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Analytica Chimica Acta (v.612, #1)
Mining in chemometrics by Lucia Mutihac; Radu Mutihac (pp. 1-18).
Some of the increasingly spread data mining methods in chemometrics like exploratory data analysis, artificial neural networks, pattern recognition, and digital image processing with their highs and lows along with some of their representative applications are discussed. The development of more complex analytical instruments and the need to cope with larger experimental data sets have demanded for new approaches in data analysis, which have led to advanced methods in experimental design and data processing. Hypothesis-driven methods typified by inferential statistics have been gradually complemented or even replaced by data-driven model-free methods that seek for structure in data without reference to the experimental protocol or prior hypotheses. The emphasis is put on the ability of data mining methods to solve multivariate–multiresponse problems on the basis of experimental data and minimal statistical assumptions only, in contrast to classical methods, which require predefined priors to be tested against some null-hypothesis.
Keywords: Chemometrics; Data mining; Exploratory analysis; Pattern recognition; Artificial neural networks; Inferential statistics; Hypothesis-driven methods; Data-driven methods
An entropy-based method for noise reduction of liquid chromatography–mass spectrometry data by Yunfei Li; Haibin Qu; Yiyu Cheng (pp. 19-22).
Entropy-based methods have been extensively used to measure the uncertainty information in a variety of fields. In this article, a novel information theory-based method for reducing noise of liquid chromatography–mass spectrometry (LC/MS) data was developed. The uncertainty existed in the LC/MS chromatograms was captured and evaluated by information entropy. By comparing the information entropy computationally derived from mass chromatograms, the good quality chromatograms and the noisy chromatograms can be distinguished. The proposed method was applied in processing LC/MS data of “Jing–Zhi–Guan–Xin” troche which is a well-known preparation of traditional Chinese medicine (TCM). The obtained result indicated that this method is beneficial to reduce noise of LC/MS data of complicated chemical samples, such as TCM.
Keywords: Liquid chromatography coupled with mass spectrometry; Noise reduction; Information entropy; Data processing
Bioelectrochemical immunoassay of polychlorinated biphenyl by Ying-Ying Lin; Guodong Liu; C.M. Wai; Yuehe Lin (pp. 23-28).
A simple, rapid, and highly sensitive bioelectrochemical immunoassay method based on magnetic beads (MBs) and disposable screen-printed electrodes (SPE) has been developed to detect polychlorinated biphenyls (PCBs). The principle of this bioassay is based on a direct competitive enzyme-linked immunosorbent assay using PCB-antibody-coated MBs and horseradish peroxidase (HRP)-labeled PCB (HRP–PCB). A magnetic process platform was used to mix and shake the samples during the immunoreactions and to separate free and unbound reagents after the liquid-phase competitive immunoreactions among PCB-antibody-coated MBs, PCB analyte, and HRP–PCB. After a complete immunoassay, the HRP tracers attached to MBs were transferred to a substrate solution containing o-aminophenol and hydrogen peroxide for electrochemical detection. The different parameters, including the amount of HRP–PCB conjugates, immunoreaction time, and the concentration of substrate that governs the analytical performance of the immunoassay have been studied in detail and optimized. The detection limit of 10pgmL−1 was obtained under optimum experimental conditions. The performance of this bioelectrochemical immunoassay was successfully evaluated with untreated river water spiked with PCBs, and the results were validated by commercial PCB enzyme-linked immunosorbent assay kit, indicating that this convenient and sensitive technique offers great promise for decentralized environmental application and trace PCBs monitoring.
Keywords: Polychlorinated biphenyls; Immunoassay; Screen-printed electrodes
A highly sensitive amperometric sensor for oxygen based on iron(II) tetrasulfonated phthalocyanine and iron(III) tetra-( N-methyl-pyridyl)-porphyrin multilayers by Juliana C. Duarte; Rita C.S. Luz; Flavio S. Damos; Auro A. Tanaka; Lauro T. Kubota (pp. 29-36).
The development of a highly sensitive sensor for oxygen is proposed using a glassy carbon (GC) electrode modified with alternated layers of iron(II) tetrasulfonated phthalocyanine (FeTsPc) and iron(III) tetra-( N-methyl-pyridyl)-porphyrin (FeT4MPyP). The modified electrode showed excellent catalytic activity for the oxygen reduction. The reduction potential of the oxygen was shifted about 330mV toward less negative values with this modified electrode, presenting a peak current much higher than those observed on a bare GC electrode. Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the oxygen reduction reaction involves 4 electrons with a heterogenous rate constant ( kobs) of 3×105mol−1Ls−1. A linear response range from 0.2 up to 6.4mgL−1, with a sensitivity of 4.12μALmg−1 (or 20.65μAcm−2Lmg−1) and a detection limit of 0.06mgL−1 were obtained with this sensor. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation (R.S.D.) was 2.0% for 10 measurements of a solution of 6.4mgL−1 oxygen. The sensor was applied to determine oxygen in pond and tap water samples showing to be a promising tool for this purpose.
Keywords: Oxygen; Iron(II) tetrasulfonated phthalocyanine; Iron(III) tetra-(; N; -methyl-pyridyl)-porphyrin; Multilayers; Amperometric sensor
Application of liquid–liquid–liquid microextraction and high-performance liquid-chromatography for the determination of sulfonamides in water by Che-Yi Lin; Shang-Da Huang (pp. 37-43).
This work presents a novel liquid–liquid–liquid microextraction (LLLME) technique for the extraction of sulfonamides from aqueous systems; it combines with high-performance liquid-chromatography-ultraviolet absorbance detection (HPLC/UV). In this experiment the sulfonamides were successively extracted from a donor phase (i.e., a water sample) into several microliters of an organic phase and then from the organic phase into an acceptor phase (i.e., an aqueous extract) by LLLME. The following separation and quantitative analyses were performed using HPLC/UV with 265nm detection. Extraction condition such as solvent identity, agitation, extraction time, acceptor phase NaOH concentration, donor phase pH, and salt addition were optimized. Relative standard deviation (RSD, 2.6–5.3%), coefficient of estimation ( R2, 0.9972–0.9999), and method detection limit (MDL, 0.11–0.77ngmL−1) were achieved under the selected conditions. The proposed method was successfully applied to the analyses of three practical water samples and the relative recoveries of sulfonamides from the spiked water samples were in the range of 86.2–108.7%. The proposed method also confirms microextraction to be robust to monitoring trace levels of sulfacetamide, sulfadiazine, sulfathiazole, sulfamerazine, sulfadimidine, sulfamonomethoxine, sulfamethoxazole, and sulfaquinoxaline in aqueous samples.
Keywords: Liquid–liquid–liquid microextraction; Sulfonamides; Trace analysis; High-performance liquid-chromatography
Comparison of low-level polycyclic aromatic hydrocarbons in sediment revealed by Soxhlet extraction, microwave-assisted extraction, and pressurized liquid extraction by Nobuyasu Itoh; Masahiko Numata; Yoshie Aoyagi; Takashi Yarita (pp. 44-52).
We analyzed polycyclic aromatic hydrocarbons (PAHs) present in lake sediment at low levels (<1μgg−1) by using Soxhlet extraction (Soxhlet), microwave-assisted extraction (MAE), and pressurized liquid extraction (PLE) in combination with gas chromatography and isotope-dilution mass spectrometry. Although all extraction techniques showed good repeatability for five target PAHs (relative standard deviation <5.2%, n=3), the results decreased in the order PLE>MAE>Soxhlet. Differences in the results originated mainly from differences in the extraction efficiencies of the techniques for native PAHs, because all techniques gave comparable recovery yields of corresponding13C-labeled PAHs (13C-PAHs) (51–84%). Since non-negligible amounts of both native PAHs and13C-PAHs were re-adsorbed on matrix in MAE, not only recovery yields of13C-PAHs but also efficiencies of extraction of native PAHs should be examined to evaluate the appropriateness of any analytical procedures.
Keywords: Polycyclic aromatic hydrocarbons (PAHs); Pressurized liquid extraction (PLE); Microwave-assisted extraction (MAE); Soxhlet extraction; Isotope-dilution mass spectrometry (IDMS)
Spectrophotometric determination of cyclotrimethylenetrinitramine (RDX) in explosive mixtures and residues with the Berthelot reaction by A. Üzer; E. Erçağ; R. Apak (pp. 53-64).
On-site colorimetric methods are a valuable, cost-effective tool to assess the nature and extent of contamination in remediated sites and to enable on-site screening for police criminology laboratories. The existing colorimetric method for cyclotrimethylenetrinitramine (RDX) based on a Griess reaction suffers from the non-quantitative reduction to nitrite and from the unstable character of HNO2 in acidic medium. Thus we propose a novel spectrophotometric RDX assay in explosive mixtures and residues, based on (Zn+HCl) reduction of RDX in a microwave oven, followed by neutralization of the reduction products to ammonia and low molecular-weight amines, and Berthelot reaction of these amine-compounds with phenol and hypochlorite in alkaline medium to give an intensely blue indophenol dye absorbing at 631nm. The molar absorptivity and limit of detection (LOD) for RDX were (1.08±0.04)×104Lmol−1cm−1 and 0.18mgL−1, respectively. Application of the method to synthetic mixture solutions of RDX and trinitrotoluene (TNT) at varying proportions showed that there was minimal interference from TNT (which could be compensated for by dicyclohexylamine colorimetry), since the Berthelot reaction was essentially non-responsive to m-substituted anilines derived from TNT upon (Zn+HCl) reduction. The proposed method was successfully applied to military-purpose explosive mixtures of (RDX+inert matter) such as Comp A5, Comp C4, and Hexal P30, and to (RDX+TNT) mixtures such as Comp B. The molar absorptivity of RDX was much higher than that of either ammonium or nitrate; RDX could be effectively separated from ammonium and nitrate in soil mixtures, based on solubility differences. The Berthelot method for RDX was statistically validated using Comp B mixtures against standard HPLC equipped with a Hypersil C-18 column with (40% MeOH–60% H2O) mobile phase, and against gas chromatography–thermal energy analysis (GC–TEA) system.
Keywords: Royal Demolition eXplosive (RDX) Assay; Cyclotrimethylenetrinitramine; Berthelot reaction; Spectrophotometry; Nitro-explosives; Trinitrotoluene
Molecularly imprinted polymer based potentiometric sensor for the determination of hydroxyzine in tablets and biological fluids by Mehran Javanbakht; Solmaz Eynollahi Fard; Ali Mohammadi; Majid Abdouss; Mohammad Reza Ganjali; Parviz Norouzi; Leila Safaraliee (pp. 65-74).
Molecular imprinting is a useful technique for the preparation of functional materials with molecular recognition properties. In this work, a biomimetic potentiometric sensor, based on a non-covalent imprinted polymer, was fabricated for the recognition and determination of hydroxyzine in tablets and biological fluids. The molecularly imprinted polymer (MIP) was synthesized by precipitation polymerization, using hydroxyzine dihydrochloride as a template molecule, methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylat (EGDMA) as a cross-linking agent. The sensor showed a high selectivity and a sensitive response to the template in aqueous system. The MIP-modified electrode exhibited a Nernstian response (29.4±1.0mVdecade−1) in a wide concentration range of 1.0×10−6 to 1.0×10−1M with a lower detection limit of 7.0×10−7M. The electrode demonstrated a response time of ∼15s, a high performance and a satisfactory long-term stability (more than 5 months). The method has the requisite accuracy, sensitivity and precision to assay hydroxyzine in tablets and biological fluids.
Keywords: Molecularly imprinted polymer; Potentiometric; Carbon paste electrode; Hydroxyzine; Biological fluids; Tablets
A novel approach based on ferricyanide-mediator immobilized in an ion-exchangeable biosensing film for the determination of biochemical oxygen demand by Hailing Chen; Tingxiu Ye; Bin Qiu; Guonan Chen; Xi Chen (pp. 75-82).
A novel biochemical oxygen demand (BOD) sensing method employing a ferricyanide (FC) mediator immobilized in an ion-exchangeable polysiloxane was developed. The ion-exchangeable polysiloxane containing alkylammonium groups (PAPS-Cl) was synthesized by sol–gel reaction of 3-(aminopropyl)trimethoxysilane (APTMOS) catalyzed by hydrochloric acid. FC was combined in PAPS-Cl via ion-association and the product was labeled as PAPS-FC, which was employed for a modified glassy carbon electrode. The apparent diffusion coefficient ( Dapp) of FC on the modified glassy carbon electrode was 9.8×10−11cm2s−1. In a three-electrode system, a linear relationship between the anodic current responses and glucose/glutamate (GGA) concentration was obtained up to 40mgO2L−1 ( r=0.994) when the reaction mixture was incubated for 30min. Single sensor and piece-to-piece reproducibility were less than 3.8 and 7.7%, respectively. The effects of dissolved oxygen, pH, temperature and co-existing substances on the BOD responses were studied. The sensor responses to nine pure organic substances were compared with the conventional BOD5 method and other biosensor methods. Detection results of seawater samples were compared with those obtained from the BOD5 method and showed a good correlation ( r=0.988).
Keywords: Biochemical oxygen demand; Ferricyanide; Polysiloxane; Ion-association; Seawater
A liposome immune lysis assay for enrofloxacin in carp and chicken muscle by Suxia Zhang; Zhongwei Liu; Naiyuan Zhou; Zhanhui Wang; Jianzhong Shen (pp. 83-88).
A homogenous complement-mediated liposome immune lysis assay (LILA) was developed for the determination of enrofloxacin (ENRO) in carp and chicken muscle. ENRO was covalently coupled to DPPE, and then immobilized onto the surface of liposomes by reverse-phase evaporation method. The performed liposome would be specifically lysed by the sequential additions of anti-ENRO monoclonal antibody (MAb) and guinea pig complement. Through a competitive assay format, the performed liposome can be used to detect ENRO in a range of 5.0–20ngmL−1 in assay buffer. The limit of detection of ENRO in carp and chicken muscle was 1ngg−1 and the limit of quantification was 2ngg−1. Recoveries ranged from 58.3% to 65.2% for carp and 55.6–63.8% for chicken muscle at spiked levels of 2–8ngg−1, with intra-assay and inter-assay variations 5.6–12.3% and 7.1–19.2%, respectively.
Keywords: Liposome; Immunoassay; Complement; Enrofloxacin; Carp; Chicken muscle
Simultaneous voltammetric detection of ascorbic acid, dopamine and uric acid using a pyrolytic graphite electrode modified into dopamine solution by Robson P. da Silva; Antonio William O. Lima; Silvia H.P. Serrano (pp. 89-98).
Pyrolytic graphite electrodes (PGE) were modified into dopamine solutions using phosphate buffer solutions, pH 10 and 6.5, as supporting electrolyte. The modification process involved a previous anodization of the working electrode at +1.5V into 0.1molL−1 NaOH followed by other anodization step, in the same experimental conditions, into dopamine (DA) solutions. pH of the supporting electrolyte performed an important role in the production of a superficial melanin polymeric film, which permitted the simultaneous detection of ascorbic acid (AA), (DA) and uric acid (UA), Δ EAA–DA=222mV; Δ EAA–UA=360mV and Δ EDA–UA=138mV, avoiding the superficial poisoning effects. The calculated detection limits were: 1.4×10−6molL−1 for uric acid, 1.3×10−5molL−1 for ascorbic acid and 1.1×10−7molL−1 for dopamine, with sensitivities of (7.7±0.5), (0.061±0.001) and (9.5±0.05)Amol−1cm−2, respectively, with no mutual interference. Uric acid was determined in urine, blood and serum human samples after dilution in phosphate buffer and no additional sample pre-treatment was necessary. The concentration of uric acid in urine was higher than the values found in blood and serum and the recovery tests (92–102%) indicated that no matrix effects were observed.
Keywords: Pyrolytic graphite modified electrode; Uric and ascorbic acids; Dopamine; Biological fluids; Differential pulse voltammetry
Preliminary evaluation of new polymer matrix for solid-phase extraction of nonylphenol from water samples by António Guerreiro; Ana Soares; Elena Piletska; Bo Mattiasson; Sergey Piletsky (pp. 99-104).
Molecularly imprinted (MIP) and blank polymers with affinity for nonylphenol were designed using computational modelling. Chromatographic tests demonstrated higher affinity of imprinted polymers towards the template nonylphenol as compared with blank polymers. The performance of both polymers in solid-phase extraction was however very similar. Both blank and imprinted polymers appeared to be suitable for the removal and pre-concentration of nonylphenol from contaminated water samples with 99% efficiency of the recovery. The commercial resins PH(EC) (Biotage) and C18 (Varian) tested in the same conditions used for comparative purposes had recovery rate <84%. The polymer capacity for nonylphenol was 231mgg−1 for blank and 228mgg−1 for MIP. The synthesised materials can have significance for sample pre-concentration and environmental analysis of this class of compounds.
Keywords: Nonylphenol; Computational design; Molecularly imprinted polymer
Narrowly dispersed molecularly imprinted microspheres prepared by a modified precipitation polymerization method by Yuan Jin; Ming Jiang; Yun Shi; Yi Lin; Yan Peng; Kang Dai; Bin Lu (pp. 105-113).
A modified precipitation polymerization (MPP) method was established to prepare narrowly dispersed molecularly imprinted polymeric microspheres. MPP was stabilizer and surfactant free and needed only small amount of porogen (about 50wt.%). Only part of alcohols and all the alkanes tested formed particles. Using a mixture of alkane and toluene as porogen, the carbon numbers of alkanes and solubility parameter of porogenic solvents were important factors in controlling particle morphology. Nearly mono-dispersed microspheres with diameter of about 2–3μm were synthesized by MPP using mineral oil:toluene=2:3 as porogen. Template did not affect the formation of globe microspheres in MPP. Microspheres prepared under the lowest reaction temperature had the highest binding capability. When used as sorbents of high performance liquid chromatography (HPLC), the microspheres prepared by MPP using bisphenol A, estradiol, and tebuconazole as template had similar binding selectivity and higher binding capability compared to microspheres synthesized by classical precipitation polymerization. Photoinitiation and low reaction temperature were important factors attributed to better binding capability of microspheres prepared by MPP.
Keywords: Molecularly imprinted polymers; Modified precipitation polymerization; Microspheres; Bisphenol A; High performance liquid chromatography
Precise determination of cadmium and lead isotopic compositions in river sediments by Bo Gao; Ying Liu; Ke Sun; Xirong Liang; Ping’an Peng; Guoying Sheng; Jiamo Fu (pp. 114-120).
A method for the accurate determination of Cd and Pb isotope compositions in sediment samples is presented. Separation of Cd and Pb was designed by using an anionic exchange chromatographic procedure. Measurements of Cd isotopic compositions were carried out by multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS), by using standard-sample bracketing technology for mass bias correction and Pb isotopic ratios were determined by thermal ionization mass spectrometry (TIMS). The factors that affect the accurate and precise Cd isotope compositions analysis, such as instrumental mass fractionation and isobaric interferences, were carefully evaluated and corrected. The Cd isotopic results were reported relative to an internal Cd solution and expressed as the δ114/110Cd. Five Cd reference solutions and one Pb standard were repeatedly measured in order to assess the accuracy of the measurements. Uncertainties obtained were estimated to be lesser than 0.11‰ (2s) for the δ114/110Cd value. Analytical uncertainties in 2s for Pb isotopic ratios were better than 0.5‰. The method has been successfully applied to the investigation of Cd and Pb isotope compositions in sediment samples collected from North River in south China.
Keywords: Cadmium; Lead; Isotopic analysis; Anion-exchange; Sediments