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Analytica Chimica Acta (v.654, #2)

Editorial Board (pp. i).

Glyphosate and glufosinate detection at electrogenerated NiAl-LDH thin films by Aicha Khenifi; Zoubir Derriche; Claude Forano; Vanessa Prevot; Christine Mousty; Erika Scavetta; Barbara Ballarin; Lorella Guadagnini; Domenica Tonelli (pp. 97-102).

An amperometric sensor based on Ni1−_xAl_x(OH)₂NO3_x· nH₂O layered double hydroxide (LDH) has been developed for the electrochemical analysis in one step of two herbicides: glyphosate ( N-(phosphonomethyl)glycine, Glyp) and glufosinate ((DL-homoalanine-4-yl)-methylphosphinic acid, Gluf). NiAl-LDH was prepared by coprecipitation or by electrodeposition at the Pt electrode surface. Inorganic films were fully characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Adsorption isotherms of Glyp onto this inorganic lamellar material have been established. Electrocatalytic oxidation of Glyp and Gluf is possible at the Ni³⁺ centres of the structure. The electrochemical responses of the NiAl-LDH modified electrode were obtained by cyclic voltammetry and chronoamperometry at 0.49V/SCE as a function of herbicide concentration in 0.1M NaOH solution. The electrocatalytic response showed a linear dependence on the Glyp concentration ranging between 0.01 and 0.9mM with a detection limit of 1μM and sensitivity 287mA/Mcm². The sensitivity found for Gluf was lower (178mA/Mcm²).

Keywords: Glyphosate; Glufosinate; Sensor; Layered double hydroxides; Amperometry; Adsorption

Surface modification of polyacrylonitrile fiber for immobilization of antibodies and detection of analyte by Swati Jain; Sruti Chattopadhyay; Richa Jackeray; Harpal Singh (pp. 103-110).

Pendent nitrile groups of multifilamentous polyacrylonitrile (PAN) fibers were reduced to amino groups using lithium aluminum hydride for different time of reduction and amine content was estimated by performing acid–base titrations. Attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC) were used for the characterization of the generated amino groups and thermal properties of the reduced fibers, respectively. The surface morphology of the fibers after reduction and immobilization was characterized using Scanning Electron Microscope (SEM). The newly formed amino groups of the fibers were activated by using glutaraldehyde for the covalent linking of Goat anti-Rabbit IgG-HRP (GAR-HRP) antibody enzyme conjugate. Modified PAN fibers were evaluated as a matrix for sandwich ELISA by using Goat anti-Rabbit antibody (GAR-IgG), Rabbit anti-Goat (RAG-IgG) as analyte and enzyme conjugate GAR-HRP. The fibers reduced for 24h were able to detect the analyte RAG-IgG at a concentration as low as 3.75ngmL⁻¹ with 12% skimmed milk as blocking reagent for the optimized concentration of primary antibody GAR-IgG 3μgmL⁻¹ and peroxidase conjugate GAR-HRP dilution of 8000 fold. The sensitivity, specificity and reproducibility of the developed immunoassay was further established with antibodies present in human blood using Rabbit anti-Human (RAH-IgG) antibody and the corresponding HRP enzyme conjugate. As low as 0.1μL of human blood was sufficient to perform the assay with the modified fibers.

Keywords: Abbreviations; PAN; Polyacrylonitrile; IgG/Ab; Antibody; Ag; AntigenPolyacrylonitrile fiber; Nitrile reduction; Antibody immobilization; Sandwich Enzyme Linked Immuno-Sorbent Assay; Rabbit anti-Human antibody

Benzimidazole carbamate residues in milk: Detection by Surface Plasmon Resonance-biosensor, using a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method for extraction by Jemma Keegan; Michelle Whelan; Martin Danaher; Steven Crooks; Regina Sayers; Aniello Anastasio; Christopher Elliott; David Brandon; Ambrose Furey; Richard O’Kennedy (pp. 111-119).

A surface plasmon resonance (SPR) biosensor screening assay was developed and validated to detect 11 benzimidazole carbamate (BZT) veterinary drug residues in milk. The polyclonal antibody used was raised in sheep against a methyl 5(6)-[(carboxypentyl)-thio]-2-benzimidazole carbamate protein conjugate. A sample preparation procedure was developed using a modified QuEChERS method. BZT residues were extracted from milk using liquid extraction/partition with a dispersive solid phase extraction clean-up step. The assay was validated in accordance with the performance criteria described in 2002/657/EC. The limit of detection of the assay was calculated from the analysis of 20 known negative milk samples to be 2.7μgkg⁻¹. The detection capability (CCβ) of the assay was determined to be 5μgkg⁻¹ for 11 benzimidazole residues and the mean recovery of analytes was in the range 81–116%. A comparison was made between the SPR-biosensor and UPLC–MS/MS analyses of milk samples ( n=26) taken from cows treated different benzimidazole products, demonstrating the SPR-biosensor assay to be fit for purpose.

Keywords: SPR-biosensors; Benzimidazole carbamates; Bovine milk; QuEChERS

Single crystal WO₃ nanoflakes as quartz crystal microbalance sensing layer for ultrafast detection of trace sarin simulant by Yingqiang Zhao; Junhui He; Mingqing Yang; Shi Gao; Guomin Zuo; Chunxiao Yan; Zhenxing Cheng (pp. 120-126).

Tungsten oxide (WO₃) nanoflakes were synthesized, and characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Thermogravimetry and X-ray photoelectron spectroscopy demonstrate the existence of strongly bound surface water molecules on the surface of tungsten oxide nanoflakes. WO₃ nanoflake functionalized quartz crystal microbalance sensors were fabricated, and firstly used for detection of trace sarin simulant, dimethyl methylphosphonate (DMMP). The sensors have better reproducibility and stability as well as much shorter response (30s) and recovery time (73s) than those functionalized by conventional hydrogen-bond acidic branched copolymers. The strongly bound surface water molecules on the surface of WO₃ nanoflakes are believed to play a key role in achieving such excellent DMMP sensing characteristics.

Keywords: Nanoflake; Tungsten oxide; Quartz crystal microbalance; Gas sensor; Dimethyl methylphosphonate

A multidimensional high performance liquid chromatography method coupled with amperometric detection using a boron-doped diamond electrode for the simultaneous determination of sulfamethoxazole and trimethoprim in bovine milk by Leonardo S. Andrade; Marcela C. de Moraes; Romeu C. Rocha-Filho; Orlando Fatibello-Filho; Quezia B. Cass (pp. 127-132).

The development and validation of a multidimensional HPLC method using an on-line clean-up column coupled with amperometric detection employing a boron-doped diamond (BDD) electrode for the simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) in bovine milk are presented. Aliquots of pre-prepared skim-milk samples were directly injected into a RAM octyl-BSA column in order to remove proteins that otherwise would interfere with milk analysis. After exclusion of the milk proteins, SMX and TMP were transferred to the analytical column (an octyl column) and the separation of the compounds from one another and from other endogenous milk components was achieved. SMX and TMP were detected amperometrically at 1.25V vs. Ag/AgCl (3.0molL⁻¹ KCl). Results with good linearity in the concentration ranges 50–800 and 25–400μgL⁻¹ for SMX and TMP, respectively, were obtained and no fouling of the BDD electrode was observed within the experimental period of several hours. The intra- and inter-assay coefficients of variation were less than 10% for both drugs and the obtained LOD values for SMX and TMP were 25.0 and 15.0μgL⁻¹, respectively.

Keywords: Multidimensional HPLC; Restricted-access media (RAM); Bovine milk; Sulfonamides determination; Electrochemical detection; Boron-doped diamond electrode

On-line monitoring of nine haloacetic acid species at the μgL⁻¹ level using post-column reaction-ion chromatography with nicotinamide fluorescence by Paul S. Simone Jr.; Patricia L. Ranaivo; Gija Geme; Michael A. Brown; Gary L. Emmert (pp. 133-140).

A laboratory-built automated instrument is reported for on-line, near real-time monitoring of nine haloacetic acids species (HAA9) in drinking water. The device uses anion-exchange chromatography to separate the HAA9 species, followed by post-column reaction with nicotinamide in basic solution with fluorescence detection. Method detection limits for HAA9 species ranged from 0.6 to 10.1μgL⁻¹, mean % recovery values ranged from 58 to 161%, and % relative standard deviation ranged from 3.5 to 32% while operating within a factor of 2.5–5 of the method detection limit. The bias between the proposed method and United States Environmental Protection Agency Method 552.3 was measured during two separate on-line studies and using grab samples collected from different distribution systems. In general, the two methods showed good agreement with biases for HAA9 of less than 10μgL⁻¹.

Keywords: Haloacetic acids; Drinking water; Ion chromatography; On-line monitoring; Disinfection by-products

Development and validation of an HPLC method for the determination of process-related impurities in pridinol mesylate, employing experimental designs by Romina M. Bianchini; Patricia M. Castellano; Teodoro S. Kaufman (pp. 141-147).

A simple high performance liquid chromatographic method for the determination of process-related impurities in bulk drug of the central anticholinergic compound pridinol mesylate, has been developed and validated. Spectroscopically characterized synthetic impurities were used as standards. The chromatographic separation was optimized employing an experimental design strategy, and was achieved on a C₁₈ column with a mobile phase containing 50mM potassium phosphate buffer (pH 6.4), MeOH and 2-propanol (20:69:11, v/v/v), delivered at a flow rate of 1.0mLmin⁻¹. UV detection was performed at 245nm. The optimized method was thoroughly validated, demonstrating to be selective, when the chromatogram was recorded with a diode-array detector and peak purities were evaluated (>0.9995). The method is robust and linear ( r²>0.99) over the range 0.05–2.5% (5–250% with regards to the 1% specification limit for both process-related impurities); it is also precise, regarding repeatability (RSD≤1.5% for all of the analytes) and intermediate precision aspects and LOQ values for the impurities are below 0.01%. Method accuracy, evidenced by low bias of the results and analyte recoveries in the range of 99.1–102.7%, was assessed at five analyte concentration levels. The usefulness of the determination was also demonstrated through the analysis of different lots of pridinol mesylate bulk substance. The results indicate that the method is suitable for the quality control of the bulk manufacturing of pridinol mesylate drug substance.

Keywords: Pridinol mesylate; Manufacturing process impurities; HPLC method development; Method validation; Experimental design; Quality control

Screening of salbutamol residues in swine meat and animal feed by an enzyme immunoassay in Taiwan by Shi-Yuan Sheu; Yi-Chih Lei; Yung-Te Tai; Tong-Hsuan Chang; Tzong-Fu Kuo (pp. 148-153).

An ELISA was developed for routine examination for extensive monitoring and screening programs for the residues of salbutamol in swine serum, animal feed, meat, and meat-related products destined for human consumption in Taiwan. Objectives of the study were to investigate the use of a new immunoassay for the detection of salbutamol residues in swine meat and animal feed samples, and to compare with a commercial kit in field test screens. A fast, simple and reliable sample preparation method for the determination of salbutamol was established. Field trials with 222 swine meat and 120 animal feed samples that were taken from local meat markets, auction markets and feed mills. The application and the results of two ELISA kits (a homemade and a commercial kit) for the screening of salbutamol were presented. Adopting 2μgkg⁻¹ salbutamol as a cut-off value for swine meat, the commercial β-agonist ELISA had a sensitivity of 85.3% and a specificity of 95.2% versus GC–MS at a cut-off of 2μgkg⁻¹. The homemade salbutamol ELISA had a sensitivity of 100% and a specificity of 90.9% and gave no false-negative rate results. Furthermore, adopting 20μgkg⁻¹ salbutamol as a cut-off value for animal feed, both the commercial and homemade ELISA showed 100% sensitivity and 100% specificity of the assays. In conclusion, a sensitive, specific salbutamol polyclonal antibody-based ELISA has been developed that could serve as a rapid screening assay, and the detection of positive samples at the place of sampling can result in more effective control of the illegal use of β-agonists.

Keywords: Immunoassay; β-Agonists; Salbutamol; Meat; Feed; Residues

High-performance liquid chromatographic method for determination of amino acids by precolumn derivatization with 4-chloro-3,5-dinitrobenzotrifluoride by Tianyu Shi; Tao Tang; Kun Qian; Fang Wang; Jianqiang Li; Yongsong Cao (pp. 154-161).

This work presents an high-performance liquid chromatography method for the determination of amino acids after precolumn derivatization with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF) which can readily react with both primary and secondary amines. The precolumn derivatization conditions, including the CNBF concentration, reaction pH, temperature and reaction time were investigated for method optimization. In pH 9.0 borate buffer, the reaction of amino acids with CNBF was carried out at 60°C for 30min, the optimized concentration of CNBF was 70mmolL⁻¹ and the molar ratio of amino acids to CNBF was 1:5.25. The chromatographic separation of 19 amino acids derivatives was performed on a Kromasil ODS C₁₈ column (250mm×4.6mm, 5μm) with good reproducibility, and ultraviolet detection was applied at 260nm. The mobile phase was a mixture of phase A (acetonitrile) and phase B (acetate buffer, acetonitrile, triethylamine; 82.8:17:0.2, pH 4.9), and the flow rate was 0.4mLmin⁻¹. The separation of all the labeled amino acids was achieved within 45min at room temperature by gradient elution mode. The method linearity, calculated for each amino acid, had a correlation coefficient higher than 0.9979, in concentrations ranging from 9.60 to 3330.00μmolL⁻¹. The detection limits of amino acids were 2.40–6.50μmolL⁻¹, at a signal-to-noise ratio of 3. The proposed method was applied for the determination of amino acids in beer with recoveries of 97.0–103.9% and relative standard deviations of 2.62–4.22%, respectively. This method showed good accuracy and repeatability that can be used for the quantification of amino acids in real samples.

Keywords: Amino acids; Precolumn derivatization; 4-Chloro-3,5-dinitrobenzotrifluoride; Liquid chromatography

Solid-phase extraction followed by liquid chromatography–tandem mass spectrometry for the determination of hydroxylated benzophenone UV absorbers in environmental water samples by N. Negreira; I. Rodríguez; M. Ramil; E. Rubí; R. Cela (pp. 162-170).

A procedure for the determination of six derivatives of 2-hydroxybenzophenone, used as UV absorbers, in water samples is presented. Compounds were first concentrated using a solid-phase extraction (SPE) cartridge and then selectively determined by liquid chromatography–tandem mass spectrometry (LC–MS/MS) using electrospray ionization (ESI). The effect of different parameters on the performance of concentration and determination steps is discussed. The highly polar and acidic 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (BP-4) required the use of ammonium acetate as modifier during desorption of SPE cartridges and also to improve the performance of its separation in the LC column. Under optimized conditions, the proposed method provided limits of quantification from less than 1 to 32ngL⁻¹, depending on the compound and the type of water sample. Recoveries from the SPE step (83–105%) remained unaffected by the nature of the matrix; however, the efficiency of electrospray ionization was compound and sample dependant. Real sample analysis reflected the presence of three of the six investigated species (BP-4, 2-hydroxy-4-methoxybenzophenone, BP-3, and 2,4-dihydroxybenzophenone, BP-1) in the aquatic environment, particularly in raw wastewater samples. In this latter matrix, BP-4 was the compound presenting the highest concentrations; moreover, it was poorly removed in sewage treatment plants and consequently it also appeared in river water.

Keywords: Hydroxylated benzophenones; UV absorbers; Liquid chromatography–tandem mass spectrometry; Water analysis

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Analytica Chimica Acta (v.654, #2)