Detection methods without mass

Separation and detection methods The common methods used to separate the Cr(III)/(VI) species are solvent extraction, chromatography and coprecipitation. In case of Cr(VI) from welding fumes trapped on a filter, a suitable leaching of the Cr(VI) from the sample matrix is needed, without reducing the Cr(VI) species. The most used detection methods for chromium are graphite furnace AAS, chemiluminescence, electrochemical methods, ICP-MS, thermal ionization isotope dilution mass spectrometry and spectrophotometry (Vercoutere and Cornelis 1995)- The separation of the two species is the most delicate part of the procedure. 

The most widely regarded approach to accomplish the determination of as many pesticides as possible in as few steps as possible is to use MS detection. MS is considered a universally selective detection method because MS detects all compounds independently of elemental composition and further separates the signal into mass spectral scans to provide a high degree of selectivity. Unlike GC with selective detectors, or even atomic emission detection (AED), GC/MS may provide acceptable confirmation of the identity of analytes without the need for further information. This reduces the need to re-inject a sample into a separate GC system (usually GC/MS) for pesticide confirmation. Through the use of selected ion monitoring (SIM), efficient ion-trap or quadrupole devices, and/or tandem mass spectrometry (MS/MS), modern GC/MS instruments provide LODs similar to or lower than those of selective detectors, depending on the analytes, methods, and detectors. 

Three different detection methods (gas chromatography with electron capture, mass spectrometric and atomic emission detectors) have been compared for the determination of polychlorobiphenyls in highly contaminated marine sediments [74], Only atomic emission detection in the chlorine-selective mode provided excellent polychlorobiphenyl profiles without interferences. However, the lower sensitivity of the atomic emission detector, compared to the other two detectors required a 10 to 20g sample size for most analyses. 

The idea that free radicals occur in many chemical reactions is as old as the study of the mechanisms of these reactions. However, direct physical evidence for the existence of free radicals and for their presence in certain reactions is comparatively recent. Such evidence has been obtained in recent years by the methods of mass spectrometry, optical spectroscopy, and electron spin resonance spectrometry. The optical method of detecting free radicals has the advantage that it simultaneously supplies information about the structure of the radical. Indeed, in many instances the nature of the free radical has been identified by the structure of the spectrum without any assumptions about the mechanism of the reaction in which it appears.1... 

The method of analysis for the final determination of the seven CB congeners used by each of the participating laboratories was based on capillary gas chromatography with electron capture detection. In addition, mass spectrometry was used for compound identification and confirmation, but not for quantification. Each laboratory used their own proven procedures for the sample preparation, clean-up, method of injection, choice of carrier gas and chromatographic condition. The fish oils were dissolved in an appropriate solvent and analysed without any preliminary extraction from the matrix. 

In general, QE-AAS, AES, AES, microwave induced plasma (MIP) and ICP-MS are used as detectors rather than the less specific FID, FPD, and ECD. The overriding reason for this is the greater sensitivity and selectivity afforded by the element-specific detectors, without which it would not be possible to determine the chemical species of interest at the low concentrations generally present in biological and environmental samples. The other main detection method that has been used is mass spectrometry in its various configurations, but particularly electrospray ionization (ESI) and atmospheric chemical ionization (APCI), which are used with HPLC and CE separations, and... 

Even if wastewater sampling and detection of dmg residues in the environment cannot lead to direct per capita consumption, it has the potential to design reliable profiles of total consumption, if monitored continuously, based on a solid and commonly applied methodology. Without additional information about user populations, their age structures, consumption habits, and patterns and frequencies of use, it will remain a subset to add to a more complex epidemiological indicator. The detection of total mass flow of substances under constant focus has some advantages, which conventional methods do not ... 

The major benefits of H NMR spectroscopy are easy quantification and determination of steric arrangements. Disadvantages are the low sensitivity of the NMR detection and the fact that inorganic counterions and parts of the molecule without attached protons cannot be detected. Mass spectrometry, in contrast, is a very sensitive and selective detection technique steric information, however, cannot readily be obtained. Therefore, these two detection methods are mutually complementary for unambiguous structure elucidation purposes, a combined evaluation of both sets of data is highly desirable. 

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