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Analytica Chimica Acta (v.644, #1-2)

Editorial Board (pp. iii).

Multi-element quantification of ancient/historic glasses by laser ablation inductively coupled plasma mass spectrometry using sum normalization calibration by Johannes T. van Elteren; Norman H. Tennent; Vid S. Šelih (pp. 1-9).

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for quantitative analysis of ancient/historic glasses is subject to calibration issues which have been addressed in this work. Since ancient/historic glasses have widely ranging matrix compositions, a complementary analysis by an alternative method is generally employed to determine at least one major element which can be used as an internal standard. We demonstrate that such a complementary analysis is unnecessary using a so-called sum normalization calibration technique (mathematically formulated) by simultaneous measurement of 54 elements and normalizing them to 100% [w/w] based on their corresponding oxide concentrations. The crux of this approach is that by assuming a random internal standard concentration of a particular major oxide, e.g. SiO₂, the normalization algorithm varies the internal standard concentration until the cumulated concentrations of all 54 elemental oxides reach 100% [w/w]. The fact that 54 elements are measured simultaneously predetermines the laser ablation mode to rastering. Nine glass standards, some replicating historic compositions, were used for calibration. The linearity of the calibration graphs (forced through the origin) represented by the relative standard deviations in the slope were between 0.1 and 6.6% using SiO₂ as an internal standard. This allows high-accuracy determination of elemental oxides as confirmed by good agreement between found and reported values for major and minor elemental oxides in some synthetic glasses with typical medieval composition (European Science Foundation 151 and 158). Also for trace elemental concentrations of lanthanides in a reference glass (P&H Developments Ltd. DLH7, a base glass composition with nominally 75μgg⁻¹ elements added) accurate data were obtained.Interferences from polyatomic species and doubly charged species on the masses of trace elements are possible, depending on the base composition of the glass, with Ba and Sb glasses showing potential interferences on some lanthanides. We showed that they may be reduced to a great extent by using an Octopole Reaction System although the overall sensitivity decreases which may be a problem for some low-level determinations.

Keywords: Laser ablation; Glasses; Calibration; Internal standardization; Interferences; Oxides normalization; Scaling algorithm

Predicting liquid chromatographic retention times of peptides from the Drosophila melanogaster proteome by machine learning approaches by Feifei Tian; Li Yang; Fenglin Lv; Peng Zhou (pp. 10-16).

Three machine learning algorithms as least-squares support vector machine (LSSVM), random forest (RF) and Gaussian process (GP) were used to model the quantitative structure–retention relationship (QSRR) for predicting and explaining the retention behavior of proteome-wide peptides in the reverse-phase liquid chromatography. Peptides were parameterized using CODESSA approach and 145 descriptors were obtained for each peptide, including diverse structural information such as constitutional, topological, geometrical and physicochemical property. Based upon that, the nonlinear LSSVM, RF and GP as well as another sophisticated linear method (partial least-squares regression (PLS)) were employed in the QSRR model development. By a series of systematic validations as internal cross-validation, external test and Monte Carlo cross-validation, the stability and predictive power of the constructed models were confirmed. Results show that regression models developed using nonlinear approaches such as LSSVM, RF and GP predict better than linear PLS models. Considering the retention times used in this work were measured in different columns and thus have a relatively large uncertainty (reproducibility within 7%), the optimal statistics obtained from GP modeling are satisfactory, with the coefficients of determination ( R²) for training set and test set of 0.894 and 0.866, respectively.

Keywords: Least-squares support vector machine; Random forest; Gaussian process; Peptide; Liquid chromatography; Quantitative structure–retention relationship

Global, local and novel consensus quantitative structure-activity relationship studies of 4-(Phenylaminomethylene) isoquinoline-1, 3 (2 H, 4 H)-diones as potent inhibitors of the cyclin-dependent kinase 4 by Beilei Lei; Lili Xi; Jiazhong Li; Huanxiang Liu; Xiaojun Yao (pp. 17-24).

Quantitative structure-activity relationship (QSAR) studies on a series of selective inhibitors of the cyclin-dependent kinase 4 (CDK4) were performed by using two conventional global modeling methods (multiple linear regression (MLR) and support vector machine (SVM)), local lazy regression (LLR) as well as three consensus models. It is remarkable that the LLR model could improve the performance of the QSAR model significantly. In addition, due to the fact that each model can predict certain compounds more accurately than other models, the above three derived models were all used as submodels to build consensus models using three different strategies: average consensus model (ACM), simple weighted consensus model (SWCM) and hat weighted consensus model (HWCM). Through the analysis of the results, the HWCM consensus strategy, firstly proposed in this work, proved to be more reliable and robust than the best single LLR model, ACM and SWCM models.

Keywords: Cyclin-dependent kinase 4 (CDK4); Quantitative structure-activity relationship (QSAR); Local lazy regression (LLR); Consensus models

Parallel calibration revisited: The second direction for shrinkage estimation of regression coefficients can be as natural and necessary as the traditional one by Lu Xu; Xiao-Ping Yu; Xiu-Lian Lu; Yi-Hang Wu; Hai-Long Wu; Jian-Hui Jiang; Guo-Li Shen; Ru-Qin Yu (pp. 25-29).

In the traditional framework of multivariate spectroscopic calibration, the most popular method, partial least squares (PLS), shrinks the regression coefficients based on the information of training sample concentrations. Motivated by the concept of parallel calibration, the second direction for shrinkage of regression coefficients, the direction towards unknown sample spectra is investigated in this paper. A different multivariate calibration method, parallel calibration model based on partial least squares, PCPLS is proposed. With both theoretical support and analysis of some real data sets, it is demonstrated that the second shrinkage direction is at least as natural and necessary as the traditional one. An interesting difference of the proposed method from traditional methods is the involvement of unknown sample spectra and consideration of their error in the training process. Some new related problems and potential applications of this method are also briefly discussed.

Keywords: Multivariate calibration; Parallel calibration; Regression coefficients shrinkage; Partial least squares; Unknown sample spectra

Metalloporphyrin-based acetate-selective electrodes as detectors for enzymatic acetylcholine determination in flow-injection analysis system by Łukasz Górski; Monika Mroczkiewicz; Mariusz Pietrzak; Elżbieta Malinowska (pp. 30-35).

In this work two Zr(IV)-porphyrins were tested as potential acetate-selective ionophores. It is shown that these compounds show increased selectivity towards acetate ion, with selectivity sequence: Cl⁻3⁻−4⁻−−, when incorporated into polymeric ion-selective membranes. Among tested ionophores, Zr(IV)-tetra(tert-butylphenyl)porphyrin was found to be the best in terms of response time (20s) and lower detection limit (2×10⁻⁴M acetate⁻).Designed electrodes were used as detectors in flow-injection analysis system for acetylcholine determination. Enzymatic hydrolysis was used to generate acetate ions from acetylcholine, employing acetylcholinesterase immobilized on Amberlite. The optimization of enzymatic reactions and flow-injection analysis system configuration were performed and enzyme immobilization procedures have been evaluated. It is shown that resulting flow-injection system exhibits good working parameters, such as reproducibility (standard deviation ≤3.5%), sampling rate (60 samples per hour) and lifetime (over a week).

Keywords: Potentiometry; Acetate; Polymeric-membrane ion-selective electrodes; Acetylcholine; Flow-injection analysis

A rapid and simple method for ultrasensitive electrochemical immunoassay of protein by an electric field-driven strategy by Feng Yan; Jie Wu; Fang Tan; Yuetian Yan; Huangxian Ju (pp. 36-41).

A sensitive, rapid and simple method for analysis of protein was proposed by introducing an electric field-driven technique to the incubation process of immunoassay and immobilizing horseradish peroxidase (HRP) labeled antibody in a newly designed gel matrix to construct an immunosensor. With an electric field-driven technique, the incubation for immuno-recognition could be completed within 2min. The immobilized HRP showed excellent direct electrochemistry in this new gel matrix, and the detection procedure was greatly simplified by directly monitoring the sensitive electrochemical signal of HRP upon the immunoreaction. Using α-fetoprotein as a model the linear detection range was from 0.02 to 2.0ngmL⁻¹ with a detection limit down to 138amolmL⁻¹. The immunosensor and the proposed detection method showed good specificity and acceptable stability and accuracy.

Keywords: Biosensors; Immunoassay; Electric field driving; Protein; α-Fetoprotein; Signal amplification

Synthesis and characterization of UO₂²⁺-ion imprinted polymer for selective extraction of UO₂²⁺ by Dhruv K. Singh; Shraddha Mishra (pp. 42-47).

Ion-imprinted polymers (IIPs) were prepared for uranyl ion (imprint ion) by formation of binary (salicylaldoxime (SALO) or 4-vinylpyridine (VP)) or ternary (salicylaldoxime and 4-vinylpyridine) complex in 2-methoxy ethanol (porogen) following copolymerization with methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking monomer using 2,2′-azobisisobutyronitrile as initiator. Control polymers (CPs) were also prepared under identical experimental conditions without using imprint ion. The above synthesized polymers were characterized by surface area measurement, microanalysis and FT-IR analysis techniques. The imprinted polymer formed with ternary complex of UO₂²⁺–SALO–VP (1:2:2, IIP₃) showed quantitative enrichment of uranyl ion from dilute aqueous solution and hence was chosen for detailed studies. The optimal pH for quantitative enrichment is 3.5–6.5. The adsorbed UO₂²⁺ was completely eluted with 10mL of 1.0M HCl. The retention capacity of IIP₃ was found to be 0.559mmolg⁻¹. Further, the distribution ratio and selectivity coefficients of uranium and other selected inorganic ions were also evaluated. Five replicate determinations of 25μgL⁻¹ of uranium(VI) gave a mean absorbance of 0.032 with a relative standard deviation of 2.20%. The detection limit corresponding to three times the standard deviation of the blank was found to be 5μgL⁻¹. IIP₃ was tested for preconcentration of uranium(VI) from ground, river and sea water samples.

Keywords: Ion-imprinted polymer; Salicylaldoxime; Uranyl ion; Preconcentration; Ternary complex

Ultra-trace determination of lead in water and food samples by using ionic liquid-based single drop microextraction-electrothermal atomic absorption spectrometry by Jamshid L. Manzoori; Mohammad Amjadi; Jafar Abulhassani (pp. 48-52).

An improved single drop microextraction procedure was developed for the preconcentration of lead prior to its determination by electrothermal atomic absorption spectrometry. Ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C₄MIM][PF₆], was used as an alternative to volatile organic solvents for extraction. Lead was complexed with ammonium pyrroldinedithiocarbamate (APDC) and extracted into a 7-μL ionic liquid drop. The extracted complex was directly injected into the graphite furnace. Several variables affecting microextraction efficiency and ETAAS signal, such as pyrolysis and atomization temperature, pH, APDC concentration, extraction time, drop volume and stirring rate were investigated and optimized. In the optimum experimental conditions, the limit of detection (3 s) and the enhancement factor were 0.015μgL⁻¹ and 76, respectively. The relative standard deviation (RSD) for five replicate determinations of 0.2μgL⁻¹ Pb was 5.2%. The developed method was validated by the analysis of certified reference materials and applied successfully to the determination of lead in several real samples.

Keywords: Single drop microextraction; Ionic liquid; Lead; Electrothermal atomic absorption spectrometry

Detection of nanomolar concentrations of copper(II) with a Tb-quinoline-2-one probe using luminescence quenching or luminescence decay time by Matejka Turel; Axel Duerkop; Alla Yegorova; Yulia Scripinets; Aleksandra Lobnik; Niko Samec (pp. 53-60).

We present a time-resolved (gated) luminescence-based method for determination of Cu²⁺ ions in microtiterplate format in the nanomolar concentration range using the novel long-lived terbium-[1-methyl-4-hydroxy-3-(N-2-ethyl-5-aminothiadiazolyl-)-carbamoyl-quinoline-2-one] (TbL) complex. The probe works best in Tb:L=1:2 stoichiometry at neutral pH. The dynamic range is from 10 to 300nmolL⁻¹ of Cu²⁺ and the limit of detection is 4.3nmolL⁻¹. This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for copper. It is shown that gating can efficiently suppress intense, short decaying background fluorescence e.g. that of Rhodamine 6G. The assay can be performed by measurement of luminescence decay time, as well. Stern-Volmer studies indicate that static quenching dominates over dynamic quenching. TbL₂ was tested for the effect of some relevant interferents and the assay was applied to the determination of copper in tap water samples. The results achieved were in good agreement with those of a reference method.

Keywords: Terbium-complex; Copper; Luminescence; Decay time; Assay

Carbon nanostructures as catalytic support for chemiluminescence of sulfur compounds in a molecular emission cavity analysis system by Afsaneh Safavi; Norouz Maleki; Mohammad Mahdi Doroodmand; Mohammad Mehdi Koleini (pp. 61-67).

The effect of different substrates including stainless steel, activated carbon, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), fullerenes (C₆₀, C₇₀, etc.) and SWCNTs doped with iron and palladium nanoparticles were compared for catalytic chemiluminescence reaction of sulfur compounds in a flame-containing cavity of molecular emission cavity analysis (MECA) system. Different forms of CNT substrates were fabricated using electric arc-discharge method. The blue emission of excited S₂ was monitored using a CCD camera. The results demonstrate that, due to the high surface area, plenty of basal planes, high thermal conductivity, and high flexibility of the carbon nanostructure as appropriate support, carbon nanostructures play an important role in catalytic chemiluminescence emission of sulfur compounds in MECA. Moreover, the presence of metallic nanoparticles doped on carbon nanostructures enhances their catalytic effect. The results revealed that under similar conditions, SWCNTs/Pd doped nanoparticles, SWCNTs/Fe doped nanoparticles, SWCNTs, MWCNTs and fullerenes have the most catalytic effects on chemiluminescence of sulfur compounds, respectively.

Keywords: Carbon nanostructures; Nanoparticles; Chemiluminescence; MECA

Off-line FIA monitoring ofd-sorbitol consumption duringl-sorbose production using a sorbitol biosensor by Jana Šefčovičová; Alica Vikartovská; Vladimír Pätoprstý; Peter Magdolen; Jaroslav Katrlík; Jan Tkac; Peter Gemeiner (pp. 68-71).

A ferricyanide mediated amperometric biosensor system implementingd-sorbitol dehydrogenase together with diaphorase for sensitive detection ofd-sorbitol was used. The biosensor system was successfully integrated into an off-line FIA system with a throughput of detection of 10h⁻¹. The device exhibited limit of detection of 20μM with an average relative standard deviation of analysis of samples of 2.2%. The signal of the biosensor was linear up to 1.1mM ford-sorbitol with sensitivity of (72±2)nAmM⁻¹, while a dynamic range was much wider up to 18mM. The sorbitol biosensor gave reliable results even in the presence of a high molar excess ofl-sorbose, a product of the biotransformation process, as judged from an excellent agreement with HPLC and GC.

Keywords: Biosensor; d; -Sorbitol; d; -Sorbitol dehydrogenase; Gluconobacter oxydans; l; -Sorbose; Off-line flow injection analysis

The preparation of reagentless electrochemical immunosensor based on a nano-gold and chitosan hybrid film for human chorionic gonadotrophin by Guangming Yang; Yanbing Chang; Hua Yang; Lin Tan; Zaisheng Wu; Xuxiao Lu; Yunhui Yang (pp. 72-77).

A novel amperometric immunosensor for determination of human serum chorionic gonadotrophin (hCG) was constructed by immobilizing hCG antibody with nano-gold and chitosan (CHIT) hybrid film electrochemical co-deposited on a glassy carbon electrode. The fabricated procedures and electrochemical behaviors of proteins on such an interface were characterized with electrochemical impedance, cyclic voltammetry and chronoamperometry. The effect of incubation time on the electrochemical behavior of immunosensor was studied and other experimental conditions such as mass ratio of CHIT and HAuCl₄, depositing time of hybrid film, the pH, and temperature were studied too. The current response of the immunosensor is in linear relationship with concentration of hCG. The resulting immunosensor offers an excellent amperometric response for hCG ranging from 0.20 to 100mIUmL⁻¹ with a detection limit of 0.1mIUmL⁻¹. A satisfactory determination of hCG in serum samples can be obtained by this immunosensor.

Keywords: Human chorionic gonadotrophin; Hybrid nanofilm; Gold; Chitosan; Immunosensor

DNA based gold nanoparticles colorimetric sensors for sensitive and selective detection of Ag(I) ions by Bingling Li; Yan Du; Shaojun Dong (pp. 78-82).

In this work, we reported both unlabeled and labeled sensing strategies for Ag(I) ions detection by using the DNA based gold nanoparticles (AuNPs) colorimetric method. In the unlabeled strategy, C-base riched single strand DNA (C-ssDNA) enwinded onto AuNPs to form AuNPs/C-ssDNA complex. In the labeled method, sulfhydryl group modified C-ssDNA (HS-C-ssDNA) was covalently labeled on AuNPs to produce AuNPs-S-C-ssDNA complex. In both strategies, C-ssDNA or HS-C-ssDNA could enhance the AuNPs stability against the salt-induced aggregation. However, the presence of Ag(I) ions in the obtained AuNPs/C-ssDNA or AuNPs-S-C-ssDNA complex would decrease such stability to display purple even blue colors due to the formation of Ag(I) ions mediated C-Ag(I)-C base pairs. Through this phenomenon, Ag(I) ions could be detected qualitatively and quantitatively using both unlabeled and labeled sensing strategies. Compared with the labeled method, the unlabeled strategy avoided the label and separation steps in common sensors, which may thus save both the time and cost for the detection. Nevertheless, the labeled strategy provided more sensitive, stable and controllable sensing results compared with the unlabeled method. By the labeled strategy, 12nM Ag(I) ions could be observed directly by naked eyes, and the lowest detectable concentration of 0.59nM was gotten under by the UV–vis spectra measurement, which was one of the most sensitive results among DNA based AuNPs colorimetric sensors for metal ions.

Keywords: Colorimetric sensors; Gold nanoparticles; Ag(I) ions; Deoxyribonucleic acid (DNA); Cytosine base

Direct electrochemistry and electrocatalysis of hemoglobin at three-dimensional gold film electrode modified with self-assembled monolayers of 3-mercaptopropylphosphonic acid by Yu Chen; Xiao-Jing Yang; Li-Rong Guo; Jing Li; Xing-Hua Xia; Li-Min Zheng (pp. 83-89).

Multilayered hemoglobin (Hb) molecules were successfully immobilized on three-dimensional gold film electrode modified with self-assembled monolayers (SAMs) of 3-mercaptopropylphosphonic acid. Direct electrochemistry of the immobilized multilayered Hb occurs with high thermal stability and electrochemical stability. In the multilayered Hb film, the most inner Hb molecules can directly transfer electron with the electrode, while the Hb protein beyond this layer communicates electron with the electrode via protein–protein electron exchange. In addition, the proposed functional interface can greatly enhance electron transfer rate of the immobilized Hb protein ( k_s=15.8±2.0s⁻¹) due to the increase of roughness of the gold substrate. Under optimized experimental conditions, the multilayered Hb film displays good bioelectrocatalytic activity toward the reduction of hydrogen peroxide. This electrochemical sensor shows fast response (less than 1s), wide linear range (7.8×10⁻⁸ to 9.1×10⁻⁵M) and low detection limit (2.5×10⁻⁸M), which can be attributed to good mass transport, large Hb proteins loading per unit area and fast electron transfer rate of Hb protein.

Keywords: Hemoglobin; Direct electrochemistry; Self-assembled monolayers; Stability; Biosensors

Measurement of plasma free choline by high performance liquid chromatography with fluorescence detection following derivatization with 1-naphthyl isocyanate by Christopher J. McEntyre; Sandy Slow; Michael Lever (pp. 90-94).

Choline is an essential nutrient which is difficult to measure because it has no native absorbance or fluorescence and only relatively unreactive functional groups. The method described here uses the reaction of the hydroxyl group on choline with 1-naphthyl isocyanate to form a stable cationic aromatic urethane that can be measured by high performance liquid chromatography (HPLC) on a cation exchange column, followed by fluorescence detection. The sample was directly added to acetonitrile and mixed with magnesium oxide and 1-naphthyl isocyanate. The 1-naphthylurethane choline derivative was separated by HPLC using a strong cation exchange column with a tetramethylammonium glycolate buffer in the mobile phase, and measured by fluorescence detection. The recoveries from blood plasma were over 94%. In this study an internal standard was not used, and quantification was achieved by calibration using standards containing known choline concentrations. The within batch and between batch coefficients of variation (CVs) were below 6%. The response was linear over the biological range investigated (8.9–58.9μmolL⁻¹, r²=0.998). This is a technically simple method that can be carried out with an inexpensive HPLC system with fluorescence detection. It has sufficient sensitivity to measure choline in biological materials such as human plasma, and is suitable for processing batches of samples.

Keywords: Choline; Hydroxyl group; Urethane derivatives; 1-Naphthyl isocyanate; High performance liquid chromatography; Cation exchange; Fluorescence detection

New 3-D microarray platform based on macroporous polymer monoliths by M. Rober; J. Walter; E. Vlakh; F. Stahl; C. Kasper; T. Tennikova (pp. 95-103).

Polymer macroporous monoliths are widely used as efficient sorbents in different, mostly dynamic, interphase processes. In this paper, monolithic materials strongly bound to the inert glass surface are suggested as operative matrices at the development of three-dimensional (3-D) microarrays. For this purpose, several rigid macroporous copolymers differed by reactivity and hydrophobic–hydrophilic properties were synthesized and tested: (1) glycidyl methacrylate -co-ethylene dimethacrylate (poly(GMA -co-EDMA)), (2) glycidyl methacrylate -co-glycerol dimethacrylate (poly(GMA -co-GDMA)), (3) N-hydroxyphthalimide ester of acrylic acid -co-glycidyl methacrylate -co-ethylene dimethacrylate (poly(HPIEAA -co-GMA -co-EDMA)), (4) 2-cyanoethyl methacrylate -co-ethylene dimethacrylate (poly(CEMA -co-EDMA)), and (5) 2-cyanoethyl methacrylate -co-2-hydroxyethyl methacrylate -co-ethylene dimethacrylate (poly(CEMA -co-HEMA -co-EDMA)). The constructed devices were used as platforms for protein microarrays construction and model mouse IgG—goat anti-mouse IgG affinity pair was used to demonstrate the potential of developed test-systems, as well as to optimize microanalytical conditions. The offered microarray platforms were applied to detect the bone tissue marker osteopontin directly in cell culture medium.

Keywords: Abbreviations; GMA; glycidyl methacrylate; EDMA; ethylene dimethacrylate; GDMA; glycerol dimethacrylate; HPIEAA; N-hydroxyphthalimide ester of acrylic acid; CEMA; 2-cyanoethyl methacrylate; HEMA; 2-hydroxyethyl methacrylate; CyOH; cyclohexanol; DoOH; dodecanol; PEG; poly(ethylene glycol); 2-D and 3-D; two- and three-dimensional, respectively; BSA; bovine serum albumin; IgG; immunoglobulin G; OPN; osteopontinMacroporous monolithic materials; Three-dimensional protein microarray; Bioanalysis

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Analytica Chimica Acta (v.644, #1-2)