Analytica Chimica Acta (v.450, #1-2)
Calendar of forthcoming meetings (N1-N3).
Supercritical fluid extraction with in situ chiral derivatization for the enantiospecific determination of ibuprofen in urine samples by Roberto Bauza; Angel Rı́os; Miguel Valcárcel (1-11).
In situ chiral derivatization was used to obtain diastereomeric amides of ibuprofen for their subsequent extraction with supercritical carbon dioxide. For this purpose, ibuprofen [racemic 2-(4-isobutylphenyl)propionic acids] was previously extracted on a C-18 SPE device and quantitatively transferred into the supercritical fluid extraction (SFE) vessel for derivatization and extraction with (R)-1-(naphthen-1-yl)ethylamine as chiral derivatizing base, and a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and 1-hydroxybenzotriazole as reagents, in order to obtain and extract the corresponding diastereoisomeric amides, which were subsequently determined by liquid chromatography. The influence of different extraction and derivatization variables (pressure, temperature, extraction time in the static and dynamic extraction modes, and amount of chiral base) on the extraction efficiency was studied. Spiked and native urine samples containing ibuprofen were used to demonstrate the application of this method. The absolute recovery, selectivity, precision and accuracy of the combined solid-phase extraction (SPE)/SFE approach were compared to those provided by conventional liquid–liquid extraction. The results indicated that SFE seems to be an effective choice for in situ derivatization since analysis times and solvent consumption were dramatically reduced.
Keywords: Supercritical fluid extraction; In situ derivatization; Enantiomers; Ibuprofen; Liquid chromatography;
Quantitative immunoassay for determining polyaromatic hydrocarbons in electrical insulating oils by In Soo Kim; Lawrence Ritchie; Steven Setford; Judith Taylor; Marjorie Allen; Gordon Wilson; Richard Heywood; Bruce Pahlavanpour; Selwayan Saini (13-25).
The development and application of a combined sample extraction and immunoassay protocol for the quantification of polyaromatic hydrocarbons (PAHs) in transformer oils is reported. Tests were performed on 12 different used transformer oils from three major manufacturers. The removal of matrix interferents was achieved by loading oil fractions onto silica solid phase extraction cartridges and eluting with non-polar solvent prior to evaporation and reconstitution in a more polar medium. Extracts were immunoassayed using two commercially available PAH test kits either having broad specificity towards priority PAHs or enhanced binding specificity toward more carcinogenic PAHs. The total and carcinogenic PAH test kits yielded PAH levels in the oil extracts 5.86-fold and 126-fold lower than the industry-standard IP346 method. The latter method, widely used by the industry, since it correlates with biological carcinogenicity tests, grossly over-estimates PAH levels in oils since it is a non-specific gravimetric solvent extraction approach. The assay was found to be unaffected by the extract sample matrix and was capable of determining PAHs at the nanogram per millilitre level. The assay protocol was simple, low-cost and rapid (<2 h) and equally amenable to operation at remote sites or high-throughput sample screening. The binding specificity of the total anti-PAH antibody was examined by preparing and loading an anti-PAH immunosorbent with oil, prior to solvent displacement of antibody-bound compounds and by gas chromatography (GC)–mass spectrometry (MS) analysis.
Keywords: Immunoassay; Polycyclic aromatic hydrocarbons; Electrical insulating oils;
Adhesives: a new class of polymer coatings for surface acoustic wave sensors for fast and reliable process control applications by U Stahl; M Rapp; T Wessa (27-36).
Fast and reliable on-line detection of organic vapors for control of chemical processes is a challenging application for a new type of analytical instruments: sensor systems based on an array of differently selective chemical sensors. In this work we present the use of mass-sensitive polymer coated surface acoustic wave sensors (SAWs). The sensors were initially coated with a standard set of polymers consisting of a known composition. But this first approach could not meet all requirements. Therefore, a new class of commercially available polymer coating, namely adhesives, was developed. The coating procedure was optimized and the aging process of the adhesives was carefully investigated. As a result the selectivity for ambitious separation problems arising from similar polarity of the components of typical solvent mixtures could be remarkably increased. The system was then applied in a real testing environment application at a chemical plant: the fast on-line control of a preparative reversed phase process HPLC (RP-PHPLC). Data from this industrial application are shown.
Keywords: SAW; On-line monitoring; Chemical sensors; Polymer coating; Microsensors;
Iodide-selective carbon paste electrodes based on recently synthesized Schiff base complexes of Fe(III) by Mojtaba Shamsipur; Ahmad Soleymanpour; Morteza Akhond; Hashem Sharghi; Mohammad Ali Naseri (37-44).
A new modified carbon paste electrode (CPE) based on a recently synthesized Schiff base complex of Fe(III) as a suitable carrier for I− ion is described. The electrode exhibits a super Nernstian slope of 71.0±0.3 mV per decade for I− ion over a wide concentration range from 1.0×10−6 to 5.0×10−1 M, with a low detection limit of 6.5×10−7 M. It has a relatively fast response time, a satisfactory reproducibility and relatively long life time. The proposed sensor shows a fairly good selectivity toward I− ion in comparison to other common anions. The potentiometric response is independent of the pH of the test solution in the pH range 3.5–10.0. Spectrophotometric studies confirmed the redox-type response mechanism of the electrode toward iodide ion. The proposed electrode was used as an indicator electrode in potentiometric titration of iodide ion.
Keywords: Iodide-ion selective electrode; Carbon paste; Schiff base–Fe3+ complex; Potentiometry;
Electrochemical DNA biosensor for the determination of benzo[a]pyrene–DNA adducts by Kagan Kerman; Burcu Meric; Dilsat Ozkan; Pinar Kara; Arzum Erdem; Mehmet Ozsoz (45-52).
The metabolites of the environmental pollutant, benzo[a]pyrene (BaP) are carcinogenic and mutagenic agents. Thus, the determination of additional products (adducts) of the interaction between DNA and BaP, attracts great interest in cancer research.In this study, the determination of interaction between BaP and calf thymus double-stranded DNA (dsDNA) was performed by using differential pulse voltammetry (DPV) and constant current chronopotentiometric stripping analysis (PSA) in connection with carbon paste electrode (CPE) or glassy carbon electrode (GCE). As a result of interaction of BaP with dsDNA, the signal obtained from the oxidation of guanine decreased and a new adduct signal at a more positive potential appeared. This new peak is attributed to the formation of an adduct from the interaction of guanine with BaP. The chemically prepared anti-7,8,9,10-tetrahydrobenzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE) adduct by using iodine oxidation was analyzed and the electrochemical signal of the adduct was observed. When the dsDNA modified GCE was immersed into various concentrations of BaP solution, the oxidation peak of guanine decreased and the adduct peak increased with the increasing BaP concentration. The partition coefficient was also obtained from the peak of BaP with dsDNA. The results revealed that the formation of adducts could be determined by using electrochemical DNA biosensors, which are fast, simple and cost-effective devices. Furthermore, this study promises that the analysis of other important adducts would benefit from the introduction of electrochemical methods.
Keywords: Benzo[a]pyrene; DNA biosensor; Adduct; Hybridization;
Influence of intramolecular hydrogen bond of templates on molecular recognition of molecularly imprinted polymers by Tieli Zhang; Feng Liu; Wen Chen; Jun Wang; Kean Li (53-61).
Three molecularly imprinted polymers (MIPs) were prepared corresponding to three structurally related template compounds 4-hydroxybenzoic acid (4-HBA), gentisic acid (GA) and salicylic acid (SA) that differ in intramolecular hydrogen bonding ability using acrylamide (AA) as a functional monomer. HPLC method was used to evaluate the binding performances of the MIPs to the templates and several analogues. The results showed that the difference in their molecular recognition ability was pronounced. The highest molecular recognition ability was observed for 4-HBA-imprinted polymer. It was proved that the hydrogen bond interaction between the functional monomer and the template (4-HBA) played a major role in the recognition process and Scatchard analysis showed that two classes of binding sites were formed in 4-HBA-imprinted polymer. Their dissociation constants were estimated to be 1.76×10−4 and 1.40×10−3 mol l−1, respectively. But for GA- or SA-imprinted polymer the molecular recognition ability was not improved compared to the blank polymer (BP). By comparison of the structures of the three templates, it was concluded that the molecular recognition ability will decrease when the template itself is able to form intramolecular hydrogen bond in the molecular imprinting process. This study will be helpful for us to understand the molecular recognition mechanism of MIPs and of instructive significance for the prediction of the selectivity of MIPs.
Keywords: Hydroxybenzoic acid; Molecular imprinting; Molecular recognition; Intramolecular hydrogen bond;
Membrane sampler for interference-free flow injection NO determination in biological fluids with chemiluminescence detection by Dachun Yao; Mamas I Prodromidis; Athanasios G Vlessidis; Miltiades I Karayannis; Nickolaos P Evmiridis (63-72).
The development of a chemiluminescence (CL) method based on the perm-selective properties of a Nafion–cellulose acetate (CA) composite membrane for the monitoring of nitric oxide (NO) in biological fluids is described. Horseradish peroxidase (HRP) was used as NO trapping solution, forming the stable compound HRP–NO. The HRP was denatured and the trapped NO was released and detected by using the luminol–H2O2 system. Using a mixed (size-exclusion and polar-based) transport control, the interference effects of various compounds were minimized. The method was used for NO monitoring in simulated samples, by using a blood specimen as sample matrix. The 3σ detection limit is 0.9×10−6 mol and linear semi-log calibration plot in the range 1.8×10−6 to 2.7×10−3 mol NO was constructed. The applied methodology was further used to prolong the NO lifetime in order to increase the sensitivity of its determination. This was based on the increase of the response in the presence of certain reductive species, which act as NO preservatives in biological fluid samples.
Keywords: Nitric oxide; Nafion–cellulose acetate composite membrane; Biological fluid sampling; Chemiluminescence;
Selective determination of total normal microcystin by colorimetry, LC/UV detection and/or LC/MS by Kunimitsu Kaya; Tomoharu Sano; Hiroko Inoue; Hiroo Takagi (73-80).
Microcystins, hepatotoxic cyclic heptapeptides, are produced by freshwater cyanobacteria, and are classified four groups according to the amino acid structure at unit 7. Normal microcystins contain N-methyldehydroalanine (Mdha) or dehydroalanine (Dha) at unit 7, and command the great part of all microcystins. As unusual microcystin classes, [Dhb7]microcystins, [d- and l-Ala7, or N-MeAla7]microcystins and [l-Ser7]microcystins have been found.On tumor initiation and/or promotion activities of microcystins, the tumor promotion activity of normal microcystins has been found, but cancer-related activities of microcystins belonging in the other classes have not been clear.To determine normal microcystins as hepatotoxic tumor promoters, a selective determination method was developed. Only Mdha or Dha in normal microcystins was reacted with glutathione (GSH). The GSH-normal microcystins conjugates were reacted with trinitrobenzene sulfonate (TNBS). The TNB–GSH-normal microcystin conjugate can be determined as the total normal microcystin by colorimetry. After methanolysis of the conjugate, dimethyl TNB–glutamate from the conjugate was determined by liquid chromatography/ultraviolet detection (LC/UV) and/or liquid chromatography/mass spectrometry (LC/MS). The detection limits of the total normal microcystin by colorimetry, LC/UV and/or LC/MS were 1 μg, 10 and 0.1 ng, respectively.
Keywords: Total normal microcystin; N-methyldehydroalanine; Glutathione; Trinitrobenzene sulfonate (TNBS); Colorimetry; Liquid chromatography/ultraviolet; Liquid chromatography/mass spectrometry (LC/MS);
Identification of isoflavone conjugates in red clover (Trifolium pratense) by liquid chromatography–mass spectrometry after two-dimensional solid-phase extraction by Bořivoj Klejdus; Dagmar Vitamvásová-Štěrbová; Vlastimil Kubáň (81-97).
A high-performance liquid chromatography–mass spectrometry (LC–MS) combined with a two-dimensional solid-phase extraction (2D-SPE) enabled the identification of fourteen isoflavone glycoside malonates (daidzin-6″-O-malonate, genistin-6″-O-malonate, orobol-7-O-β-d-glucoside-6″-O-malonate, 3-methylorobol-7-O-β-d-glucoside-6″-O-malonate, calycosin-7-O-β-d-glucoside-6″-O-malonate, pratensein-7-O-β-d-glucoside-6″-O-malonate, pseudobaptigenin-7-O-β-d-glucoside-6″-O-malonate, formononetin-7-O-β-d-glucoside-6″-O-malonate, irilone-4′-O-β-d-glucoside-6″-O-malonate, afrormosin-7-O-β-d-glucoside-6″-O-malonate, biochanin A-7-O-β-d-glucoside-6″-O-malonate, texasin-7-O-β-d-glucoside-6″-O-malonate, 5,7,2′-trihydroxy-6-methoxyisoflavone-7-O-β-d-glucoside-6″-O-malonate, prunetin-4′-O-β-d-glucoside-6″-O-malonate) and six acetyl glycosides (daidzin-6″-O-acetate, formononetin-7-O-β-d-glucoside-6″-O-acetate, pseudobaptigenin-7-O-β-d-glucoside-6″-O-acetate, irilone-4′-O-β-d-glucoside-6″-O-acetate, biochanin A-7-O-β-d-glucoside-6″-O-acetate and prunetin-4′-O-β-d-glucoside-6″-O-acetate) isolated from red clover (Trifolium pratense). Eight isoflavone glycoside malonates and six acetyl glycosides were firstly identified in red clover. The analyses of crude extracts with those using 2D-SPE extracts were compared. UV spectra, mass spectra of protonated molecules and their fragmentation and subsequent conversion to known flavonoid glycosides were the basis for the identification of the substances.
Keywords: High-performance liquid chromatography–mass spectrometry (LC–MS); Solid-phase extraction (SPE); Trifolium pratense; Red clover; Isoflavone glycoside 6″-O-malonates; Isoflavone glycoside 6″-O-acetates;
Evaluation of separation quality in two-dimensional hyphenated chromatography by Fan Gong; Yi-Zeng Liang; Qing-Song Xu; Foo-Tim Chau; King-Man Ng (99-114).
In this paper, a novel criterion named the overlap index (OVI) has been proposed to evaluate the separation quality in two-dimensional hyphenated chromatography. This criterion, which is obtained from the maximum value of the Gram determinant constructed by the key spectra, can reveal the degree of two-dimensional hyphenated chromatographic separation. The key spectra are selected based on the so-called D-optimal criterion. According to its geometrical sense meaning the volume spanned by the constructed vectors, OVI criterion can practically reflect the overlap degree of chromatographic peaks. The OVI criterion is further interpreted by comparing the resolution of two-dimensional data into pure chromatograms and spectra. The successful application of this OVI criterion to both of simulated two-dimensional hyphenated data and the real case in analyzing the six reference phenolic compounds from Ginkgo biloba L-leaves shows its reliability and practicality.
Keywords: Hyphenated chromatography; Separation quality; Overlap index; D-optimum;
Semi-quantitative trace analysis of nuclear fast red by surface enhanced resonance Raman scattering by I.T Shadi; B.Z Chowdhry; M.J Snowden; R Withnall (115-122).
The dye nuclear fast red has been detected and determined semi-quantitatively by means of surface enhanced resonance Raman scattering (SERRS) and surface enhanced Raman scattering (SERS), using laser exciting wavelengths of 514.5 and 632.8 nm, respectively, by employing a citrate-reduced silver colloid. A good linear correlation is observed for the dependence of the intensities of the SERRS bands at 989 cm−1 (R=0.9897) and 1278 cm−1 (R=0.9872) on dye concentration over the range 10−9 to 10−7 M, when using an exciting wavelength of 514.5 nm. At dye concentrations above 10−7 M, the concentration dependence of the SERRS signals is non-linear. This is almost certainly due to the coverage of the colloidal silver particles being in excess of a full monolayer of the dye. A linear correlation is also observed for the dependence of the intensities of the SERS bands at 989 cm−1 (R=0.9739) and 1278 cm−1 (R=0.9838) on the dye concentration over the range 10−8 to 10−6 M when using an exciting wavelength of 632.8 nm. Strong fluorescence prevented collection of resonance Raman scattering (RRS) spectra from powdered samples or aqueous solutions of the dye using an exciting wavelength of 514.5 nm, but weak bands were observed in the spectra obtained from both powdered and aqueous samples of the dye using an exciting wavelength of 632.8 nm. A study of the pH dependence of SERRS/SERS and UV–VIS absorption spectra revealed the presence of different ionisation states of the dye. The limits of detection for nuclear fast red by SERRS (514.5 nm), SERS (632.8 nm) and visible spectroscopy (535 nm) are 9, 89 and 1000 ng ml−1, respectively.
Keywords: Nuclear fast red; Silver sol; Surface enhanced resonance Raman spectroscopy (SERRS); Surface enhanced Raman spectroscopy (SERS); Resonance Raman spectroscopy (RRS); Raman spectroscopy (RS); Trace analysis;
Mutlivariate calibration with Raman data using fast principal component regression and partial least squares methods by F. Estienne; D.L. Massart (123-129).
Linear and non-linear calibration methods (principal component regression (PCR), partial least squares regression (PLS), and neural networks (NN)) were applied to a slightly non-linear Raman data set. Because of the large size of this data set, recently introduced linear calibration methods, specifically optimised for speed, were also used. These fast methods achieve speed improvement by using the Lanczos decomposition for the singular value decomposition steps of the calibration procedures, and for some of their variants, by optimising the models without cross-validation (CV). Linear methods could deal with the slight non-linearity present in the data by including extra components, therefore, performing comparably to NNs. The fast methods performed as well as their classical equivalents in terms of precision in prediction, but the results were obtained considerably faster. It, however, appeared that CV remains the most appropriate method for model complexity estimation.
Keywords: Multivariate calibration; Raman spectroscopy; Lanczos decomposition; Fast calibration methods;
Calibration of somatic cell count in milk based on near-infrared spectroscopy by V Pravdova; B Walczak; D.L Massart; S Kawano; K Toyoda; R Tsenkova (131-141).
A PLS model for prediction of somatic cell count (SCC) based on near-infrared (NIR) spectra of unhomogenized milk is presented in the study. Samples of raw milk were collected from cows in the early lactation period (from 7th to 29th day after parturition). The NIR spectra were measured in the region 400–1100 nm. As reference method a fluoro-opto-electronic method was applied. Different preprocessing methods were investigated. The robust version of PLS regression was applied to handle outliers present in the dataset and the uninformative variable elimination–partial least squares (UVE–PLS) method was used to eliminate uninformative variables. The final model is acceptable for prediction of SCC in raw milk.
Keywords: Robust PLS; UVE–PLS; Somatic cell count; NIR;
Validation of a multivariate calibration method for the determination of chlorophyll a, b and c and their corresponding pheopigments by Ludvig Moberg; Bo Karlberg (143-153).
This work concerns the validation of a previously described multivariate method for determining chlorophylls and their corresponding pheopigments. The meaning of the term validation is discussed, and the work is divided into two parts, concerning model validation and method validation. The model validation showed that 40 standards are sufficient to ensure that the Y-domain is adequately spanned, and that differentiation of the data improves the models. The wavelength range was restricted to 510–770 nm, thus, eliminating interfering signals from carotenoids that had not been included in the calibration solutions. This restriction does not affect the predictive ability towards any analytes except pheophytin a. For accurate predictions of pheophytin a the wavelength region between 350 and 415 nm was included in the model. All model evaluations were based on partial least squares regression for one y-variable (PLS1). A criterion used to quantify the performance of the model was the deviation, which is an estimate of variance calculated for predictions of samples, taking into account the model’s predictive ability, the leverage and the x-residuals. In the method validation section, predictions of samples by the proposed method are compared with results obtained using an HPLC reference method. It was found for chlorophyll a that the root mean square error of cross validation (RMSECV) calculated from the model was several times higher than the corresponding root mean square error of prediction (RMSEP) calculated from the HPLC analysis. A likely explanation for this is that the RMSECV is determined in the presence of severely interfering compounds, a desired consequence of spanning the Y-space. Samples were extracted (then measured and predicted) from algal cultures, representing six different taxonomic divisions of phytoplankton. The pigment composition of these species is known, so the analyst knows in advance which chlorophylls are present. Predictions by the models are consistent with a priori knowledge of the pigment composition. To evaluate the potential of these models to deal with data recorded by different instruments, the absorption spectra for a set of samples were registered with two instruments. The results show that there is a minor and negligible bias between the predictions obtained using these instruments, probably due to a slight shift in the wavelengths recorded by them.
Keywords: Chlorophyll a, b and c; Pheophytin a and b; Pheoporphyrin c; Multivariate calibration; Partial least squares regression;
Multivariate versus univariate calibration for nonlinear chemiluminescence data by L.A. Tortajada-Genaro; P. Campı́ns-Falcó; J. Verdú-Andrés; F. Bosch-Reig (155-173).
Multivariate calibration is tested as an alternative to model chromium(III) concentration versus chemiluminescence registers obtained from luminol-hydrogen peroxide reaction. The multivariate calibration approaches included have been: conventional linear methods (principal component regression (PCR) and partial least squares (PLS)), nonlinear methods (nonlinear variants and variants of locally weighted regression) and linear methods combined with variable selection performed in the original or in the transformed data (stepwise multiple linear regression procedure). Both the direct and inverse univariate approaches have been also tested.The use of a double logarithmic transformation previous to the linear regression has been also evaluated. A new double logarithmic transformation previous to the linear regression is proposed in order to avoid the effect of the noise in the calibration model. Pre-processing, optimization and prediction ability of the multivariate calibration models has been studied at nine different experimental conditions including batch and FIA measurements. Box-plots, PCA and cluster analysis have been employed to test the prediction ability of the different models tested. Nonlinear PCR and nonlinear PLS provide the best results. Real samples have been analyzed and compared with the reference method. The results confirm the successful use of the proposed methodology.
Keywords: Univariate and multivariate nonlinear calibration; Chemiluminescence; Chromium determination; Luminol-hydrogen peroxide reaction;
Factorial analysis of a chemiluminescence system for bromate detection in water by Joaquim C.G. Esteves da Silva; José R.M. Dias; Júlia M.C.S. Magalhães (175-184).
A chemiluminescent flow system for bromate detection, based on the reaction of bromate with sulphite in acid medium and using the steroid hydrocortisone as sensitiser, was studied. A factorial analysis strategy for the study of the effect on the system response of the experimental factors, flow rates of two pumps (Q 1 — acid sulphite plus hydrocortisone aqueous solution; Q 2 — carrier, water), sample injection volume (V L), reactor volume (V R), sulphite concentration (C S), hydrocortisone concentration (C H) and acid concentration (C A), was used. Screening analysis of the system performance was made using Plackett Burman designs. The system optimisation procedure was achieved by three levels three factors full factorial designs. V L and C H are the most significant factors — a quadratic C H term was also observed to be significant. The optimised system responded linearly (logarithm of the detector signal as function of the logarithm of the bromate concentration) in the concentration range between 3.6×10−7 and 5.0×10−4 M with a limit of detection of about 8.0×10−8 M (about 10 microg/l). An analysis of some interfering ions was made and it was suggested that bromide and chloride begin to quench chemiluminescence when they are in a 10-fold excess relatively to bromate concentration.
Keywords: Bromate ion; Chemiluminescence; Sulphite; Hydrocortisone; Factorial designs; Optimisation;
Continuous wavelet transform and its application to resolving and quantifying the overlapped voltammetric peaks by Lei Nie; Shouguo Wu; Jianwei Wang; Longzhen Zheng; Xiangqin Lin; Lei Rui (185-192).
In order to resolve and quantify the overlapped peaks of voltammetry that can be described by sech2-function, continuous wavelet transform (CWT) is employed. Through CWT by using Marr wavelet, qualitative and quantitative analysis for the mixed solution of Cd(II) and In(III) can be performed from unresolved square wave voltammogram (SWV) and relevant theoretical basis is provided. A new method to construct the baseline for quantitative determination is also proposed. The results of analysis indicate that the overlapped voltammogram can be resolved and quantified effectively, conveniently and satisfactorily via CWT.
Keywords: Resolve and quantify; Cd(II) and In(III); Continuous wavelet transform; Marr wavelet;
Ultrasensitive determination of heavy metals at the sub-picogram per gram level in ultraclean Antarctic snow samples by inductively coupled plasma sector field mass spectrometry by Frédéric A.M. Planchon; Claude F. Boutron; Carlo Barbante; Eric W. Wolff; Giulio Cozzi; Vania Gaspari; Christophe P. Ferrari; Paolo Cescon (193-205).
Assessing changes in heavy metals concentrations in Antarctic snow dated from the last century is of high interest to determine to which extent the most remote regions of our planet are contaminated for these metals, and to have a better understanding into their long-range transport from the different natural and anthropogenic source areas to the Antarctic continent. Such investigations are unfortunately very difficult because the concentrations to be measured are exceedingly low, down to the sub-picogram per gram level. They require a strict control of contamination problems from field sampling to laboratory analysis, and the use of ultrasensitive analytical techniques.We present here important advances in the analytical protocols for obtaining reliable data on the occurrence of heavy metals in Antarctic snow. Utmost precautions were taken to obtain a series of large size ultraclean snow blocks from the wall of a 8.3 m clean hand-dug pit at a remote site in Coats Land, Antarctica. These blocks were then sub-sampled inside a laminar flow clean bench in a cold room, using ultraclean protocols, to provide high-resolution heavy metal times series. V, Cr, Mn, Cu, Ag, Ba, Pb, Bi and U were then determined directly, without any pre-concentration step, by the ultrasensitive inductively coupled plasma sector field mass spectrometry (ICP-SFMS) technique in clean room conditions. Calibration of the instrument was performed using ultralow concentrations standards, and extreme precautions were taken to ensure the cleanliness of the instrument and its introduction system. The results show that it is possible to accurately measure a variety of heavy metals in Antarctic snow, down to the sub-picogram per gram level, using this approach. Examples of the data obtained for the Coats Land site are finally presented. For U, the observed concentrations range from 0.004 to 0.21 pg/g; they are the first data ever obtained for this metal for Antarctic snow and ice.
Keywords: Heavy metals; Antarctica; Snow; Inductively coupled plasma sector field mass spectrometry; Ultratrace analysis;
Determination of arsenic and antimony by microwave plasma atomic emission spectrometry coupled with hydride generation and a PTFE membrane separator by Zhenbin Gong; Wing Fat Chan; Xiaoru Wang; Frank S.-C Lee (207-214).
The performance of a microwave plasma torch (MPT) discharge atomic emission spectrometry (AES) system directly coupled with hydride generation (HG) for the determination of As and Sb has been studied. The argon MPT system can sustain a stable plasma over a wide range of carrier and support gas flow rates with optimum performance at 250 and 1450 ml min−1, respectively. The presence of trace amount of water in the MPT discharge is found to affect the detection limits and the signal to noise ratio. A PTFE membrane separator is applied for hydride introduction and water rejection. In addition, the membrane cell separator also improves the signal to noise ratio by serving as a pressure buffer to minimize noise due to pressure fluctuation. Detection limits (3σ) of 8.1 and 3.2 ng ml−1 are obtained with the analytical lines As I 228.812 nm and Sb I 259.809 nm, respectively at an MPT power of 135 W. The detection limits are improved when a concentrated sulfuric acid cell is placed after the membrane cell to further remove water. This double cell system yields detection limits of 5.3 and 2.1 ng ml−1 for As and Sb, respectively under the same operating conditions. Linear dynamic ranges of three orders of magnitude could be obtained.
Keywords: Membrane cell separator; Hydride generation; Microwave plasma torch; Atomic emission spectrometry; Arsenic; Antimony;
Determination of cadmium, copper, lead and zinc in water samples by flame atomic absorption spectrometry after cloud point extraction by Jianrong Chen; Khay Chuan Teo (215-222).
Cloud point extraction (CPE) has been used for the simultaneous pre-concentration of cadmium, copper, lead and zinc after the formation of a complex with 1-(2-thiazolylazo)-2-naphthol (TAN), and later analysis by flame atomic absorption spectrometry (FAAS) using octylphenoxypolyethoxyethanol (Triton X-114) as surfactant. The chemical variables affecting the separation phase and the viscosity affecting the detection process were optimized. At pH 8.6, pre-concentration of only 50 ml of sample in the presence of 0.05% Triton X-114 and 2×10−5 mol l−1 TAN permitted the detection of 0.099, 0.27, 1.1 and 0.095 ng ml−1 cadmium, copper, lead and zinc, respectively. The enhancement factors were 57.7, 64.3, 55.6 and 63.7 for cadmium, copper, lead and zinc, respectively. The proposed method has been applied to the determination of cadmium, copper, lead and zinc in water samples and a standard reference material (SRM).
Keywords: Cloud point extraction; Flame atomic absorption spectrometry; Surfactant-rich phase;
Application of a new resin functionalised with 6-mercaptopurine for mercury and silver determination in environmental samples by atomic absorption spectrometry by Bhim Chandra Mondal; Debasis Das; Arabinda K Das (223-230).
Polystyrene–divinylbenzene (8%) has been functionalised by coupling it through an NN group with 6-mercaptopurine. The resulting chelating resin has been characterised by using elemental analysis, thermogravimetric analysis and infrared spectra. The resin is highly selective for Hg(II) and Ag(I) and has been used for preconcentrating Hg(II) and Ag(I) prior to their determination by atomic absorption spectrometry. The maximum sorption capacity for Hg(II) and Ag(I) was found to be 1.74 and 0.52 mmol g−1, respectively, over the pH range 5.5–6.0. The calibration range for Hg(II) was linear up to 10 ng ml−1 with a 3σ detection limit of 0.02 ng ml−1; the calibration range for Ag(I) was linear up to 5 μg ml−1 with a detection limit of 29 ng ml−1. The recoveries of the metals were found to be 99.7±3.8 and 101.3±4.1% at the 95% confidence level for both Hg(II) and Ag(I). In column operation, it has been observed that Hg(II) and Ag(I) in trace quantities can be selectively separated from geological, medicinal and environmental samples.
Keywords: Solid phase extraction; Chelating resin; 6-Mercaptopurine; Mercury; Silver; Atomic absorption spectrometry; Microwave-assisted digestion; Environmental samples;
Efficiency and mechanism of new poly(acryl-phenylamidrazone phenylhydrazide) chelating fiber for adsorbing trace Ga, In, Bi, V and Ti from solution by Xijun Chang; Xiulan Yang; Xinjie Wei; Kangbing Wu (231-238).
A new po1y(acrylphenylamidrazone phenylhydrazide) chelating fiber is synthesized from polyacrylonitrile fiber and used for preconcentration and separation of trace Ga(III), In(III), Bi(III), V(V) and Ti(IV) from solution (5–50 ng ml−1 Ti(IV) or V(V) and 50–500 ng ml−1 Ga(III), In (III) or Bi(III) in 1000–100 ml of solution can be enriched quantitatively by 0.15 g of fiber at a 4 ml min−1 flow rate in the pH range 5–7 with recoveries >95%). These ions can be desorbed quantitatively with 20 ml of 4 M hydrochloric acid at 2 ml min−1 from the fiber column. When the fiber which had been treated with concentrated hydrochloric acid and washed with distilled water until neutral was reused eight times, the recoveries of the above ions by enrichment were still >95%. Two-hundred-fold to 10 000-fold excesses of Cu(II), Zn(II), Ca(II), Mn(II), Cr(III), Fe(III), Ba(II) and Al(III) caused little interference in the determination of these ions by inductively coupled plasma-atomic emission spectrometers (ICP-AES). The relative standard deviations for enrichment and determination of 50 ng ml−1 Ga, In or Bi and 10 ng ml−1 V or Ti are in the range 1.2–2.7%. The contents of these ions in real solution samples determined by this method were in agreement with the certified values of the samples with average errors <3.7%.
Keywords: Poly(acrylphenylamidrazone phenylhydrazide) chelating fiber; Gallium; Indium; Bismuth; Vanadium; Titanium; Inductively coupled plasma-atomic emission spectrometry (ICP-AES);
Selective solid phase extraction and preconcentration of iron(III) based on silica gel-chemically immobilized purpurogallin by Mohamed E Mahmoud; Mohammed S.M Al Saadi (239-246).
The immobilization of purpurogallin on the surface of amino group containing silica gel phase for the formation of a newly synthesized silica gel-bound purpurogallin (SGBP) is described. The surface modification was studied and evaluated by determination of the surface coverage value by both the elemental analysis and metal probe testing method, which was found to be 0.485 and 0.460 mmol g−1, respectively. The metal sorption properties of SGBP were examined by a series of di- and tri-valent metal ions. The metal capacity values (mmol g−1) for this series of metal ions were also determined under different buffer solutions (pH 1.0–6.0) as well as shaking times by the batch equilibrium technique. The results of this study confirmed the strong affinity and selectivity as well as the fast equilibration and interaction processes of SGBP and Fe(III) compared to the other tested metal ions. The reduction–oxidation process of iron(II)/iron(III) by SGBP was also studied and the results indicated only 2.1% reduction of iron(III) into iron(II). The selectivity incorporated into silica gel phase via the immobilization of purpurogallin was intensively studied for a several binary mixtures containing iron(III)—another interfering metal ion. The determined percentage extraction values of iron(III) from these mixtures were found to be in the range of 94–100%. The potential applications of SGBP as a selective solid extractor for iron(III) from natural tap water samples and real matrices were also studied and the results revealed good percentage extraction values of iron(III) (93.5−94.9±4.6−5.3%) of the spiked iron(III) in the acidified tap water samples as well as a high preconcentration factor of 500 was also established when SGBP was used as a selective solid phase extractor and preconcentration of iron(III) from acidified soft drink samples with percentage recovery values of (98.0−97.4±4.7−5.3%) of the spiked iron(III).
Keywords: Selective solid phase extraction; Iron(III); Silica gel-chemically immobilized purpurogallin;
Interference from arsenate when determining phosphate by the malachite green spectrophotometric method by Kathryn L Linge; Carolyn E Oldham (247-252).
The effect of arsenate on phosphate determination by the malachite green spectrophotometric method was investigated. The molar absorptivities of the molybdophosphate and malachite green–molybdoarsenate species at 625 nm and a final acidity of 0.38 M were calculated as 10.4±0.13×104 and 7.2±0.17×104 l mol−1 cm−1 respectively, indicating that arsenate could interfere in phosphate measurement. Arsenate concentrations as low as 23 μg l−1 caused increase in colour development in phosphate solutions. However, the extent of colour development for both anions depended on the final acid concentration of the solution. An acidified sodium sulphite solution (0.83 M NaSO3, 0.83 M H2SO4) quantitatively prevented arsenate colour development up to 300 μg l−1 As(V). It was also demonstrated that the method removed As(V) interferences in mixed As/P solutions and therefore can be used to treat natural water samples with elevated arsenate concentrations before phosphate measurement.
Keywords: Malachite green; Phosphate; Arsenate interference; UV-visible spectrophotometry;
Pulsed amperometric detection of furan compounds in transformer oil by Timothy Bosworth; Steven Setford; Richard Heywood; Selwayan Saini (253-261).
The failure of high voltage transformers can result in significant cost and supply implications to both power supplier and consumer alike and in extreme cases may result in explosion, serious injury or death. Transformer failure can be predicted by measuring furanics present in the oil, produced by the thermolytic breakdown of cellulosidic insulators. Failing units can have furanic levels of up to 10 μg ml−1. The use of pulsed amperometric detection (PAD) to measure furanics in transformer oils in real time is reported here. Oils were examined by pre-extraction or direct suspension in aqueous measurement solution or by solubilisation and direct PAD measurement in organic solvents. Linear relationships between PAD response and furanic concentration was found for 2-furaldehyde and furfuryl alcohol (F-OH) across the range of 0–10 μg ml−1, with PAD proving most sensitive to the latter compound. PAD was performed directly in the organic phase in t-butanol with 0.1 M tetramethyl ammonium hydroxide, with aged oils containing >2 μg ml−1 of 2-furaldehyde yielding data within close agreement (<9%) of a standard chromatographic method. The simplicity and rapidity of this method offers the power transmission industry a means of monitoring furanic levels in transformers in real time, thereby reducing the risk of uncontrolled transformer failure.
Keywords: PAD; Transformer oil; Furanics;
Amperometric detection of cytochrome c by capillary electrophoresis at a sol–gel carbon composite electrode by S.N. Tan; L. Hua (263-267).
Capillary electrophoresis (CE) was employed for the determination of cytochrome c using a wall-jet amperometric detector consisting a copper(I) oxide-modified sol–gel carbon composite electrode (CCE), which exhibits a sensitive electrocatalytic response for the oxidation of cytochrome c. The optimum conditions of separation and detection are 0.08 M NaOH for the separation solution, 12 kV for separation voltage and +0.60 V versus saturated calomel electrode (SCE) for the detection potential. Calibration was linear over the concentration range 1–600 μM with the limit of detection of 3.4 μM, based on a signal-to-noise ratio (S/N) of 3.
Keywords: Capillary electrophoresis; Cytochrome c; Wall-jet electrode; Sol–gel carbon composite electrode;
Author Index (269-271).