Analytical Letters

Pinto, Frederico Garcia; Junior, Rainério Escalfoni; Saint'Pierre, Tatiana Dillenburg

doi: 10.1080/00032719.2012.677778pmid: N/A

The presence of rare earth elements (REE) in geological materials provides important information about the formation and the geochemical processes that rocks undergo. Therefore, there is a constant necessity for accurate data and reliable and fast analytical methods. However, the low concentrations of these elements typically found in rocks require quantification by sufficiently sensitive techniques, such as Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The preparation of these samples to the introduction in ICP-MS is a critical part of the process. Traditional wet dissolution methods, such as acid digestion or alkaline fusion followed by dissolution are mostly employed. The acid digestion requires a mixture of strong acids due to the presence of low soluble constituents common in rock samples, such as silicates or clays. The alkaline fusion is fast and efficient, but the dissolution of the melted material results in solutions with a high amount of total dissolved solids (TDS), which can be a problem due to the possibility of deposition in parts of the ICP-MS. Other instrumental approaches have been spread rapidly, as the coupling of a laser ablation accessory or an electrothermal vaporizer to the ICP-MS, as they can allow the direct sample introduction, or at least with minimum preparation. This paper presents a review of sample preparation methods, aimed at the quantification of rare earth elements by ICP-MS and focusing on works published in the last decade.

Dai, Xinhua; Zhao, Yingchen; Li, Ming; Fang, Xiang; Li, Xiaomin; Li, Hongmei; Xu, Bei

doi: 10.1080/00032719.2012.677779pmid: N/A

A definitive method based on liquid chromatography isotope dilution mass spectrometry (LC-IDMS) has been developed for the determination of milk urea, an indicator of nutrition status for the lactating animals. The milk samples were treated twice by sequentially adding acetonitrile and chloroform to precipitate proteins and then were directly separated using normal phase liquid chromatography without chemical derivatization. After the matrix separation, exact matching IDMS was used for the determination of milk urea, with high accuracy, high precision, good linearity and low uncertainty. The recoveries obtained for the four spiked milk samples were 100.6–102.2%. The linear range of signal responses was 10–2000 mg · kg−1 with a linearity coefficient of 0.9995. The intraday and interday precisions in terms with relative standard deviations (RSDs) were 0.17–0.38% and 0.28–0.40%, respectively. The uncertainties of the whole sample analysis process were estimated to be 0.83%, 0.60%, and 0.64% for three samples with concentrations of 151.28, 184.36, and 266.66 mg · kg−1.

Sun, Haiyan; Wang, Yan

doi: 10.1080/00032719.2012.677783pmid: N/A

Hollow fiber liquid phase microextraction (HF-LPME) was developed for the determination of potential allelochemicals by gas chromatography-mass spectrometry (GC-MS). Biomass method was applied to study the allelopathic effect. The applicability of the proposed procedure was evaluated through extraction of three potential allelochemicals in recirculating hydroponic culture solution of chili. The parameters affecting extraction. The optimum extraction conditions were obtained with 15 µL toluene as acceptor phase at an extraction time, of 30 min, an extraction temperature of 50°C, a stirring rate of 800 rpm, 9% (w/v) sodium chloride, and pH of 6 in a 10 mL sample. The calibration curves showed a high linearity level in the range of 0.1–-5 µg · mL−1, relative standard deviations between 5.51% and 8.94%, and enrichment factors that had 6.3–12.5 were obtained for 2,6-DTBP, DPA, and DIBP. Recoveries, ranging from 81.4% to 118.7% and an RSD below 10.3% were obtained when the method was applied to determine three potential allelochemicals in root exudates of real samples of 10 d, 20 d, and 30 d after cultivation.

Deng, Xiaodong; Sun, Hong; Gao, Xing; Gong, Haojun; Lu, Wenbo; Chu, Yong; Zhou, Lu; Ye, Deyong

doi: 10.1080/00032719.2012.677780pmid: N/A

Sphingomyelin synthase (SMS) is a key enzyme for the synthesis of mammalian sphingomyelin. The use of SMS plays diverse roles in physiology and pathology; thus, it could be a useful disease marker and/or drug target. We report here a novel and sensitive method for SMS activity measurement. Using a HPLC column (C18-RP), SMS activity was monitored by measuring a decrease of the fluorescent substrate C6-4-nitrobenzo-2-oxa-1,3-diazole (NBD)-ceramide (C6-NBD-Cer) and increase of the product (C6-NBD-SM). Time- and protein-dependent formation of C6-NBD-SM was investigated and enzyme kinetics was determined [K m  = 7.49 ± 0.48 µM (C6-NBD-Cer) and V max  = 27.86 ± 0.73fmol/h/mg homogenate protein]. This method is feasible, rapid, accurate, highly reproducible, and suitable for quantifying SMS enzyme activity in SMS inhibitor screening studies. A known SMS inhibitor, D609, was employed to evaluate the assay and its IC50 value has been determined. [Supplementary materials are available for this article. Go to the publisher's online edition of Analytical Letters for the following free supplemental resources: Tables and figures]

Lv, Pin; Liu, PeiPei; Wang, Hongfang; Qiu, Lijuan; Wang, George

doi: 10.1080/00032719.2012.677787pmid: N/A

Human Epidermal Growth Factor Receptor 2 (HER2) is an ideal target for anti-tumor drug development especially for breast cancer. Based on this target, either for new drug, bio-better, bio-similar screening at discovery level, or for drug substance and drug product release at QC or industry level, a reliable and robust biological potency assay is urgently needed. In this study, a BT-474 cell based anti-proliferation biological potency assay targeting HER2 was developed after an optimization of some key aspects, including cell line, seeded cell density, incubation time, and usable method for viable cell staining. Following optimization, the assay was validated to identify its specificity, precision, accuracy, linearity, range, and robustness. It was proven a highly accurate assay with good fit (R2 > 0.98), low RSD (even <5%) of replicates, and broad range (50%–150%) and could be used for drug candidates screening and quality control. This study also provides a good example for cell-based biological potency assay development aimed at other targets.

Sun, Xia; Li, Qingqing; Wang, Xiangyou; Du, Shuyuan

doi: 10.1080/00032719.2012.677782pmid: N/A

In this paper, a novel amperometric immunosensor for the determination of carbofuran based on gold nanoparticles (GNPs), magnetic Fe3O4 nanoparticles-functionalized multiwalled carbon nanotubes-chitosan (Fe3O4-FCNTs-CS), and bovine serum albumin (BSA) composite film was proposed. First, GNPs were immobilized onto the glassy carbon electrode (GCE) surface, and then the magnetic Fe3O4 nanoparticles mixed with chitosan-functionalized multiwall carbon nanotubes (CS-FCNTs) homogeneous composite (CS-FCNTs-Fe3O4) was immobilized onto the GNPs layer by electrostatic interactions between amino groups of CS and GNPs. Because chitosan (CS) contains many amino groups, it can absorb more antibodies. FCNTs have high surface area, high electrical conductivity, and it can enhance the electron transfer rate; Magnetite (Fe3O4) nanoparticles can provide a favorable microenvironment for biomolecules immobilization due to their good biocompatibility, strong superparamagnetic property, and low toxicity; and GNPs possess high surface-to-volume reaction, stability, and high conductivity. Gold Nanoparticles/Fe3O4-FCNTs-CS composite film was constructed onto the GCE surface, which had significant synergistic effects toward immunoreaction signal amplification. The stepwise assembly process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. Under the optimal conditions, the current response was proportional to the concentration of carbofuran ranging from 1.0 ng/mL to 100.0 ng/mL and from 100.0 ng/mL to 200 µg/mL with the detection limit 0.032 ng/mL. The proposed immunosensor exhibited good accuracy, high sensitivity, and stability, and it can be used for detection of carbofuran pesticide.

Liang, Chizhou; Zou, Mingqiang; Guo, Lianghong; Huang, Guoyang; Lu, Jianfei; Xu, Yong; Shou, Linfei

doi: 10.1080/00032719.2012.677784pmid: N/A

Four ELISA formats, antigen-coated indirect, antigen-coated direct, antibody-coated, and the secondary antibody-coated, were developed using monoclonal antibody to determine cephalexin. Results showed that the secondary antibody-coated method of ELISA had a better performance in the establishment of standard curves. The optimized secondary antibody-coated ELISA was used to determine cephalexin spiked in pig muscle, pig kidney, pig liver, chicken muscle, chicken liver, and cow's milk. The limits of detection were 0.09 ng/g, 0.15 ng/g, 0.26 ng/g, 0.13 ng/g, 0.19 ng/g, and 0.08 ng/mL in pig muscle, pig kidney, pig liver, chicken muscle chicken liver, and cow's milk, respectively. A mean recovery of 77.2–128.5% and coefficient of variation of 2.6–14.7% were obtained. The results given by the ELISA method were in agreement with those of the LC-MS/MS method, which confirmed the potential of the ELISA method for the monitoring of cephalexin in milk and animal tissues.

Liu, Xuan; Sun, Sijuan; Tang, Yuhai; Li, Shisen; Chang, Jianhua; Guo, Li'An; Zhao, Yanding

doi: 10.1080/00032719.2012.677785pmid: N/A

The preparation of Zn(II)-immobilized glutaraldehyde-crosslinked chitosan microspheres which was modified with epichlorohydrin, tetraethylenepentamine, and bromoacetic acid was presented in this work. The Zn(II)-immobilized value of the microspheres (Ac-TEPA-CS) is 43.6 mg g−1, which is higher than the blank microspheres. The adsorption of urea onto Zn-Ac-TEPA-CS was studied in a batch system. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherm and isotherm constant, and the kinetic of adsorption process were estimated. These data fits well with Langmuir isotherm and also indicated that the adsorption process is exothermic and follow the pseudo-second-order kinetics. The adsorption capacity depends upon the pH, the temperature and the initial concentration of urea. It observed that Zn-Ac-TEPA-CS could be repeatedly used by elution and regeneration without significant loss of adsorption capacity.

Karthikeyan, R.; Uskaikar, H. P.; Berchmans, Sheela

doi: 10.1080/00032719.2012.677786pmid: N/A

This work describes the construction of a mediatorless microbial fuel cell (MFC) using the microorganism Acetobacter aceti as the biocatalyst in the anode compartment with glucose as a fuel. The periplasmic membrane bound pyrroloquinoline quinone (PQQ) containing enzymes of these genera provide fast and highly efficient oxidation of a wide variety of substrates and helps in the direct routing of electrons to the anode. We describe our preliminary findings with regard to the use of electrochemically deposited manganese oxide films on carbon substrates as cathode materials in MFCs. Manganese oxide was electrochemically deposited on carbon paper in the presence and in the absence of the surfactant, sodium lauryl sulfate (SLS). Electrochemical characterizations of the electrodeposited films are carried out by cyclic voltammetry and impedance spectroscopy. Structural characterization of the film is carried out by XRD, XPS, and SEM. The XPS studies reveal that the presence of Mn4+ (as MnO2) in the absence of SLS and Mn3+/2+ (as Mn3O4or Mn2O3 or MnOOH) ion in the presence of SLS. The power output obtained from MnO2 cathode was 666 ± 9 mW m−3 and it is the highest value reported for MFCs with cubical configuration with the same cathode.

Wang, Shi; Qi, Zheqiong; Huang, Hongke; Ding, Hong

doi: 10.1080/00032719.2012.677790pmid: N/A

Methotrexate is widely used for treatment of various neoplastic diseases. The present work details the voltammetric analysis of Methotrexate at a multi-walled carbon nanotube (MWNT) modified screen-printed electrode (SPE). The fabrication and evaluation of MWNT-derived screen-printed electrochemical sensors based on a MWNT ink are reported. The fabricated MWNT strips combine the attractive advantages of CNT materials and disposable screen printed electrodes. The anodic voltammetric behavior of methotrexate was studied using cyclic and square-wave voltammetric techniques in tris-HCl (pH = 7.5) solution. The oxidation of methotrexate was an irreversible adsorptive-driven process. The experimental conditions such as carbon ink, MWNT, pH, the concentration, and nature of buffer were investigated to optimize the determination of methotrexate. Under optimum conditions, the square-wave voltammetric peak currents were in a linear relationship to methotrexate concentrations in the range of 5.0 × 10−7M–1.0 × 10−4 M with a detection limit of 1.0 × 10−7 M. The MWNT/SPE showed good stability, selectivity, and was successfully used to quantify methotrexate in pharmaceutical formulations.