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Analytica Chimica Acta (v.670, #1-2)

Editorial Board (pp. iii).

A review on applications of chemiluminescence detection in food analysis by Meilin Liu; Zhen Lin; Jin-Ming Lin (pp. 1-10).

There is an increasing interest by consumers for high quality food products with a specified composition. Suitable analytical techniques are needed for the quality control. Chemiluminescence (CL) detection has become quite a useful tool in the last years due to its simplicity, low cost and high sensitivity. Moreover, no external light source is needed. CL is often described as a dark-field technique: the absence of strong background light level reduces the background signal and leads to improved detection limits. Due to these advantages, CL methods have been widely applied to food analysis in recent years. Navas and Jiménez had reviewed the CL methods in food analysis in 1996. The present review covers the papers since 1996, including the CL determinations of nitrogen containing components, sugars, chemical preservatives, metals, hormonal anabolics and metabolites, and other compounds in foods. 122 references have been cited.

Keywords: Chemiluminescence; Determination; Food; Review; Applications

Alpha/beta pulse shape discrimination in plastic scintillation using commercial scintillation detectors by H. Bagán; A. Tarancón; G. Rauret; J.F. García (pp. 11-17).

Activity determination in different types of samples is a current need in many different fields. Simultaneously analysing alpha and beta emitters is now a routine option when using liquid scintillation (LS) and pulse shape discrimination. However, LS has an important drawback, the generation of mixed waste. Recently, several studies have shown the capability of plastic scintillation (PS) as an alternative to LS, but no research has been carried out to determine its capability for alpha/beta discrimination. The objective of this study was to evaluate the capability of PS to discriminate alpha/beta emitters on the basis of pulse shape analysis (PSA).The results obtained show that PS pulses had lower energy than LS pulses. As a consequence, a lower detection efficiency, a shift to lower energies and a better discrimination of beta and a worst discrimination of alpha disintegrations was observed for PS. Colour quenching also produced a decrease in the energy of the particles, as well as the effects described above. It is clear that in PS, the discrimination capability was correlated with the energy of the particles detected.Taking into account the discrimination capabilities of PS, a protocol for the measurement and the calculation of alpha and beta activities in mixtures using PS and commercial scintillation detectors has been proposed. The new protocol was applied to the quantification of spiked river water samples containing a pair of radionuclides (³H–²⁴¹Am or⁹⁰Sr/⁹⁰Y–²⁴¹Am) in different activity proportions. The relative errors in all determinations were lower than 7%. These results demonstrate the capability of PS to discriminate alpha/beta emitters on the basis of pulse shape and to quantify mixtures without generating mixed waste.

Keywords: Plastic scintillation; Liquid scintillation; Alpha/beta discrimination; Pulse shape analysis; River water samples; Mixed waste

Speciation and determination of ultra trace amounts of inorganic tellurium in environmental water samples by dispersive liquid–liquid microextraction and electrothermal atomic absorption spectrometry by Nahid Mashkouri Najafi; Hamed Tavakoli; Reza Alizadeh; Shahram Seidi (pp. 18-23).

A simple and powerful method has been developed for the rapid and selective determination of Te(IV) and Te(VI), employing dispersive liquid–liquid microextraction combined with electrothermal atomic absorption spectrometry using palladium as permanent modifier. Under acidic conditions pH 1, only Te(IV) can form a complex with ammonium pyrrolidine dithiocarbamate (APDC) and therefore be extracted into fine droplets of carbon tetrachloride (extraction solvent) which are dispersed with ethanol into the water sample solution. After centrifugation, Te(IV) was determined in the sedimented organic phase while Te(VI) remained in the aqueous phase. Total inorganic tellurium was determined after the reduction of the Te(VI) to Te(IV). Te(VI) was calculated as the difference between the measured total inorganic tellurium and Te(IV) content. The effective parameters for improving the efficiency of microextraction process were investigated by using experimental and central composite designs. Under optimal conditions the enrichment factor was 125 and the calibration graph was linear in the range of 0.015–1ngmL⁻¹ with detection limit and characteristic mass of 0.004ngmL⁻¹ and 0.033pg, respectively. The relative standard deviation for 0.5ngmL⁻¹ of tellurium measurement was 3.6% ( n=6) at ash and atomization temperature, 900 and 2600°C, respectively. The recoveries of spiked Te(IV) and Te(VI) to the environmental water samples were 89.6–101.3% and 96.6–99.1%, respectively. The accuracy is also evaluated by applying the proposed method to certified reference material (NIST SRM 1643e), for which the result was in a good agreement with the certified values reported for this CRM (95% confidence level).

Keywords: Tellurium; Speciation; Dispersive liquid–liquid microextraction; Experimental design; Permanent modifier; Natural waters

The dissociation kinetics of Cu-dissolved organic matter complexes from soil and soil amendments by F. Amery; F. Degryse; C. Van Moorleghem; M. Duyck; E. Smolders (pp. 24-32).

Complexes between dissolved organic matter (DOM) and copper (Cu) that dissociate very slowly can theoretically facilitate Cu leaching to the groundwater. Data on dissociation kinetics of Cu–DOM complexes present in soil and in soil amendments are limited. The dissociation kinetics of different Cu–DOM complexes from soil, wastewater, pig manure and sewage sludge was measured with the Competitive Ligand Exchange Method (CLEM) and Diffusive Gradient in Thin films (DGT) technique. The solutions were set at constant pH, Ca concentration and free Cu²⁺ activity to allow comparison between the different samples. The average dissociation rate constant k_d of the complexes, as measured by CLEM, was about 10⁻³s⁻¹ and the fractions of dissolved Cu that were undissociated after 8h ranged from <1% to 25%. These fractions determined by CLEM were significantly correlated with the non-labile fractions (0–82%) determined in the DGT tests and data analysis show that DGT data can be predicted from CLEM data. The dissociation rates decreased when Cu–DOM complexes had been equilibrated at lower Cu²⁺ activities. Increasing the Cu–DOM contact time (7–297 days) decreased the dissociation rate. The non-labile fractions were positively correlated with the specific UV absorbance suggesting that aromatic moieties in DOM hold non-labile Cu. All natural Cu–DOM complexes contained a detectable fraction with a dissociation rate constant k_d lower than 10⁻⁵s⁻¹ which can theoretically lead to non-equilibrium conditions and leaching risks in soil.

Keywords: Copper; Dissolved organic matter; Complexation; Dissociation; Kinetics; Soil

Use of constrained mixture design for optimization of method for determination of zinc and manganese in tea leaves employing slurry sampling by Marcos Almeida Bezerra; Jacira Teixeira Castro; Reinaldo Coelho Macedo; Douglas Gonçalves da Silva (pp. 33-38).

A slurry suspension sampling technique has been developed for manganese and zinc determination in tea leaves by using flame atomic absorption spectrometry. The proportions of liquid-phase of the slurries composed by HCl, HNO₃ and Triton X-100 solutions have been optimized applying a constrained mixture design. The optimized conditions were 200mg of sample ground in a tungsten carbide balls mill (particle size<100μm), dilution in a liquid-phase composed by 2.0molL⁻¹ nitric, 2.0molL⁻¹ hydrochloric acid and 2.5% Triton X-100 solutions (in the proportions of 50%, 12% and 38% respectively), sonication time of 10min and final slurry volume of 50.0mL. This method allowed the determination of manganese and zinc by FAAS, with detection limits of 0.46 and 0.66μgg⁻¹, respectively. The precisions, expressed as relative standard deviation (RSD), are 6.9 and 5.5% ( n=10), for concentrations of manganese and zinc of 20 and 40μgg⁻¹, respectively. The accuracy of the method was confirmed by analysis of the certified apple leaves (NIST 1515) and spinach leaves (NIST 1570a). The proposed method was applied for the determination of manganese and zinc in tea leaves used for the preparation of infusions. The obtained concentrations varied between 42 and 118μgg⁻¹ and 18.6 and 90μgg⁻¹, respectively, for manganese and zinc. The results were compared with those obtained by an acid digestion procedure and determination of the elements by FAAS. There was no significant difference between the results obtained by the two methods based on a paired t-test (at 95% confidence level).

Keywords: Slurry sampling; Constrained mixture design; Manganese; Zinc; Tea leaves

Micro near infrared spectroscopy (MicroNIRS) based on on-line enrichment: Determination of trace copper in water using glycidyl methacrylate-based monolithic material by Guiping Chen; Yuan Mei; Wei Tao; Cheng Zhang; Huirong Tang; Jibran Iqbal; Yiping Du (pp. 39-43).

A micro near infrared spectroscopy (MicroNIRS) technique based on monolithic column enrichment has been developed to detect low concentration metallic ions in water. Glycidyl methacrylate–ethylene dimethacrylate–iminodiacetic acid (GMA–EDMA–IDA) monolithic material was synthesized to construct an enrichment device, which can enrich metallic ions more efficiently than chelating resin materials such as D401. Cu²⁺ solutions passed through the enrichment device and concentrated on the surface of the material, and then diffuse reflection NIR (DRNIR) spectra were measured by touching the NIR probe on the surface. The spectra were pretreated with multiplicative scatter correction (MSC) and the MSC-pretreated spectra showed high linear correlation to the Cu²⁺ concentrations in spectral regions of 900–1350nm, 1420–1480nm and 1970–2050nm for all concentration ranges. PLS models built with leave-one-out cross-validation also yielded good features. The mean relative error (MRE) of prediction was 10.0% in the 0.0001–0.0010μgmL⁻¹ range. The concentration has low to ppb-level, but the MRE was not more than 10%, which was acceptable for trace analysis. The results revealed that the MicroNIRS technique enhanced the sensitivity of NIRS dramatically and widened the NIRS technique to micro and trace analysis field.

Keywords: Micro near infrared spectroscopy; Enrichment; Trace copper; Partial least squares; Monolithic material

Simultaneous chemiluminescence determination of amoxicillin and clavulanic acid using least squares support vector regression by F. Hasanpour; Ali A. Ensafi; T. Khayamian (pp. 44-50).

In this work, both the batch and flow injection chemiluminescence (CL) methods have been proposed for the simultaneous determination of two structurally similar β-lactams including amoxicillin and clavulanic acid (CLAV). Chemiluminescence spectral overlap of these two structurally similar β-lactams is the main limitation for the simultaneous analysis of the two compounds. Least squares support vector regression (LS-SVR) was applied to relate concentration of both the compounds to their CL profiles. The parameters of the model, consisting of kernel parameter, σ², and the regularization parameter, γ, were optimized by constructing different LS-SVR models and the model with the minimum root mean squared error of cross-validation (RMSECV) for the calibration set was selected as the best model and its parameters were chosen as the optimized values. The performance of LS-SVR model was compared with Partial Least Squares (PLS) and the results revealed the superiority of the LS-SVR over PLS model. Under the optimized experimental conditions for both the compounds, when LS-SVR was applied, the detection limits obtained were 0.2 and 0.60μmolL⁻¹ in the batch mode and 0.3 and 0.5μmolL⁻¹ in the flow injection mode for CLAV and amoxicillin, respectively. The proposed method was utilized for the simultaneous determination of the compounds in pharmaceutical formulations and spiked plasma samples.

Keywords: Clavulanic acid; Amoxicillin; Chemiluminescence; Support vector machine

Direct electrochemistry and electrocatalysis of horseradish peroxidase with hyaluronic acid–ionic liquid–cadmium sulfide nanorod composite material by Zhihong Zhu; Xia Li; Yan Wang; Yan Zeng; Wei Sun; Xintang Huang (pp. 51-56).

A new composite material consisted of hyaluronic acid (HA), ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) and cadmium sulfide (CdS) nanorod was fabricated and used for the immobilization of horseradish peroxidase (HRP) on the surface of a carbon ionic liquid electrode (CILE), which was prepared with 1-ethyl-3-methyl-imidazolium ethylsulphate ([EMIM]EtOSO₃) as modifier. Spectroscopic results indicated that HRP remained its native structure in the composite film. Based on the synergistic effect of the materials used, an obvious promotion to the direct electron transfer efficient between HRP and CILE was achieved with a pair of well-defined redox peaks appeared in 0.1molL⁻¹ phosphate buffer solution, indicating the realization of the direct electrochemistry of HRP. The immobilized HRP showed good electrocatalytic activity towards the reduction of trichloroacetic acid and H₂O₂ with the electrochemical parameters calculated. Based on the fabricated electrode, a new third-generation electrochemical biosensor was constructed with good stability and reproducibility.

Keywords: Hyaluronic acid; Horseradish peroxidase; Cadmium sulfide nanorod; 1-Butyl-3-methylimidazolium tetrafluoroborate; Direct electrochemistry; Carbon ionic liquid electrode

Electrochemical biosensor for the detection of H₂O₂ from living cancer cells based on ZnO nanosheets by Qi Rui; Kikuo Komori; Yang Tian; Haiqing Liu; Yongping Luo; Yasuyuki Sakai (pp. 57-62).

In this work, direct electron transfer of cytochrome c (cyt. c)—a model for studying the electron transfer of enzymes is achieved at hexagonal ZnO nanosheets by one-step electrodeposition. UV–vis spectra and electrochemical data demonstrate that such ZnO nanosheets can supply a bio-compatible surface to keep the bioactivity of cyt. c. The redox formal potential ( E⁰′) of cyt. c is estimated to be 338.2±4.3mV (vs. AgǀAgCl) at the nanostructured ZnO surface. This value is much more positive than those of enzymes previously obtained at other metal oxides and zeolite surfaces. Experiment data show, under the optimized potential of 0.0V (vs. AgǀAgCl), the electrochemical determination of H₂O₂ is free from not only anodic interferences like ascorbic acid (AA) and dopamine (DA), but also a cathodic interference—O₂. Such an excellent selectivity enable the present H₂O₂ biosensor determine the extracellular H₂O₂ released from living human hepatoma cells.

Keywords: ZnO nanosheets; Cytochrome; c; H; ₂; O; ₂; Electrochemical biosensor; Living cells

Validation of an analytical method for analysis of cannabinoids in hair by headspace solid-phase microextraction and gas chromatography–ion trap tandem mass spectrometry by Elissandro Soares Emídio; Vanessa de Menezes Prata; Haroldo Silveira Dórea (pp. 63-71).

The development of an analytical method for the determination of Δ⁹-tetrahydrocannabinol (THC), cannabidiol (CBD) and cannabinol (CBN) in samples of human hair is described. Samples were subjected to a procedure based on the combination of headspace solid-phase microextraction (HS-SPME) with gas chromatography linked with mass spectrometry operating in tandem mode (GC–MS/MS). A 10mg aliquot of sample was firstly decontaminated using petroleum ether, deionized water and dichloromethane (2mL of each solvent), for 10min under sonication, and then digested in alkaline solution (1molL⁻¹ NaOH). The method variables evaluated were pH, mass of hair, fiber type, extraction temperature, desorption time, ionic strength, pre-equilibrium time and extraction time. Parameters concerning operation of the tandem mode MS/MS were also assessed and optimized. Validation of the method demonstrated excellent linearity in the range 0.1–8.0ngmg⁻¹, with regression coefficients better than 0.994. Precision was determined using two different concentrations (upper and lower limits of the linear range), and RSD values were between 6.6 and 16.4%. Absolute recoveries (measured in triplicate) were in the range 1.1–8.7%, and limits of detection and quantification were 0.007–0.031ngmg⁻¹ and 0.012–0.062ngmg⁻¹, respectively. The LOQ for THC (0.062ngmg⁻¹) was below the cut-off value (LOQ≤0.1ngmg⁻¹) established by the Society of Hair Testing (SOHT), the Society of Toxicological and Forensic Chemistry (STFCh) and the Société Française de Toxicologie Analytique (SFTA). The optimized SPME method was applied in analysis of hair samples from Cannabis drug users, showing that CBN and CBD were present in all samples analyzed.

Keywords: Cannabinoids; Hair analysis; Headspace solid-phase microextraction; Gas chromatography–ion trap tandem mass spectrometry

Selective enrichment and determination of nicosulfuron in water and soil by a stir bar based on molecularly imprinted polymer coatings by Lieqing Yang; Xiaomin Zhao; Jie Zhou (pp. 72-77).

A new molecularly imprinted stir bar was prepared using nicosulfuron, a sulfonylurea herbicide, as a template. To achieve the selective and direct extraction of a target analyte from aqueous samples, several main parameters, including extraction time, pH value and contents of inorganic salt in the sample matrix, were investigated. Competitive sorption experiments showed that using six sulfonylureas as substrates the imprinted stir bar gave high selectivity and imprinted effect on the template nicosulfuron in comparison with the non-imprinted stir bar. Evidence was also presented by the scanning electronic microscopic images of the imprinted and non-imprinted stir bars. This resulted in a combined imprinted stir bar–HPLC-UV method allowing the determination of trace nicosulfuron from the sample matrix. Based on a signal to noise ratio of 3, the detection limits were 0.75nM for the tap water and 12.0nmolkg⁻¹ for the soil. The method showed good recoveries and precision, 93.4% (RSD 1.5%, n=3) for 100mL of tap water spiked with 2.0nmol and 81.3% (RSD 2.6%, n=3) for 10g of soil spiked with 0.80nmol, suggesting that the imprinted stir bar can be successfully applied to the preconcentration of nicosulfuron in real samples.

Keywords: Stir bar extraction; Molecularly imprinted polymer-coating; Nicosulfuron; In situ polymerization

Analytical particle measurements in an optical microflume by Joseph D. Taylor; Alex Terray; Sean J. Hart (pp. 78-83).

In this work, microscopic particles in a fluid flow are manipulated using forces generated by a high power laser beam. The resulting manipulations on the particles are imaged using a microscope lens connected to a CCD camera. Differential forces on particles of varying physical and chemical composition have been measured. The goal is to measure the optical forces on a diverse range of particles and catalog the associated chemical and physical differences to understand which properties and mechanisms result in the largest force differentials. Using these measurements our aim is to better understand differences between similar microspheres in terms of size, morphology, or chemical composition. Particles of the same size, but different composition show large variations in optical pressure forces and are easily discernable in the present analytical system. In addition, we have demonstrated the ability to differentiate a 70nm size difference between two NIST precision size standard polystyrene microspheres, corresponding to a 2.0pN difference in optical force. Lastly, the instrument was used to measure differences between biological samples of similar size, demonstrating the ability to make precise analytical measurements on microorganism samples.

Keywords: Abbreviations; OC; optical chromatography; PS; polystyrene; PMMA; poly(methylmethacrylate); Si; silica; MF; melamine formaldehyde resin; Ba; Bacillus anthracis; (Sterne strain); Bt; Bacillus thuringiensis; Geobacter; Geobacter sulfurreducens; (strain DL-1)Optical chromatography; Laser; Pressure; Microfluidics; Optofluidic; Optical trapping; Pneumatics

Simultaneous determination of plasma epinephrine and norepinephrine using an integrated strategy of a fully automated protein precipitation technique, reductive ethylation labeling and UPLC–MS/MS by Chengjie Ji; Justin Walton; Yi Su; Max Tella (pp. 84-91).

A novel, automated, simple, sensitive, specific, accurate, precise and high-throughput liquid chromatography tandem mass spectrometry (LC–MS/MS)-based method has been developed for simultaneous determination of epinephrine (E) and norepinephrine (NE) in plasma by using the combination of a fully automated protein precipitation technique for plasma sample preparation, reductive ethylation labeling with UPLC–MS/MS. A simple protein precipitation procedure was used to clean up 50μL calibration samples prepared in stripped human plasma and 50μL quality control plasma samples containing 25μL plasma and 25μL stabilizing additives. The supernatants were subsequently dried down and then reconstituted with commercially available and cost-effective reductive ethylation labeling reagents, followed by UPLC–MS/MS analysis. All liquid handling during sample preparation was automated using a Hamilton MicroLab Star Robotic workstation, which included the preparation of standards and quality control samples, shaking of 96-well plates, adding and transferring liquids. Processing time, which included the preparation of standards and quality control samples, protein precipitation and reductive ethylation labeling, is less than 2h per 96-well plate. The chromatographic run time is 3.5min per sample. The limits of detection of UPLC–MS/MS-based methods for E and NE, with/without reductive ethylation labeling, are 0.025/0.40 and 0.025/2.00ngmL⁻¹, respectively. Reductive ethylation labeling of amino groups of E and NE affords 16 and 80 times increased detection sensitivity of corresponding native counterparts during the UPLC–MS/MS analysis. The linearity of this method was established from 0.05 to 25ngmL⁻¹ for E and NE with accuracy and precision within 15% at all concentrations. The intra-run and inter-run assay accuracy (%RE) and coefficient of variations (CV%) are all within 15% for all QC samples prepared in commercially purchased plasma samples.

Keywords: Ultra performance liquid chromatography-tandem mass spectrometry; Reductive ethylation; Quantification; Plasma epinephrine and norepinephrine; Automation; Protein precipitation

A low cost short wave near infrared spectrophotometer: Application for determination of quality parameters of diesel fuel by Fabiano Barbieri Gonzaga; Celio Pasquini (pp. 92-97).

A low cost absorption spectrophotometer for the short wave near infrared spectral region (850–1050nm) is described. The spectrophotometer is basically composed of a conventional dichroic lamp, a long-pass filter, a sample cell and a Czerny–Turner type polychromator coupled to a 1024 pixel non-cooled photodiode array. A preliminary evaluation of the spectrophotometer showed good repeatability of the first derivative of the spectra at a constant room temperature and the possibility of assigning some spectral regions to different C–H stretching third overtones. Finally, the spectrophotometer was successfully applied for the analysis of diesel samples and the determination of some of their quality parameters using partial least squares calibration models. The values found for the root mean square error of prediction using external validation were 0.5 for the cetane index and from 2.5 to 5.0°C for the temperatures achieved during distillation when obtaining 10, 50, 85, and 90% (v/v) of the distilled sample, respectively.

Keywords: Short wave near infrared; Diesel fuel; Cetane index; Partial least squares; Instrumentation

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Analytica Chimica Acta (v.670, #1-2)