Selected-ion recording

By connecting a gas chromatograph to a suitable mass spectrometer and including a data system, the combined method of GC/MS can be used routinely to separate complex mixtures into theii individual components, identify the components, and estimate their amounts. The technique is widely used. 

Schematic diagram showing injection of a mixture of four substances (A, B, C, D) onto an LC column, followed by their separation into individual components, their detection, and the display (chromatogram) of the separated materials emerging at different times from the column. 

Schematic diagram of a mass spectrometer. After insertion of a sample (A), it is ionized, the ions are separated according to m/z value, and the numbers of ions (abundances) at each m/z, value are plotted against m/z to give the mass spectrum of A. By studying the mass spectrum, A can be identified. 

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In a process similar to that described in the previous item, the stored data can be used to identify not just a series of compounds but specific ones. For example, any compound containing a chlorine atom is obvious from its mass spectrum, since natural chlorine occurs as two isotopes, Cl and Cl, in a ratio of. 3 1. Thus its mass spectrum will have two molecular ions separated by two mass units (35 -i- 2 = 37) in an abundance ratio of 3 1. It becomes a trivial exercise for the computer to print out only those scans in which two ions are found separated by two mass units in the abundance ratio of 3 1 (Figure 36.10). This selection of only certain ion masses is called selected ion recording (SIR) or, sometimes, selected ion monitoring (SIM, an unfortunate... 

Full (repetitive) scan data collection vs. selected ion recording... 

Ser SIM SIR SRM TFA Thr TIC ToF Trp TSP Tyr UV V vol/vol Val serine selected-ion monitoring selected-ion recording selected-reaction monitoring trifluoroacetic acid threonine total-ion current time-of-flight tryptophan thermospray tyrosine ultraviolet volt volume by volume valine... 

Fig. 4 Selected ion recording of the derivatives of 14C-labelled and the non-labelled estradiol- 17/J after processing of a human serum sample...

Heptachlor, - -Trifluralin, S-triazines GC-MS with selected ion recording 1 ppb [52]... 

The technique known variously as multiple ion detection (MID), selected ion recording (SIR), and selected ion monitoring (SIM) employs the mass spectrometer to monitor only a few significant ions. In this way both die sensitivity and selectivity are increased markedly, the former by a factor ap-... 

A special application of gas chromatographic determination of nicotine in biological fluids is its determination in the breast fluid of non-lactating women. By using a combination of gas chromatography, mass spectrometry and a selected ion recording technique, Petra-47... 

Aliphatic sulfonates and sulfates can be separated by RPLC with ammonium acetate and detected by their molecular anions in selected ion recording (SIR). Secondary alkane sulfonates may be analyzed under similar conditions to the LAS. For alkylphenol ethoxysulfonates, mixed-mode RP/anion-exchange chromatography with ammonium acetate as buffer has been used, which provided separation according to the number of ethoxylate units. 

When using an internal standard the same amount of the standard is added to each analyte solution. Selected ion recording is used to measure the peak areas for both standard and analyte, and the ratio of these areas is plotted against the concentration of the analyte. Statistical procedures are used to calculate the equation of the regression line and the coefficient of variation due to the sampling errors. 

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