Thermal lens spectrometric determination of hexavalent chromium

The applicability of thermal lens spectrometry (TLS) for quantification and routine determination of hexavalent chromium was investigated by using a collinear dual beam thermal lens spectrometer. In aqueous solutions the LOD of 0.1 μg l⁻¹ was obtained for Cr(VI) by using 160 mW laser power. The performance of the technique was verified by the determination of hexavalent chromium in standard reference water samples (NIST SRM 1643a and NIST SRM 1643c) and comparing the results for Cr(VI) in CCA (Cr, Cu, As)-treated timber extracts to concentrations obtained by atomic absorption spectrometry (AAS). Good agreement between the TLS results and reported values for Cr(VI) in SRMs as well as AAS results for Cr(VI) in CCA-treated timbers confirmed that TLS is a reliable and accurate analytical technique applicable for the determination of Cr(VI) in aqueous solutions at concentration levels 0.5–100 μg l⁻¹.     

Resolving the copper interference effect on the stripping chronopotentiometric response of lead(II) obtained at bismuth film screen-printed electrode

As copper(II) is a common ion in a variety of analytical samples, its effect on the stripping response of lead(II) at bismuth film screen-printed carbon electrode (BFSPCE) was investigated. The study was conducted using a screen-printed three-electrode system (working, counter and reference electrodes), with the carbon-working electrode plated in situ with bismuth film. Copper present at significant concentration level in samples was found to affect the sensitivity of the electrode by reducing the constant current stripping chronopotentiometric (CCSCP) response of lead(II). Recovery of the lead stripping response at the BFSPCE in the presence of copper was obtained when 0.1 mM ferricyanide was added to the test solution. The ferricyanide added circumvents the detrimental effect of copper(II) by selectively masking the copper ions by forming a complex. The analytical utility of the procedure is illustrated by the stripping chronopotentiometric determinations of lead(II) in soil extracts.     

一氧化二氮—乙炔火焰原子吸收法测定镍—镉浸渍液中硅

提出用一氧化二氮-乙炔火焰原子吸收法分析镍-镉浸渍液中硅.方法具有良好的灵敏度,干扰少,重现性好.硅量在5～50μg.ml~(-1)范围内与吸光度呈线性关系.测定样品中硅34.0μg.ml~(-1)(n=10)时,相对标准偏差为2.2%.标准加入回收率在98%～103%范围内,适用于镍-镉浸渍液中硅的分析.     

Application of the Hall™ electrolytic conductivity detector for the analysis of chloroanilines and chloronitroanilines in POTW sludges

Simultaneous detection with a 700-A Hall? and an NPD detector is an effective technique for characterizing chloro-and chloronitroanilines in highly complex Publicly Owned Water Treatment Works (POTW) sludges. The utilization of a modified Varian effluent splitter and a SE-54 fused silica capillary column permitted the detection of mid-picogram quantities of the polar chloroanilines without sacrificing peak shape. The response of the Hall? detector in the halogen mode was roughly proportional to the number of chlorine atoms present, while the response of the Hall? in the nitrogen mode and the NPD was less predictably influenced by the presence of one or more nitro groups. When combined with retention time data, the ratio of the NPD response to the Hall? response has been found to substantiate the presence of chloro- and chloronitroanilines in sludge extracts.     

痕量砷流动注射在线还原氢化物发生原子吸收测定

方法采用流动注射停流技术使水及土壤浸出液中Ａｓ（Ｖ）在线还原为Ａｓ（Ⅲ），不经手工还原，用氢化物发生原子吸收光谱法直接测定砷的含量。含４ｍｏｌ／Ｌ ＨＣｌ的样品溶液与３０％碘化钾溶液在编结式反应器中混合，并在采样环中停流４０ｓ，达完全还原后注入到载流中与硼氢化钠反应，采样速度５５次／ｈ，检出限（３δ）０．１μｇ／Ｌ，对自来水和土壤浸出液的加标回收结果满意。     

Determination of three compounds in Aloe vera by capillary electrophoresis

A capillary electrophoretic assay for determining aloe-emodin (AE), methyl p-coumarate (MC), and 3,4-dihydro-6,8-dihydroxyl-[(3s)-2'-acetyl-3'-hydroxyl-5'-methoxy-benzyl]-isocoumarin (DDI) in Aloe vera has been developed. Baseline separation was achieved within 15 min using a running buffer of 20 mm borax containing 10% (v/v) acetonitrile at pH 10.5. A linear relationship between the peak area and the concentration of the analytes was found in the ranges 5-500, 10-1000 and 2-1000 micro g/mL for AE, MC and DDI, respectively, with correlation coefficients of 0.9992-0.9998. The relative standard deviations of migration time and peak area were within 0.17-0.19 and 1.52-3.37%, respectively. The recoveries of AE, MC and DDI were 105, 102 and 96.4%. The contents of AE, MC and DDI in Aloe vera were measured to be 5.13, 0.768 and 1.30 mg/g, respectively.     

Rapid liquid chromatographic-mass spectrometric analysis of withanolides in crude plant extracts by use of a monolithic column

Summary A rapid analytical method has been developed for the mutual resolution of three steroidal compounds, withaferin A, iochromolide, and withacnistin. Liquid chromatography was performed on a Chromolith analytical column (4.6 mm i.d.×50 mm), made from a cylindrical silica rod, operated at a flow rate of 4 mL min⁻¹ with a simple linear gradient prepared from 0.1% aqueous formic acid and 0.1% formic acid in acetonitrile. Under optimum conditions simultaneous separation of the compounds was achieved in less than 7 min, one eighth the time required for conventional LC separation. The overall analysis time was reduced without sacrificing chromatographic performance—essential for the resolution of positional isomers such as iochromolide and withacnistin. The column was coupled to a single-quadrupole mass spectrometer and the method was characterized by good performance in terms of repeatability, selectivity, linearity, and sensitivity. Detection limits in the single-ion-monitoring mode were 0.15 μg mL⁻¹ or below. Finally, the developed method was successfully applied to the determination of withanolides in extracts fromlochroma gesnerioides obtained by three different processes—traditional Soxhlet extraction and two faster methods, microwave-assisted extraction and pressurized solvent extraction.     

Strategies for differentiation of isobaric flavonoids using liquid chromatography coupled to electrospray ionization mass spectrometry

Flavonoids are a class of secondary plant metabolites existing in great variety in nature. Due to this variety, identification can be difficult, especially as overlapping compounds in both chromatographic separations and mass spectrometric detection are common. Methods for distinguishing isobaric flavonoids using MS² and MS³ have been developed. Chromatographic separation of various plant extracts was done with RP‐HPLC and detected with positive ESI‐MS operated in information‐dependent acquisition (IDA) mode. Two methods for the determination of flavonoid identity and substitution pattern, both featuring IDA criteria, were used together with the HPLC equipment. A third method where the collision energy was ramped utilized direct infusion. With the developed strategies, it is possible to differentiate between many isobaric flavonoids. Various classes of flavonoids were found in all of the plant extracts, in the red onion extract 45 components were detected and for 29 of them the aglycone was characterized, while the substituents were tentatively identified for 31 of them. For the strawberry extract, those numbers were 66, 30 and 60, and for the cherry extract 99, 56 and 71. The great variety of flavonoids, several of them isobaric, found in each of the extracts highlights the need for reliable methods for flavonoid characterization. Methods capable of differentiating between most of the isobars analyzed have been developed. Copyright © 2014 John Wiley & Sons, Ltd.