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Analytica Chimica Acta (v.628, #1)

Editorial Board (pp. iii).

Contents (pp. v-vi).

Fabrication of 1D nanofluidic channels on glass substrate by wet etching and room-temperature bonding by Qiaohong He; Shuang Chen; Yuan Su; Qun Fang; Hengwu Chen (pp. 1-8).

In this paper, a simple and facile technique for fabricating one-dimensional (1D) glass nanofluidic chips was developed. Instead of using expensive nanolithography, the standard UV lithography and wet chemical etching technique was used to fabricate 1D nanochannels on a glass substrate. Smooth channel surfaces were obtained by adding HNO₃ into conventional HF–NH₄F etching solution. The calibrated etching rate of 3.6nmmin⁻¹ was achieved using 1.5×10⁻²molL⁻¹ HF–7.5×10⁻³molL⁻¹ NH₄F–7.5×10⁻³molL⁻¹ HNO₃ as etchant at 40°C. Inter-day preparation gave a R.S.D. of 6.8% in channel depth. The substrate was bonded with a glass cover plate at room temperature. A minimum aspect ratio (depth to width) of 5.0×10⁻⁵ for the nanochannels was achieved. The channel depth before bonding was measured by an a-surface profilometer, and the depth uniformity of nanochannels after bonding was demonstrated by cross-section scanning electron microscopy (SEM) analysis. With this technique, we successfully fabricated a nanofluidic device integrating nanochannel with microchannels and demonstrated the ion enrichment-depletion phenomena.

Keywords: Fabrication; Glass nanofluidic chip; Room-temperature bonding; Ion-enrichment and depletion

Recent strategies to improve resolution in capillary electrophoresis—A review by Anne Varenne; Stephanie Descroix (pp. 9-23).

Besides the classical approaches used in capillary electrophoresis (CE) to improve separation, new strategies have been more recently introduced. This review presents some targeted strategies that have been recently developed in order to enhance the resolution of electrokinetic separations. Both novel electrolytes (non-aqueous and isoelectric buffers) and additives (ionic liquids) are presented in terms of performances and mechanisms involved to increase separation resolution. The advantages of innovative methodologies employed in electrokinetic miniaturization are also presented, that allow resolution enhancement. Finally, an insight into the complementarity of a specific hyphenated detection, i.e. mass spectrometry (MS), is performed, as an original strategy to help for better characterization of complex mixtures separation.

Keywords: Resolution; Capillary electrophoresis; Non-aqueous solvents; Isoelectric buffers; Ionic liquids; Mass spectrometry hyphenation; Miniaturization

Determination of testosterone propionate in cosmetics using excitation-emission matrix fluorescence based on oxidation derivatization with the aid of second-order calibration methods by Jinfang Nie; Hailong Wu; Xuemei Wang; Yun Zhang; Shaohua Zhu; Ruqin Yu (pp. 24-32).

A sensitive excitation-emission fluorescence method was proposed to determine testosterone propionate (TP) in several cosmetics with the aid of second-order calibration methods based on the self-weighted alternating trilinear decomposition (SWATLD) and parallel factor analysis (PARAFAC) algorithms. TP can be transformed into a highly fluorescent derivative through oxidation reaction with concentrated sulfuric acid (H₂SO₄). Both algorithms have been recommended to enhance the selectivity and attain TP concentration in cosmetics free from interference from potential interfering matrix contaminants introduced during simple cosmetic pretreatment procedure, even in the presence of other homogeneous drugs. Satisfactory results have been achieved for TP in complicated cosmetics, fully exploiting “second-order advantage”. The correlation coefficients of TP obtained by using both SWATLD and PARAFAC with N=3 are 0.9968 and 0.9974, and the average recoveries, 99.3±4.7% and 101.3±5.9%, respectively. Furthermore, in order to investigate the performance of the proposed methods, some statistical parameters and figures of merit of SWATLD and PARAFAC, i.e., sensitivity (SEN), selectivity (SEL) and limit of detection (LOD) were evaluated, and the accuracy of both algorithms was also validated by the elliptical joint confidence region (EJCR) test.

Keywords: Testosterone propionate; Self-weighted alternating trilinear decomposition; Parallel factor analysis; Oxidation derivatization; Second-order calibration

Study on different pre-treatment procedures for metal determination in Orujo spirit samples by ICP-AES by Julia Barciela; Manuela Vilar; Sagrario García-Martín; Rosa M. Peña; Carlos Herrero (pp. 33-40).

In this work several pre-treatment methods were studied for metal (Na, K, Mg, Cu and Ca) determination in Orujo spirit samples using inductively coupled plasma atomic emission spectrometry (ICP-AES). Dilution, digestion, evaporation, and cryogenic desolvatation techniques were comparatively evaluated. Because of their analytical characteristics, digestion and evaporation with nitrogen current were found to be appropriate procedures for the determination of metals in alcoholic spirit samples. Yet, if simplicity and application time are to be considered, the latter—evaporation in a water bath with a nitrogen current—stands out as the optimum procedure for any further determinations in Orujo samples by ICP-AES. Low detection levels and wide linear ranges (sufficient to determine these metals in the samples studied) were achieved for each metal. The recoveries (in the 97.5–100.5% range) and the precision (R.S.D. lower than 5.6%) obtained were also satisfactory. The selected procedure was applied to determine the content of metals in 80 representative Galician Orujo spirit samples with and without a Certified Brand of Origin (CBO) which had been produced using different distillation systems. The metal concentrations ranged between 0.37 and 79.7mgL⁻¹ for Na, −1 for K, 0.02–4.83mgL⁻¹ for Mg content, −1 for Cu and 0.03–13.10mgL⁻¹ for Ca.

Keywords: Metal content; Inductively coupled plasma atomic emission spectrometry; Digestion; Evaporation; Dilution; Cryogenic desolvatation; Orujo; spirits

Sensitive determination of cadmium in water samples by room temperature ionic liquid-based preconcentration and electrothermal atomic absorption spectrometry by Estefanía M. Martinis; Roberto A. Olsina; Jorgelina C. Altamirano; Rodolfo G. Wuilloud / (pp. 41-48).

A sensitive preconcentration methodology for Cd determination at trace levels in water samples was developed in this work. 1-Butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]) room temperature ionic liquid (RTIL) was successfully used for Cd preconcentration, as cadmium-2–(5-bromo-2-pyridylazo)-5-diethylaminophenol complex [Cd–5-Br-PADAP]. Subsequently, Cd was back-extracted from the RTIL phase with 500μL of 0.5molL⁻¹ nitric acid and determined by electrothermal atomic absorption spectrometry (ETAAS). A preconcentration factor of 40 was achieved with 20mL of sample. The limit of detection (LOD) obtained under optimum conditions was 3ngL⁻¹ and the relative standard deviation (R.S.D.) for 10 replicates at 1μgL⁻¹ Cd²⁺ concentration level was 3.5%, calculated at peak heights. The calibration graph was linear from concentration levels near the detection limits up to at least 5μgL⁻¹. A correlation coefficient of 0.9997 was achieved. Validation of the methodology was performed by standard addition method and analysis of certified reference material (CRM). The method was successfully applied to the determination of Cd in river and tap water samples.

Keywords: 1-Butyl-3-methylimidazolium hexafluorophosphate; Room temperature ionic liquid; Cadmium; Preconcentration

Small molecule–biopolymer interactions: Ultraviolet–visible and fluorescence spectroscopy and chemometrics by Yongnian Ni; Shaojing Su; Serge Kokot (pp. 49-56).

Interactions between small molecules with biopolymers e.g. the bovine serum albumin (BSA protein), are important, and significant information is recorded in the UV–vis and fluorescence spectra of their reaction mixtures. The extraction of this information is difficult conventionally and principally because there is significant overlapping of the spectra of the three analytes in the mixture. The interaction of berberine chloride (BC) and the BSA protein provides an interesting example of such complex systems. UV–vis and fluorescence spectra of BC and BSA mixtures were investigated in pH 7.4 Tris–HCl buffer at 37°C. Two sample series were measured by each technique: (1) [BSA] was kept constant and the [BC] was varied and (2) [BC] was kept constant and the [BSA] was varied. This produced four spectral data matrices, which were combined into one expanded spectral matrix. This was processed by the multivariate curve resolution–alternating least squares method (MCR–ALS). The results produced: (1) the extracted pure BC, BSA and the BC–BSA complex spectra from the measured heavily overlapping composite responses, (2) the concentration profiles of BC, BSA and the BC–BSA complex, which are difficult to obtain by conventional means, and (3) estimates of the number of binding sites of BC.

Keywords: Alternating least squares; Spectrofluorimetry; Ultraviolet–vis absorbance spectroscopy; Bovine serum albumin; Berberine chloride

Ultraviolet resonance Raman spectroscopy as a robust spectroscopic tool for in situ sunscreen analysis by Sulayman A. Oladepo; Glen R. Loppnow (pp. 57-66).

Current techniques being used for sunscreen analysis are incapable of direct determination of the active ingredients in sunscreen formulations. Therefore, the development of methodologies for rapid in situ analysis of sunscreens is desirable. This paper describes the application of ultraviolet resonance Raman spectroscopy (UVRRS) to the direct in situ analysis of sunscreen formulations. High-quality UV resonance Raman spectra were obtained for five sunscreen active ingredients (AIs), mixtures of the AIs and real sunscreen formulation samples. The spectra from the sunscreen formulations gave distinct spectral signatures indicative of the sunscreen AIs in each sample, with essentially no interference from the complex sunscreen matrix. Also, despite the fact that many of the AIs are fluorescent, no fluorescence interferences in the resonance Raman spectra were observed. Excitation wavelength-dependent studies throughout the 244–275nm region demonstrate that the best discrimination of the AIs was achieved at an excitation wavelength of 244nm. Thus, by tuning the excitation wavelength within the absorption bands of the AIs, complete identification of these analytes can be achieved in situ without any sample pretreatment or separation. The limit of detection found for a common AI in situ with this technique is 0.23% (w/w), the limit of quantitation is 0.78% (w/w), while the dynamic range is between 0.8% and 50% (w/w). The technique is fast, robust, lacks any major interference, and can be adapted for routine online quality control.

Keywords: UV resonance Raman spectroscopy; Sunscreens; In situ; analysis; DNA damage and protection; Absorption spectroscopy; Fluorescence spectroscopy

Determination of isoniazid among pharmaceutical samples and the patients’ saliva samples by using potassium ferricyanide as spectroscopic probe reagent by Hua Zhang; Lingli Wu; Quanmin Li; Xinzhen Du (pp. 67-72).

A novel method to determine isoniazid with high sensitivity and good selectivity has been established by using potassium ferricyanide as spectroscopic probe reagent. In the presence of potassium ferricyanide, it has been demonstrated that iron(III) is reduced to iron(II) by isoniazid at pH 4.0. In addition, the in situ formed iron(II) reacts with potassium ferricyanide to give soluble prussian blue. The absorbance of soluble prussian blue is measured at the absorption maximum of 735nm, and the amount of isoniazid can be calculated based on this absorbance. A good linear relationship of the concentration of isoniazid versus absorbance is observed with a linear range of 0.040–8.00μgmL⁻¹. The linear regression equation is A=−0.00286+0.28588 C (μgmL⁻¹) with a correlation coefficient of 0.9992. The detection limit (3 σ/ k) is 0.037μgmL⁻¹, and its relative standard deviation (R.S.D.) is 0.35% ( n=11). Moreover, the apparent molar absorption coefficient of indirect determination of isoniazid is 3.92×10⁴Lmol⁻¹cm⁻¹. The parameters with regard to determination are optimized, and the reaction mechanism is discussed. This method has been successfully applied to the determination of isoniazid in pharmaceutical samples and saliva samples of patients.

Keywords: Potassium ferricyanide; Isoniazid; Soluble prussian blue; Spectrophotometry

Trace analysis of contraceptive drug levonorgestrel in wastewater samples by a newly developed indirect competitive enzyme-linked immunosorbent assay (ELISA) coupled with solid phase extraction by Chun Pu; Ya-Fei Wu; Hong Yang; An-Ping Deng (pp. 73-79).

A sensitive and specific enzyme-linked immunosorbent assay for the detection of levonorgestrel (LNG) in wastewater samples was developed. The carbonyl group at position 3 on LNG molecule was reduced to hydroxyl group, which was then linked to ethyl bromoacetate. After hydrolysis, the LNG derivative with carboxylic group at the end of a spacer arm was obtained and covalently coupled to carrier proteins. The conjugates of LNG–bovine serum albumin and LNG–ovalbumin were used as immunogen and coating antigen, respectively. The superior polyclonal antibody was characterized in terms of sensitivity and specificity. The ELISA standard curve for LNG was constructed in the concentration range of 0.1–100ngmL⁻¹. For eight standard curves run in 4 weeks, IC₅₀ values were found within 0.9±0.2ngmL⁻¹ and the limit of detection was about 0.07ngmL⁻¹. The antiserum displayed 19.6% cross-reactivity with 17α-ethynylestradiol, but only lesser than 0.1% cross-reactivity with other seven tested compounds. The parameters of the assay demonstrate the high sensitivity, specificity and stability of the established ELISA. Recoveries of LNG in spiked water samples were found in range of 95.0–123.5% with the relative standard deviations of 5.3–11.5%. Coupled with solid phase extraction, the ELISA was applied for the determination of LNG in influent and effluent obtained from wastewater treatment plant and the results were confirmed by HPLC. The results measured by ELISA were very similar to those of HPLC. The proposed ELISA provides an alternative method for the determination of trace LNG in wastewater samples.

Keywords: Levonorgestrel; Enzyme-linked immunosorbent assay; Steroids; Progestogens; Wastewater sample

A electrochemiluminescence aptasensor for detection of thrombin incorporating the capture aptamer labeled with gold nanoparticles immobilized onto the thio-silanized ITO electrode by Lanyun Fang; Zhaozi Lü; Hui Wei; Erkang Wang (pp. 80-86).

A novel electrochemiluminescence (ECL) aptasensor was proposed for sensitive and cost-effective detection of the target thrombin adopted an aptamer-based sandwich format. To detect thrombin, capture aptamers labeled with gold nanoparticles (AuNPs) were first immobilized onto the thio-silanized ITO electrode surface through strong Au–S bonds. After catching the target thrombin, signal aptamers tagged with ECL labels were attached to the assembled electrode surface. As a result, an AuNPs-capture-aptamer/thrombin/ECL-tagged-signal-aptamer sandwich type was formed. Treating the resulting electrode surface with tri- n-propylamine (TPA) and applying a swept potential to the electrode, ECL response was generated which realized the detection of target protein. Spectroscopy and electrochemical impedance techniques were used to characterize and confirm the fabrication of the ECL aptasensor. AuNPs amplification and smart sensor fabrication art were implemented for the sensitive and cost-effective detection purpose. Signal-to-dose curve excellently followed a sandwich format equation and could be used to quantify the protein, and the detection limit was estimated to be 10nM. Other forms of thrombin such as β- and γ-thrombins had negligible response, which indicated a high specificity of α-thrombin detection. The aptasensor opened up new fields of aptamer applications in ECL domain, a highly sensitive technique, and had a promising perspective to be applied in microarray analysis.

Keywords: Electrochemiluminescence (ECL); Aptasensor; Thrombin; Gold nanoparticle

Uniformly sized β-cyclodextrin molecularly imprinted microspheres prepared by a novel surface imprinting technique for ursolic acid by Hanmao Liu; Chunhai Liu; Xiaojing Yang; Songjun Zeng; Yuanqin Xiong; Weijian Xu (pp. 87-94).

A novel surface imprinting technique was reported to synthesize uniformly sized molecularly imprinted microspheres (MIMs) using ursolic acid (UA) as the template. Three kinds of MIMs were prepared using uniformly sized functionalized poly (glycidyl methacrylate) microspheres (F-P_GMA) as the support matrix. Adsorption experiments indicated the imprinting factor of MIMs-1 prepared with bonded β-cyclodextrin (β-CD) and acrylamide (AA) in combination was superior to those prepared with bonded β-CD (MIMs-2) or AA (MIMs-3) individually, and the binding isotherm of MIMs-1 was in good agreement with the two-site binding model. The results of chromatographic evaluation indicated that baseline separation could be achieved on MIMs-1 column for UA and oleanolic acid (OA). Compared with NIMs-1 and the traditional reverse phase C18 column, MIMs-1 showed good affinity and efficiency for separation of UA and OA. The results show the possibility for application of MIMs-1 as high performance liquid chromatography (HPLC) stationary phase to separate and determinate UA and OA. MIMs-1 was applied to separate UA from Ilex kudingcha C. J. Tseng extract and good results were obtained, which developed a new adsorbent material to solid-phase extract UA from herbs.

Keywords: Surface imprinting; Molecularly imprinted microsphere; Ursolic acid; β-Cyclodextrin

Prediction of retention times and peak shape parameters of unknown compounds in traditional Chinese medicine under gradient conditions by ultra performance liquid chromatography by Gaowa Jin; Xingya Xue; Feifang Zhang; Xiuli Zhang; Qing Xu; Yu Jin; Xinmiao Liang (pp. 95-103).

A method for the prediction of retention times and peak shape parameters of compounds of unknown structures in complex sample under linear gradient mobile phase conditions was established. Taking traditional Chinese medicine (TCM)— Rhizoma Corydalis as an example, the chromatographic retention parameters and peak shape parameters of 24 compounds were studied. After recognition of each peak under five different linear gradient conditions, the binary parameters equation was established to calculate the retention parameters on ultra performance liquid chromatography (UPLC) with 2.1mm i.d. column packed with 1.7μm particles. And further retention times under other binary gradient conditions were predicted. The largest relative error of predicted retention time for each compound in R. Corydalis was 0.75%. The exponentially modified Gaussian (EMG) model and automatic peak curve-fitting method were used to resolve the overlapping peaks, to calculate the peak shape parameters and to obtain the peak shape rules. The peak shape parameters σ, τ and W h_/2 possessed the linear relationship with the equivalent retention timetR*. Based on peak shape rules, peak shape parameters under other mobile phase conditions were predicted. The predicted peak shape parameters were coincident with the experimental results.

Keywords: Prediction; Retention time; Peak shape parameter; Peak recognition; Traditional Chinese medicine; Ultra performance liquid chromatography

Determination of some flavan-3-ols and anthocyanins in red grape seed and skin extracts by HPLC-DAD: Validation study and response comparison of different standards by Susanna Muñoz; Montserrat Mestres; Olga Busto; Josep Guasch (pp. 104-110).

Herein is presented a fully validated method that allows simultaneous determination of nine flavonoid compounds (4 flavan-3-ols and 5 anthocyanins) in skin and seed extracts of red grape varieties. On the other hand, the use of the appropriate standard for each compound studied to build the calibration graphs, avoids the error that implies the quantification of anthocyanins by using the malvidin-3-glucoside as the only reference standard. All these considerations ensure the quantification of the compounds studied in real samples. The high performance liquid chromatography (HPLC) with diode array detector (DAD) method developed exhibits good quality parameters: repeatability with R.S.D.<5.2% and intermediate precision with R.S.D.<8.1%.

Keywords: Anthocyanins; Comparison; Flavan-3-ols; Grape seeds; Grape skins; High performance liquid chromatography (HPLC); Validation; Wine

Rapid and simultaneous determination of salvianolic acid A and salvianolic acid B by complex chromatography and study on related mechanism of coordination by Beibei Zhou; Jian Pan; Jia Wang (pp. 111-116).

Salvianolic acid A (Sal A) and salvianolic acid B (Sal B) are water-soluble phenolic acids in Danshen extract and they have high medicinal value. A rapid and novel complex high-performance liquid chromatography (HPLC) method has been developed and validated for the simultaneous determination of Sal A and Sal B within 10min. The determination of Sal A and Sal B was carried out on a Waters Symmetry Shield RP18 column (5μm, 3.9mm×150mm), using methanol-deionized water (55:45, v/v, with 5mmolL⁻¹ CaCl₂ and 1% acetic acid) as the mobile phase at the flow rate of 0.8mLmin⁻¹ within 10min. The wavelength was set at 280nm. It changed the peak sequence of Sal A and Sal B and improved their effect of determination by adding CaCl₂ in the mobile phase because Sal A and Sal B coordinated with Ca²⁺. The mechanism of coordination between Sal A, Sal B and Ca²⁺ has been studied by way of Fourier transform infrared spectroscopy (FTIR), electrospray ionization mass spectrometry (ESI-MS) and computer model. The possible structures of the complex and complex ratio are provided in this article. The experiments have facilitated the study of Sal A–Ca²⁺ complex, Sal B–Ca²⁺ complex and provide a theoretical basis for industrialized extraction of Sal A and Sal B in the future.

Keywords: Salvianolic acid B; Calcium chloride; Complex chromatography; Fourier transform infrared spectroscopy; Electrospray ionization mass spectrometry; Computer model

Engine lubricating oil classification by SAE grade and source based on dielectric spectroscopy data by L. Guan; X.L. Feng; G. Xiong (pp. 117-120).

Dielectric spectroscopy (DS) is one of the most powerful and prevailing structural analysis techniques for dielectric materials. Engine lubricating oil is a typical dielectric material. But DS for qualitative or quantitative analysis of engine lubricating oil has received little attention. In this paper, DS in association with support vector machines (SVM) classification technique was employed to classify 20 samples of engine lubricating oils from Mobil, Shell and Esso by Society of Automotive Engineers (SAE) viscosity grade and source (manufacturer). Both distinguishing the multi-grade from the single-grade according to SAE grade and classification according to manufacturer were done perfectly, which proved that DS can provide useful compositional and structural information on engine lubricating oil. The work in this article has laid the foundation for further quantitative determination of properties of engine lubricating oil and will be a good start to application of DS to petroleum analysis and testing.

Keywords: Dielectric spectroscopy; Engine lubricating oil; Qualitative analysis; Support vector machines

Erratum to “A caveat concerning the application of the jack-knife to designed data” [Anal. Chim. Acta 603 (2007) 155–158] by Nicolaas (Klaas) M. Faber (pp. 121-122).

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Analytica Chimica Acta (v.628, #1)