Detection methods without mass spectrometry

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. 

EARLY DETECTION METHODS POSSIBILITIES AND LIMITATIONS OF ASSAYS WITHOUT MASS SPECTROMETRY... 

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 method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

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. 

Principles and Characteristics Ionisation processes are the basis for mass-spectrometric detection. Each of the ionisation techniques occupies its own position in mass spectrometry. The optimum performance of any ionisation method (and therefore the result) will depend critically on the characteristics and reliability of the mass spectrometer. Ionisation may occur in the gas, liquid or condensed phase, and may be either hard or soft , i.e. with or without extensive... 

Mass spectrometry (MS) is widely used to ascertain the purity, total mass of the protein produced, and detect any covalent modifications (Cohen and Chait, 2001). Both electrospray ionization (ESI) and MALDI may be used although for intact proteins ESI has the advantage of being accurate to 1 Da. Using the simple protocol described in Protocol 2.11, the MS of whole protein samples can be readily automated without the need for sample preparation. This method has proved successful for the... 

HPLC with column switching and mass spectrometry was applied to the online determination and resolution of the enantiomers of donepezil HC1 in plasma [38]. This system employs two avidin columns and fast atom bombardment-mass spectrometry (FAB-MS). A plasma sample was injected directly into an avidin trapping column (10 mm x 4.0 mm i.d.). The plasma protein was washed out from the trapping column immediately while donepezil HC1 was retained. After the column-switching procedure, donepezil HC1 was separated enantioselectivity in an avidin analytical column. The separated donepezil HC1 enantiomers were specifically detected by FAB-MS without interference from metabolites of donepezil HC1 and plasma constituents. The limit of quantification for each enantiomer of donepezil HC1 in plasma was 1.0 ng/ml and the intra-and inter-assay RSDs for the method were less than 5.2%. The assay was validated for enantioselective pharmacokinetic studies in the dog. 

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