Analytica Chimica Acta (v.605, #2)

Contents (iii-iv).

A review on novel developments and applications of immunosensors in food analysis by Francesco Ricci; Giulia Volpe; Laura Micheli; Giuseppe Palleschi (111-129).
The present review deals with novel developments in immunosensors destined for final application in food analysis. In this perspective particular emphasis will be given to the most important approaches which recently have been used for immunosensor construction and assembling. For this reason, electrochemical, surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) techniques will be explored in detail and recent and practical examples on food matrices will be reviewed. Objective of this survey is to give a general overview of the possible application of immunosensors to the food analysis field.
Keywords: Immunosensor; Food analysis; Surface plasmon resonance; Electrochemical; Quartz crystal microbalance;

A low pressure microwave assisted vapor phase dissolution procedure for silicon nitride and volatilization of in situ generated SiF4 has been developed using H2SO4, HF and HNO3 for the determination of trace impurities present in silicon nitride. Sample was taken in minimum amount (0.5 mL for 100 mg) of H2SO4 and treated with vapors generated from HF and HNO3 mixture in presence of microwaves in a closed container. An 80 psi pressure with ramp and hold times of 30 min and 60 min respectively, operated twice, resulted in 99.9% volatilization of Si. Matrix free solutions were analyzed for impurities using DRC-ICP-MS. The recoveries of Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Y, Cd, Ba and Pb were between 80 and 100% after volatilization of Si. The blanks were in lower ng g−1 with method detection limits in lower ng g−1 to sub ng g−1 range. The method was applied for the analysis of two silicon nitride samples.
Keywords: Ceramic; Silicon nitride; Dynamic reaction cell inductively coupled plasma-mass spectrometry; Vapor phase digestion/volatilization;

Classification of multiway analytical data based on MOLMAP approach by Davide Ballabio; Viviana Consonni; Roberto Todeschini (134-146).
A new method for the study of molecule chemical information organized into three-way data structures (MOLMAP) was recently proposed in literature. Basically, MOLMAP molecular fingerprints are calculated by projecting bond properties of molecules into Kohonen networks and used to generate molecular descriptors for QSAR modeling. Since this technique has never been applied to other kinds of chemical multiway data, in this study classification models were carried out by means of MOLMAP approach on three-way analytical datasets of electronic nose and fluorescence data. For comparing purposes, other classification methods were applied to the same datasets: Discriminant Analysis on the PARAFAC scores and Partial Least Square-Discriminant Analysis (PLS-DA) on the unfolded data.Since the MOLMAP approach provided good results for the analyzed datasets, here, we propose the MOLMAP approach to be used as a general technique for the classification of multiway datasets. Actually, besides the good classification performances, other advantages came out: (a) the MOLMAP scores appeared as effective fingerprints for data characterization; (b) the role and importance of each portion of the multiway data can be analyzed in a comprehensive way; (c) it is possible to understand which variables have greater discriminant power and consequently apply data reduction.
Keywords: Classification; Multiway; MOLecular Map of Atom-level Properties; Fluorescence; Electronic nose;

A simple and efficient binary solvent-based two-phase hollow fiber membrane (HFM)-protected liquid-phase microextraction (BN-LPME) technique for moderately polar compounds was developed. Six organophosphorous pesticides (OPPs) (triethylphosphorothioate, thionazin, sulfotep, phorate, disulfoton, methyl parathion and ethyl parathion) were used as model compounds and extracted from 10-mL wastewater with a binary-solvent (toluene:hexane, 1:1) mixture. Some important extraction parameters, such as extraction time, effect of salt, sample pH and solvent ratio composition were optimized. BN-LPME combined with gas chromatography/mass spectrometric (GC/MS) analysis provided repeatability (R.S.D.s ≤ 12%, n  = 4), and linearity (r  ≤ 0.994) and solid-phase microextraction provides comparable of R.S.D.s ≤ 13%, n  = 4 and linearity (r  = ≤0.966) for spiked water samples. The limits of detection (LODs) were in the range of 0.3–11.4 ng L−1 for BN-LPME and 3.1–120.5 ng L−1 for SPME at (S/N = 3) under GC/MS selective ion monitoring mode. In addition to high enrichment, BN-LPME also served as a sample cleanup procedure, with the HFM act as a filtering medium to prevent large particles and extraneous materials from being extracted. To investigate and compare their applicability, the BN-LPME and SPME procedures were applied to the detection of OPPs in domestic wastewater samples.
Keywords: Liquid-phase microextraction; Binary solvent; Solid-phase microextraction; Organophosphorous pesticides; Environmental analysis;

Dynamic drop-to-drop solvent microextraction (DDSME) combined with atmospheric pressure-matrix assisted laser desorption/ionization mass spectrometry (AP-MALDI/MS) has been successfully applied on the bioanalysis of quinine using micro liter volume (30 μL) of human urine and plasma samples. The method is based on the movement of aqueous phase (AP) in and out of the microsyringe, which increases the transfer and diffusion rate of the quinine drug from aqueous phase to organic phase (OP). The optimization parameters including the effect of solvent selection, number of samplings, sampling volume, volume of aqueous phase, volume of organic phase, addition of salt and pH were investigated for obtaining higher extraction efficiency of the analyte. The limits of detections (LODs) of quinine, using the dynamic DDSME/AP-MALDI/MS in urine and plasma samples were 0.18 and 0.24 μM, respectively. The superiority of dynamic DDSME over static DDSME and liquid–liquid extraction (LLE) was also demonstrated for the determination of quinine in aqueous solution. This method is promising in clinical application and pharmacokinetic studies, in which the availability of sample amount is extremely small.
Keywords: Quinine; Dynamic drop-to-drop solvent microextraction; Biological samples; Atmospheric pressure-matrix assisted laser desorption/ionization mass spectrometry;

A dodecylsulfate-doped polypyrrole (PPy-DS) film was prepared by electrochemical fiber coating (EFC) technique and applied as a new fiber for headspace solid-phase microextraction (HS-SPME) of phenolic compounds from water samples. Electrochemically polymerized PPy is formed on the surface of a platinum wire and will contain charge-compensating anion (dodecylsulfate) incorporated during synthesis. The efficiency of this fiber for microextraction of phenols was evaluated using a HS-SPME device coupled with gas chromatography-flame ionization detection (GC-FID). The results shows that PPy-DS as a SPME fiber coating is suitable for the successful extraction of phenolic compounds. Parameters like ionic strength, agitation of the sample, sample pH, temperature of the sample, and adsorption/desorption times were studied and optimized to obtain the best extraction results. This method provided good repeatability (R.S.D.s < 7.2%) for spiked water samples. The calibration graphs were linear in the range of 2–100 ng mL−1 with the square of the correlation coefficient R 2  > 0.991 and detection limits were between 0.57 and 1.82 ng mL−1. The capability of PPy-DS to extract phenolic compounds has been compared with the results obtained with literature data for several fibers and this laboratory-made fiber showed comparable analytical parameter for the studied compounds.
Keywords: Headspace solid-phase microextraction; Polypyrrole film; Electrochemical fiber coating; Phenolic compounds; Water pollutant analysis;

Capillary scale light emitting diode based multi-reflection absorbance detector by Santosh K. Mishra; Purnendu K. Dasgupta (166-174).
We describe a light emitting diode (LED) based multi-reflection capillary scale absorbance detector based on both square and round capillaries and compare their performance with a conventional single-pass on-tube detector. The optical path length is extended by silver coating, the external surface of the capillary. The reflective geometry has been reported to be less prone to artifacts induced by refractive index changes; we do find this to be true. Although the detection volume/illuminated volume is increased some, a multi-reflection cell based on a 180 μm bore capillary with a ∼2-cm long illuminated volume shows over a 50-fold gain in signal-to-noise (S/N) compared to a single-pass on-tube configuration with the same capillary. The limit of detection (LOD) is 4.4 fmol (2.6 pg, 1 μL of 22.0 nM injected dye) BTB under pulseless (pneumatic) flow conditions. The cells behave as multipath devices where the effective path lengths are greater at low absorbance values. In our experiments, where non-coherent light is launched through optical fibers that are large compared to capillary bore dimensions, increase in the effective path length of the cell do not occur in a predictable fashion with the angle of incidence of the light beam. Although the effective path length almost linearly increases with increasing distance between the light entry and exit windows, the absolute values of the effective path lengths are always lower than this physical distance, suggesting that after some passage through the solution, light largely travels through or along the glass wall. Square capillaries have better light transmission and offer some performance advantages. Multi-reflection cells can indeed be of value for sensitive detection in microflow systems.
Keywords: Capillary; Absorbance detection; Light emitting diode; Multi-reflection;

In this paper, a detailed theoretical model is developed for studying the capillary filling dynamics of a non-Newtonian power-law obeying fluid in a microchannel subject to electrokinetic effects. Special attention is devoted to model the effects of the electroosmotic influences in the capillary advancement process, variable resistive forces acting over different flow regimes, and the dynamically evolving contact line forces, in mathematically closed forms. As an illustrative case study, in which the flow parameters are modeled as functions of the hematocrit fraction in the sample, the capillary dynamics of a blood sample are analyzed. Flow characteristics depicting advancement of the fluid within the microfluidic channel turn out to be typically non-linear, as per the relative instantaneous strengths of the capillary forces, electroosmotic forces and viscous resistances. Non-trivial implications of the blood hematocrit level and the imposed electric field on the progression of the capillary front are highlighted, which are expected to be of significant consequence towards the dynamics of electroosmotically aided capillary filling processes of biofluidic samples.
Keywords: Capillary filling; Non-Newtonian; Electroosmotic;

Fluorimetric determination of phytic acid in urine based on replacement reaction by Yingyu Chen; Jingwen Chen; Kang Ma; Shuhong Cao; Xiaoqing Chen (185-191).
A sensitive fluorimetric method for determination of phytic acid in human urine samples was described. The method was based on a fluorimetric replacement reaction, in which the added phytic acid replaced the Cu2+ ion from Cu2+–gelatin complex, liberating the fluorescent gelatin molecule. The fluorescence of the solution was accordingly recovered proportionally to the amount of the foreign phytic acid. The excitation wavelength was 273.5 nm and the characteristic emission wavelength was 305.0 nm, respectively. The calibration graph was obtained by plotting the recovered fluorescent intensity at maximum 305.0 nm against the added standard phytic acid, and was divided into two sections. One section was linear over the range of 0.40–2.40 mg L−1 with a linear regression equation of I f  = −0.895 + 15.146c (R 2  > 0.9993), and the other over the range of 2.40–9.20 mg L−1 with a linear regression equation of I f  = −29.526 + 26.113c (R 2  > 0.9996), respectively. The relative standard deviation (R.S.D.) at 95% confidence degree for a 2.0 mg L−1 of standard phytic acid within 1 month was less than 1.26% (n  = 5), indicating the procedure is reproducible. The detection and the quantification limits of phytic acid were estimated to be 0.23 and 0.40 mg L−1, respectively. The proposed method was applied to the determination of phytic acid in urine samples and the found concentrations of phytic acid in urine were in the range of 0.49–0.75 mg L−1 with recoveries of 96.2–108.8%. Comparison of the obtained results with the reported HPLC was performed, indicating the proposed method was reliable.
Keywords: Determination; Fluorescence; Phytic acid; Replacement reaction;

Synthesis and applications of surface-grafted Th(IV)-imprinted polymers for selective solid-phase extraction of thorium(IV) by Qun He; Xijun Chang; Qiong Wu; Xinping Huang; Zheng Hu; Yunhui Zhai (192-197).
A new functional monomer N-(o-carboxyphenyl)maleamic acid (CPMA) was synthesized and chosen for the preparation of surface-grafted ion-imprinted polymers (IIPs) specific for thorium(IV). Polymerizable double bond was introduced to silica gel surface by amidation reaction between –NH2 and maleic anhydride. In the ion-imprinting process, thorium(IV) was complexed with the carboxyl groups, then was imprinted in the polymers grafted to the silica gel surface. The imprinted Th(IV) was removed with 3 mol L−1 HCl. The obtained imprinted particles exhibited excellent selectivity and rapid kinetics process for Th(IV). The relatively selective factor (α r) values of Th(IV)/La(III), Th(IV)/Ce(III), Th(IV)/Nd(III), Th(IV)/U(VI), and Th(IV)/Zr(IV) were 85.7, 88.9, 26.6, 64.4, and 433.8, respectively, which were greater than 1. The precision (R.S.D.), the detection limit (3σ), and the quantification limit (10σ) of the method were 1.9%, 0.51 ng mL−1 and 1.19 ng mL−1, respectively. The prepared IIPs as solid-phase extractants were successfully applied for the preconcentration of trace thorium in natural and certified samples prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES) with satisfactory results.
Keywords: Ion-imprinted polymers; N-(o-carboxyphenyl)maleamic acid; Solid-phase extraction; Inductively coupled plasma atomic emission spectrometry; Thorium(IV);

Acid-catalyzed isomerization and decomposition of ketone-2,4-dinitrophenylhydrazones by Shigehisa Uchiyama; Toshiro Kaneko; Hiroshi Tokunaga; Masanori Ando; Yasufumi Otsubo (198-204).
The quantitative analysis of ketones using DNPH is usually conducted in the presence of an acid catalyst. However, this method may cause an analytical error because 2,4-dinitrophenylhydrazones have both E- and Z-stereoisomers. Purified ketone-2,4-dinitrophenylhydrazone comprised only the E-isomer. However, under the addition of acid, both E- and Z-isomers were seen. In the case of 2-butanone-, 2-pentanone- and 2-hexanone-2,4-dinitrophenylhydrazone, the equilibrium Z/E isomer ratios were 0.20, 0.21 and 0.22, respectively. In addition, when trace water was added to the hydrazone derivatives in acetonitrile solution, the concentration of ketone derivatives were seen to decrease and the concentration of free DNPH was seen to increase. The decomposition rate of 2-butanone-2,4-dinitrophenylhydrazone was dependent on the concentration of acid-catalysis and reached an equilibrium state – carbonyl, DNPH, hydrazone-derivative and H2O – within 10 h at 0.1 mol L−1 phosphoric acid solution. The equilibrium constants of ketone-2,4-dinitrophenylhydrazones, [carbonyl] [DNPH]/[hydrazone] [H2O], were relatively large and ranged from 0.74 × 10−4 to 5.9 × 10−4. Hydrazone derivatives formed from 2-ketones such as 2-pentanone, 2-hexanone and 4-methyl-2-pentanone showed lower equilibrium constants than corresponding 3-ketones. Consequently, only a minimum concentration of catalytic acid must be added. The best method for the determination of ketone-2,4-dinitrophenylhydrazones by HPLC or GC is to add phosphoric acid to both the standard reference solution and samples, forming a 0.001 mol L−1 acid solution, and analyze after 27 h.
Keywords: 2,4-Dinitrophenylhydrazine; Ketones; 2,4-Dinitrophenylhydrazone; Isomerization; Equilibrium state;

We have developed and described a highly sensitive, accurate and precise reversed-phase high-performance liquid chromatography (RP-HPLC) method for the simultaneous determination of l-arginine and 12 molecules participating in its metabolic cycle in human urine samples. After pre-column derivatization with ortho-phthaldialdehyde (OPA) reagent containing 3-mercaptopropionic acid (3MPA), the fluorescent derivatives were separated by a gradient elution and detected by fluorescence measurement at 338 nm (excitation) and 455 nm (emission). l-Arginine (ARG) and its metabolites: l-glutamine (GLN), N G-hydroxy-l-arginine (NOHA), l-citrulline (CIT), N G-monomethyl-l-arginine (NMMA), l-homoarginine (HARG), asymmetric N G,N G-dimethyl-l-arginine (ADMA), symmetric N G,N G′-dimethyl-l-arginine (SDMA), l-ornithine (ORN), putrescine (PUT), agmatine (AGM), spermidine (SPERMD) and spermine (SPERM) were extracted in a cation-exchange solid-phase extraction (SPE) column and after derivatization separated in a Purospher® STAR RP-18e analytical column. The calibration curves of analysed compounds are linear within the range of concentration: 45–825, 0.2–15, 16–225, 12–285, 0.1–32, 15–235, 0.1–12, 0.1–12, 10–205, 0.02–12, 0.1–24, 0.01–10 and 0.01–8 nmol mL−1 for GLN, NOHA, CIT, ARG, NMMA, HARG, ADMA, SDMA, ORN, PUT, AGM, SPERMD and SPERM, respectively. The correlation coefficients are greater than 0.9980. Coefficients of variation are not higher than 6.0% for inter-day precision. The method has been determined or tested for limits of detection and quantification, linearity, precision, accuracy and recovery. All detection parameters of the method demonstrate that it is a reliable and efficient means of the comprehensive determination of ARG and its 12 main metabolites, making this approach suitable for routine clinical applications. The levels of analysed compounds in human urine can be successfully determined using this developed method with no matrix effect.
Keywords: l-Arginine; Metabolites; Human urine; Solid phase extraction; Ortho-phthaldialdehyde derivative; Validations;