Check out our New Publishers' Select for Free Articles

Analytica Chimica Acta (v.613, #2)

Editorial Board (pp. i).

Contents (pp. iii-iv).

Chemometric methods for evaluation of chromatographic separation quality from two-way data—A review by Lu Xu; Li-Juan Tang; Chen-Bo Cai; Hai-Long Wu; Guo-Li Shen; Ru-Qin Yu; Jian-Hui Jiang (pp. 121-134).

Most traditional chromatographic separation criteria or response functions are defined on chromatograms recorded by single-channel detectors, e.g. a spectrometer measuring the absorbance at a single wavelength or a thermal conductivity detector. When the peaks are seriously overlapped, usually there is a lack of the information concerning the total number of chemical components, overlap degree of the peaks and peak purity. Such information characterizes some crucial aspects of separation process and lack of it will lead to an inaccurate and misleading evaluation of separation quality as well as some computational ambiguity for many traditional response functions. In contrast, hyphenated chromatography–(multi-channel) spectroscopy instruments together with chemometric methods will largely increase the information content available in chromatographic detection. Such information, if properly used, can cast a new light on evaluation of chromatographic separation quality. The main objective of this article is to review chemometric methods devoted to estimation of the number of chemical components, determination of elution sequence and assessment of peak purity. Some newly defined response functions or separation criteria based on extracted information by chemometric methods are also introduced. The methods reviewed are limited to those for treating two-way data obtained by hyphenation of high-performance liquid chromatography with multi-channel detectors. We prefer to provide a comprehensive view of such methods rather than present a full list of all the methods developed. Further details of some important methods are touched upon in favor of employment and understanding of them by researchers not very familiar with chemometrics.

Keywords: Chromatography; Evaluation of separation quality; Chemometrics; Analysis of two-way data; New separation criteria

Titanium dioxide determination in sunscreen by energy dispersive X-ray fluorescence methodology by F.L. Melquiades; D.D. Ferreira; C.R. Appoloni; F. Lopes; A.G. Lonni; F.M. Oliveira; J.C. Duarte (pp. 135-143).

Nowadays there are many sun-protection cosmetics incorporating chemical and/or physical UV filters as active ingredients and there are no official methods to determine these kinds of compounds in sunscreen cosmetics. The objective of this work is to estimate TiO₂ concentration, without sample preparation, employing a portable energy dispersive X-ray fluorescence (EDXRF), aiming to estimate the sun protection factor (SPF) due to the physical barrier in sunscreen composition, and also identify the metals present in the samples. A portable EDXRF system was used for the analysis of fifteen commercial samples. It was also prepared three formulations estimated in FPS-30 using TiO₂ at 5%. Quantification was performed using calibration curves with standards from 1 to 30%. The physical barrier contribution in the SPF, associated to Ti concentration, was determined for all samples. The presence of some elements, like K, Zn, Br and Sr was detected in the sunscreen, identifying chemical elements that were not cited in the formulations. Three commercial samples were analyzed for total SPF determination and the result shows that the measured value is 10% lower than the nominal one.

Keywords: Sunscreen; Titanium dioxide; Energy dispersive X-ray fluorescence; Metal

A new strategy for solving matrix effect in multivariate calibration standard addition data using combination of H-point curve isolation and H-point standard addition methods by Abbas Afkhami; Maryam Abbasi-Tarighat; Morteza Bahram; Hamid Abdollahi (pp. 144-151).

This work presents a new and simple strategy for solving matrix effects using combination of H-point curve isolation method (HPCIM) and H-point standard addition method (HPSAM). The method uses spectrophotometric multivariate calibration data constructed by successive standard addition of an analyte into an unknown matrix. By successive standard addition of the analyte, the concentrations of remaining components (interferents) remain constant and therefore give constant cumulative spectrum for interferents in the unknown mixture. The proposed method firstly extracts such spectrum using H-point curve isolation method and then applies the obtained cumulative interferents spectrum for determination of analyte by H-point standard addition method. In order to evaluate the applicability of the method a simulated as well as several experimental data sets were tested. The method was then applied to the determination of paracetamol in pharmaceutical tablets and copper in urine samples and in a copper alloy.

Keywords: H-point curve isolation method; H-point standard addition method; Unknown interferents; Standard addition; Pharmaceutical; Copper alloy

Electrogenerated chemiluminescence: An oxidative-reductive mechanism between quinolone antibiotics and tris(2,2′-bipyridyl)ruthenium(II) by Matthew S. Burkhead; Heeyoung Wang; Marcel Fallet; Erin M. Gross (pp. 152-162).

The cyclic voltammetry and electrogenerated chemiluminescent (ECL) reactions of a series of quinolone and fluoroquinolone antibiotics were investigated in a flow injection analysis (FIA) system. 7-Piperazinyl fluoroquinolone antibiotics were found to participate as a coreactant in an oxidative-reductive ECL mechanism with tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) as the luminescent reagent. The reaction mechanism was investigated in order to understand and optimize the processes leading to light emission. The optimal conditions included a solution pH ∼7 at a flow rate of 3.0mLmin⁻¹ with no added organic modifier and application of 1.2V vs. a Pt quasi-reference electrode (QRE). Fluoroquinolones containing a tertiary distal nitrogen on the piperazine ring, such as enrofloxacin and ofloxacin, reacted to produce more intense ECL than those with a secondary nitrogen, such as ciprofloxacin and norfloxacin. The method linear range, precision, detection limits, and sensitivity for the detection of enrofloxacin and ciprofloxacin were compared to that of tripropylamine. The method was applied to the determination of the ciprofloxacin content in a pharmaceutical preparation. The assay is discussed in terms of its analytical figures of merit, ease of use, speed, accuracy and application to pharmaceutical samples.

Keywords: Electrochemiluminescence; Fluoroquinolone antibiotics; Flow-injection analysis; Cyclic voltammetry; Tris(2,2′-bipyridyl)ruthenium(II)

Label-free aptasensor for platelet-derived growth factor (PDGF) protein by Tesfaye Hailu Degefa; Juhyoun Kwak (pp. 163-168).

A label-free aptasensor for platelet-derived growth factor (PDGF) protein is reported. The aptasensor uses mixed self-assembled monolayers (SAMs) composed of a thiol-modified PDGF binding aptamer and 6-mercaptohexanol (MCH) on a gold electrode. The SAMs were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV) before and after binding of the protein using [Fe(CN)₆]^3−/4−, a redox marker ion as an indicator for the formation of a protein–aptamer complex. The CVs at the PDGF modified electrode showed significant differences, such as changes in the peak currents and peak-to-peak separation, before and after binding of the target protein. The EIS spectra, in the form of Nyquist plots, were analyzed with a Randles circuit while the electron transfer resistance R_ct was used to monitor the binding of the target protein. The results showed that, without any modification to the aptamer, the target protein can be recognized effectively at the PDGF binding aptamer SAMs at the electrode surface. Control experiments using non-binding oligonucleotides assembled at the electrode surfaces also confirmed the results and showed that there was no formation of an aptamer–protein complex. The DPV signal at the aptamer functionalized electrode showed a linearly decreased marker ion peak current in a protein concentrations range of 1–40nM. Thus, label-free detection of PDGF protein at an aptamer modified electrode has been demonstrated.

Keywords: Aptamer; Target protein; Label-free; Aptasensor

A combination of statistical and analytical evaluation methods as a new optimization strategy for the quantification of pharmaceutical residues in sewage effluent by Eliane A. Suchara; Dilma Budziak; Edmar Martendal; Lea L.F. Costa; Eduardo Carasek (pp. 169-176).

In this study, a new solid-phase microextraction (SPME) method for simultaneous extraction of pharmaceutical compounds with acidic and basic characteristics (ibuprofen, fenoprofen, diclofenac, diazepam and loratadine) from residual water samples is proposed. In this procedure, the extraction is processed using two distinct sample pH values. The extraction is begun at pH 2.5 to promote the sorption of acidic pharmaceuticals and after 35min the sample pH is changed to 7.0 by adding 0.4molL⁻¹ disodium hydrogenphosphate, so that the basic compounds can be sorbed by the fiber (20min). The pH change is performed without interruption of the extraction process. A comparison between the proposed method and the SPME method applied to each group of the target compounds was performed. Gas chromatography coupled to mass spectrometry was used for separation and detection of analytes. The extraction conditions for the three methods were optimized using full factorial experimental design, response surface through a Doehlert matrix and central composite design. Limits of detection (0.02–0.43μgL⁻¹) and correlation coefficients (0.9970–0.9998) were determined for the three methods. The proposed extraction procedure was applied to samples of sewage treatment plant effluent and untreated wastewater. Recovery and relative standard deviation values ranged from 67 to 116% and 4.6 to 14.5%, respectively, for all compounds studied. Modification of sample pH during the extraction procedure was shown to be an excellent option for all of the compounds and may be extended to the simultaneous extraction of other compounds with different acid-base characteristics.

Keywords: Pharmaceuticals; Solid-phase microextraction; Sewage treatment plant effluents; Experimental design

Flow methodology for methanol determination in biodiesel exploiting membrane-based extraction by André R.T.S. Araujo; M. Lúcia M.F.S. Saraiva; José L.F.C. Lima; M. Graças A. Korn (pp. 177-183).

A methodology based in flow analysis and membrane-based extraction has been applied to the determination of methanol in biodiesel samples. A hydrophilic membrane was used to perform the liquid–liquid extraction in the system with the organic sample fed to the donor side of the membrane and the methanol transfer to an aqueous acceptor buffer solution. The quantification of the methanol was then achieved in aqueous solution by the combined use of immobilised alcohol oxidase (AOD), soluble peroxidase and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The optimization of parameters such as the type of membrane, the groove volume and configuration of the membrane unit, the appropriate organic solvent, sample injection volume, as well as immobilised packed AOD reactor was performed. Two dynamic analytical working ranges were achieved, up to 0.015% and up to 0.200% (m/m) methanol concentrations, just by changing the volume of acceptor aqueous solution. Detection limits of 0.0002% (m/m) and 0.007% (m/m) methanol were estimated, respectively. The decision limit (CCα) and the detection capacity (CCβ) were 0.206 and 0.211% (m/m), respectively. The developed methodology showed good precision, with a relative standard deviation (R.S.D.) <5.0% ( n=10). Biodiesel samples from different sources were then directly analyzed without any sample pre-treatment. Statistical evaluation showed good compliance, for a 95% confidence level, between the results obtained with the flow system and those furnished by the gas chromatography reference method. The proposed methodology turns out to be more environmental friendly and cost-effective than the reference method.

Keywords: Biodiesel; Methanol; Membrane-based extraction; Immobilised enzyme; Flow analysis

Analysis of alkaloids in Coptis chinensis Franch by accelerated solvent extraction combined with ultra performance liquid chromatographic analysis with photodiode array and tandem mass spectrometry detections by Junhui Chen; Fengmei Wang; Jie Liu; Frank Sen-Chun Lee; Xiaoru Wang; Huanghao Yang (pp. 184-195).

A new method based on accelerated solvent extraction (ASE) followed by ultra performance liquid chromatography (UPLC) analysis has been developed for the identification and quantification of major alkaloids in extracts of Coptis chinensis Franch. The UPLC system consisted of a dual detection system of photodiode array detector (PDA) and positive ion electrospray ionization-tandem mass spectrometry (ESI-MS/MS) in sequential configuration. The operational parameters of ASE including extraction solvent, extraction temperature, static extraction time and extraction cycles were optimized. UPLC analysis was performed on an ACQUITY UPLC BEH C₁₈ column eluted by a mobile phase of acetonitrile spiked with a buffer solution consisting of 0.50% acetic acid and 20mmolL⁻¹ ammonium acetate. A tandem quadrupole spectrometer operating in either full scan mode or in MS/MS mode for multiple reaction monitoring (MRM) was used for the identification and quantitative analysis of eight major alkaloids in C. chinensis Franch extracts. The samples were also analyzed on a high-performance liquid chromatography–electrospray ionization-time-of-flight mass spectrometry (HPLC-ESI-TOF-MS) system to confirm the identification results. Three of the eight major alkaloids, berberine, palmatine and jatrorrhizine were quantified by UPLC–PDA and UPLC–MS/MS. The results indicated that both UPLC–PDA and UPLC–MS/MS methods were simple, sensitive and reliable for the determination of alkaloids in C. chinensis Franch. Seven Huanglian samples from different locations were analyzed using the established methods. UPLC fingerprints based on the distribution of the eight major alkaloids can serve as a rapid and reliable method for the authentication and quality evaluation of traditional Chinese medicine (TCM) herbs.

Keywords: Coptis chinensis; Franch; Alkaloids; Accelerated solvent extraction; Ultra performance liquid chromatography–tandem mass spectrometry; Fingerprint

Chemometric determination of arsenic and lead in untreated powdered red paprika by diffuse reflectance near-infrared spectroscopy by J. Moros; I. Llorca; M.L. Cervera; A. Pastor; S. Garrigues; M. de la Guardia (pp. 196-206).

It has been evaluated the potential of near-infrared (NIR) diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) as a way for non-destructive measurement of trace elements at μgkg⁻¹ level in foods, with neither physical nor chemical pre-treatment. Predictive models were developed using partial least-square (PLS) multivariate approaches based on first-order derivative spectra. A critical comparison of two spectral pre-treatments, multiplicative signal correction (MSC) and standard normal variate (SNV) was also made. The PLS models built after using SNV provided the best prediction results for the determination of arsenic and lead in powdered red paprika samples. Relative root-mean-square error of prediction (RRMSEP) of 23% for both metals, arsenic and lead, were found in this study using 20 well characterized samples for calibration and 13 additional samples as validation set. Results derived from this study showed that NIR diffuse reflectance spectroscopy combined with the appropriate chemometric tools could be considered as an useful screening tool for a rapid determination of As and Pb at concentration level of the order of hundred μgkg⁻¹.

Keywords: Arsenic; Lead; Near-infrared spectroscopy; Partial least-squares; Paprika; Diffuse reflectance; First derivative; Standard normal variate; Multiplicative signal correction

Simultaneous analysis of riboflavin and aromatic amino acids in beer using fluorescence and multivariate calibration methods by Ewa Sikorska; Anna Gliszczyńska-Świgło; Małgorzata Insińska-Rak; Igor Khmelinskii; Denis De Keukeleire; Marek Sikorski (pp. 207-217).

The study demonstrates an application of the front-face fluorescence spectroscopy combined with multivariate regression methods to the analysis of fluorescent beer components. Partial least-squares regressions (PLS1, PLS2, and N-way PLS) were utilized to develop calibration models between synchronous fluorescence spectra and excitation–emission matrices of beers, on one hand, and analytical concentrations of riboflavin and aromatic amino acids, on the other hand. The best results were obtained in the analysis of excitation–emission matrices using the N-way PLS2 method. The respective correlation coefficients, and the values of the root mean-square error of cross-validation (RMSECV), expressed as percentages of the respective mean analytic concentrations, were: 0.963 and 14% for riboflavin, 0.974 and 4% for tryptophan, 0.980 and 4% for tyrosine, and 0.982 and 19% for phenylalanine.

Keywords: Tyrosine; Fluorescence; Beer; Riboflavin; Total luminescence; Tryptophan; Phenylalanine

A novel application of nylon membranes to the luminescent determination of benzo[a]pyrene at ultra trace levels in water samples by S.A. Bortolato; J.A. Arancibia; G.M. Escandar (pp. 218-227).

Very simple and highly sensitive methods are presented for the determination of benzo[ a]pyrene, one of the most carcinogenic polycyclic aromatic hydrocarbons (PAHs). The approaches are based on solid-phase extraction of the analyte on a nylon membrane via a syringe procedure, and its fluorescent or phosphorescent determination on the solid surface. While the native fluorescence of benzo[ a]pyrene retained on a nylon surface is measured directly, room-temperature phosphorescence is induced by spotting a few microlitres of thallium(I) nitrate solution on the surface (heavy-atom effect). An enhancement of the phosphorescence signal was corroborated when the measurements were carried under a nitrogen atmosphere. The analytical figures of merit obtained under the best experimental conditions demonstrate the capability of detecting benzo[ a]pyrene at a sub-parts-per-trillion (sub-ngL⁻¹) level. The potential interference from other common PAHs and also from different metal ions was studied. The feasibility of determining benzo[ a]pyrene in real samples was successfully evaluated through the analysis of spiked tap, underground and mineral water samples of different origins. Recoveries obtained from spiked river waters were successfully compared with those provided by a reference method, through rigorous statistical analysis.

Keywords: Fluorescence; Room-temperature phosphorescence; Solid-phase extraction; Nylon; Benzo[; a; ]pyrene

Profiling of 19-norsteroid sulfoconjugates in human urine by liquid chromatography mass spectrometry by Emmanuel Strahm; Serge Rudaz; Jean-Luc Veuthey; Martial Saugy; Christophe Saudan (pp. 228-237).

19-Nortestosterone (nandrolone) major metabolites in human urine are excreted as sulfoconjugated and glucuroconjugated forms. A sensitive and selective liquid chromatography/tandem mass spectrometry (LC/MS/MS) method in negative ESI mode was developed for direct quantification of 19-norandrosterone sulfate (19-NAS) and 19-noretiocholanolone sulfate (19-NES). For both sulfoconjugates, the [M−H]⁻ ion at m/ z 355 and the fragment ion at m/ z 97 were used as the precursor and product ions, respectively. The purification method involved a complete and rapid separation of sulfates and glucuronides in two extracts after loading the sample on a weak anion exchange solid phase extraction support (SPE Oasis^® WAX). Then, sulfates were separated by LC (Uptisphere^® ODB, 150mm×3.0mm, 5μm) and analyzed on a linear trap and a triple quadrupole mass spectrometer. The lower limit of detection (LLOD) and lowest limit of quantification (LLOQ) were of 100pgmL⁻¹ and 1ngmL⁻¹, respectively. Assay validation demonstrated good performances in terms of trueness (92.0–104.9%), repeatability (0.6–7.2%) and intermediate precision (1.3–10.8%) over the range of 1–2500ngmL⁻¹. Finally, 19-NAS and 19-NES in urine samples collected after intake of 19-norandrostenedione (nandrolone precursor) were quantified. This assay may be easily implemented to separate glucuronide and sulfate steroids from urine specimens prior to quantification by LC/MS/MS.

Keywords: Nandrolone; Phase II metabolites; Linear ion trap mass spectrometry; Quantification

Sections

Personal tools

Analytica Chimica Acta (v.613, #2)

Sections

Personal tools

Local resources

Analytica Chimica Acta (v.613, #2)