Treatments sample

This chapter focuses on LC—MS/MS applied to pesticide residue analysis, as this technique is the most attractive and efficient nowadays for developing MRMs [11], including both parent pesticides and metabolites. Sample treatment (mainly extraction and cleanup) are briefly commented on, with emphasis on those commonly applied in MRMs. A brief mention is made of problematic pesticides that do not fit in MRMs and consequently need to be determined with individual-specific LC—MS/MS methods. The use of HR MS in combination with LC also is briefly treated, either for the investigation of parent pesticides or for metabolite research, as this is a field of major interest at present. 

Sample treatment in PRA includes several steps, like extraction of pesticides, cleanup of the sample extracts, evaporation, and solvent exchange, as the most commonly applied. In some cases, a derivatization reaction is required to make the analytes compatible with their chromatographic determination. These steps are time consuming and involve sample manipulation, and they can be the source of important analytical errors. 

Sample treatment depends on the matrix and analytes imder study, also on the analytical technique applied for the final measurement. Currently, there is a clear trend toward the simplification of this stage, which has been favored by the improvement of analytical techniques in terms of sensitivity and selectivity. MRMs require the application of simple and universal sample treatments, which can be applied to a large number of compoimds, even with different pysicochemical characteristics. Restrictive treatments are normally avoided in MRMs, and they are reserved for particular analyte—matrix combinations of special difficulty. 

Solid-phase extraction (SPE) is widely applied to liquid samples (e.g., water, fruit juice, wine), whereas solvent extraction (typically using acetone, ethyl acetate, methanol, or acetonitrile) is the most imiversal technique applied for solid samples. The efficiency of sample extraction can be improved using accelerated-solvent extraction (ASE) or microwave-assisted solvent extraction (MASE), among other techniques. 

A popular approach for sample treatment is the QuECHERS method, which is gaining increasing recognition in PRA laboratories [12]. It is based on the use of acetonitrile (ACN) and MgS04 for salting-out 

Prior to quantitation of analyte by atomic spectrometry it is usually necessary to destroy the organic matrix and bring the element into solution. Most of the multitude of decomposition procedures reported fall into one of two classes, wet digestion and dry ashing. Often many variants of each procedure provide adequate results with a variety of analytes and matrices. Several commonly used procedures of general applicability are described below specific details are found in the sections dealing with the determination of individual elements. The reader is referred to several good sources of information on sample decomposition for fuller details and discussion [8h, 34,138—140]. The procedures described below result in essentially 

The spectrophotometric determination of cadmium in natural waters involving in-line formation of an aqueous dithizone suspension [121] illustrates another application of in-line suspension addition. Solid dithizone reagent was packed in a mini-column through which a surfactant (Triton X-100) stream was allowed to flow. The emerging suspension formed was added by confluence to the main analytical channel of a flow-injection system. With this innovation, good sensitivity was achieved without the need for an analyte separation/concentration LLE step and the entire procedure was carried out in the aqueous phase. 

It is a difficult task to define broad terms related to sample preparation, sample (or analyte) extraction and analyte separation/concentration, which becomes even more difficult when physico-chemical processes, e.g., microwave, UV or ultrasound irradiation, are involved. In this monograph, in-line sample digestion, bleaching, hydrolysis, oxidation and related approaches are therefore discussed under the general term sample treatment. 

Initial attempts to perform in-line digestion of plant tissues were made inl960 [122]. The Kjeldahl digestion procedure was implemented in a segmented flow analyser by adding the solid sample and the digestion mixture (500 mL L 1 sulphuric acid + 3.0 mL L-1 perchloric 

Microwaves are a form of electromagnetic radiation produced in magnetrons, which can be absorbed by a process called dielectric heating. Dipolar molecules, e.g., water, undergo rotation in order to try to align 

Domestic or focussed microwave ovens have mostly been used and deliver electromagnetic radiation characterised by a frequency around 2.45 GHz ( 12.2 cm). Consequently, the amount of energy absorbed is 

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The development of analytical strategies for the regulatory control of dmg residues in food-producing animals has also been reviewed (128). Because of the complexity of biological matrices such as eggs (qv), milk, meat, and dmg feeds, weU-designed off-line or on-line sample treatment procedures are essential. 

Sample pre-treatment. Novel procedures of electrochemical sample treatment have been proposed to decrease the signal interference with native cholinesterase inhibitors present in fruits and vegetables. Polyphenolic compounds were removed by electrolysis with soluble A1 anode followed by the oxidation of thionic pesticides with electrogenerated chlorine. The procedure proposed makes it possible to decrease the background current and the matrix effect by 80-90%. Thus, the detection limits of about 5 ppb of Pai athion-Methyl and Chloropyrifos-Methyl were obtained in spiked grape juice without any additional sepai ation or pre-concentration stages. 

The effect of electrochemical sample treatment on the signal selectivity in multi-component mixtures is discussed. 

Other O2 Measurement Techniques The oxygen concentration in the emission gases of combustion processes is often measured based on the strong paramagnetic character of oxygen. A sampling line with appropriate sample treatments is required with this method. 

Koch, P.L., Tuioss, N. and Fogel, M.L. 1997 The effects of sample treatment and diagenesis on the isotopic integrity of carbonate in hiogenic hydroxylapatite. Journal of Archaeological Science 24 417--t29. 

General sample treatments for eggs, milk, and meat... 

INPUT SAMPLE TREATMENT DATA. data treat ... 

INPUT SAMPLE TREATMENT AND TIME TO DEATH DATA. data death ... 

HPLC coupled to MS was used for the determination of dimethyl xanthine metabolites in plasma.82 There have also been a number of methods published on the use of HPLC with a PDA detector. In 1996, Mei published a method for the determination of adenosine, inosine, hypoxanthine, xanthine, and uric acid in microdialysis samples using microbore column HPLC with a PDA detector.63 In this method, samples were directly injected onto the HPLC without the need for any additional sample treatment. 

Diffuse reflectance FTIR (DRIFT) spectra were recorded on a Bio-Rad FTIR spectrometer (EXCALIBUR FTS3000). A high-temperature cell was attached to a flow system that allows in-situ sample treatment, adsorption and desorption of probe molecules at different temperatures. 

In contrast to combined systems, hyphenated techniques consist of two or more analytical systems each of which is independently applicable as an analytical technique. Usually, the connection is realized by means of an interface and the system is controlled by a computer. With regard to integrated sample treatment, separation and transfer, hyphenated methods like GC-MS, HPLC-MS, GC-IR, GC-IR-MS, GC-AAS, GC-ICP-MS, MS-MS, and... 

Detailing the course of sample treatment and analytical procedures... 

The infrared spectra of the different samples were taken with a Fourier Transform infrared spectrometer (Digilab FTS-14) using the double beam mode vs. air as reference. 150 scans per sample and 100 scans per reference, at a resolution of 4 cm-l, were taken for every sample. All spectra were stored on tape, and a digital substraction of the after- and- before UV exposure (or any other sample treatment) spectra was performed, whenever needed, by an on-line computer, thus permitting a better visualization of the spectral changes in the polymer by UV- photooxidation. 

Despite the complexity of the chemical composition of the resinous materials, in a few minutes such techniques provide a mass spectral fingerprint, which highlights the compounds that are the main components in the sample. They avoid any sampling treatment before analysis. They have thus enabled diterpenoid resinous materials from Coniferae, and several triterpenoid materials to be clearly identified. In particular, the DE-MS technique is able to distinguish between different triterpenoid materials such as mastic resin, frankincense resin and birch bark tar. In fact, using PCA on DE-MS mass... 

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