Analysis of Polar Thermally Labile Pesticides using Different Solid-Phase Extraction (SPE) Materials with GC and HPLC Techniques

Abstract

In the present study, an efficient method for extraction, separation and determination of a limited number (30) of polar pesticides in aqueous matrices has been developed. Pesticides were extracted with high recoveries (usually >85%) from 1 L water samples, using the solid-phase extraction (SPE) technique. Affinities to different SPE materials (C-18 and XAD resins) have been studied for all pesticides. Special attention has been paid to the following 5 pesticides (which have classified by the EC as compounds which are particularly difficult to analyse): benazolia, bromofenoxim, ethofumesate, fenamiphos and phenmediphain. Thermally labile compounds have been determined with high pressure liquid chromatography (HPLC) and UV detection in comparison to TSP-LC-MS. Absolute limits of detection (LODs) for the HPLC technique are usually below 1 ng at 220 nm. Thermospray LC-MS determination shows usually limits of detection of 1-10 ng (SCAN) and 60-800 pg (SIM). All pesticides, which are amenable to GC have been detected in a comparative study with the following detectors: flame ionization detector (FID), nitrogen-phosphorus detector (NPD), electron capture detector (ECD) and atomic emission detector (AED). Element-specific detection of various functional groups of these pesticides has been achieved using GC-AED. Thus, while the FID has the lowest specificity, the AED is the most specific detector. LODs are usually < 300 pg (FID < 20 pg, NPD < 1 pg, ECD < 1 pg, AED < 300 pg). Spiked river water samples (from the River Leine and River Weser in Lower Saxony, Germany) have been used to test the employed method. With the spiked surface water samples recoveries were usually >80%.     

Interferences in Thermospray Flame Furnace AAS: Co and Mn Behavior

ABSTRACT

The effects caused by concomitants [Na(I), K(I), Ca(II), and Mg(II)] on the atomization of cobalt and manganese by thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) were here studied. The main concomitants were chosen according to typical major elements found in foods and beverages. Severe interference effects were caused by all concomitants. The interferences varied from ?101.0% to +360.0% and ?117.5% to +175.5% for Co and Mn, respectively. These data demonstrated a frequently paradoxical situation in spectrochemical analysis, that is, efforts are directed toward the introduction of a higher amount of sample, however, when this condition is attained, there is the manifestation of severe processes of interferences. These interference processes require the application of either previous separation steps or special strategies of calibration.     

用低功率微波热雾化器与十字交叉气动雾化器作为ICP-AES进样装置的比较

在 ICP- AES中 ,最常用来引入液体样品的方法是雾化法 .因此 ,雾化器雾化效率的高低直接影响到 ICP- AES的分析性能 [1,2 ] .目前 ,在 ICP- AES中最常用的雾化器是气动雾化器 (PN) .它的优点是简单、稳定性好 ;缺点是产生的雾滴的直径范围很宽 (一般为 1～ 50 μm) ,进样效率低 ,一般仅为 1 %～3% [3] .热雾化器是近年发展起来的一种雾化效率较高的雾化法 ,已被越来越多地用于 ICP- AES[4～ 7] .热雾化法的雾化原理与同轴气动雾化法类似 ,不同之处在于 :对于热雾化法来说 ,(1 )雾化所需的气体来自于液体样品本身而不是外加的惰性…     

Determination of arsenic compounds by high-pressure liquid chromatography–graphite furnace atomic absorption spectrometry and thermospray mass spectrometry

Biologically important arsenic species such as arsenobetaine, arsenocholine iodide, tetramethylarsonium iodide, methylarsonic acid, and dimethylarsinic acid can be separated and quantitated by HPLC. The pH-sensitive separations on a weak anion-exchange column are described, as well as separations on a reverse-phase column with the aid of tetrabutylammonium nitrate or heptanesulfonic acid as ion-pairing agents. The thermospray mass spectra of these arsenicals in addition to those of sodium arsenate and an arsenosugar derivative are described. This technique is suitable for HPLC MS studies.     

Ultra-trace Analysis of Metosulam,a New Triazolopyrimidine Herbicide,in Soil Using LC-UV and TSP-LC-MS

Abstract

Metosulam (DE-511), N-(2,6-dichloro-m-tolyl)-5,7-dimethoxy-[1,2,4] triazolo [1,5a]pynmidine-2-sulphonamide is a new selective herbicide developed for the control of broadleaf weeds in cereals and maize.

The application of new generation low use rate herbicides, such as metosulam, has in turn created the need for the development of ultra-trace residue methodologies. To help investigate the environmental impact of metosulam, levels at sub-part per billion (μg/kg) in soil were determined.

Application of capillary gas chromatography, with various injector systems, was unable to analyse metosulam methyl derivative due to the inherent thermal instability of the molecule. Liquid chromatography with ultraviolet detection (LC-UV) was used to quantify residues of the herbicide following a series of selective clean-up procedures. The chosen methodology used simple reagents plus standard equipment and although the molar absorbtivity of metosulam is poor, analysis of soils of various texture classes at the desired sensitivity level, was achieved.

Thermospray Liquid chromatography with mass spectrometry (TSP-LC-MS) was used as a confirmatory technique for the analysis of metosulam in the same soils. Excellent agreement between the two techniques was observed.

Details of the clean-up procedures used to produce desired selectivity and the relative merit of the two detection systems are discussed.     

Online Preconcentration/Determination of Cadmium Using Grape Bagasse in a Flow System Coupled to Thermospray Flame Furnace Atomic Absorption Spectrometry

Abstract

Thermospray flame furnace atomic absorption spectrometry (TS‐FF‐AAS) was employed for Cd(II) determination after online preconcentration. In this system, Cd(II) ions were adsorbed onto a minicolumn packed with grape bagasse. The elution of the metal ions was made with 1 mol L^?1 HCl. Various parameters, such as pH, eluent type, concentration, volume, flow rate for preconcentration, and effect of interfering ions on the retention of the metal ions have been studied. The optimum pH for the adsorption was 3.0. The enrichment factor was 33.7. The limits of detection and quantification for Cd(II) were 0.03 and 0.11 µg L^?1, respectively. The repetitivity and precision were 5.0 (5 minicolumns) and 4.6% (n=18). The stability of the minicolumns was evaluated from successive preconcentration/elution cycles (80 cycles, RSD 3.9%). The proposed method was applied for cadmium determination from certified reference materials, and good agreement was obtained at the 95% confidence level.     

Flame Furnace Atomic Absorption Spectrometry: A Review

Abstract

Flame atomic absorption spectrometry (FAAS) is one of the most widespread traditional analytical techniques for trace element determination, but it often suffers from poor sensitivity due to the low nebulization efficiency and the short residence time of free atoms in the flame. On the basis of conventional FAAS, flame furnace atomic absorption spectrometry (FF-AAS) is developed with a tube (flame furnace) placed on top of the FAAS burner for the atomization. Sample is introduced via beam injection (BIFF-AAS) or thermospray (TS-FF-AAS). Due to the total sample introduction and prolonged residence time of free atoms in the flame furnace, marked sensitivity improvement is obtained for volatile and semivolatile elements over conventional FAAS. TS-FF-AAS can be employed as an element-selective detector for GC, HPLC, or CE for studying of metal speciation analysis and metallomics. In addition, three newly developed sample introduction methods, including ultrasonic nebulization, hydride generation, and pneumatic nebulization, are discussed. The analytical figures of merit and practical applications of FF-AAS in analytical atomic spectrometry are reviewed in this article.     

Electrochemistry/mass spectrometry as a tool in metabolism studies—A review

The combination of electrochemistry (EC) and mass spectrometry (MS) has become a more and more frequently used approach in metabolism studies in the last decade. This review provides insight into the importance of metabolism studies during the drug development process and gives a short overview about the conventionally used methods since electrochemistry is often intended to substitute or minimize animal-based studies. The optimization of the electrochemical conditions is of great importance for a successful comparison with in vitro approaches. The type of metabolism reactions, which can be simulated by EC, has been extended with new cell types and working electrodes. Although the mechanism differs from the enzyme-catalyzed turnover, electrochemistry can be used to simulate a significant number of the respective reactions.     

低功率微波热雾化器与同轴气动雾化器作为电感耦合等离子体发射光谱法进样装置的比较

对用低功率微波热雾化器(MWTN)和同轴气动雾化器(PN)作为电感耦合等离子体发射光谱仪(ICP-AES)进样装置时，仪器的操作条件(样品提升速率(Q1)、载气流速(Fc))进行了选择和比较。在选定的条件下，比较了两种雾化器的分析性能。发现HCI的浓度对两种雾化器的影响不同，对于MWTN，Cr、Cd、Co、Mn和Ls，谱线的发射强度随HCl浓度的增加而略有增加；而对于PN，谱线的发射强度随HCl浓度的增加而略有降低；MWTN对于上述5种元素的检出限均优于PN，而精密度则不如后者。     

The effect of arsenicals on alkaloid production by cell suspension cultures of Catharanthus roseus

The effect of arsenic compounds on indole alkaloid production by cell suspension cultures of Catharanthus roseus was investigated. The analysis of indole alkaloids was achieved by using thermospray liquid chromatography-mass spectrometry (LC MS) which facilitated the rapid screening of alkaloid composition in cultures treated with different arsenicals at different times in their growth cycle. Treatment with dimethylarsinate (DMA), a non-selective herbicide, has a drastic inhibitory effect on alkaloid production although it is the least toxic arsenical to growth. Tryptamine, an early precursor in the biosynthesis of indole alkaloids, accumulates in cells treated with DMA, indicating that the initial step of condensation of tryptamine with secologanin is inhibited. Treatment with DMA during the early stationary phase of culture growth enhances the accumulation of some alkaloids, although some, such as catharanthine, are suppressed. The arsenicals arsenate and methylarsonate (MMA) have an inhibitory effect on alkaloid production when applied during the early growth stages. In contrast to MMA and DMA, arsenate has a stimulatory effect on catharanthine production when introduced to the culture during its early stationary phase. Thus the changes in the pattern of alkaloid accumulation on addition of arsenicals are dependent on the arsenic species and its concentration, as well as the time of application. This variable response indicates that each arsenical has a distinct mode of action on the secondary metabolic pathways of C. roseus.