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Analytica Chimica Acta (v.635, #2)

Editorial Board (pp. i).

Artificial neural networks in foodstuff analyses: Trends and perspectives A review by Federico Marini (pp. 121-131).

Artificial neural networks are a family of non-linear computational methods, loosely inspired by the human brain, that have found application in an increasing number of fields of analytical chemistry and specifically of food control. In this review, the main neural network architectures are described and examples of their application to solve food analytical problems are presented, together with some considerations about their uses and misuses.

Keywords: Food analysis; Chemometrics; Artificial neural networks; Food science

Field-flow fractionation in bioanalysis: A review of recent trends by Barbara Roda; Andrea Zattoni; Pierluigi Reschiglian; Myeong Hee Moon; Mara Mirasoli; Elisa Michelini; Aldo Roda (pp. 132-143).

Field-flow fractionation (FFF) is a mature technique in bioanalysis, and the number of applications to proteins and protein complexes, viruses, derivatized nano- and micronsized beads, sub-cellular units, and whole cell separation is constantly increasing. This can be ascribed to the non-invasivity of FFF when directly applied to biosamples. FFF is carried out in an open-channel structure by a flow stream of a mobile phase of any composition, and it is solely based on the interaction of the analytes with a perpendicularly applied field. For these reasons, fractionation is developed without surface interaction of the analyte with packing or gel media and without using degrading mobile phases. The fractionation device can be also easily sterilized, and analytes can be maintained under a bio-friendly environment. This allows to maintain native conditions of the sample in solution.In this review, FFF principles are briefly described, and some pioneering developments and applications in the bioanalytical field are tabled before detailed report of most recent FFF applications obtained also with the hyphenation of FFF with highly specific, sensitive characterization methods. Special focus is finally given to the emerging use of FFF as a pre-analytical step for mass-based identification and characterization of proteins and protein complexes in proteomics.

Keywords: Field-flow fractionation; Mass spectrometry; Multi-angle light scattering detection; Immunoassays; Cell sorting; Protein analysis; Proteomics

Factorial-based response-surface modeling with confidence intervals for optimizing thermal-optical transmission analysis of atmospheric black carbon by J.M. Conny; G.A. Norris; T.R. Gould (pp. 144-156).

Thermal-optical transmission (TOT) analysis measures black carbon (BC) in atmospheric aerosol on a fibrous filter. The method pyrolyzes organic carbon (OC) and employs laser light absorption to distinguish BC from the pyrolyzed OC; however, the instrument does not necessarily separate the two physically. In addition, a comprehensive temperature protocol for the analysis based on the Beer–Lambert Law remains elusive. Here, empirical response-surface modeling was used to show how the temperature protocol in TOT analysis can be modified to distinguish pyrolyzed OC from BC based on the Beer–Lambert Law. We determined the apparent specific absorption cross sections for pyrolyzed OC ( σ_Char) and BC ( σ_BC), which accounted for individual absorption enhancement effects within the filter. Response-surface models of these cross sections were derived from a three-factor central-composite factorial experimental design: temperature and duration of the high-temperature step in the helium phase, and the heating increase in the helium–oxygen phase. The response surface for σ_BC, which varied with instrument conditions, revealed a ridge indicating the correct conditions for OC pyrolysis in helium. The intersection of the σ_BC and σ_Char surfaces indicated the conditions where the cross sections were equivalent, satisfying an important assumption upon which the method relies. 95% confidence interval surfaces defined a confidence region for a range of pyrolysis conditions. Analyses of wintertime samples from Seattle, WA revealed a temperature between 830°C and 850°C as most suitable for the helium high-temperature step lasting 150s. However, a temperature as low as 750°C could not be rejected statistically.

Keywords: Atmospheric aerosol; Light-absorbing carbon; Elemental carbon; Thermal-optical analysis; Response-surface modeling

A spectral similarity measure using Bayesian statistics by Feng Gan; Philip K. Hopke; Jiajun Wang (pp. 157-161).

A spectral similarity measure was developed that can differentiate subtle differences between two spectra. The spectra are digitalized into a vector. The difference between the two spectra is defined by a difference vector, which is one spectrum minus the other. The spectral similarity measure is transformed into a hypothesis test of the similarities and differences between the two spectra. The scalar mean of the difference vector is used as the statistical variable for the hypothesis test. A threshold for the hypothesis that the spectra are different was proposed. The Bayesian prior odds ratio was estimated from multiple spectra of the same sample. The posterior odds ratio was used to quantity the spectral similarity measure of the two spectra. Diffuse reflectance near-infrared spectra of tobacco samples of two formulations were used to demonstrate this method. The results show that this new method can detect subtle differences between the spectra.

Keywords: Spectral similarity measure; Bayesian statistics; Near-infrared spectrum; Tobacco

Stir bar sorptive extraction–gas chromatography–mass spectrometry analysis of tetramethylene disulfotetramine in food: Method development and comparison to solid-phase microextraction by Lowri S. De Jager; Gracia A. Perfetti; Gregory W. Diachenko (pp. 162-166).

A stir bar sorptive extraction–gas chromatography–mass spectrometry (SBSE–GC–MS) method for the determination of tetramethylene disulfotetramine is presented. The limits of detection (LOD) of the optimized method was 0.2ngg⁻¹ for extractions from water and 0.3–2.1ngg⁻¹ for extractions from foods. Recovery was highly matrix dependent (36–130%) and quantification required standard addition calibrations. Standard addition calibration lines had high linearity ( R²>0.97) and replicate extractions had good reproducibility (R.S.D.=4.4–9.8%). A comparison of the SBSE method and a previously developed headspace (HS)-solid-phase microextraction (SPME) method was performed. Generally, SBSE provided higher sensitivity with decreased analysis time.

Keywords: Tetramine; Stir bar sorptive extraction; Solid-phase microextraction; Food analysis; Food defense; Tetramethylene disulfotetramine

Headspace solid phase microextraction and gas chromatography–quadrupole mass spectrometry methodology for analysis of volatile compounds of marine salt as potential origin biomarkers by Isabel Silva; Sílvia M. Rocha; Manuel A. Coimbra (pp. 167-174).

The establishment of geographic origin chemical biomarkers for the marine salt might represent an important improvement to its valorisation. Volatile compounds of marine salt, although never studied, are potential candidates. Thus, the purpose of this work was the development of a headspace solid phase microextraction (SPME) combined with gas chromatography–quadrupole mass spectrometry (HS-SPME/GC–qMS) methodology to study the volatile composition of marine salt. A 65μm carbowax/divinylbenzene SPME coating fibre was used. Three SPME parameters were optimised: extraction temperature, sample quantity, and presentation mode. An extraction temperature of 60°C and 16g of marine salt in a 120mL glass vial were selected. The study of the effect of sample presentation mode showed that the analysis of an aqueous solution saturated with marine salt allowed higher extraction efficiency than the direct analysis of salt crystals. The dissolution of the salt in water and the consequent effect of salting-out promote the release of the volatile compounds to the headspace, enhancing the sensitivity of SPME for the marine salt volatiles. The optimised methodology was applied to real matrices of marine salt from different geographical origins (Portugal, France, and Cape Verde). The marine salt samples contain ca. 40 volatile compounds, distributed by the chemical groups of hydrocarbons, alcohols, phenols, aldehydes, ketones, esters, terpenoids, and norisoprenoids. These compounds seem to arise from three main sources: algae, surrounding bacterial community, and environment pollution. Since these volatile compounds can provide information about the geographic origin and saltpans environment, this study shows that they can be used as chemical biomarkers of marine salt.

Keywords: Marine salt; Saltpans; Volatiles; Headspace solid phase microextraction combined with gas chromatography–quadrupole mass spectrometry; Geographic origin chemical biomarkers

Characterization of the quantitative relationship between signal-to-noise (S/N) ratio and sample amount on-target by MALDI-TOF MS: Determination of chondroitin sulfate subsequent to enzymatic digestion by Ariane Nimptsch; Stephanie Schibur; Matthias Schnabelrauch; Beate Fuchs; Daniel Huster; Jürgen Schiller (pp. 175-182).

Chondroitin sulfate (CS) is an important glycosaminoglycan of the extracellular matrix and its quantitative detection is of interest in different pathologies. Although there are already methods of quantitative CS determination, many of them are laborious, require time-consuming sample workup and/or suffer from low sensitivity. It will be shown here that the CS content of biological samples can be easily assessed in the picomole range subsequent to enzymatic digestion. MALDI-TOF MS (matrix-assisted laser desorption and ionization time-of-flight mass spectrometry) was used to determine the concentrations of the unsaturated disaccharide of CS obtained by enzymatic digestion of native CS with chondroitin ABC lyase. The signal-to-noise (S/N) ratio can be used as a quantitative measure: amounts of CS (measured as the disaccharide) down to at least 500fmol could be detected and there is a direct correlation between the S/N ratio and the amount of CS between about 2 and 200pmol although the curve per se is sigmoidal. The influence of different parameters such as the used matrix, the applied laser intensity and different methods of data analysis were also tested. Advantages and drawbacks of this approach are critically discussed. Finally, the method was validated by the determination of the CS content in samples of known concentration as well as in enzymatically digested bovine nasal cartilage and compared with two further established methods of CS determination (Carbazole and Alcian Blue method).

Keywords: Chondroitin sulfate; Chondroitin ABC lyase; Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry; Signal-to-noise (S/N) ratio; Extracellular matrix; Glycosaminoglycan

A cataluminescence gas sensor for carbon tetrachloride based on nanosized ZnS by Lan Luo; He Chen; Lichun Zhang; Kailai Xu; Yi Lv (pp. 183-187).

A novel and sensitive gas sensor was proposed for the determination of carbon tetrachloride based on its cataluminescence (CTL) by oxidation in the air on the surface of nanosized ZnS. The luminescence characteristics and the optimal conditions were investigated in detail. Under the optimized conditions, the linear range of the CTL intensity versus the concentration of carbon tetrachloride was 0.4–114μgmL⁻¹, with a correlation coefficient ( R) of 0.9986 and a limit of detection (S/N=3) of 0.2μgmL⁻¹. The relative standard deviation (R.S.D.) for 5.9μgmL⁻¹ carbon tetrachloride was 2.9% ( n=5). There was no or weak response to common foreign substances including methanol, ethanol, benzene, acetone, formaldehyde, acetaldehyde, dichloromethane, xylene, ammonia and trichloromethane. There was no significant change of the catalytic activity of the sensor for 40h over 4 days, with a R.S.D. of less than 5% by collecting the CTL intensity once an hour. The proposed method was simple and sensitive, with a potential of detecting carbon tetrachloride in environment and industry grounds. The possible mechanism was also discussed briefly.

Keywords: Gas sensor; Carbon tetrachloride; Cataluminescence; Nanosized ZnS

Rapid and novel discrimination and quantification of oleanolic and ursolic acids in complex plant extracts using two-dimensional nuclear magnetic resonance spectroscopy—Comparison with HPLC methods by Vassiliki G. Kontogianni; Vassiliki Exarchou; Anastassios Troganis; Ioannis P. Gerothanassis (pp. 188-195).

A novel strategy for NMR analysis of mixtures of oleanolic and ursolic acids that occur in natural products is described. These important phytochemicals have similar structure and their discrimination and quantification is rather difficult. We report herein the combined use of proton–carbon heteronuclear single-quantum coherence (¹H–¹³C HSQC) and proton–carbon heteronuclear multiple-bond correlation (¹H–¹³C HMBC) NMR spectroscopy, in the identification and quantitation of oleanolic acid (OA) and ursolic acid (UA)in plant extracts of the Lamiaceae and Oleaceae family. The combination of¹H–¹³C HSQC and¹H–¹³C HMBC techniques allows the connection of the proton and carbon-13 spins across the molecular backbone resulting in the identification and, thus, discrimination of oleanolic and ursolic acid without resorting to physicochemical separation of the components. The quantitative results provided by 2D¹H–¹³C HSQC NMR data were obtained within a short period of time (∼14min) and are in excellent agreement with those obtained by HPLC, which support the efficiency of the suggested methodology.

Keywords: Oleanolic acid; Ursolic acid; NMR; Mixture analysis; ¹; H–; ¹³; C heteronuclear single-quantum coherence; ¹; H–; ¹³; C heteronuclear multiple-bond correlation

Imaging fingerprinting of excitation emission matrices by Muhammad Ali Malik; Emanuela Gatto; Stephen Macken; Corrado DiNatale; Roberto Paolesse; Arnaldo D’Amico; Ingemar Lundström; Daniel Filippini (pp. 196-201).

The spectral fingerprinting of the excitation emission matrix (EEM) of fluorescent substances is demonstrated using polychromatic light sources and tri-chromatic image detectors. A model of the measured fingerprints explaining their features and classification performance, based on the polychromatic excitation of the indicators is proposed.Substantial amount of spectral information is retained in the fingerprints as corroborated by multivariate analysis and experimental conditions that favor such situation are identified.In average, for five different substances, the model shows a fitting goodness measured by the Pearson's r coefficient and the root mean square deviation of 0.8541 and 0.0247 respectively, while principal component classification patterns satisfactorily compare with the EEM spectroscopy classification and respectively explain 96% and 93% of the information in the fist two principal components.The measurements can be performed using regular computer screens as illumination and web cameras as detectors, which constitute ubiquitous and affordable platforms compatible with distributed evaluations, in contrast to regular instrumentation for EEM measurements.

Keywords: Chemical sensing; Optical sensing; Excitation emission matrix; Computer screen photo-assisted technique; Spectral fingerprinting

Determination of dextrin based on its self-aggregation by resonance light scattering technique by Zhanguang Chen; Li Zhu; Tianhe Song; Jinhai Huang; Yali Han (pp. 202-206).

A novel free-probe assay of dextrin was established based on the resonance light scattering (RLS) enhancement in aqueous solution due to the self-aggregation of dextrin. The RLS intensity was well proportional to the concentration of dextrin over the wide range 0.2–14μgmL⁻¹ and a detection limit 0.02μgmL⁻¹ was obtained in the optimum conditions. The effect factors such as pH, buffer medium, holding time, ionic strength and temperature were studied in detail. Little or no interference was presented in the detection when adding coexisting substances including various metal ions and some saccharine in the solution. The assay proposed owns the advantages of easy operation, rapidity, sensitivity and practicability. Three synthetic samples and three kinds of medicine samples were analyzed with satisfactory results.

Keywords: Self-aggregation; Free-probe; Resonance light scattering (RLS); Dextrin

Development of a fluorescent chelating ligand for gallium ion having a quinazoline structure with two Schiff base moieties by Junko Kimura; Hiroshi Yamada; Hayato Ogura; Takehiko Yajima; Takeshi Fukushima (pp. 207-213).

A novel chelating ligand, 2,4-[bis-(2,4-dihydroxybenzylidene)]-dihydrazinoquinazoline (DBHQ), was synthesized, and the fluorescence characteristics of its complex with metal ions were investigated.Thirty-five different metal ions were tested for the emission of fluorescence in the presence of DBHQ in aqueous solutions in a pH range of 3.0–10.5 (at a difference of 0.5 for each metal).It was observed that DBHQ fluoresces intensely at 470nm with an excitation wavelength of 405nm in the presence of Ga³⁺ or Al³⁺ in the pH range 3.0–4.0. The other metal ions did not show fluorescence with DBHQ. Although the presence of Cu²⁺, Co²⁺ and Fe³⁺ decreased the fluorescence intensity of DBHQ–Ga³⁺, the addition of a fluoride ion (NaF) recovered the fluorescence by masking the interfering ions. In addition, the fluoride ions were found to enhance the sensitive determination of Ga³⁺ because the fluorescence intensity of DBHQ–Ga³⁺ was further increased approximately 2.5-fold in the presence of F⁻ ( ϕ=0.658) from that in the absence of F⁻ ( ϕ=0.401). The fluoride ions also masked the Al³⁺ ions, which emit fluorescence on chelation with DBHQ. Therefore, a selective and sensitive detection of Ga³⁺ was achieved by using DBHQ in the presence of F⁻. The detection limit of Ga³⁺ was approximately 50nmolL⁻¹ (3.5ppb). The proposed method was applicable to determine Ga³⁺ in river water.

Keywords: Metal–ion complex; Fluorescence; Galium ion; Fluoride ion; 2,4-[Bis-(2,4-dihydroxybenzylidene)]-dihydrazinoquinazoline

Quantification approach for assessment of sparkling wine volatiles from different soils, ripening stages, and varieties by stir bar sorptive extraction with liquid desorption by Elisabete Coelho; Manuel A. Coimbra; J.M.F. Nogueira; Sílvia M. Rocha (pp. 214-221).

Stir bar sorptive extraction with liquid desorption followed by large volume injection coupled to gas chromatography–quadrupole mass spectrometry (SBSE-LD/LVI-GC–qMS) was applied for the quantification of varietal and fermentative volatiles in sparkling wines. The analytical data were performed by using suitable standards of monoterpene hydrocarbons (α-pinene), monoterpenols (linalool), sesquiterpenoids ( E, E-farnesol, Z-nerolidol, and guaiazulene), C₁₃ norisoprenoids (β-ionone), aliphatic and aromatic alcohols (hexanol and 2-phenylethanol), and esters (hexyl acetate and ethyl decanoate) as model compounds. The wine volatiles were quantified using the structurally related standards. The methodology showed good linearity over the concentration range tested, with correlation coefficients ranging from 0.950 to 0.997, and a reproducibility of 9–18%. The SBSE-LD/LVI-GC–qMS methodology allowed, in a single run, the quantification of 71 wine volatiles that can be quantified accurately at levels lower than their respective olfactory thresholds. This methodology was used for assessment of sparkling wine volatiles from different soils, ripening stages, and varieties. The variety and soil influenced significantly the volatile composition of sparkling wines; lower effect was observed for the ripening stage of grapes picked up one week before or after the maturity state.

Keywords: Stir bar sorptive extraction (SBSE); Liquid desorption; GC–qMS; Sparkling wines; Volatile compounds; Ripening stage; Soil type

Residue determination of glyphosate in environmental water samples with high-performance liquid chromatography and UV detection after derivatization with 4-chloro-3,5-dinitrobenzotrifluoride by Kun Qian; Tao Tang; Tianyu Shi; Fang Wang; Jianqiang Li; Yongsong Cao (pp. 222-226).

A pre-column derivatization high-performance liquid chromatographic method for glyphosate analysis has been developed. Derivatization of glyphosate was performed with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF). In pH 9.5 H₃BO₃–Na₂B₄O₇ media, the reaction of glyphosate with CNBF completed at 60°C for 30min. The labeled glyphosate was separated on a Kromasil C18 column (250mm×4.6mm, 5μm) at room temperature and UV detection was applied at 360nm. The separation of labeled glyphosate was achieved within 15min by gradient elution mode. Compared to other pre-column derivatization, this derivatization was performed more mildly, the derivative was more stable, and the detection limits of a few reagents were higher than CNBF, except 9-fluorenylmethyl chloroformate (FMOC-Cl) using fluorescence and mass spectrometry, however, this reagent avoid to be removed after derivatization like FMOC-Cl. The detection limit of glyphosate was 0.009mgL⁻¹ (S/N=3) without preconcentration and reach MRL, which is set at the level of 0.1mgL⁻¹ in China. The method linearity correlation coefficient was 0.9999, in concentrations ranging from 0.3 to 48.5mgL⁻¹. The proposed method has been applied to the quantitative determination of glyphosate in environmental water with recoveries of 91.80–100.20% and R.S.D. of 2.27–6.80, depending on the sample investigated.

Keywords: Glyphosate; Pre-column derivatization; 4-Chloro-3,5-dinitrobenzotrifluoride; High-performance liquid chromatography

Application of principal component analysis to the thermal characterization of silanized nanoparticles obtained at supercritical carbon dioxide conditions by C.A. García-González; J.M. Andanson; S.G. Kazarian; C. Domingo; J. Saurina (pp. 227-234).

Samples resulting from reaction of TiO₂ with octyltriethoxysilane, developed using a supercritical carbon dioxide procedure, have been studied by infrared and Raman spectroscopies and thermogravimetric analysis. Different reaction conditions have been applied to the preparation of samples in order to study the influence of experimental factors on the sample properties. Vibrational techniques have first been used to verify the presence of silanized structures on the surface of TiO₂ through the detection of specific bands characteristic of the Si–O–Si cross-linking. Thermogravimetric profiles consisting of weight loss values as a function of temperature have been analyzed by principal component analysis to extract information about the characteristics of the linkage between silane and TiO₂ as well as the thermal stability of the prepared materials. The mathematical treatment of data has provided conclusions on the properties of the samples and analogies and differences with respect to the commercial material.

Keywords: Silanization; Titanium dioxide nanoparticles; Supercritical processes; Vibrational spectroscopies; Thermogravimetric analysis; Principal component analysis

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Analytica Chimica Acta (v.635, #2)