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Analytica Chimica Acta (v.613, #1)

Editorial Board (pp. iii).

Contents (pp. v-vi).

Methodological aspects about in vitro evaluation of antioxidant properties by Luís M. Magalhães; Marcela A. Segundo; Salette Reis; José L.F.C. Lima (pp. 1-19).

Several of the most commonly used methods for in vitro determination of antioxidant capacity are reviewed in the present paper. The chemical principles of methods based either on biological oxidants (peroxyl radical, superoxide radical anion, hydrogen peroxide, hydroxyl radical, hypochlorous acid, singlet oxygen, nitric oxide radical, and peroxynitrite) or on non-biological assays (scavenging of 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical cation (TEAC assay), scavenging of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH assay), ferric reducing antioxidant power (FRAP assay), Folin–Ciocalteu reducing capacity (FC assay), electrochemical total reducing capacity) are outlined and critically discussed. The scope of application, the advantages and shortcomings of each method are also highlighted.

Keywords: Antioxidants; Scavenging capacity; Reactive oxygen species; Reactive nitrogen species

Microfluidic ion-sensing devices by R. Daniel Johnson; Vasilis G. Gavalas; Sylvia Daunert; Leonidas G. Bachas (pp. 20-30).

Quantitative determinations of ions in a variety of media have been performed traditionally via one of three approaches: optical instrumental methods (e.g., atomic absorption, and inductively-coupled plasma-optical emission or mass spectrometry), “wet” methods, or ion-selective sensors. Each of the approaches, though, possesses limitations including: power/reagent consumption and lack of portability for instrumental techniques; laborious sample-treatment steps for wet methods; and lack of selectivity and sensitivity with sensors when employed with complex samples. Microfluidic device have emerged as a solution to some of these challenges associated with ion analysis. Such systems can integrate multiple sample handling, calibration, and detection steps (“lab-on-a-chip” concept) into a footprint amenable to portability, while requiring small amounts of sample and power. Furthermore, devices can be constructed for multi-analyte detection, either through multiple parallel fluidic architectures or by using arrays of detection elements. This paper reviews recent progress in the development of total-analysis systems for ionic species. Fabrication techniques and various fluid-handling operations are discussed briefly, followed by a number of more mature strategies for microfluidic ion analysis. A variety of approaches expected to comprise the next generation of devices are also presented.

Keywords: Microfluidics; Lab-on-a-chip; Micro-total analysis system; Ion-selective sensors; Ion analysis

Comparative chemometric analyses of geographic origins and compositions of lavandin var. Grosso essential oils by mid infrared spectroscopy and gas chromatography by I. Bombarda; N. Dupuy; J.-P. Le Van Da; E.M. Gaydou (pp. 31-39).

Lavandin, a sterile hybrid of Lavandula angustifolia P. Mill.× Lavandula latifolia (L.f.) Medikus (Lamiaceae) is a plant widely cultivated for essential oil production in the South of France. Chemometric treatment by mid-infrared (MID-IR) spectroscopy data was assessed for the differentiation of Grosso Lavandin Essential Oils of Controlled Area (GLEOCA) and results were compared to those obtained by gas chromatography for MID-IR short time technique validation. The quantification of the main 13 hydrocarbons and oxygenated compounds generally controlled by industrial perfumers in GLEOCA samples ( n=83) of three geographic origins: “Simiane”, “Puimoisson” (with two producers) and “Richerenches” and their classification were successfully obtained by partial least square discriminant analysis (PLS-DA) by comparison with gas chromatography. The best prediction results were obtained using first derivate spectral data in the 1800–700cm⁻¹ range. The spectroscopic interpretation of regression vectors showed that each geographic origin was correlated to components of GLEOCA. Chemometric MID-IR spectra treatments allowed us to obtain similar results than those obtained by time consuming analytical techniques such as GC and therefore constitute a robust and help fast method for authentication of GLEOCA and should be extended to other essential oils for authentication of geographic origin.

Keywords: Chemometric; Partial least square; Partial least square discriminant analysis; Lavandin var. Grosso; Essential oil; Infrared; Gas chromatography

Chemometric study of the aggregation of alcohol dehydrogenase and its suppression by β-caseins: A mechanistic perspective by Mostafa Hassanisadi; Abolfazl Barzegar; Reza Yousefi; Michèle Dalgalarrondo; Jean-Marc Chobert; Thomas Haertlé; Ali Akbar Saboury; Ali Akbar Moosavi-Movahedi (pp. 40-47).

Molecular chaperones interact preferentially with certain aggregation-prone intermediates of target protein molecules. An estimation of the chaperone activity based on suppression of aggregation is required to be mechanistically understood. In this study, the multivariate curve resolution chemometric technique was applied on horse alcohol dehydrogenase (ADH) UV-spectra under thermal stress, to obtain the required information about the number and change in concentrations of the species involved. Chemometric analysis of UV-absorption spectra of horse ADH under thermal stress, led to the existence of three different molecular species including native ( N), aggregation-prone intermediate ( I) and final aggregate ( A) species. Appearance and buildup of two molecular species I and A were connected to the disappearance of N-species. In the presence of β-caseins (BCN), however, a new complex between I and BCN ( I–BCN) was formed. Meanwhile, by accretion of concentration of I–BCN complex, the light scattering intensity diminished. The data presented in this study clearly demonstrate that the interaction of BCN as a chaperone molecule with I-species takes place in a temperature-dependent manner and leads to a reversible I–BCN complex. In the absence of chaperones, I-state is subsequently converted to the final aggregate species. In the presence of BCN, this molecular species could be converted to the final aggregate state and/or form the I–BCN complex.

Keywords: Abbreviations; ADH; alcohol dehydrogenase; BCN; β-casein; BSA; bovine serum albumin; EFA; evolving factor analysis; FT; flow-through; MCR; multivariate curve resolution; ALS; alternating least squares; PCA; principal component analysis; SVD; singular value decomposition; WCF; whole casein fractionβ-Casein; Aggregation; Alcohol dehydrogenase (ADH); Chaperone; Chemometrics; Multivariate curve resolution (MCR)

Statistical mixture design—Varimax factor optimization for selective compound extraction from plant material by Patrícia Kaori Soares; Roy E. Bruns; Ieda S. Scarminio (pp. 48-55).

Varimax-transformed chromatograms of compounds extracted from Erythrina speciosa Andrews leaves by simplex centroid design mixtures of dichloromethane, hexane, ethanol and acetone are reported and compared with principal component results. Six varimax factors were investigated focusing on the three main groups of extracted compounds with retention times of 1.7, 3.1 and 6.6min. Varimax models provide chromatographic loading profiles that are simpler than their principal component counterparts. Furthermore varimax score models in terms of extraction medium compositions are simpler to interpret. The first varimax model results in an optimum extraction mixture of 71% dichloromethane–29% acetone although substitution of acetone by ethanol results in an almost identical extraction profile. The second varimax score model predicts optimum extraction binary mixtures with hexane proportions ranging from 50 to 100% for complementary proportions of either acetone or ethanol. The third varimax factor provides a response surface that is very similar to the one found for the third PC. Confirmatory experiments were performed to validate the model predictions.

Keywords: Varimax rotation; Principal component analysis; Mixture designs; Erythrina speciosa; Andrews leaves; Solvent extraction

Cold-induced aggregation microextraction: A novel sample preparation technique based on ionic liquids by Majid Baghdadi; Farzaneh Shemirani (pp. 56-63).

In this research, a novel microextraction technique based on ionic liquids (ILs) termed cold-induced aggregation microextraction (CIAME) is developed. In this method, very small amounts of 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim][PF₆] and 1-hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [Hmim][Tf₂N] (as extractant solvents) were dissolved in a sample solution containing Triton X-114 (as an anti-sticking agent). Afterwards, the solution was cooled in the ice bath and a cloudy solution was formed. After centrifuging, the fine droplets of extractant phase were settled to the bottom of the conical-bottom glass centrifuge tube.CIAME is a simple and rapid method for extraction and preconcentration of metal ions from water samples and can be applied for the sample solutions containing high concentration of salt and water miscible organic solvents. Furthermore, this technique is much safer in comparison with the organic solvent extraction.Performance of the technique was evaluated by determination of the trace amounts of mercury as a test analyte in several real water samples. Michler thioketone (TMK) was chosen as a complexing agent. Analysis was carried out using spectrophotometric detection method. Type and amount of IL and the surfactant, temperature and the other parameters were optimized. Under the optimum conditions, the limit of detection (LOD) of the method was 0.3ngmL⁻¹ and the relative standard deviation (R.S.D.) was 1.32% for 30ngmL⁻¹ mercury.

Keywords: Cold-induced aggregation microextraction; Ionic liquid; Sample preparation; Mercury; Real water samples; Spectrophotometry

Determination of volatile fatty acid ethyl esters in raw spirits using solid phase microextraction and gas chromatography by Beata Plutowska; Waldemar Wardencki (pp. 64-73).

An analytical method for the determination of fatty acid ethyl esters in raw spirits of different quality or produced from various raw materials has been developed and optimized. A combination of headspace solid phase microextraction (HS-SPME) as the extraction technique and gas chromatography with flame ionization detection (GC-FID) as the determination technique was utilized. HS-SPME conditions such as: type of the stationary phase of the fiber, ethanol content, sample volume, extraction temperature and time, salt addition and sample agitation were investigated to determine the most suitable conditions for the analysis of volatile fatty acid ethyl esters in raw spirits. The quantification method was an internal standardization using methyl octanoate as the internal standard. The method's detection limits (MDLs) for the individual ethyl esters ranged from 26.8 to 0.0470μgL⁻¹ 20% EtOH. The feasibility of SPME for the quantitative analysis of fatty acid ethyl esters in raw spirits of different organoleptic quality was demonstrated. High precision and simple sample preparation enable the use of this method for routine investigations in both industrial and research laboratories.

Keywords: Volatile compounds; Aroma; Fatty acid ethyl esters; Raw spirits; Solid phase microextraction

Rapid identification of oleanane-type saponins in the roots of Stephanotis mucronata by liquid chromatography/electrospray tandem mass spectrometry by Juanjuan Chen; Yiping Ye; Cuirong Sun; Yuanjiang Pan (pp. 74-82).

The liquid chromatography/electrospray tandem mass spectrometry method was developed for analyses and characterization of oleanane-type saponins in the roots of Stephanotis mucronata. Collision-induced dissociation have been performed in order to elucidate the degradation pathways for the [M+Na]⁺ ions and their predominant product ions. The following characteristic fragmentation was observed from the title saponins: when the substituent (except hydroxyl group) located at C₂₁ position, direct loss of terminal sugar residue from the [M+Na]⁺ ion was observed; when the substituent (except hydroxyl group) linked to C₂₂ position, the loss of the terminal sugar cannot occur. To further confirm the structures, offline Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR-MSⁿ) was performed. The structures of four proposed saponins have been identified by 1D and 2D NMR experiments. In this study, 12 saponins were identified. Among them, to our knowledge, four saponins were reported in this plant for the first time and four saponins were presumed to be new compounds. Hence, the described method has wide applicability to rapidly screen and provide structural information of oleanane-type saponins in crude materials.

Keywords: Stephanotis mucronata; Oleanane-type saponins; Liquid chromatography/electrospray tandem mass spectrometry; Fourier transform ion cyclotron resonance tandem mass spectrometry

Effects of interaction of folic acid with uranium (VI) and basic triphenylmethane dyes on resonance Rayleigh scattering spectra and their analytical applications by Cunxian Xi; Zhongfang Liu; Ling Kong; Xiaoli Hu; Shaopu Liu (pp. 83-90).

In pH 4.2–4.8 HAc–NaAc buffer solution, folic acid (FA) could react with uranium (VI) to form a 2:1 anionic chelate which further reacted with some basic triphenylmethane dyes (BTPMD) such as Ethyl Violet (EV), Methyl Violet (MV) and Crystal Violet (CV) to form 1:2 ion-association complexes. As a result, not only the absorption spectra were changed, but also the intensities of resonance Rayleigh scattering (RRS) were enhanced greatly and the new RRS spectra were observed. The maximum RRS wavelengths were located at 328nm for EV system, 325nm for MV system and 328nm for CV system. The fading degree (Δ A) and RRS intensities (Δ I) of three systems were different. Under given conditions, the Δ A and Δ I were all directly proportional to the concentration of FA. The linear ranges and the detection limits of RRS methods were 0.0039–5.0μgmL⁻¹ and 1.2ngmL⁻¹ for EV system, 0.0073–4.0μgmL⁻¹ and 2.2ngmL⁻¹ for MV system, 0.014–3.5μgmL⁻¹ and 4.7ngmL⁻¹ for CV system. The RRS methods exhibited higher sensitivity, so they are more suitable for the determination of trace FA. The optimum conditions, the influencing factors and the effects of coexisting substances on the reaction were investigated. The method can be applied to the determination of FA in serum and urine samples with satisfactory results. The structure of the ternary ion-association complex and the reaction mechanism were discussed in this work.

Keywords: Folic acid; Resonance Rayleigh scattering; Uranium (VI); Basic triphenylmethane dyes

Rosmarinic acid determination using biomimetic sensor based on purple acid phosphatase mimetic by Murilo Santhiago; Rosely A. Peralta; Ademir Neves; Gustavo Amadeu Micke; Iolanda Cruz Vieira (pp. 91-97).

A new heterodinuclear Fe(III)Zn(II) complex which mimics the active site of the hydrolytic enzyme red kidney bean purple acid phosphatase was synthesized and characterized by IR, CHN and X-ray crystallographic analyses. This complex, [Fe^IIIZn^II(μ-OH)bpbpmp-CH₃](ClO₄)₂, containing the ligand (H₂bpbpmp-CH₃={2-[bis(2-pyridylmethyl)aminomethyl]-6-[(2-hydroxy-5-methylbenzyl) (2-pyridyl-methyl) aminomethyl]-4-methyl-phenol}) was employed in the construction of a biomimetic sensor and used in the determination of rosmarinic acid in plant extract samples. The response parameters and optimization of the biomimetic sensor design were evaluated. The best performance of this sensor was obtained for 75:15:10% (w/w/w) of the graphite powder:nujol:Fe(III)Zn(II) complex, 0.1molL⁻¹ phosphate buffer solution (pH 7.5), 1.19×10⁻⁴molL⁻¹ hydrogen peroxide with frequency, pulse amplitude, and scan increment at 30Hz, 100mV, and 0.6mV, respectively. The rosmarinic acid concentration was linear in the range of 2.98×10⁻⁵ to 3.83×10⁻⁴molL⁻¹ ( r=0.9991) with a detection limit of 2.30×10⁻⁶molL⁻¹. This biomimetic sensor demonstrated long-term stability (300 days; 900 determinations) and reproducibility, with a relative standard deviation of 12.0%. The recovery study of rosmarinic acid in plant extract samples gave values from 90.3 to 98.3% and the concentrations determined showed agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level.

Keywords: Rosmarinic acid; Biomimetic sensor; Purple acid phosphatase; Plant extract

Improved determination of quinolones in milk at their MRL levels using LC–UV, LC–FD, LC–MS and LC–MS/MS and validation in line with regulation 2002/657/EC by M.P. Hermo; E. Nemutlu; S. Kır; D. Barrón; J. Barbosa (pp. 98-107).

This paper reports the multi-residue determination of quinolones included in the European Union regulations (marbofloxacin, ciprofloxacin, danofloxacin, enrofloxacin and flumequine) in bovine milk, using liquid chromatography with ultraviolet (LC–UV), fluorescence (LC–FD), mass spectrometry (LC–MS) and tandem mass spectrometry detection (LC–MS/MS). The methods were validated, in line with EU requirements (Commission Decision 2002/657/EC). Linearity, decision limit (CCα), detection capability (CCβ), detection limit (LOD), quantification limits (LOQ), recoveries, precision, selectivity and stability were determined and adequate results were obtained. Recoveries higher than 80% were obtained for all quinolones. The methods developed were used to quantify enrofloxacin and its main metabolite, ciprofloxacin, in milk from animals treated with enrofloxacin.

Keywords: Milk; Quinolones; EU criteria; Liquid chromatography–ultraviolet detection; Liquid chromatography–fluorescence detection; Liquid chromatography–mass spectrometry; Liquid chromatography–tandem mass spectrometry

On-line concentration and separation of indolamines, catecholamines, and metanephrines in capillary electrophoresis using high concentration of poly(diallyldimethylammonium chloride) by Wei-Lung Tseng; Sheng-Min Chen; Chih-Yao Hsu; Ming-Mu Hsieh (pp. 108-115).

This paper tackles a simple and efficient method for the simultaneous separation and stacking of neurotransmitters in capillary electrophoresis with UV detection. By using poly(diallyldimethylammonium chloride) (PDDAC) as a buffer additive, the high and reversed EOF are observed. Moreover, the mobility of indolamines and catecholamines decreases as the PDDAC concentration increases. Based on the difference in mobility in the presence and absence of PDDAC, the analytes were simply stacked between the boundary of the sample zone and the background electrolyte containing PDDAC. The separation of 14 analytes including indolamines, catecholamines, and metanephrines was accomplished within 33min under optimal conditions (1.2% PDDAC and 5mM formic acid at pH 4.0), and the values of relative standard deviation of their migration time were less than 3.1%. By applying stacking methods for fourteen analytes, we observed: (a) the sample injection volume of sample is up to 216nL, (b) the limits of detection at signal-to-noise of 3 range from 15.4 to 122.1nM, and (c) the sensitivity enhancements, compared to normal injection (12nL), range from 110- to 220-fold. Under the optimal stacking conditions, the present method has been applied to analyze of vanillomandelic acid, 5-hydroxyindole-3-acetic acid, dopamine, tryptamine, and 3-indoxyl sulfate in urine samples.

Keywords: Neurotransmitters; Capillary electrophoresis; Stacking; Polyelectrolyte

A reliable high-performance liquid chromatography with ultraviolet detection for the determination of sulfonamides in honey by Rodrigo H.M.M. Granja; Alfredo M. Montes Niño; Fernanda Rabone; Alessandro Gonzalez Salerno (pp. 116-119).

The sulfonamides are stable chemotherapeutics used against the bacterial disease affecting bees, known as American foulbrood (Bacillus larvae), so their residues could appear in the honey of treated bees. Their presence at a concentration above the limit value is a potential hazard to human health. Brazilian authorities have included in the National regulatory monitoring program, the control of the three most widely used sulfonamides in honey production, i.e., sulfathiazole, sulfamethazine and sulfadimethoxine. A method for the determination of residual sulfonamides in honey, using sulfapyridine as an internal standard has been developed, optimized and validated. Some changes were implemented on current available methodologies for the analysis of sulfonamides in honey in order to adopt such procedures to Brazilian honey samples. Sulfonamides were extracted from honey with dichloromethane after dissolution with 30% sodium chloride, and cleaned up with solid phase extraction on Florisil columns. The eluate was analyzed by high-performance liquid chromatography with ultraviolet detection. The limit of detection was determined at 3μgkg⁻¹, 4μgkg⁻¹ and 5μgkg⁻¹ for sulfathiazole, sulfamethazine and sulfadimethoxine, respectively with average recoveries of 61.0% for sulfathiazole; 94.5% for sulfamethazine and 86.0% for sulfadimethoxine at the 100μgkg⁻¹ level. As the final step of validation procedure, the analysts were submitted to a blind spiked sample prepared by the quality assurance officer which results were successfully obtained regarding recovery and deviations.

Keywords: Honey; Changes; High-performance liquid chromatography; Residues; Sulfonamides

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Analytica Chimica Acta (v.613, #1)