Evaluation of an on-line coupled continuous flow liquid membrane extraction and precolumn system as trace enrichment technique by liquid chromatographic determination of bisphenol A

An on-line coupled continuous flow liquid membrane extraction (CFLME) and C₁₈ precolumn system was developed for sample preconcentration in liquid chromatography determination. After preconcentration by CFLME, which is based on the combination of continuous flow liquid–liquid extraction and supported liquid membrane, bisphenol A (BPA) was enriched in 960 μl of 1 mol l⁻¹ NaOH used as acceptor. This acceptor was on-line neutralized and transported onto the C₁₈ precolumn where analytes were absorbed and focused. Then the focused analytes were injected onto a C₁₈ analytical column for separation and detected at 220 nm with a diode array detector. CFLME related parameters such as flow rates, pH of donor and acceptor, and enrichment time were optimized. The proposed method presents a detection limit of 0.03 μg l⁻¹ (S/N=3) when 60 ml samples was enriched with an enrichment time of 30 min. Compared with C₁₈ based column-switching procedure, this proposed procedure presents similar sample throughput and lower detection limits. The proposed method was successfully applied to determine BPA in tap water, river water, and municipal sewage effluent samples.     

Determination of phenols in water by on-line solid-phase disk extraction and liquid chromatography with electrochemical detection

Poly(styrene-divinylbenzene) (PS-DVB) membrane extraction disks were used as sorbents for the on-line solid phase extraction of 13 phenols (nitro and chlorophenols) in river and tap waters. Determination was performed by liquid chromatography with electrochemical detection (LC-ED). An acetate buffer-acetonitrile-methanol mixture as mobile phase and amperometric detection at +1100 mV were used. High water volumes, up to 250 ml, can be preconcentrated without loss of phenols (recoveries between 80% and 100%) except for the more polar ones. Moreover, detection limits between 0.01 and 0.1 μg l⁻¹ in tap water and between 0.1 and 1.0 μg⁻¹ in river water were obtained. The method has been applied to the analysis of two river water samples.     

Chromium speciation using activated alumina microcolumns and sequential injection analysis-flame atomic absorption spectrometry

A new procedure has been developed for chromium speciation in water by sequential injection analysis and flame atomic absorption spectrometry. The method involves the online retention of Cr(VI) anionic species and Cr(III) cationic species on alumina microcolumns, prepared by packing activated alumina in polytetrafluoroethylene tubes, followed by selective elution of Cr(VI) with 2 mol l⁻¹ NH₄OH and of Cr(III) with 0.2 mol l⁻¹ HNO₃. Studies were carried out on the effect of retention and elution conditions for both Cr species. The limit of detection values, established as the concentration corresponding to three times the standard deviation of blank measurements divided by the slope of the calibration line, achieved were 42 μg l⁻¹ for Cr(VI) and 81 μg l⁻¹ for Cr(III). The relative standard deviation of three independent determination of natural spiked samples were lower than 10% for concentration levels between 0.5 and 2 mg l⁻¹ of Cr. The developed procedure was applied to the analysis of two effluent sewage waters, and results obtained compared well with those obtained by a batch procedure. Recovery studies on natural spiked samples provided results between 93 and 103% for Cr(VI) and from 100 to 106% for Cr(III) for samples spiked with single species. For samples spiked with both Cr(VI) and Cr(III), the average recoveries varied from 86 to 101% for Cr(VI) and from 91 to 117% for Cr(III).     

Differential-pulse voltammetric determination of low μg l cyanide levels using EDTA, Cu(II) and a hanging mercury drop electrode

The proposed method for cyanide determination at the ultratrace level by differential pulse voltammetry is based in the sensitivity enhancement obtained when both Cu(II) and EDTA are present in the background electrolyte. Comparison of the detection limits and linear dynamic ranges using the conventional borate (pH 9.75), and the proposed borate-EDTA–Cu(II) background electrolytes was carried out. Best results have been obtained with the addition of 0.5 mmol l⁻¹ EDTA and 0.02 mmol l⁻¹ of Cu(II), which allow a detection limit of 1.7 μg l⁻¹ CN⁻ (65 nmol l⁻¹ — absolute detection limit 34 ng) with a precision better than ±2% for a 40 μg l⁻¹ level. Calibration range extended from detection limit up to 100 μg l⁻¹. Cyclic voltammetry indicates that the measured cyanide peak is obtained when the electrogenerated CuCN adsorbed onto the hanging mercury drop electrode surface, is oxidised at positive going potential scan. The method has been successfully applied to various industrial waste waters such as metal-finishing waste waters, water/sand mixtures from cleaning processes of coke production, leachates from wastes obtained from electrolytic cells of aluminium production, and liquors from gold extraction industry. Results obtained by the proposed method showed good agreement with those obtained by the standard methods (ion-selective potentiometry and the spectrophotometric pyridine method).     

Speciation of chromium in mineral waters and salinas by solid-phase extraction and graphite furnace atomic absorption spectrometry

A simple GF-AAS method for speciation analysis of chromium in mineral waters and salinas was developed. Cr(VI) species were separated from Cr(III) by solid-phase extraction with APDC (ammonium pyrrolidinedithiocarbamate). The APDC complexes were formed in the sample solution under proper conditions, adsorbed on Diaion HP-2MG resin and the resin was separated from the sample. After elution with concentrated nitric acid Cr(VI) was determined by GF-AAS. Total chromium was determined by GF-AAS directly in the sample and Cr(III) concentration was calculated as the difference between those results.

The detection limit of the method defined as 3 s of background variation was 0.03 μg l⁻¹ for Cr(VI) and 0.3 μg l⁻¹ for total chromium. RSD for Cr(VI) determination at the concentration of 0.14 μg l⁻¹ was 9%, and for total chromium at the concentration of 5.6 μg l⁻¹ was 5%. The recovery of Cr(VI) was in the range of 94–100%, dependently on type of the sample.

The investigation of recovery of the spiked Cr(VI) showed that at concentration levels near 1 μg l⁻¹ and lower recovery may be reduced significantly even by pure reagents that seem to be free from any reductants.     

Determination of bisphenol A (BPA) in the presence of phenol by first-derivative fluorescence following micro liquid-liquid extraction (MLLE)

Bisphenol A (BPA) in the presence of phenol is determined using a method based on first-derivative spectrofluorimetry. The proposed method involves a micro liquid–liquid extraction of sodium chloride saturated water samples with diethyl ether followed by direct fluorimetric analysis of extracts. The excitation spectra of both compounds in diethyl ether are recorded between 200 and 290 nm, with the emission wavelength at 306 nm. The first-derivative spectra were calculated, measuring the analytical signal for BPA at 239 nm. The concentration range over which the method was applied was 0.5–10.0 μg·l⁻¹ of BPA with relative standard deviations of 2.9% for a concentration of 4.0 μg·l⁻¹ of BPA. The detection limit was 0.07 μg·l⁻¹. The proposed method was applied satisfactorily to the determination of BPA in synthetic mixtures and water samples from different sources previously spiked with different amounts of these chemicals. Recovery values ranging from 93% to 112% were obtained for water samples.     

Determination of chlorite in drinking water by on-line coupling of capillary isotachophoresis and capillary zone electrophoresis

An isotachophoresis (ITP)–capillary zone electrophoresis (CZE) combination was used for the determination of chlorite in drinking waters. No sample preparation is needed and no interfering by other anions in tap water was observed. The reached limits of detection with conductivity detector were 0.012–0.017 mg l⁻¹. By four-fold sample loading with a 30 μl valve, 0.005 mg l⁻¹ of chlorite was determined with R.S.D.=3.3%. The concentrations of 0.05 and 0.20 mg l⁻¹ were measured with R.S.D. of 2.2 and 2.7%, respectively. The recoveries of chlorite from drinking water were 96–106% in the range of 0.02–0.20 mg l⁻¹. The R.S.D. values of migration times (inter-day) were up to 1.3%. The time for analysis is about 15 min.     

Determination of chemical warfare agents and related compounds in environmental samples by solid-phase microextraction with gas chromatography

Solid phase microextraction (SPME) is an increasingly common method of sample isolation and enhancement. SPME is a convenient and simple sample preparation technique for chromatographic analysis and a useful alternative to liquid-liquid extraction and solid phase extraction. SPME is speed and simply method, which has been widely used in environmental analysis because it is a rather safe method when dealing with highly toxic chemicals. A combination of SPME and gas chromatography (GC) permits both the qualitative and quantitative analysis of toxic industrial compounds, pesticides and chemical warfare agents (CWAs), including their degradation products, in air, water and soil samples. This work presents a combination of SPME and GC methods with various types of detectors in the analysis of CWAs and their degradation products in air, water, soil and other matrices. The combination of SPME and GC methods allows for low detection limits depending on the analyte, matrix and detection system. Commercially available fibers have been mainly used to extract CWAs in headspace analysis. However, attempts have been made to introduce new fiber coatings that are characterized by higher selectivities towards different analytes of interest. Environmental decomposition of CWAs leads to the formation of more hydrophilic products. These compounds may be isolated from samples using SPME and analyzed using GC however, they must often be derivatized first to produce good chromatography. In these cases, one must ensure that the SPME method also meets the same needs. Otherwise, it is helpful to use derivatization methods. SPME may also be used with fieldportable mass spectrometry (MS) and GC-MS instruments for chemical defense applications, including field sampling and analysis. SPME fibers can be taken into contaminated areas to directly sample air, headspaces above solutions, soils and water.     

Simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional ion-selective electrodes in series

An on-line automated system for the simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional calcium-selective and fluoride-selective membrane electrodes as sensors in series is described. Samples (30 μl) are injected into a TISAB II (pH=5.50) carrier solution as an ionic strength adjustment buffer. The sample-buffer zone formed is first channeled to a fluoride-selective membrane electrode and then via the calcium-selective membrane electrode to the reference electrodes. The system is suitable for the simultaneous on-site monitoring of calcium (linear range 10⁻⁵–10⁻² mol l⁻¹ detection limit 1.94×10⁻⁶ mol l⁻¹ recovery 99.22%, RSD<0.5%) and fluoride (linear range 10⁻⁵–10⁻² mol l⁻¹ detection limit 4.83×10⁻⁶ mol l⁻¹ recovery 98.63%, RSD=0.3%) at a sampling rate of 60 samples h⁻¹.     

Optimisation of solid-phase microextraction of volatiles

The results of a systematic study on the precision and repeatability of measurements of the headspace solid phase micro-extraction (SPME) with open-cap vials in combination with capillary gas chromatography in comparison with septum-sealed vials are reported. Benzene, toluene, ethylbenzene, and xylene isomers (BTEX) were used as the target analytes in the investigation of spiked water samples at concentration levels of 42.5 μg l⁻¹. The dependence of a sample volume versus peak area showed maximum SPME recovery. The influence of sample volume on the precision and the time of taking the sample on the losses of volatile analytes was examined.     

β-Cyclodextrin epichlorohydrin copolymer as a solid-phase extraction adsorbent for aromatic compounds in water samples

A novel solid-phase extraction (SPE) procedure for trace aromatic compounds in water samples has been developed using 12 aromatic compounds as model compounds and GC-MS and UV spectrophotometry for detection. The method is based on the fact that β-cyclodextrin (β-CD) epichlorohydrin (ECH) copolymer (β-CDEP) can extract non-ionized aromatic compounds quantitatively from aqueous samples. The polymer used is a colorless, transparent and insoluble solid with a maximum capacity of 0.82 μmol aromatic compounds per gram. It was synthesized by co-polymerization of β-CD and ECH and characterized by FT-IR and UV. β-CDEP does not contain double bonds, and therefore it does not have appreciable absorbance in the UV region. The optimum pH range for the extraction of aromatic compounds is 2.5-5.0. The method has high extraction efficiency with the recoveries between 90 and 101% for aromatic compounds at 0.02-1.67 ppm levels, and the analytes can be easily eluted by methanol washing after preconcentration.     

Voltammetric determination of phytochelatins using copper solid amalgam electrode

Voltammetric determination of synthetically prepared phytochelatins (γ-Glu-Cys)₂Gly (PC₂) and (γ-Glu-Cys)₃Gly (PC₃) has been studied using new type of copper solid amalgam electrode. The determination, based on the formation of cuprous complexes in buffer pH 8.1, is suitable for concentrations of PC in the range 10–100 nmol l⁻¹. Reproducibility, employing electrochemical cleaning of the electrode surface, was statistically evaluated. The achieved limit of detection (2.1–2.6×10⁻⁹ mol l⁻¹ for DCV measurement) together with the robust character of the electrode offer its use for detection of PCs in separated extracts of real samples.     

Determination of physiological noble metals in human urine using liquid-liquid extraction and Zeeman electrothermal atomic absorption spectrometry

An extremely sensitive, reliable and simple procedure is described for the determination of physiological palladium, platinum and gold in human urine. The urine samples were adjusted to pH 4 (Pd, Au) or pH 5 (Pt), followed by conversion of the analytes to their pyrrolidinedithiocarbamate complexes. These complexes were separated from the matrix by liquid-liquid extraction into 4-methyl-2-pentanone resulting in a 25-fold enrichment. Determination was by electrothermal atomic absorption spectrometry (ET-AAS) using longitudinal inverse alternating current Zeeman-effect background correction. The limits of detection calculated from three standard deviations of the blank values were 20 ng l⁻¹ for Pd and Au and 70 ng l⁻¹ Pt. Within-day precision (n = 10, 5 μg l⁻¹) ranged 5.2%–7.7%. The procedure is successfully applied to determine urinary palladium, platinum and gold in nine unexposed persons. Palladium levels in urine ranged < 20–80 ng l⁻¹ (arithmetical MEAN=38.7 ng l⁻¹), while gold levels ranged < 20–130 ng l⁻¹ (36.0 ng l⁻¹). Physiological platinum levels in urine were all < 70 ng l⁻¹. The accuracy of the procedure was checked by analyzing a series of urine samples by a second independent method (magnetic sector field inductively-coupled plasma-mass spectrometry) in combination with UV photolysis.     

Coupling of flow injection wetting-film extraction without segmentation and phase separation to flame atomic absorption spectrometry for the determination of trace copper in water samples

A flow injection wetting-film extraction system without segmentor and phase separator has been coupled to flame atomic absorption spectrometry for the determination of trace copper. Isobutyl methyl ketone (MIBK) was selected as coating solvent and 8-hydroxyquinoline (oxine) as the chelating reagent. By switching of a 8-channel valve and alternative initiation of two peristaltic pumps, MIBK, sample solution containing copper chelate of oxine, and air-segment sandwiched eluting solution (1.0 mol l⁻¹ nitric acid) were sequentially aspirated into an extraction coil made of PTFE tubing of 360 cm length and 0.5 mm i.d. The formation of organic film in the wall of the extraction coil, extraction of the copper chelate into the organic film and back-extraction of the analyte into the eluting solution occurred consecutively when these zones aspirated into the extraction coil were propelled down the extraction coil by a carrier solution at a flow rate of 2 ml min⁻¹. After leaving the extraction coil, the concentrated zone was transported to the nebulizer at its free uptake rate for atomization. Under the optimized conditions, an enrichment factor of 43 and a detection limit of 0.2 μg l⁻¹ copper were achieved at a sample throughput rate of 30 h⁻¹. Eleven determinations of a standard copper solution of 60 μg l⁻¹ gave a relative standard deviation of 1.5%. Foreign ions possibly present in tap water and natural water did not interfere with the copper determination. The developed method has been successfully used to the determination of copper content of tap water and river water.     

Determination of iron(II) and total iron in environmental water samples by flow injection analysis with column preconcentration of chelating resin functionalized with N-hydroxyethylethylenediamine ligands and chemiluminescence detection

A flow injection analysis (FIA) technique for the determination of Fe(II) and total-Fe in environmental water samples has been developed with a high sensitivity. The resin used for preconcentration of iron was the macroporous resin, Amberlite XAD-4 functionalized by N-hydroxyethylethylenediamine (HEED) groups. The technique employed was FIA by combination of on-line chelate resin preconcentration and chemiluminescence detection (CL), using brilliant sulfoflavine and hydrogen peroxide reagent solutions. The interference by coexisting Fe(III) could be eliminated by addition of 1×10⁻⁶ mol of deferrioxamine B solution. The detection limits of Fe(II) and total-Fe were 0.80 and 0.36 nmol l⁻¹ for 5.6-ml seawater samples with a concentration of 2 nmol l⁻¹. The relative standard deviations for both samples were less than ±4%. A typical analysis for Fe(II) can be performed in 7.5 min. The technique was ascertained by comparing the analytical value of total-Fe with the certified value of Fe in the reference standard seawater CASS-3.     

Flow injection determination of nitrite by fluorescence quenching

A simple, sensitive and selective fluorimetric method for the determination of nitrite ion in waters using a merging zones flow injection system is described. The fluorimetric determination is based on the measurement of the quenching effect produced by nitrite on proflavine (3,6-diaminoacridine) fluorescence (λ_ex/λ_em=290/519 nm).

The optimum experimental conditions were investigated by merging 0.5 ml of the sample and 0.5 ml of a solution of 5 mg l⁻¹ of proflavine (in 0.1 M HCl) in a flow injection system, on-line connected to a flow-cell placed in the conventional sample compartment of a spectrofluorimeter. The selected carrier solution and final flow rate were 0.1 M HCl and 0.5 ml min⁻¹, respectively. A reaction coil of 2 ml was used. As a result of the simplicity of this system, a sample throughput of about 50 samples h⁻¹ can be achieved with the proposed methodology.

The detection limit was 1.1 ng ml⁻¹ (3σ criterion) of nitrite. The repeatability for five sample injections containing 100 ng ml⁻¹ of nitrite was ±0.3% and the observed linear range extended up to 400 ng ml⁻¹. Also, the effect of interferences from various metals and anions commonly present in waters was also studied.

The method was successfully applied to the determination of low levels of nitrite in different water samples (river, fountain, tap and commercial drinking waters).     

Spectrophotometric determination of total phenolics by solvent extraction and sorbent extraction optosensing using flow injection methodology

Flow injection analysis (FIA) procedures for the Spectrophotometric determination of phenol involving in-line concentration by solvent and sorbent extraction have been developed. The imine product formed in the reaction between phenol and 4-aminoantipyrine (4-AAP) is either extracted into chloroform (solvent extraction) or is temporarily retained on C₁₈-modified silica material contained in a microcolumn (sorbent extraction). In the latter case two variants of detection have been used namely the Spectrophotometric measurement of the methanolic eluent containing the concentrated dye and at-column optosensing of the retained reaction product followed by methanol elution to maintain reversibility of the process. In the solvent extraction procedure a 10-fold increase of sensitivity compared to the common FIA method without extraction is achieved but no corresponding improvement in detectability is observed. Under optimized conditions the detection limit amounts to 8 μg l⁻¹. Using sorbent extraction methodology, high concentration factors can be obtained when large sample volumes are used. The only limitation in getting correspondingly lower detection limits are an increasingly high and variable blank value with sampling volume. The detection limits obtained for measurement of the absorbance in the eluent and on-column optosensing are 11 μg l⁻¹ and 0.4 μg l⁻¹, respectively. A study of the extractability of various phenol derivates using both solvent and sorbent extraction revealed lower relative response rates compared to the FIA method without extraction. Phenolics that possess an additional acidic group are present in ionized form at the high pH of the assay and are not extractable at all.     

Biosorption of heavy metals on Aspergillus fumigatus immobilized Diaion HP-2MG resin for their atomic absorption spectrometric determinations

A solid phase extraction procedure based on biosorption of copper(II), lead(II), zinc(II), iron(III), nickel(II) and cobalt(II) ions on Aspergillus fumigatus immobilized Diaion HP-2MG has been investigated. The analytical conditions including amounts of A. fumigatus, eluent type, flow rates of sample and eluent solutions were examined. Good recoveries were obtained to the spiked natural waters. The influences of the concomitant ions on the retentions of the analytes were also examined. The detection limits (3sigma, N = 11) were 0.30 μg l⁻¹ for copper, 0.32 μg l⁻¹ for iron, 0.41 μg l⁻¹ for zinc, 0.52 μg l⁻¹ for lead, 0.59 μg l⁻¹ for nickel and 0.72 μg l⁻¹ for cobalt. The relative standard deviations of the procedure were below 7%. The validation of the presented procedure is performed by the analysis of three standard reference materials (NRCC-SLRS 4 Riverine Water, SRM 1515 Apple leaves and GBW 07605 Tea). The procedure was successfully applied for the determination of analyte ions in natural waters microwave digested samples including street dust, tomato paste, black tea, etc.     

Use of poly(ester-sulfonic acid) film-coated electrodes as amperometric detectors in flow injection analysis

Within the past several years significant advances have been made towards the development and incorporation of chemically modified electrodes as selective detectors for high performance liquid chromatography and flow injection analysis. In many cases the chemically modified electrode systems closely approach the “ideal” detector specifications of chemical and mechanical stability along with a significant linear response region. This paper will discuss the characterization and incorporation of ionomeric poly(ester-sulfonic acid) coated electrodes as nonaqueous electrochemical detectors. The orientation of the electrodes in the detector system as well as the increased sensitivity levels to 10⁻¹⁰ g ml⁻¹ for cationic species and 10⁻⁹ g ml⁻¹ for neutral species will be presented. Also the applicability of the ionomer coated electrodes as nonelectrolyte detectors achieved a reproducible response with detection limits to 10⁻⁶ g ml⁻¹. Overall this system performed as well as, or better than, more specialized and expensive thin layer electrochemical detectors.     

A multisyringe flow injection method for the automated determination of sulfide in waters using a miniaturised optical fiber spectrophotometer

In this paper, a fully software-controlled multisyringe flow injection (MSFIA) spectrophotometric system is proposed for the determination of sulfide in environmental and waste waters. The implementation of ancillary solenoid valves into the flow network allows a multitude of injection modalities to be explored, the selected modality being directly dependent on the aim of the assays. The multicommuted sandwich-type approach is introduced in this work as an efficient means to warrant high sensitivity for the particular assay with excellent repeatabilities and a considerable reagent saving. Moreover, a high injection frequency may be easily attained by carrying out a multiple injection modality during a single forward displacement of the piston driver bar. The interfacing of the robust and versatile multisyringe piston pump with an optical fiber plug-in spectrophotometer furnished with a light emitting diode enables the miniaturization of the flow analyzer, which is thus readily adaptable to in-situ and real-time monitoring schemes. The flow method is based on the coupling Fischer’s reaction of sulfide with N,N-dimethyl-p-phenylenediamine in the presence of Fe(III) as oxidizing reagent in a 0.7 M HCl medium. Careful selection of the physical and chemical variables enabled coefficients of variations better than 1.5% (n = 10) at the 1 mg l⁻¹ level for both injection modalities. Dynamic working ranges of 0.2–2.0 and 0.5–5 mg l⁻¹ sulfide for sandwich and multiple injection techniques, and detection limits of 0.09 and 0.15 mg l⁻¹, respectively, were obtained. Furthermore, the sandwich modality featured an average slope of 0.43 ± 0.02 l mg⁻¹ calculated from 10 day-to-day calibration plots. This result reveals better sensitivity than other flowing stream methods described in the literature. The multiple injection technique allowed an improvement of the injection throughput up to 80 h⁻¹, although a decrease of sensitivity was concomitantly observed (average slope of 0.17 ± 0.01 l mg⁻¹).

The multisyringe flow method was successfully applied to the determination of sulfide in different spiked water matrices (namely, mineral, tap, freshwater, seawater and wastewater) with recoveries ranging from 96 to 104%. Good agreement was also found in water samples between the MSFIA results and those of the batch APHA-standard method.