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Analytica Chimica Acta (v.607, #1)

Contents (pp. v-vi).

Editorial Board (pp. co1).

Trends in speciation analysis of vanadium in environmental samples and biological fluids—A review by Zu Liang Chen; Gary Owens (pp. 1-14).

A comprehensive review is presented addressing recent trends in the speciation and determination of vanadium in environmental and biological sample matrices, including important analytical aspects such as sample clean up, pre-concentration and method development. Methodology based on both separation and spectroscopic techniques for the determination of vanadium speciation is discussed. A brief outline of analytical principles, together with an overview of the recent developments and applications of vanadium speciation determination is included. The newer methods for detecting metal ions including hyphenated spectroscopic techniques and sample preparation schemes are also discussed.

Keywords: Vanadium; Speciation; Sample pretreatment; Separation method; Spectroscopy

A review of the recent achievements in capacitively coupled contactless conductivity detection by Pavel Kubáň; Peter C. Hauser (pp. 15-29).

Capacitively coupled contactless conductivity detection (C⁴D) in the axial electrode configuration was introduced in 1998 as a quantification method for capillary electrophoresis. Its universality allows the detection of small inorganic ions as well as organic and biochemical species. Due to its robustness, minimal maintenance demands and low cost the popularity of this detector has been steadily growing. Applications have recently also been extended to other analytical methods such as ion chromatography, high-performance liquid chromatography and flow-injection analysis. C⁴D has also found use for detection on electrophoresis based lab-on-chip devices. Theoretical aspects of C⁴D in both the capillary and microchip electrophoresis format have been comprehensively investigated. Commercial devices are now available and the method can be considered a mature detection technique. In this article, the achievements in C⁴D for the time period between September 2004 and August 2007 are reviewed.

Keywords: Capillary electrophoresis; Contactless conductivity detection; Flow injection analysis; Liquid chromatography; Microchip capillary electrophoresis; Review

Direct electrochemistry of hemoglobin and myoglobin at didodecyldimethylammonium bromide-modified powder microelectrode and application for electrochemical detection of nitric oxide by Zhimou Guo; Jian Chen; Huan Liu; Chuansin Cha (pp. 30-36).

Hemoglobin (Hb) and myoglobin (Mb) were immobilized at the didodecyldimethylammonium bromide (DDAB)-modified powder microelectrode (PME) to fabricate Hb–DDAB–PME and Mb–DDAB–PME. Direct electrochemistry of Hb and Mb were achieved on the DDAB-modified PME. The formal potential was −0.224V for Hb and −0.212V for Mb (vs. SCE). The apparent surface concentration of Hb and Mb at the electrode surface was 2.83×10⁻⁸ and 9.94×10⁻⁸molcm⁻². The Hb–DDAB–PME and Mb–DDAB–PME were successfully applied for measurement of NO in vitro. The anodic current peaks for NO oxidation at +0.7V and the cathodic current peaks for NO reduction at −0.85V on the CV curves were obtained on the modified electrodes. For detection of NO at +0.7V, the sensitivity is 3.31mAμM⁻¹cm⁻² for Hb–DDAB–PME and 0.6mAμM⁻¹cm⁻² for Mb–DDAB–PME. The detection limit is 5nM for Hb–DDAB–PME and 9nM for Mb–DDAB–PME. The linear response range is 9–100 and 28–330nM for Hb- and Mb-modified PME, respectively. For the electrochemical detection of NO at −0.85V by using Hb–DDAB–PME, the detection sensitivity is 39.56μAμM⁻¹cm⁻²; the detection limit is as low as 0.2μM; and the linear response range is 1.90–28.08μM.

Keywords: Hemoglobin; Myoglobin; Direct electrochemistry; Powder microelectrode; Nitric oxide

Analysis of emerging contaminants in sewage effluent and river water: Comparison between spot and passive sampling by Zulin Zhang; Andrew Hibberd; John L. Zhou (pp. 37-44).

Passive sampling is highly complimentary to spot sampling in environmental analysis. A polar organic chemical integrative sampler (POCIS) was extensively tested to optimize its performance under both controlled and field conditions. The passive sampler was subsequently used for the sampling and analysis of estrone, 17β-estradiol, 17α-ethynylestradiol, bisphenol A, propranolol, sulfamethoxazole, meberverine, thioridazine, carbamazepine, tamoxifen, indomethacine, diclofenac and meclofenamic acid in sewage effluent and river water. Under laboratory conditions, the kinetics of compound uptake by POCIS were linear during 10-day of exposure. POCIS sampling rates of the target compounds were significantly greater by using polyethersulfone instead of polysulfone membrane, and enhanced with increasing sorbent exposure area. Together with spot water sampling, the optimized POCIS was deployed in the River Ouse, West Sussex, UK to obtain field-derived sampling rates which, for endocrine disrupting chemicals (EDCs), were significantly higher than those from laboratory experiments. Both spot and passive sampling demonstrated that most of the target chemicals were frequently detected in sewage effluent and river waters, and that the daily changes in the pollutant concentrations were greater for pharmaceuticals than for EDCs. The aqueous concentrations of all compounds were elevated at a sewage outfall, which is confirmed to be an important source of the target compounds in the river. The validated POCIS was then successfully used to estimate the concentrations of the target compounds in effluent and river water, which were in good agreement with those from spot sampling for pharmaceuticals.

Keywords: Passive sampling; Pharmaceuticals; Endocrine disrupting chemicals; Liquid chromatography–tandem mass spectrometry; Gas chromatography–mass spectrometry

A microfluidic hollow fiber membrane extractor for arsenic(V) detection by Kamilah Hylton; Somenath Mitra (pp. 45-49).

Microfluidic membrane extraction using a conventional hollow fiber membrane is presented for continuous, on-line extraction of arsenic. Previously reported micro-scale devices used flat membranes. These modules were relatively complex, difficult to seal, and high pressure drops made them prone to leaks. The present design is simpler, has higher active surface area per unit volume, and allows faster flow rates leading to enhanced mass transfer. On-line membrane extraction of As(V) via chelation through a supported liquid membrane was followed by conventional colorimetric detection with a UV–vis spectrophotometer. Enrichment factors were close to 30, and the detection limit was 27μgL⁻¹. The extraction was linear and reproducible. The relative standard deviation of six repeat extractions was less than 3%.

Keywords: Microfluidic; Membrane extraction; Arsenic

Non-invasive detection of cocaine dissolved in beverages using displaced Raman spectroscopy by C. Eliasson; N.A. Macleod; P. Matousek (pp. 50-53).

We demonstrate the potential of Raman spectroscopy to detect cocaine concealed inside transparent glass bottles containing alcoholic beverages. A clear Raman signature of cocaine with good signal-to-noise was obtained from a ∼300g solution of adulterated cocaine (purity 75%) in a 0.7L authentic brown bottle of rum with 1s acquisition time. The detection limit was estimated to be of the order of 9g of pure cocaine per 0.7L (∼0.04molesL⁻¹) with 1s acquisition time. The technique holds great promise for the fast, non-invasive, detection of concealed illicit compounds inside beverages using portable Raman instruments, thus permitting drug trafficking to be combated more effectively.

Keywords: Raman; Illicit drugs; Cocaine; Spatially Offset Raman Spectroscopy; Non-invasive

Design of molecular imprinted polymers compatible with aqueous environment by Elena V. Piletska; Antonio R. Guerreiro; Maria Romero-Guerra; Iva Chianella; Anthony P.F. Turner; Sergey A. Piletsky (pp. 54-60).

The main problem of poor water compatibility of molecularly imprinted polymers (MIPs) was addressed in examples describing design of synthetic receptors with high affinity for drugs of abuse. An extensive potentiometric titration of 10 popular functional monomers and corresponding imprinted and Blank polymers was conducted in order to evaluate the subtleties of functional groups ionisation under aqueous conditions. It was found that polymers prepared using 2-trifluoromethacrylic acid (TFMAA) in combination with toluene as porogen possess superior properties which make them suitable for effective template recognition in water. The potential impact of phase separation during polymerisation on formation of high quality imprints has been discussed. Three drugs of abuse such as cocaine, deoxyephedrine and methadone were used as template models in polymer preparation for the practical validation of obtained results. The polymer testing showed that synthesized molecularly imprinted polymers have high affinity and selectivity for corresponding templates in aqueous environment, with imprinting factors of 2.6 for cocaine and 1.4 for methadone and deoxyephedrine. Corresponding Blank polymers were unable to differentiate between analytes, suggesting that imprinting phenomenon was responsible for the recognition properties.

Keywords: Potentiometric titration; Cocaine; Deoxyephedrine; Methadone; Molecular imprinting

Potentiometric determination of the ‘formal’ hydrolysis ratio of aluminium species in aqueous solutions by Agathe C. Fournier; Kirill L. Shafran; Carole C. Perry (pp. 61-73).

The ‘formal’ hydrolysis ratio ( h= C(OH⁻)_added/ C(Al)_total) of hydrolysed aluminium-ions is an important parameter required for the exhaustive and quantitative speciation–fractionation of aluminium in aqueous solutions. This paper describes a potentiometric method for determination of the formal hydrolysis ratio based on an automated alkaline titration procedure. The method uses the point of precipitation of aluminium hydroxide as a reference ( h=3.0) in order to calculate the initial formal hydrolysis ratio of hydrolysed aluminium-ion solutions. Several solutions of pure hydrolytic species including aluminium monomers (AlCl₃), Al₁₃ polynuclear cluster ([Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺), Al₃₀ polynuclear cluster ([Al₃₀O₈(OH)₅₆(H₂O)₂₆]¹⁸⁺) and a suspension of nanoparticulate aluminium hydroxide have been used as ‘reference standards’ to validate the proposed potentiometric method. Other important variables in the potentiometric determination of the hydrolysis ratio have also been optimised including the concentration of aluminium and the type and strength of alkali (Trizma-base, NH₃, NaHCO₃, Na₂CO₃ and KOH). The results of the potentiometric analysis have been cross-verified by quantitative²⁷Al solution nuclear magnetic resonance (²⁷Al NMR) measurements. The ‘formal’ hydrolysis ratio of a commercial basic aluminium chloride has been measured as an example of a practical application of the developed technique.

Keywords: Aluminium ions; Speciation; Fractionation; Aqueous solutions; Hydrolysis ratio; Potentiometric titrations; ²⁷; Al nuclear magnetic resonance

Solid-phase microextraction (SPME) for the determination of pyrethroids in cucumber and watermelon using liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection by P. Parrilla Vázquez; Ahmed R. Mughari; M. Martínez Galera (pp. 74-82).

A sensitive and efficient solid-phase microextraction (SPME) method for the determination of seven pyrethroid insecticides including fenpropathrin, λ-cyhalothrin, deltamethrin, fenvalerate, permethrin, τ-fluvalinate and bifenthrin in cucumber and watermelon samples using high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (SPME–HPLC–PIF–FD) was developed and validated. The optimum SPME conditions were used for the extraction of samples of both matrices (extraction time 30min, stirring rate 1100rpm, extraction temperature 65°C, sample pH 3, soaking time 7min, desorption time 5min, ACN content 25%, desorption and soaking solvent was the mobile phase and in static mode). The method was validated in terms of limits of detection (LODs) and the limits of quantification (LOQs) in both IUPAC and EURACHEM criteria. LODs and LOQs were achieved in values lower than the maximum residue levels (MRLs) established in the Spanish regulations for all pesticides in this study (MRLs range between 0.01 and 0.1mgkg⁻¹ for all pyrethroid insecticides in both matrices). LOQs according to the second criterion were between 1.5 and 5μgkg⁻¹ for cucumber; and between 1.3 and 5μgkg⁻¹ for watermelon samples. Precision and recovery studies were evaluated at two concentration levels for each matrix. Good precision was obtained and relative standard deviation values were less than 10% in all cases. Recovery values were calculated at 0.05 and 0.5mgkg⁻¹ levels ( n=6) and they ranged between 93% and 108% for cucumber and between 91% and 110% for watermelon samples. Applicability of the method to pyrethroids in cucumber and watermelon of commercial samples was demonstrated.

Keywords: Solid-phase microextraction; Pyrethroids; Photochemically induced fluorescence; Liquid chromatography separation; Vegetables; Fruits

Analytical artefacts in the speciation of arsenic in clinical samples by Zdenka Šlejkovec; Ingrid Falnoga; Walter Goessler; Johannes T. van Elteren; Reingard Raml; Helena Podgornik; Peter Černelč (pp. 83-91).

Urine and blood samples of cancer patients, treated with high doses of arsenic trioxide were analysed for arsenic species using HPLC-HGAFS and, in some cases, HPLC-ICPMS. Total arsenic was determined with either flow injection-HGAFS in urine or radiochemical neutron activation analysis in blood fractions (in serum/plasma, blood cells). The total arsenic concentrations (during prolonged, daily/weekly arsenic trioxide therapy) were in the μgmL⁻¹ range for urine and in the ngg⁻¹ range for blood fractions. The main arsenic species found in urine were As(III), MA and DMA and in blood As(V), MA and DMA.With proper sample preparation and storage of urine (no preservation agents/storage in liquid nitrogen) no analytical artefacts were observed and absence of significant amounts of alleged trivalent metabolites was proven. On the contrary, in blood samples a certain amount of arsenic can get lost in the speciation procedure what was especially noticeable for the blood cells although also plasma/serum gave rise to some disappearance of arsenic. The latter losses may be attributed to precipitation of As(III)-containing proteins/peptides during the methanol/water extraction procedure whereas the former losses were due to loss of specific As(III)-complexing proteins/peptides (e.g. cysteine, metallothionein, reduced GSH, ferritin) on the column (Hamilton PRP-X100) during the separation procedure. Contemporary analytical protocols are not able to completely avoid artefacts due to losses from the sampling to the detection stage so that it is recommended to be careful with the explanation of results, particularly regarding metabolic and pharmacokinetic interpretations, and always aim to compare the sum of species with the total arsenic concentration determined independently.

Keywords: Cancer treatment; Arsenic trioxide; Analytical losses; Acute promyelocytic leukaemia (APL); Multiple myeloma (MM)

Direct hapten coated immunoassay format for the detection of atrazine and 2,4-dichlorophenoxyacetic acid herbicides by Jasdeep Kaur; Robin C. Boro; Nishima Wangoo; Kumar Rajesh Singh; C. Raman Suri (pp. 92-99).

A novel immunoassay format employing direct coating of small molecular hapten on microtiter plates is reported for the detection of atrazine and 2,4-dichlorophenoxyacetic (2,4-D). In this assay, the polystyrene surface of microtiter plates was first treated with an acid to generate –NO₂ groups on the surface. Acid treated plates were further treated with 3-aminoprpyltriethoxysilane (APTES) to functionalize the plate surface with amino groups for covalent linkage to small molecular hapten with carboxyl groups. The modified plates showed significantly high antibody binding in comparison to plates coated with hapten–carrier protein conjugates and presented excellent stability as a function of the buffer pH and reaction time. The developed assay employing direct hapten coated plates and using affinity purified atrazine and 2,4-D antibodies demonstrated very high sensitivity, IC₅₀ values for atrazine and 2,4-D equal to 0.8ngmL⁻¹ and 7ngmL⁻¹, respectively. The assay could detect atrazine and 2,4-D levels in standard water samples even at a very low concentration upto 0.02 and 0.7ngmL⁻¹ respectively in the optimum working range between 0.01 and 1000ngmL⁻¹ with good signal reproducibility ( p values: 0.091 and 0.224 for atrazine and 2,4-D, respectively). The developed immunoassay format could be used as convenient quantitative tool for the sensitive screening of pesticides in samples.

Keywords: Polystyrene surface; Silanization; Atrazine; 2,4-Dichlorophenoxyacetic acid; Immunoassay

Development of an enzyme-linked immunosorbent assay (ELISA) using highly-specific monoclonal antibodies against plumbagin by Seiichi Sakamoto; Waraporn Putalun; Ryota Tsuchihashi; Satoshi Morimoto; Junei Kinjo; Hiroyuki Tanaka (pp. 100-105).

Plumbagin (PL; 5-hydroxy-2-methyl-1,4-naphthoquinone) is a natural compound mainly isolated from Plumbago zeylanica. This plant is distributed in Southeast Asia, and well known as Ayurvedic medicine in India for its medicinal properties. PL has been shown to have various pharmacological activities. We have successfully prepared monoclonal antibodies against PL, and developed an enzyme-linked immunosorbent assay (ELISA) system for determination of PL. 3-(5-Hydroxy-2-methyl-1,4-naphthoquinone-3-yl) propanoic acid was synthesized and purified to prepare PL–bovine serum albumin conjugate (PL–BSA), which was used as an immunogen. PL–BSA conjugate was administered into BALB/c male mice for production of monoclonal antibodies against PL. The monoclonal antibody against PL which is secreted from established hybridoma cell line 3A3 (MAb 3A3) has been proven to have highly-specific to PL resulting from cross-reactivities test. The range for calibration of PL by ELISA was 0.2–25μgmL⁻¹. Based on validation analysis, this analytical method by ELISA is a precise, accurate, and sensitive method for the determination of PL in plant.

Keywords: Plumbagin; Plumbago zeylanica; Enzyme-linked immunosorbent assay; Monoclonal antibody

Development and validation of a sensitive enzyme immunoassay for surveillance of Cry1Ab toxin in bovine blood plasma of cows fed Bt-maize (MON810) by Vijay Paul; Kerstin Steinke; Heinrich H.D. Meyer (pp. 106-113).

The increasing global adoption of genetically modified (GM) plant derivatives in animal feed has provoked a strong demand for an appropriate detection method to evaluate the existence of transgenic protein in animal tissues and animal by-products derived from GM plant fed animals. A highly specific and sensitive sandwich enzyme immunoassay for the surveillance of transgenic Cry1Ab protein from Bt-maize in the blood plasma of cows fed on Bt-maize was developed and validated according to the criteria of EU-Decision 2002/657/EC. The sandwich assay is based on immuno-affinity purified polyclonal antibody raised against Cry1Ab protein in rabbits. Native and biotinylated forms of this antibody served as capture antibody and detection antibody for the ELISA, respectively. Streptavidin-horseradish peroxidase conjugate and TMB substrate provided the means for enzymatic colour development.The immunoassay allowed Cry1Ab protein determination in bovine blood plasma in an analytical range of 0.4–100ngmL⁻¹ with a decision limit (CCα) of 1.5ngmL⁻¹ and detection capability (CCβ) of 2.3ngmL⁻¹. Recoveries ranged from 89 to 106% (mean value of 98%) in spiked plasma.In total, 20 plasma samples from cows ( n=7) fed non-transgenic maize and 24 samples from cows ( n=8) fed transgenic maize (collected before and, after 1 and 2 months of feeding) were investigated for the presence of the Cry1Ab protein. There was no difference amongst both groups (all the samples were below 1.5ngmL⁻¹; CCα). No plasma sample was positive for the presence of the Cry1Ab protein at CCα and CCβ of the assay.

Keywords: Cry1Ab toxin; Enzyme immunoassay; Bovine blood plasma; Bt-maize (MON810)

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Analytica Chimica Acta (v.607, #1)