Selected ion monitoring technique

KK Midha, C Charette, JK Cooper, IJ McGilveray. Comparison of a new GLC-AFID method with a GLC-MS selected ion monitoring technique and a radioimmunoassay for the determination of plasma concentrations of imipramine and desipramine. J Anal Toxicol 4 237, 1980. 

Negative chemical ionization high-resolution gas chroma-tography/mass spectrometry with on-column injection (NCI HRGC/MS) provides sensitivity and selectivity for the detection of nitro-aromatics. The limit of detection is approximately 50 pg for the mono-nitro-aromatics and di-nitro-pyrenes in the full mass scan data acquisition mode. The limit of detection can be improved, if necessary by using selected ion monitoring techniques. 

J. K., and McGilveray, I. J. Comparison of a New GLC-AFID Method with GLC-MS Selective Ion Monitoring Technique and a Radioimmunoassay for the Determination of Plasma Concentrations of Imipra-mine and Desipramine J. Anal. Toxicol. 4(5) 237-243 (1980) CA 94 57q... 

A large number of different interactions are exploited for SPE (Figure 2.2). Selective extractions can be achieved by a suitable choice of adsorption materials. If the eluate is used for GC-MS the detection characteristics of the mass spectrometer in particular must be taken into account. Unlike an ECD, which is still widely used as a selective detector for substances with high halogen content in environmental analysis, a GC-MS system can be used to detect a wide range of non-halogenated substances. The use of a selected ion monitoring technique (SIM, MID, multiple ion detection) therefore requires better purification of the... 

Quantitative mass spectrometry, also used for pharmaceutical appHcations, involves the use of isotopicaHy labeled internal standards for method calibration and the calculation of percent recoveries (9). Maximum sensitivity is obtained when the mass spectrometer is set to monitor only a few ions, which are characteristic of the target compounds to be quantified, a procedure known as the selected ion monitoring mode (sim). When chlorinated species are to be detected, then two ions from the isotopic envelope can be monitored, and confirmation of the target compound can be based not only on the gc retention time and the mass, but on the ratio of the two ion abundances being close to the theoretically expected value. The spectrometer cycles through the ions in the shortest possible time. This avoids compromising the chromatographic resolution of the gc, because even after extraction the sample contains many compounds in addition to the analyte. To increase sensitivity, some methods use sample concentration techniques. 

In this chapter, the main aspects of mass spectrometry that are necessary for the application of LC-MS have been described. In particular, the use of selected-ion monitoring (SIM) for the development of sensitive and specific assays, and the use of MS-MS for generating structural information from species generated by soft ionization techniques, have been highlighted. Some important aspects of both qualitative and quantitative data analysis have been described and the power of using mass profiles to enhance selectivity and sensitivity has been demonstrated. 

Selected ion monitoring is a technique in which only the ions at a limited number ofmjz ratios chosen to be characteristic of the analyte(s)... 

Selected-ion monitoring A technique in which the mass spectrometer is used to monitor only a small number of ions characteristic of the analyte of interest. 

The MS detection system can be such that the full mass spectrum is observed (at least five peaks) or just selected ions monitored (SIM) with three or four identification points. For some analyses, it may be necessary to use MS-MS" techniques [8]. In LC-MS, it is important to make sure that ionization of the compounds of interest has been achieved. For all of these approaches, the criteria for matching of the analyte with the standard should be established during validation studies. 

Selecting an approach Since the chromatograms appeared identical using the FID, a different technique is needed to allow detection of the off-flavor. GC-mass spectrometry (GC-MS) provides more information than GC-FID and, in selected ion monitoring mode, can detect lower concentrations. 

Lopez-Avila et al. [36] used a stable isotope dilution gas chromatography-mass spectrometric technique to determine down to O.lppb of pentachlorophenol (also Atrazine, Diazinon and lindane) in soil. Soil samples are extracted with acetone and hexane. Analysis is performed by high-resolution gas chromatography-mass spectrometry with mass spectrometer operated in the selected ion monitoring mode. Accuracy greater than 86% and a precision better than 8% were demonstrated by use of spiked samples. 

What is selected-ion monitoring and what are the advantages of using this technique ... 

Gross contamination can overload the HPLC or GC columns with obvious and usually rapid deterioration of chromatographic performance. This can occur with so called rapid techniques where the detector is used as a filter, e.g., selected ion monitoring (SIM) MS, or where the clean-up method has been overloaded (e.g., excess of lipid). This problem can be overcome by using and monitoring more selective clean-up techniques. 

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