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Analytica Chimica Acta (v.606, #2)

Editorial Board (pp. co1).

Contents (pp. iii-iv).

Achievements in resonance Raman spectroscopy by Evtim V. Efremov; Freek Ariese; Cees Gooijer (pp. 119-134).

In an extended introduction, key aspects of resonance Raman spectroscopy (RRS) such as enhanced sensitivity and selectivity are briefly discussed in comparison with normal RS. The analytical potential is outlined. Then achievements in different fields of research are highlighted in four sections, with emphasis on recent breakthroughs: (1) The use of visible RRS for analyzing carotenoids in biological matrices, for pigments and dyes as dealt with in art and forensics, and for characterizing carbon nanotubes. (2) The use of RRS in the deep UV (excitation below 260nm) in the bioanalytical and life sciences fields, including nucleic acids, proteins and protein–drug interactions. Metalloproteins can be studied by visible RRS in resonance with their chromophoric absorption. (3) Progress in theoretical calculations of RRS excitation profiles and enhancement factors, which ultimately might facilitate analytical RRS. (4) Instrumental and methodological achievements including fiber-optic UV–RRS, coupling of RRS to liquid chromatography and capillary electrophoresis. Sensitivities can approach the single-molecule level with surface-enhanced RRS or tip-enhanced RRS. Last but not least, promising fluorescence background rejection techniques based on time-gated detection will be presented. This review ends with a concluding section on future expectations for RRS, in particular its potential as an analytical technique.

Keywords: Bioanalytical applications; Carotenoids; Metalloproteins; Carbon nanotubes; Excitation profiles; Fiber optics; Surface-enhanced Raman; Tip-enhanced Raman; Fluorescence rejection; Gated detection

Biomonitoring: An appealing tool for assessment of metal pollution in the aquatic ecosystem by Qunfang Zhou; Jianbin Zhang; Jianjie Fu; Jianbo Shi; Guibin Jiang (pp. 135-150).

Wide occurrence of aquatic metal pollution has caused much attention. Biomonitoring offers an appealing tool for the assessment of metal pollution in aquatic ecosystem. The bioindicators including algae, macrophyte, zooplankton, insect, bivalve mollusks, gastropod, fish, amphibian and others are enumerated and compared for their advantages and disadvantages in practical biomonitoring of aquatic metal pollution. The common biomonitoring techniques classified as bioaccumulation, biochemical alterations, morphological and behavior observation, population- and community-level approaches and modeling are discussed. The potential applications of biomonitoring are proposed to mainly include evaluation of actual aquatic metal pollution, bioremediation, toxicology prediction and researches on toxicological mechanism. Further perspectives are made for the biomonitoring of metal pollution in aquatic ecosystem.

Keywords: Biomonitoring; Metal pollution; Aquatic ecosystem

Potential of front face fluorescence associated to PLS regression to predict nutritional parameters in heat treated infant formula models by R. Diez; M.C. Ortiz; L. Sarabia; I. Birlouez-Aragon (pp. 151-158).

This work shows that front face fluorescence spectroscopy associated to partial least squares (PLS) calibration is a fast and simple method to assess the nutritional impact of heat treatment on milk samples.Emission spectra of tryptophan (Trp) and of advanced Maillard products (AMP) were recorded on intact milk samples non-heated and heated at seven temperatures (72°C, 80°C, 87°C, 95°C, 100°C, 110°C and 115°C) for six different times (from 2min to 9.5min) by means of front face fluorescence. PLS calibrations were constructed in order to indirectly quantify three indicators: vitamin C, protein denaturation and accumulation of Maillard products using the fluorescence of advanced Maillard products and soluble tryptophan method (FAST). The prediction models allowed obtaining an estimation of these indicators with a relative error of 12% for vitamin C and about 18% for the FAST index and soluble whey protein ratio.

Keywords: Front face fluorescence; PLS calibration; FAST; Vitamin C; Soluble protein; Infant milk formula

Chemometric analysis of diesel fuel for forensic and environmental applications by Amber M. Hupp; Lucas J. Marshall; Dahlia I. Campbell; Ruth Waddell Smith; Victoria L. McGuffin (pp. 159-171).

Diesel fuel samples were analyzed using gas chromatography–mass spectrometry (GC–MS) and chemometric procedures to associate and discriminate samples for potential use in forensic and environmental applications. Twenty-five diesel samples, representing 13 different brands, were collected from service stations in the Lansing, Michigan area. From the GC–MS data, mass-to-charge ratios were identified to represent aliphatic ( m/ z 57) and aromatic ( m/ z 91 and 141) compounds. The total ion chromatogram (TIC) and extracted ion chromatograms (EICs) of the chosen ions were evaluated using Pearson product moment correlation (PPMC) and principal component analysis (PCA). Diesel samples from the same brand showed higher PPMC coefficients, while those from different brands showed lower values. EICs generally provided a wider range of correlation coefficients than the TIC, with correspondingly increased discrimination among samples for EIC m/ z 91. PCA grouped the diesel samples into four distinct clusters for the TIC. The first cluster consisted of four samples from the same brand, two clusters contained one diesel sample each of different brands, and the fourth cluster contained the remaining diesel samples. The same trend was observed using each EIC, with an increase in the number of clusters formed for EIC m/ z 57 and 91. Both statistical procedures suggest aromatic components (specifically, those with m/ z 91) provide the greatest discrimination among diesel samples. This conclusion was supported by identifying the chemical components that contribute the most to the variance. The relative amount of aliphatic versus aromatic components was found to cause the greatest discrimination among samples in the data set.

Keywords: Diesel; Gas chromatography–mass spectrometry; Forensic science; Environmental science; Pearson product moment correlation; Principal component analysis

Numerical analysis of the Gran methods A comparative study by Tadeusz Michałowski; Krzysztof Kupiec; Maciej Rymanowski (pp. 172-183).

The paper concerns mainly the modified Gran methods, considered as extrapolative standard addition methods. Particularly, the approximation:ln(1+x1)−ln(1−x2)≅11/x1+1/ξ+11/x2−1/ξwhereξ≅2, is applied for the needs of the modified Gran I methods, in accurate and simplified versions, denoted as MG(I)A and MG(I)S methods. These methods are compared with Gran II methods, in original (G(II)) and modified accurate (MG(II)A) versions. All the methods were tested with use of results obtained from simulated potentiometric titrations. The effects involved with a pre-assumed slope ϑ^*-value for a redox indicator electrode and in errors in potential ( E) and volume ( V) readouts on the error in equivalence volume ( V_eq) value thus determined is considered. It is recognized that MG(I)A and MG(II)A appear to be the best methods applicable for V_eq determination among ones considered hitherto. Moreover, the MG(I)S method is the best choice for determination of the true slope ϑ-value for the redox indicator electrode.

Keywords: Abbreviations; a; parameter in Eq. (15); C; concentration of reagent in T; C; ₀; concentration of analyte in D; D; titrand; E; voltage; G(I) and G(II); original Gran I and Gran II methods; MG(I)S and MG(I)A; modified Gran I methods in simplified and accurate versions, resp.; MG(II)A; modified form of G(II) method; T; titrant; ϑ, ϑ; ^*; ϑ; ₀; true, pre-assumed and Nernstian slopes, resp.; V; volume of T added; V; ₀; volume of D; V; _eq; equivalence volume; V; _eq0; (=10; mL); theoretical; V; _eq; value; z; see Eq. (44)Titration; Curve fitting; Gran methods

Single hollow fiber SLM extraction of polyamines followed by tosyl chloride derivatization and HPLC determination by Katarzyna Dziarkowska; Jan Ǻke Jönsson; Piotr P. Wieczorek (pp. 184-193).

Determination of polyamines in biological fluids possesses medical diagnostic relevance. Despite the vast panel of analytical methods developed for polyamines they are not applied in routine clinical usage, mainly due to the time and labor consuming sample preparation step and complicated derivatization procedures. Thus, new simpler methods are needed. This paper describes a single hollow fiber SLM extraction method of polyamines followed by simple pre-column derivatization with tosyl chloride and HPLC-UV analysis. The influence of different parameters such as the extraction time, organic phase composition, acceptor pH, donor pH, acceptor volume, donor volume and stirring speed on the transport parameters and enrichment was studied and discussed. The optimized method was applied to real matrices such as urine and plasma.

Keywords: Polyamines; Supported liquid membrane; Hollow fiber membrane; Extraction technique

On-line coupling of solid-phase extraction to high-performance liquid chromatography for determination of estrogens in environment by Shuo Wang; Wei Huang; Guozhen Fang; Jinxing He; Yan Zhang (pp. 194-201).

A method based on on-line solid-phase extraction (SPE) coupling to high-performance liquid chromatography (HPLC) for the determination of estrogens has been developed. This method can continuously perform extraction of estrone, estradiol, estriol and diethylstilbestrol from aqueous samples without any other pretreatment, which can then be analyzed by HPLC with a UV detector at 230nm. A pre-concentration column was adapted with methanol/water for chromatographic separation and two kinds of sorbents were involved, which are octadecyl-bonded silica and cigarette filter. The condition of pH of samples, sample loading flow rate and desorption time were all optimized, and the performances of both two sorbents were satisfactory. The on-line SPE system requires very low maintenance and just involved a switching-valve-filter system and a flow-inject pump, and the operation of the whole SPE-HPLC instrumentation is quite simple. The detection limits for pre-concentrating 50mL of standard solution using cigarette filter as sorbent ranged from 0.98 to 78.1ngL⁻¹. The enhancement factors were in the range of 197–326. The recoveries of estrogens spiked in real water samples ranged from 85 to 112%. The precisions for nine replicate measurements of a standard mixture (5.0μgL⁻¹) were in the range of 1.0–3.4%.

Keywords: Estrogen; On-line solid-phase extraction; Quantitative analysis; High-performance liquid chromatography

Extraction and determination of organophosphorus pesticides in water samples by a new liquid phase microextraction–gas chromatography–flame photometric detection by Mohammad Reza Khalili-Zanjani; Yadollah Yamini; Najmeh Yazdanfar; Shahab Shariati (pp. 202-208).

A rapid, sensitive and efficient liquid phase microextraction (LPME) method was developed to determine trace concentrations of some organophosphorus pesticides in water samples. This method combines liquid phase microextraction with gas chromatographic (GC) analysis in a simple and inexpensive apparatus involving very little organic solvent consumption. It involves exposing a floated drop of an organic solvent on the surface of aqueous solution in a sealed vial. Experimental parameters which control the performance of LPME such as type of organic solvent, organic solvent and sample volumes, sample stirring rate, sample solution temperature, salt addition and exposure time were investigated and optimized. Finally, the enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated by the water samples spiked with organophosphorus pesticides. Using optimum extraction conditions, very low detection limits (0.01–0.04μgL⁻¹) and good linearities (0.9983< r²<0.9999) were achieved. The LPME was performed for determination of organophosphorus pesticides in different types of natural water samples and acceptable recoveries (96–104%) and precisions (3.5

Keywords: Liquid phase microextraction; Organophosphorus pesticides; Gas chromatography; Flame photometric detection

Square wave adsorptive cathodic stripping voltammetry automated by sequential injection analysis by Luciana B.O. dos Santos; Jorge C. Masini (pp. 209-216).

This paper describes the development and evaluation of a sequential injection method to automate the determination of methyl parathion by square wave adsorptive cathodic stripping voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. Accumulation and stripping steps are made in the sample medium conditioned with 40mmolL⁻¹ Britton–Robinson buffer (pH 10) in 0.25molL⁻¹ NaNO₃. The homogenized mixture is injected at a flow rate of 10μLs⁻¹ toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode. After a suitable deposition time, the flow is stopped and the potential is scanned from −0.3 to −1.0V versus Ag/AgCl at frequency of 250Hz and pulse height of 25mV. The linear dynamic range is observed for methyl parathion concentrations between 0.010 and 0.50mgL⁻¹, with detection and quantification limits of 2 and 7μgL⁻¹, respectively. The sampling throughput is 25h⁻¹ if the in line standard addition and sample conditioning protocols are followed, but this frequency can be increased up to 61h⁻¹ if the sample is conditioned off-line and quantified using an external calibration curve. The method was applied for determination of methyl parathion in spiked water samples and the accuracy was evaluated either by comparison to high performance liquid chromatography with UV detection, or by the recovery percentages. Although no evidences of statistically significant differences were observed between the expected and obtained concentrations, because of the susceptibility of the method to interference by other pesticides (e.g., parathion, dichlorvos) and natural organic matter (e.g., fulvic and humic acids), isolation of the analyte may be required when more complex sample matrices are encountered.

Keywords: Methyl parathion; Adsorptive voltammetry; Sequential injection; Waters

Parallel analysis of stimulants in saliva and urine by gas chromatography/mass spectrometry: Perspectives for “in competition” anti-doping analysis by Sabina Strano-Rossi; Cristiana Colamonici; Francesco Botrè (pp. 217-222).

Stimulants are banned by the World Anti-Doping Agency (WADA) if used “in competition”. Being the analysis of stimulants presently carried out on urine samples only, it might be useful, for a better interpretation of analytical data, to discriminate between an early intake of the substance and an administration specifically aimed to improve the sport performance. The purpose of the study was to investigate the differences, in terms of excretion/disappearance of drugs, between urine and oral fluid, a sample that can reflect plasmatic concentrations.Oral fluid and urine samples were collected following oral administration of the following stimulants: modafinil (100mg), selegiline (10mg), crotetamide/cropropamide (50mg each), pentetrazol (100mg), ephedrine (12mg), sibutramine (10mg), mate de coca (a dose containing about 3mg of cocaine); analysis of drugs/metabolites was carried out by gas chromatography/mass spectrometry (GC/MS) in both body fluids.Our results show that both the absolute concentrations and their variation as a function of time, in urine and in oral fluid, are generally markedly different, being the drugs eliminated from urine much more slowly than from oral fluid. Our results also suggest that the analysis of oral fluid could be used to successfully complement the data obtained from urine for “in competition” anti-doping tests; in all those cases in which the metabolite(s) concentration of a substance in urine is very low and the parent compound is not detected, it is indeed impossible, relying on urinary data only, to discriminate between recent administrations of small doses and remote administrations of higher doses.

Keywords: Biological samples; Doping analysis; Drug monitoring/drug screening; Forensic/toxicology; Mass spectrometry; Oral fluid and urine analysis

Dual sensing of oxygen and temperature using quantum dots and a ruthenium complex by P.A.S. Jorge; C. Maule; A.J. Silva; R. Benrashid; J.L. Santos; F. Farahi (pp. 223-229).

A scheme for the simultaneous determination of oxygen and temperature using quantum dots and a ruthenium complex is demonstrated. The luminescent complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)]²⁺ is immobilized in a non-hydrolytic sol–gel matrix and used as the oxygen sensor. The temperature information is provided by the luminescent emission of core–shell CdSe–ZnS semiconductor nanocrystals immobilized in the same material. Measurements of oxygen and temperature could be performed with associated errors of ±2% of oxygen concentration and ±1°C, respectively. In addition, it is shown that while the dye luminescence intensity is quenched both by oxygen and temperature, the nanocrystals luminescent emission responds only to temperature. Results presented demonstrate that the combined luminescence response allows the simultaneous assessment of both parameters using a single optical fiber system. In particular, it was shown that a 10% error in the measured oxygen concentration, induced by a change in the sample temperature, could be compensated using the nanocrystals temperature information and a correction function.

Keywords: Quantum dots; Luminescence; Optical fiber; Oxygen sensors; Temperature

Development of an aminocarboxylic acid-modified infrared chemical sensor for selective determination of tyrosine in urine by Huei-Chi Lin; Yi-Hsin Chou; Jyisy Yang (pp. 230-238).

An infrared (IR) chemical sensor based on immobilization of an acidified tris(2-aminoethyl)amine (ATAA) for the detection of tyrosine in urine is described. The sensing phase (i.e., coating) was saturated with nickel ions so that it would interact with tyrosine molecules in aqueous solution through the formation of stable ATAA–Ni²⁺–tyrosine complexes. Investigation of the signals of nine amino acids shows that only the three containing phenyl groups could be detected by this sensor system. A unique spectral feature located at 1515cm⁻¹ allowed tyrosine to be discriminated from the other two amino acids. To examine the performance of the ATAA sensing phase in the quantitative analysis of tyrosine, the effects of several factors were examined. pH affected the ability of tyrosine to form complexes; the optimal signal occurred at ca . pH 8. The concentration of ammonia buffer also affected the analytical signals through a competition effect; lower concentrations of ammonia buffer provided higher intensity signals. It was found that nickel ions are the most useful for detection of tyrosine. Although the concentration of nickel ions had less influence on the analytical signal than did the concentration of the ammonia buffer, the signal intensity was optimal when the nickel ions and the target molecule had similar concentrations. The detected time profiles indicated that the ATAA sensor phase functioned via a surface adsorption mechanism. The linear range of signal intensities was up to 600μM with a detection limit of 30μM.

Keywords: Infrared; Optical sensor; Evanescent wave; Amino acids; Tyrosine

Isolation of Pu-isotopes from environmental samples using ion chromatography for accelerator mass spectrometry and alpha spectrometry by E. Chamizo; M.C. Jiménez-Ramos; L. Wacker; I. Vioque; A. Calleja; M. García-León; R. García-Tenorio (pp. 239-245).

A radiochemical method for the isolation of plutonium-isotopes from environmental samples, based on the use of specific extraction chromatography resins for actinides (TEVA^®, Eichrom Industries, Inc.), has been set up in our laboratory and optimised for their posterior determination by alpha spectrometry (AS) or accelerator mass spectrometry (AMS). The proposed radiochemical method has replaced in our lab a well-established one based on the use of a relatively un-specific anion-exchange resin (AG^® 1X8, Bio-rad Laboratories, Inc.), because it is clearly less time consuming, reduces the amounts and molarities of acid wastes produced, and reproducibly gives high radiochemical yields.In order to check the reliability of the proposed radiochemical method for the determination of plutonium-isotopes in different environmental matrixes, twin aliquots of a set of samples were prepared with TEVA^® and with AG^® 1X8 resins and measured by AS. Some samples prepared with TEVA^® resins were measured as well by AMS. As it is shown in the text, there is a comfortable agreement between AS and AMS, which adequately validates the method.

Keywords: Plutonium; Accelerator mass spectrometry; Alpha spectrometry; TEVA

Rapid determination of acetaminophen and p-aminophenol in pharmaceutical formulations using miniaturized capillary electrophoresis with amperometric detection by Qingcui Chu; Lianmei Jiang; Xiuhui Tian; Jiannong Ye (pp. 246-251).

Capability of fast analysis of a novel miniaturized capillary electrophoresis with carbon disk electrode amperometric detection (mini-CE-AD) system was demonstrated by determining acetaminophen and p-aminophenol in dosage forms. Factors influencing the separation and detection processes were examined and optimized. Under the optimum conditions, the end-capillary 300μm carbon disc electrode amperometric detector offered favorable signal-to-noise characteristics at a relatively low potential (+600mV versus Ag/AgCl) for detecting acetaminophen and p-aminophenol. Two analytes can been separated within 150s in a 8.5cm length capillary at a separation voltage of 2000V using a Na₂B₄O₇–KH₂PO₄ running buffer (pH 7.2). Acetaminophen and p-aminophenol could be detected down to the 1.4×10⁻⁶–5.9×10⁻⁷molL⁻¹ level with linearity up to the 1.0×10⁻³molL⁻¹ level examined. The inter-day repeatability for analytes in peak current (R.S.D.≤2.3%) and migration times (R.S.D.≤1.3%) were excellent. The proposed mini-CE-AD system should find a wide range of analytical applications in pharmaceutical formulations as an alternative to conventional CE and μ-CE.

Keywords: Capillary electrophoresis; Amperometric detection; Miniaturization; Acetaminophen; p; -Aminophenol

Selectivity and recovery performance of phosphate-selective molecularly imprinted polymer by Akimitsu Kugimiya; Hideo Takei (pp. 252-256).

A phosphate-selective molecularly imprinted polymer was prepared using 1-allyl-2-thiourea as a functional monomer, and the binding ability and selectivity of the polymer were evaluated. The imprinted polymer showed high binding ability to and selectivity for phosphate in aqueous media. The recoverability of phosphate from the imprinted polymer was also examined, and nearly 70% of highly concentrated phosphate could be recovered.

Keywords: Molecular imprinting; Phosphate; Thiourea group; Recovery; Molecular recognition

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Analytica Chimica Acta (v.606, #2)