material La_0.58Sr_0.4Co_0.2Fe_0.8O_3 − δ (L58SCF) is coated on the yttria-stabilized zirconia electrolyte by screen-printing technique. Several key fabrication parameters including selection of additives (binder and pore former), effect of coating thickness, sintering temperature and time on the microstructure, and electrochemical performance of cathode are investigated by scanning electron microscopy and electrochemical impedance spectroscopy. We study the microstructure and the electrochemical property of the cathode with different kinds of additives. Results show that the cathode possesses fine microstructure, enough porosity, and ideal electrochemical property when polyvinyl butyral serves as both binder and pore former in the cathode. The cathode with three screen-printing coats (thickness 28 ± 7 μm, weight 6.07 ± 0.72 mg cm⁻²) sintering at 1,000 °C for 2 h shows lower polarization resistance of 0.183 Ω cm² at 800 °C. Based on the optimized parameters, the polarization resistances of the L58SCF–Ce_0.8Gd_0.2O_{1.9 – δ} composite cathode display the R _p values of 0.067 Ω cm² at 800 °C, 0.106 Ω cm² at 750 °C, 0.225 Ω cm² at 700 °C, and 0.550 Ω cm² at 650 °C.     

A green flow-based procedure for fluorimetric determination of acid-dissociable cyanide in natural waters exploiting multicommutation

A flow system designed with solenoid valves is proposed for determination of weak acid dissociable cyanide, based on the reaction with o-phthalaldehyde (OPA) and glycine yielding a highly fluorescent isoindole derivative. The proposed procedure minimizes the main drawbacks related to the reference batch procedure, based on reaction with barbituric acid and pyridine followed by spectrophotometric detection, i.e., use of toxic reagents, high reagent consumption and waste generation, low sampling rate, and poor sensitivity. Retention of the sample zone was exploited to increase the conversion rate of the analyte with minimized sample dispersion. Linear response (r = 0.999) was observed for cyanide concentrations in the range 1–200 μg L⁻¹, with a detection limit (99.7% confidence level) of 0.5 μg L⁻¹ (19 nmol L⁻¹). The sampling rate and coefficient of variation (n = 10) were estimated as 22 measurements per hour and 1.4%, respectively. The results of determination of weak acid dissociable cyanide in natural water samples were in agreement with those achieved by the batch reference procedure at the 95% confidence level. Additionally to the improvement in the analytical features in comparison with those of the flow system with continuous reagent addition (sensitivity and sampling rate 90 and 83% higher, respectively), the consumption of OPA was 230-fold lower.     

Determination of 11 priority pollutant phenols in wastewater using dispersive liquid—liquid microextraction followed by high-performance liquid chromatography—diode-array detection

Dispersive liquid—liquid microextraction coupled with high-performance liquid chromatography—diode-array detection was applied for the extraction and determination of 11 priority pollutant phenols in wastewater samples. The analytes were extracted from a 5-mL sample solution using a mixture of carbon disulfide as the extraction solvent and acetone as the dispersive solvent. After extraction, solvent exchange was carried out by evaporating the solvent and then reconstituting the residue in a mixture of methanol–water (30:70). The influences of different experimental dispersive liquid—liquid microextraction parameters such as extraction solvent type, dispersive solvent type, extraction and dispersive solvent volume, salt addition, and pH were studied. Under optimal conditions, namely pH 2, 165-μL extraction solvent volume, 2.50-mL dispersive solvent volume, and no salt addition, enrichment factors and limits of detection ranged over 30–373 and 0.01–1.3 μg/L, respectively. The relative standard deviation for spiked wastewater samples at 10 μg/L of each phenol ranged between 4.3 and 19.3% (n = 5). The relative recovery for wastewater samples at a spiked level of 10 μg/L varied from 65.5 to 108.3%.