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Analytica Chimica Acta (v.661, #2)

Editorial Board (pp. i).

Additional knowledge for determining and interpreting feasible band boundaries in self-modeling/multivariate curve resolution of two-component systems by Róbert Rajkó (pp. 129-132).

Recently Tauler's mcrbands Matlab script and Maeder's grid method were used by Abdollahi et al. to calculate the elements of transformation matrix for obtaining feasible band boundaries in multivariate curve resolution of a two-component system. Neither method is analytical, instead they are iterative. For long time it is well-known that Lawton and Sylvestre's approach can provide the feasible band boundaries analytically and non-iteratively. In this paper, firstly in the literature, the clear relationship is given between Lawton and Sylvestre's approach and Tauler's approach (as well as Maeder's approach). It was found that all approaches are identical for noiseless or moderately noisy two-component systems and, it was illustrated by figures and tables provided in .

Keywords: Self-modeling curve resolution (SMCR); Band boundaries of feasible solutions; Signal contribution function; Grid method

Data fusion in multivariate calibration transfer by Wangdong Ni; Steven D. Brown; Ruilin Man (pp. 133-142).

We report the use of stacked partial least-squares regression and stacked dual-domain regression analysis with four commonly used techniques for calibration transfer to improve predictive performance from transferred multivariate calibration models. The predictive performance from three conventional calibration transfer methods, piecewise direct standardization (PDS), orthogonal signal correction (OSC) and model updating (MUP), requiring standards measured on both instruments, was significantly improved from data fusion either by stacking of wavelet scales or by stacking of spectral intervals, as demonstrated by transfer of calibrations developed on near-infrared spectra of synthetic gasoline. Stacking did not produce as significant an improvement for calibration transfer using a finite impulse response (FIR) filter, but application of SPLS regression to FIR-transferred spectra improves predictive performance of the transferred model.

Keywords: Calibration transfer; Stacked partial least-squares regression; Wavelet domain regression analysis; Data fusion

Application of Fourier transform infrared spectroscopy and orthogonal projections to latent structures/partial least squares regression for estimation of procyanidins average degree of polymerisation by Cláudia P. Passos; Susana M. Cardoso; António S. Barros; Carlos M. Silva; Manuel A. Coimbra (pp. 143-149).

Fourier transform infrared (FTIR) spectroscopy has being emphasised as a widespread technique in the quick assess of food components. In this work, procyanidins were extracted with methanol and acetone/water from the seeds of white and red grape varieties. A fractionation by graded methanol/chloroform precipitations allowed to obtain 26 samples that were characterised using thiolysis as pre-treatment followed by HPLC-UV and MS detection. The average degree of polymerisation ( DPn) of the procyanidins in the samples ranged from 2 to 11 flavan-3-ol residues. FTIR spectroscopy within the wavenumbers region of 1800–700cm⁻¹ allowed to build a partial least squares (PLS1) regression model with 8 latent variables (LVs) for the estimation of the DPn, giving a RMSECV of 11.7%, with a R² of 0.91 and a RMSEP of 2.58. The application of orthogonal projection to latent structures (O-PLS1) clarifies the interpretation of the regression model vectors. Moreover, the O-PLS procedure has removed 88% of non-correlated variations with the DPn, allowing to relate the increase of the absorbance peaks at 1203 and 1099cm⁻¹ with the increase of the DPn due to the higher proportion of substitutions in the aromatic ring of the polymerised procyanidin molecules.

Keywords: Fourier transform infrared spectroscopy; Orthogonal projections to latent structures; Partial least squares regression-1; Grape seed; Flavan-3-ols; Graded procyanidin fractionation

Comparison of several extraction techniques for multiclass analysis of veterinary drugs in eggs using ultra-high pressure liquid chromatography–tandem mass spectrometry by Antonia Garrido Frenich; María del Mar Aguilera-Luiz; Jose Luis Martínez Vidal; Roberto Romero-González (pp. 150-160).

This study compared four extraction methods for the simultaneous determination of tetracyclines, macrolides, quinolones, sulphonamides and anthelmintics (including benzimidazoles and avermectins) in eggs by ultra-high pressure liquid chromatography coupled to tandem mass spectrometry (UHPLC–MS/MS). Solvent extraction, solid-phase extraction (SPE), matrix solid-phase dispersion (MSPD) and modified QuEChERS procedure were compared in terms of recovery and number of veterinary drugs extracted. The solvent extraction procedure with a clean-up step provided better results than the other tested procedures. The QuEChERS procedure was simpler and faster, but extracted fewer compounds than solvent extraction. MSPD did not extract tetracyclines and quinolones, whereas macrolides and tetracyclines were not extracted when SPE was applied. The solvent extraction procedure was validated, obtaining recoveries ranging from 60% (sulfaquinoxaline) to 119% (levamisole) with repeatability values (expressed as relative standard deviations, RSDs) lower than 20% at two concentration levels (10 and 100μgkg⁻¹), except for erythromycin, emamectin and ivermectin that showed RSD values close to 25% at 10μgkg⁻¹. Limits of quantification (LOQs) were always equal or lower than 5μgkg⁻¹. Finally the method was applied to egg samples, and erythromycin, enrofloxacin, difloxacin, thiabendazole, emamectin and fenbendazole were detected in four samples.

Keywords: Ultra-high pressure liquid chromatography; Extraction method; Multiclass analysis; Veterinary drugs; Eggs

Ion chromatography for rapid and sensitive determination of fluoride in milk after headspace single-drop microextraction with in situ generation of volatile hydrogen fluoride by Hang Yiping; Wu Caiyun (pp. 161-166).

In this article, we report a new method that involves headspace single-drop microextraction and ion chromatography for the preconcentration and determination of fluoride. The method lies in the in situ hydrogen fluoride generation and subsequent sequestration into an alkaline microdrop (15μL) exposed to the headspace above the stirred aqueous sample. The NaF formed in the drop was then determined by ion chromatography. The influences of some crucial single-drop microextraction parameters such as the extraction temperature, extraction time, sample stirring speed, sulphuric acid concentration and ionic strength of the sample, on extraction efficiency were investigated. In the optimal condition, an enrichment factor of 97 was achieved in 15min. The calibration working range was from 10μgL⁻¹ to 2000μgL⁻¹ ( R²=0.998), and the limit of detection (signal to noise ratio of 3) was 3.8μgL⁻¹ of fluoride. Finally, the proposed method was successfully applied to the determination of fluoride in different milk samples. The recoveries of fluoride (at spiked concentrations of 200μgL⁻¹ and 600μgL⁻¹ into milk) in real samples ranged from 96.9% to 107.7%. Intra-day precision ( N=3) in terms of peak area, expressed as relative standard deviation, was found to be within the range of 0.24–1.02%.

Keywords: Headspace; Single-drop microextraction; Ion chromatography; Fluoride; Milk

High-throughput salting-out assisted liquid/liquid extraction with acetonitrile for the simultaneous determination of simvastatin and simvastatin acid in human plasma with liquid chromatography by Jun Zhang; Ramona Rodila; Eric Gage; Mathew Hautman; Leimin Fan; Linda L. King; Huaiqin Wu; Tawakol A. El-Shourbagy (pp. 167-172).

Simvastatin (SS) is an effective cholesterol-lowering medicine, and is hydrolyzed to simvastatin acid (SSA) after oral administration. Due to SS and SSA inter-conversion and its pH and temperature dependence, SS and SSA quantitation is analytically challenging. Here we report a high-throughput salting-out assisted liquid/liquid extraction (SALLE) method with acetonitrile and mass spectrometry compatible salts for simultaneous LC–MS/MS analysis of SS and SSA. The sample preparation of a 96-well plate using SALLE was completed within 20min, and the SALLE extract was diluted and injected into an LC–MS/MS system with a cycle time of 2.0min/sample. The seamless interface of SALLE and LC–MS eliminated drying down step and thus potential sample exposure to room or higher temperature. The stability of SS and SSA in various concentration ratios in plasma was evaluated at room and low (4°C) temperature and the low temperature (4°C) was found necessary to maintain sample integrity. The short sample preparation time along with controlled temperature (2–4°C) and acidity (pH 4.5) throughout sample preparation minimized the conversion of SS→SSA to ≤0.10% and the conversion of SSA→SS to 0.00% The method was validated with a lower limit of quantitation (LLOQ) of 0.094ngmL⁻¹ for both SS and SSA and a sample volume of 100μL. The method was used for a bioequivalence study with 4048 samples. Incurred sample reproducibility (ISR) analysis of 362 samples from the study exceeded ISR requirement with 99% re-analysis results within 100±20% of the original analysis results.

Keywords: Simvastatin; Simvastatin acid; High-throughput; Salting-out; Salting-out assisted liquid/liquid extraction; Liquid chromatography

Synthesis and application of multi-walled carbon nanotubes–molecularly imprinted sol–gel composite material for on-line solid-phase extraction and high-performance liquid chromatography determination of trace Sudan IV by Zhaohui Zhang; Huabin Zhang; Yufang Hu; Shouzhuo Yao (pp. 173-180).

A novel composite material of multi-walled carbon nanotubes (MWNTs)–Sudan IV molecularly imprinted polymers (MIPs) was prepared by surface molecular imprinting technique in combination with sol–gel technology. The MWNTs–MIPs were evaluated by scanning electron micrograph (SEM), Fourier transform infrared spectroscopy (FT-IR), and adsorption experiments. The results showed that the MWNTs–MIPs exhibited good selective recognition to Sudan IV. The maximum saturated binding capacity ( Q_max) is 63.2μmolg⁻¹. Applied as sorbent, the MWNTs–MIPs were used for the determination of trace Sudan IV in chilli powder by on-line solid-phase extraction–high-performance liquid chromatography (SPE–HPLC). The results showed that an enrichment factor of 741 was achieved with a loading flow rate of 1.0mLmin⁻¹ for sampling 50mL. The MWNTs–MIPs provided a fast and convenience determination platform for Sudan IV in real samples.

Keywords: Molecular imprinting; Multi-walled carbon nanotubes; Sudan IV; On-line solid-phase extraction; High-performance liquid chromatography

Analysis of ergosterol for the detection of mold in soils by automated on-fiber derivatization headspace extraction–SPME-GC/MS by D.-R. Parkinson; J.M. Warren; J. Pawliszyn (pp. 181-187).

The estimate of ergosterol ([5,7,22-ergostatrien-3β-ol] has been used by many to relate its concentration to the amount of mold in soils. This new method using on-fiber derivatization–solid phase microextraction-GC/MS method for the analysis of ergosterol presents a quick and straightforward method where low detection limits (1.5ppb) and good limit of quantitation range (3ppb to 90ppm) can be achieved with careful control of analytical parameters. After saponification of real soil samples, sampling without extensive workup can be performed and analysis by a standard addition method can be utilized to deduce the original sample concentration of ergosterol. Peak area extraction analysis by MS SIM on selected characteristic fragment ions gives results with RSD≤2.2%.

Keywords: Ergosterol; Derivatization; Solid phase microextraction-gas chromatography/mass spectrometry; Method development; Soil

Detecting trace pesticides in real time using single particle aerosol mass spectrometry by Zachary Barker; Veena Venkatchalam; Audrey N. Martin; George R. Farquar; Matthias Frank (pp. 188-194).

Pesticides are toxic substances and may cause unintentional harm if improperly used. The ubiquitous nature of pesticides, with frequent use in agriculture and the household, and the potential for harm that pesticides pose to non-target organisms such as wildlife, humans, and pets, demonstrate the need for rapid and effective detection and identification of these compounds. In this study, single particle aerosol mass spectrometry (SPAMS) was used to rapidly detect compounds from four classes of pesticides commonly used in agricultural and household applications. These include permethrin (pyrethroid class), malathion and dichlorvos (organophosphate class), imidacloprid (chloronicotinyl class), and carbaryl (carbamate class). Analytical standards of each compound were diluted and aerosolized using a nebulizer to create particles for analysis in the SPAMS instrument. The resultant dual-polarity time-of-flight mass spectra were then analyzed to identify the characteristic peaks of the compound in each sample. In addition, samples of commercial products containing pesticides, a commercial insecticide spray, containing permethrin, and a canine flea collar, containing carbaryl, were analyzed in their original form using SPAMS without any significant sample preparation. The characteristic mass spectral peaks of the active pesticides in these samples were identified using the mass spectra obtained earlier from the pesticide analytical standards. By successfully identifying pesticides in analytical standards and in commercial products, it is demonstrated herein that the SPAMS system may be capable of pesticide detection in numerous environmental and agricultural situations.

Keywords: Pesticide analysis; Single particle; Mass spectrometry; Aerosol analysis

AChE biosensor based on zinc oxide sol–gel for the detection of pesticides by Ravi Sinha; Mallikarjunarao Ganesana; Silvana Andreescu; Lia Stanciu (pp. 195-199).

Zinc oxide has been used as a matrix for immobilization of acetylcholinesterase (AChE) and detection of the pesticide paraoxon. The immobilized enzyme retained its enzymatic activity up to three months when stored in phosphate buffered saline (pH 7.4) at 4°C. An amperometric biosensor for the detection of paraoxon was designed. The biosensor detected paraoxon in the range 0.035–1.38ppm and can be used to detect other AChE inhibiting organophosphate pesticides.

Keywords: Zinc oxide; Sol–gel; Pesticide biosensor; Paraoxon; Acetylcholinesterase

Fabrication of core-shell structured nanoparticle layer substrate for excitation of localized surface plasmon resonance and its optical response for DNA in aqueous conditions by Tatsuro Endo; Daisuke Ikeda; Yukari Kawakami; Yasuko Yanagida; Takeshi Hatsuzawa (pp. 200-205).

LSPR from nanostructured noble metals such as gold and silver offers great potential for biosensing applications. In this study, a core-shell structured nanoparticle layer substrate was fabricated and the localized surface plasmon resonance (LSPR) optical characteristics were investigated for DNA in aqueous conditions. Factors such as DNA length dependence, concentration dependence, and the monitoring of DNA aspects (ssDNA or dsDNA) were measured. Different lengths and concentrations of DNA solutions were introduced onto the surface of the substrate and the changes in the LSPR optical characteristics were measured. In addition, to monitor the changes in LSPR optical characteristics for different DNA aspects, a DNA solutions denatured by means of heat or alkali were introduced onto the surface, after which optical characterization of the core-shell structured nanoparticle substrate was carried out. With this core-shell structured nanoparticle layer for the excitation of LSPR, the dependence upon specific DNA conditions (length, concentration, and aspect) could be monitored. In particular, the core-shell structured nanoparticle layer substrate could detect DNA of length 100–5000bp and 400-bp DNA at a concentration of 4.08ngmL⁻¹ (1×10⁷ DNA moleculesmL⁻¹). Furthermore, the changes in LSPR optical characteristics with DNA aspect could be monitored. Thus, LSPR-based optical detection using a core-shell structured nanoparticle layer substrate can be used to determine the kinetics of biomolecular interactions in a wide range of practical applications such as medicine, drug delivery, and food control.

Keywords: Localized surface plasmon resonance (LSPR); Biosensor; DNA analysis; Nanoparticles; Core-shell structure

Metal associations to microparticles, nanocolloids and macromolecules in compost leachates: Size characterization by asymmetrical flow field-flow fractionation coupled to ICP-MS by E. Bolea; F. Laborda; J.R. Castillo (pp. 206-214).

A methodological approach based on the size characterization of environmental microparticles (size larger than 1μm), nanocolloids (1μm to 15nm) and macromolecules (lower than 1000kDa) by asymmetrical flow field-flow fractionation (AsFlFFF), taking advantage of both normal and steric elution modes, is presented. The procedure was optimized to minimize the potential alteration of the size distribution and metal associations of the species characterized. Prior to separation by AsFlFFF, samples are subjected to gravitational settling of the solid suspension, followed by a centrifugation of the settled sample. The comparison between the fractograms of the settled and the centrifuged samples allows the characterization of the microparticles, which are eluted in steric mode in the AsFlFFF system. The characterization of nanocolloids and macromolecules is carried out on the centrifuged sample by applying different operational conditions under normal mode in the AsFlFFF system. A comparison with the conventional frontal filtration through 0.45μm pore size membranes have shown that filtration removes particles below their nominal pore size, modifying the size distribution of the samples respect to the centrifugation. The methodology proposed has been applied to the size characterization of compost leachates. The contribution of these three differentiated fractions to the mobilization of metals has been determined by coupling the AsFlFFF system to an inductively coupled plasma mass spectrometer (ICP-MS).

Keywords: Asymmetrical flow field-flow fractionation; ICP-MS; Environmental microparticles; Colloids; Macromolecules; Metal associations

Selective solid-phase extraction of dibutyl phthalate from soybean milk using molecular imprinted polymers by Juan He; Ruihe Lv; Jing Zhu; Kui Lu (pp. 215-221).

An analysis method is reported for dibutyl phthalate and related compounds with high selectivity and sensitivity by using the selective molecularly imprinted solid-phase extraction (MISPE) technique. In this report, dibutyl phthalate (DBP) is employed as the template molecule, and the molecularly imprinted polymers (MIPs) are synthesized through the bulk polymerization of methacrylic acid (MAA). The Scatchard plot suggests that the template–polymer system has two-site binding behavior with the dissociation constants of 0.5187 and 0.01898mmolL⁻¹, respectively. The rebinding test, based on the MISPE column technique, shows the recoveries of soybean milk samples spiked with 5 phthalates are in the range of 75.8–107.5% with the relative standard deviations of 1.80–10.08%, indicating the feasibility of the prepared MIPs for phthalates extraction. Finally, the method is used to analyze the trace level of phthalates in commercial soybean milk.

Keywords: Molecularly imprinted polymers; Dibutyl phthalate; Solid-phase extraction; Soybean milk

Liquid chromatographic analysis of oxcarbazepine and its metabolites in plasma and saliva after a novel microextraction by packed sorbent procedure by Maria Addolorata Saracino; Katianna Tallarico; Maria Augusta Raggi (pp. 222-228).

A rapid and reliable analytical method suitable for the simultaneous determination of the antiepileptic drug, oxcarbazepine and its metabolites in human plasma and saliva by means of liquid chromatography with diode array detection (DAD) has been developed. Oxcarbazepine and its metabolites (10,11-dihydro-10-hydroxycarbamazepine, trans-10,11-dihydro-10,11-dihydroxycarbamazepine and 3-hydroxycarbamazepine) were baseline separated within 6.5min on a reversed-phase C18 column with a phosphate buffer–acetonitrile–triethylamine mixture as the mobile phase. The DAD detector was set at 240nm. A sample preparation method for biological samples using a microextraction by packed sorbent technique has been implemented, employing a C18 sorbent inserted into a microvolume syringe and using only a small volume (25μL) of plasma or saliva. The extraction yield values were satisfactory for all analytes (>86.5%) as well as the precision data, which were always in the low percentage of relative standard deviation values (<4.6%). The method was successfully applied to both plasma and saliva samples drawn from psychiatric and neurological patients undergoing treatment with oxcarbazepine (Tolep^®) tablets.

Keywords: Abbreviations; OXCBZ; oxcarbazepine; CBZ; carbamazepine; CBZ-10OH; 10,11-dihydro-10-hydroxy-5H-dibenzo[b,f]azepine-5-carboxamide; CBZ-DiOH; trans; -10,11-dihydro-10,11-dihydroxy-5H-dibenzo[b,f]azepine-5-carboxamide; CBZ-3OH; 3-hydroxy-5H-dibenz[b,f]azepine-5-carboxamide; TDM; therapeutic drug monitoring; CNS; central nervous system; DAD; diode array detectionOxcarbazepine; Metabolites; Liquid chromatography; Microextraction by packed sorbent; Saliva; Plasma

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Analytica Chimica Acta (v.661, #2)