Analytical Letters

Ayarza, Nerea; Góngora, Juan M. G.; Alonso, Rosa M.

doi: 10.1080/00032719.2014.984191pmid: N/A

A simple ion chromatographic method has been applied to the determination of anionic impurities chloride, bromide, nitrate, and sulfate in hexafluorotitanic acid and hexafluorozirconic acid samples. Industrial samples analyzed may contain high levels of fluorinated species at pH values lower than 1.0, which represents a handicap for the instrumental analysis of these matrixes. Up to now, these samples have been analyzed by chemical methods, which have interferences, involving detection of the final point in chloride determination by volumetry and coprecipitation in sulfate determination by gravimetry. The optimization of the method was carried out using industrial samples. In order to obtain the best chromatographic resolution, the dilution factor of the samples, flow rate, and eluent concentration were studied using isocratic elution. The ion chromatographic method was suitable for the determination of anionic impurities in acidic matrixes, except for chloride in hexafluorozirconic acid. The analytes were separated in hexafluorotitanic acid and hexafluorozirconic acid, without using any sample treatment apart from dilution, with good linearity with correlation coefficients higher than 0.99 and inter- and intra-day repeatability lower than 15 percent, expressed in terms of the relative standard deviation.

He, Yuting; Peng, Jingdong; Tang, Jinxia; Zhou, Mingqiong; Zhang, Cheng

doi: 10.1080/00032719.2014.986678pmid: N/A

A novel resonance Rayleigh scattering (RRS) detection approach combined with high–performance liquid chromatography (HPLC) was developed for the determination of reserpine, deserpidine, and ajmalicine. The resonance Rayleigh scattering signal increased when the analytes were bound to diiodofluorescein in Britton–Robinson buffer (pH 4.2). Separation was performed using a C18 column with a mobile phase consisting of acetonitrile–5 millimolar ammonium acetate buffer at pH 4.2 (44:56, volume by volume). Resonance Rayleigh scattering was measured at excitation and emission wavelengths of 320 nanometers. The experimental parameters affecting the separation and the scattering intensity were carefully optimized. Possible mechanisms for the resonance Rayleigh scattering enhancement of the indole alkaloid–diiodofluorescein system were explored by scanning electron microscopy, nuclear magnetic resonance, and ultraviolet-visible absorption spectroscopy. The method was employed for the determination of the analytes in human urine and pharmaceutical tablets.

Zhu, Kaixiang; Gong, Shuguo; Dai, Yunhui; Tuo, Suxing; Liu, Zhenghua; Qian, Liangyou; Peng, Jia; Zhou, Fangqin

doi: 10.1080/00032719.2014.984193pmid: N/A

This study establishes an analytical method for the determination of eighteen preservatives in water-based adhesives. The method was based on liquid–liquid extraction by methyl tertiary-butyl ether and subsequent determination by gas chromatography–mass spectrometry. Experimental conditions (instrumental parameters, extraction solvent, extraction mode, dispersant volume, and extraction time) were optimized and validated. When the method was applied to water-based adhesives, the limits of detection and recovery were 2.29–17.59 milligrams per kilogram and 85.7 − 93.9 percent, respectively, and the repeatability was below 5 percent for all analytes. None of the analytes were found in five cigarette adhesives.

Xi, Tao; Zhan, Xuejia; Xing, Haibo; Cao, Chengxi; Zhou, Pei

doi: 10.1080/00032719.2014.984192pmid: N/A

Copper was conjugated to two carrier proteins using penicillin G sodium salt to synthesize artificial antigens for copper. The antigens were identified by ultraviolet spectrometry, circular dichroism, and inductively coupled plasma–optical emission spectrometry. The results of ultraviolet spectrometry showed characteristic absorption peak shifts between haptens and carrier proteins. Circular dichroism showed that the secondary structure of the conjugates was an α-helix. These results suggested that the artificial antigens for copper were synthesized successfully. The polyclonal antibodies of copper were produced by immunizing New Zealand white rabbits with copper antigens. An indirect competitive enzyme-linked immunosorbent assay based on the polyclonal antibodies was developed. The concentration of copper ion was quantified based on the ability of its ethylenediaminetetraacetic acid complexes to inhibit the binding of the goat anti-rabbit immunoglobulin G conjugated with horseradish peroxidase and, subsequently, color formation in the assay. The assay showed an IC50 value of 0.475 microgram per milliliter with a detection limit of 0.007 microgram per milliliter. The antibody showed high affinity with copper and low cross-reactivity with other metals. The recovery of copper from fortified water was between 78.0 and 122 percent. The results indicate that the assay is a convenient supplemental analytical tool for monitoring copper ions in aquatic environments.

Jiang, Huan; Zhang, Dongxia; He, Zhifang; Lian, Qianwen; Xue, Zhonghua; Zhou, Xibin; Lu, Xiaoquan

doi: 10.1080/00032719.2014.984188pmid: N/A

A novel tryptophan-functionalized graphene nanocomposite was employed for the simultaneous determination of hydroquinone and catechol. The analyte electrochemical behavior on the surface of tryptophan-functionalized graphene was investigated by cyclic voltammetry and differential pulse voltammetry. Compared to conventional graphene, enhanced peak currents were obtained that were attributed to the large number of defects on tryptophan-functionalized graphene that accelerated electron transfer between the electrode and analytes. The peak potential difference between hydroquinone and catechol at the tryptophan-functionalized graphene modified glassy carbon electrode was 104 millivolt, which was sufficiently wide to simultaneously determine hydroquinone and catechol. This method was used for the analysis of tap water.

Zhao, Zongya; Zhang, Mingming; Li, Youjun; Cheng, Shuaiqi; Chen, Xiang; Wang, Jue

doi: 10.1080/00032719.2014.984189pmid: N/A

Two gold nanoparticle-graphene nanocomposites were electrochemically obtained by the one-step constant potential coreduction of graphene oxide and gold ions or the electrodeposition of gold nanoparticles on graphene oxide followed by electrochemical reduction of graphene oxide. The surface morphology, electron transfer rate, and electrocatalytic activity toward the oxidation of dopamine on these nanocomposites were systematically studied. The results showed that both preparations synthesized gold nanoparticle-graphene nanocomposites. The nanocomposite obtained by the one-step synthesis showed higher electron transfer kinetics and electrocatalytic activity toward dopamine than the material obtained by the two-step synthesis. Consequently, the one-step nanocomposite was used to modify a glassy carbon electrode to form a dopamine sensor. Differential pulse voltammetry was used to detect dopamine with a detection limit of 0.1 micromolar and a linear dynamic range from 0.2 to 20 micromolar. The sensor displayed good stability, high reproducibility, and was used for the determination of dopamine in human urine.

Calixto, Carolina Maria Fioramonti; Cavalheiro, Éder Tadeu Gomes

doi: 10.1080/00032719.2014.984194pmid: N/A

The performance of a bare graphite-polyurethane composite electrode (60 percent graphite, m/m) for the determination of tetracycline in human urine and oxytetracycline in human and bovine urine was evaluated. Using optimized differential pulse voltammetry, limits of detection as low as 2.6 micromoles per liter (tetracycline) and 1.7 micromoles per liter (oxytetracycline) were found in phosphate buffer at pH 2.5. The sample preparation included acidification and centrifugation to remove solid proteins followed by direct analysis. Recoveries between 96 and 100 percent were obtained for the determination of tetracycline and oxytetracycline in fortified urine.

Xu, Juan; Li, Tianbao; Shen, Shaofei; Zhao, Lei; Ma, Chao; Mahmoud, Abd Elaal; Wang, Jinyi

doi: 10.1080/00032719.2014.986677pmid: N/A

An electrochemically reduced carboxyl graphene modified glassy carbon electrode (ERCGr/GCE) was prepared from a carboxyl graphene modified glassy carbon electrode (CGr/GCE) and employed for the simultaneous determination of guanine and adenine. The ERCGr/GCE showed an enhanced voltammetric response toward the oxidation of guanine and adenine compared with the CGr/GCE because the conductivity and electrochemical active surface area increased during the reduction process. The voltammetric peak current was linearly dependent on guanine and adenine concentration over the ranges of 0.5–10 and 2.5–50 µmol L−1, respectively. The detection limits were 0.15 µmol L−1 for guanine and 0.10 µmol L−1 for adenine in 50 µmol L−1 phosphate buffer at pH 6.86. Determination of guanine and adenine in thermally denatured herring sperm DNA showed that the ratio of guanine/adenine was 0.758 demonstrating practical application of the ERCGr/GCE.

Gu, Congying; Tang, Qianqian; Xiang, Bingren; Xu, Jianping

doi: 10.1080/00032719.2014.986680pmid: N/A

The feasibility of the determination of fenitrothion in water is reported using two-dimensional correlation spectroscopy to select the modeled spectral regions for near-infrared spectroscopy. Partial least squares discriminant analysis (PLSDA) and least squares support vector machines discriminant analysis (LSSVM) were used to model and predict the spectra of fenitrothion aqueous solutions. Spectral regions from 5365 to 6757 per centimeter and 6944 to 7800 per centimeter were selected according to the dynamic spectra and the two-dimensional correlation synchronous spectra. Four classification methods (random division 1, random division 2, Kennard-Stone 1, and Kennard-Stone 2) were used to divide the samples into calibration and validation sets. The classification methods impacted both PLSDA and LSSVM, but the impact was larger on PLSDA than on LSSVM. In addition, different pretreatment methods (mean center, standard normal variate transformation, and orthogonal signal correction) were applied to PLSDA; the pretreatments also affected the predictions. Both PLSDA and LSSVM models were used to characterize real water samples and yielded satisfactory results. These methods allowed the direct and rapid determination of fenitrothion in water.

Li, Zhan-Ku; Wei, Xian-Yong; Yang, Zhu-Sheng; Yan, Hong-Lei; Wei, Zhe-Hao; Li, Yan; Zong, Zhi-Min

doi: 10.1080/00032719.2014.989529pmid: N/A

Geting bituminous coal (GBC) was exhaustively extracted with isometric carbon disulfide/acetone at ambient temperature to provide twenty extracts and a residue. The extracts were characterized by gas chromatography/mass spectrometry (GC/MS), Fourier transform infrared spectroscopy, and atmospheric pressure solids analysis probe time-of-flight mass spectrometry. GBC and its residue were observed with a scanning electron microscope. The total extract yield is ca. 11.5%. The GC/MS-detectable compounds in extract 1 can be classified into alkanes, cyclanes, arenes, cyclenes, and heteroatomic compounds, among which arenes are predominant. The number of detected compounds decreases and they have higher molecular masses with increasing extraction times. The combination of multiple techniques facilitates understanding the molecular composition of the extractable species from coals.