Matrix Enhancement Effects Research Articles

Determination of chlorpyrifos 20% EC (Dursban 20 EC) in scented rose and its products

The method for determination of chlorpyrifos is validated and dissipation behaviour of residue in scented rose and percent transfer in different products is described. GC–electron-capture detection with a HP-1, 30 m × 0.53 mm, 3.0 μm capillary column and nitrogen at 1 ml/min was used in the study. Plant matrices studied were: leaves, flowers, soil, rose water, absolute and concrete. Detector response linearity and sensitivity, limit of detection and determination, percent recovery were determined based on area response (mm 2) of the standard. Analytical field and laboratory samples (rose water by hydro-distillation of the flowers, concrete and absolute by hexane extraction and condensation) were analysed for evaluation of the method. Samples were extracted with acetone, partitioned with water, saturated sodium chloride solution and dichloromethane. The organic layer was rotary-evaporated to 2 ml for cleanup with silica–carbon column. The column was eluted with dichloromethane–toluene–acetone (10:2:2, v/v/v) and the derived solution was rotary-evaporated to 5 ml for end analysis. Matrix enhancement effect was observed for leaf and soil samples for which corrective approach was followed to compensate for overestimation of the residue. Limit of detection for chlorpyrifos standard was 0.05 mg/l with good linearity of detector response ( R 2 = 0.99). Percent recovery ranged from 78 to 117% in different plant matrices (fortification level 1, 4 and 8 mg/l). Dissipation behaviour showed that chlorpyrifos was below detection limit by the 12th day of application on the scented rose with half life of 3.40 days on leaves and 3.10 days on flowers at 0.1% dosage. Percent transfer studies showed that 5.71, 46.91 and 38.80% of the residue from flowers was transferred to rose water, concrete and absolute, respectively.

Analysis of pesticides in water and sediment under different storage conditions using gas chromatography.

This paper describes the process of testing a simple low-solvent method for simultaneously extracting five classes of pesticides (triazines, organophosphates, organochlorines, pyrethroids, and carbamates) from reconstituted water and sediment. This method uses techniques available in most laboratories, namely solid phase extraction (SPE) and sonication in combination with gas chromatography. The recoveries of pesticides ranged from 60 to 120% with the exception of carbaryl, dicofol, and methoxychlor that had higher recoveries. Methods were further tested with pond water and soil samples. The recoveries of pesticides from soil were comparable with those from sediments, while in pond water, recoveries of the organochlorines exceeded 100%. A matrix enhancement effect was suspected to be the cause for the observed elevated recoveries. In order to determine time range and conditions in which the samples can be stored without significant losses, recoveries of pesticides in water and sediment were monitored for 28 days. Water samples were most stable when extracted immediately and stored in SPEs in the freezer. These samples remained stable for up to six weeks in the freezer, whereas sediment samples were stored for a month without a significant decrease in pesticide concentrations.

Rapid multi-residue method for the determination of azinphos methyl, bromopropylate, chlorpyrifos, dimethoate, parathion methyl and phosalone in apricots and peaches by using negative chemical ionization ion trap technology

A rapid, selective and sensitive multi-residue method for the determination of six common pesticides in stone fruit samples is described. The proposed method involves the extraction of the pesticides with the use of acetone solvent followed by liquid–liquid partition with a mixture of dichloromethane and light petroleum (40–60 °C) and subsequent determination by a gas chromatographic–mass spectrometry system using ion trap technology in negative ion chemical ionization mode. The average percent recoveries of bromopropylate and phosalone in the concentration range 0.2–2.0 mg/kg were 97.3±6.7 to 120±1.0%, while the recoveries of chlorpyrifos and parathion methyl examined in the concentration range 0.02–0.2 mg/kg were 95.5±7.5 to 145±3.6%, the recoveries of azinphos methyl in the range 0.05–0.5 mg/kg were 74.8±29.6 to 96.5±13% and those of dimethoate in the range 0.1–1.0 mg/kg were 73.1±5.7 to 92.8±2.8% for n=3 for all the above pesticides. The high mean recovery (145%) for chlorpyrifos is attributed to a matrix enhancement effect. The limits of quantitation in apricots were 0.01 mg/kg for chlorpyrifos, 0.02 mg/kg for dimethoate and parathion methyl, 0.05 mg/kg for azinphos methyl and phosalone and 0.1 mg/kg for bromopropylate. The usefulness of tandem mass spectrometry for confirmation purposes was also examined. The method was applied successfully to the determination of the target pesticides in 32 samples of stone fruits (apricots and peaches).

Does further clean-up reduce the matrix enhancement effect in gas chromatographic analysis of pesticide residues in food?

Sample extracts of apples, peas, green beans, oranges, raspberries, clementines, carrots, and wheat obtained using the Food and Drug Administration (acetone extraction) and Canadian Pest Management Regulatory Agency (acetonitrile extraction) multiresidue methods for pesticides were subjected to clean-up using different solid-phase extraction (SPE) cartridges in an attempt to reduce or eliminate the matrix enhancement effect. The matrix enhancement effect is related to the blocking of active sites on the injector liner by matrix components, thereby increasing signal in the presence of matrix versus standards in solvent in which the pesticides themselves interact with the active sites. Graphitized carbon black (GCB) was often used in combination with various anion-exchange SPE cartridges. The extracts were then spiked with organophosphorus insecticides. These process standards were then compared to standards in acetone of the same concentration using gas chromatography with flame photometric detection or ion trap mass spectrometric detection. Sample matrix enhancement varied from little to no effect for some pesticides (e.g. chlorpyrifos, malathion) to >200% in the case of certain susceptible pesticides. The GCB removed color components but showed little effect in reducing matrix enhancement by itself. The anion-exchange cartridges in combination with GCB or not, substantially reduced the matrix enhancement effect but did not eliminate it.

Thickness measurements of thin films: comparison of techniques using characteristic X-ray line ratio techniques

In this research, two characteristic X-ray line ratio techniques are experimentally investigated. One technique uses the ratio of the characteristic L X-ray line to the characteristic Kα X-ray line of the substrate. The other techniques uses the ration between one characteristic X-ray line of the substrate and one characteristic X-ray line of the thin film overlay. Experimental measurements were taken for both techniques by bombarding a coated sample with electrons and measuring the ratio of the areas under the characteristic X-ray line peaks. The samples used in the experiment consisted of a copper substrate coated with aluminum and a molybdenum substrate coated with aluminum. The data are presented by plotting the characteristic X-ray line ratio vs. the thin film thickness from 400 to 7000 Å for 20, 25 and 30 keV electron bombardment. On the basis of these experiments, it was found that the ratio of the characteristic X-ray lines from the substrate (L:Kα ratio) is not suitable for thin film measurements because of the complication caused by matrix enhancement effects. However, matrix enhancement effects are also partly responsible for producing a large ratio change (80%) over the range of 5000 Å of overlay coating for the ratio technique that uses an X-ray line from the substrate and an X-ray line from the thin film overlay. This ratio was independent of accelerating electron energy and inversely proportional to the thickness.

Investigation of UV matrix-assisted laser desorption Fourier transform mass spectrometry for peptides

Ultraviolet matrix-assisted laser desorption can be used to enhance formation of [M + H] +, [M + Na] +, and [M + K] + ions from small peptides for Fourier transform mass spectrometry (FTMS). In accord with laser desorption (LD) time-of-flight experiments, matrices such as nicotinic acid and 2-pyrazinecarboxylic acid exhibit strong enhancement effects (i.e., formation of abundant protonated and cationized molecules for the analyte with virtually no fragment ions) for 266 nm LD/FTMS, whereas pyrazinedicarboxylic acid provides no matrix enhancement at this wavelength. Both sinapinic acid and coumarin-120 provide strong matrix enhancement effects for the 355-nm LD of peptides. For the small peptides examined in this study, no significant differences in the abundance of fragment ions were observed between the 266- and 355-nm wavelengths. Matrix-assisted LD/FTMS is useful for the generation and characterization of ions corresponding to protonated and cationized molecules from virtually all biological compounds with molecular weights up to 2000. The lack of observation of biological ions with m/ z > 2500 may be related to inefficient trapping of these laser-desorbed ions or instrumental detection limitations of FTMS and is under further investigation.

Development of a Calibration Method for Quantitative X-ray Powder Diffraction of Size-Segregated Aerosols

X-ray powder diffraction (XPD) is an important tool for the chemical characterization of atmospheric aerosol samples particularly when combined with elemental analysis obtained from X-ray fluorescence (XRF) measurements of the same specimen. Aerosol samples obtained in typical monitoring studies consist of thin, uniform deposits of particles corresponding to a known size distribution with aerodynamic equivalent diameters of less than 10 microns.This is an ideal form for X-ray fluorescence analysis since absorption and matrix enhancement effects are minimized. However, the ability to perform quantitative X-ray powder diffraction without the use of internal standards is restricted by several factors which affect the linearity of response between diffracted intensity and sample concentration. In addition to the normal photoelectric absorption due to passage of the X-rays through the sample, XPD intensities can be affected by primary and secondary extinction due to diffraction of the incident beam, particle size effects and preferred orientation of particles.

Trace elemental analysis of extracted dust from lungs and lymph nodes of domestic animals using X-ray fluorescence technique.

Samples of dust extracted from the lungs and lymph nodes of certain domestic animals from West Bengal, Orissa, Bihar provinces of India were quantitatively analysed using photon excited energy dispersive X-ray fluorescence technique. Thin specimens were prepared for analysis to minimize matrix enhancement and absorption effects. Amongst the various elements analysed, Hg, Fe, Cu, Zn and Pb were found to be present in appreciable amounts. An important finding was the presence of a very high concentration of Hg in extracted dust samples from West Bengal. The significance of the various results obtained in this investigation is discussed.

X-Ray Cross-Sections in Design and Analysis of Non-Dispersive Systems

AbstractIn designing a radioisotope, energy-dispersive (proportional counter) x-ray fluorescence spectrometer for elemental analysis of geologic specimens, a theoretical framework has been developed to model instrument response. This model is based upon the fundamental physics of x-ray excitation, absorption, and scattering, and employs the most modern available values of the applicable physical constants. The model includes matrix absorption and enhancement effects. By explicitly including scattering in the model and the measurements, element concentrations can be calculated from the shape alone of the x-ray spectrum and the presence of elements having non-observable fluorescences can be detected.

Applications of a Portable Radioisotope X-Ray Fluorescence Spectrometer to Analysis of Minerals and Alloys*

AbstractA portable, battery-operated X-ray fluorescence analyzer weighing 15 lb is described, consisting of a Nal(Tl) scintillation-counter probe and an electronic unit with a single-channel pulse-height analyzer and reversible scaler. Radioisotope X-ray sources are used for excitation of the sample and, where necessary, balanced filters for resolution of neighboring characteristic X-rays. Emphasis has been placed on designing and producing an instrument that is easy and convenient to operate in laboratory, factory, or field conditions and that can equally well be used to measure extended surfaces, such as rock faces, or finite samples in the form of powders, briquettes, or liquids. The feasibility of the following analyses has been studied by using for each determination the appropriate radioisotope source and filters: sulfur in coal; calcium and iron in cement raw mix; copper in copper ores; and vanadium, chromium, molybdenum, and tungsten in steels. Detection limits, based on counting statistics obtained in count times of 10 to 100 sec, range from 0.03% for copper in ores to 0.2% for sulfur in coal. Both matrix absorption and enhancement effects were encountered and were eliminated or reduced substantially by suitable choice of source energy, by the use of nomograms, or by semiempirical correction factors based on attenuation or scattering coefficients.