Selected ion current profiles

LC separation applying ion chromatography in combination with ion spray mass spectrometric detection was applied for the examination of a synthetic mixture of alkyl sulfonates (CnH2n+i-SO3 re = 8) and AS with different alkyl chain lengths in the selected ion monitoring (SIM) ESI-MS(—) mode [53], Selected ion current profiles provided the separation of the compounds. The ionic matrix constituents of the eluent were removed by a suppressor module prior to MS detection to improve the signal to noise (S/N) ratio. 

First of all, the isotope composition of the labeled compound is measured by recording a selected ion current profile corresponding to the molecular ions of zero-, mono-, di-, tri-, and n-labeled analog. Preferably the integration time on each channel should be adjusted in order to produce ion statis-... 

The resolution criteria must be evaluated using measurements made on the selected ion current profile (SICP) for the appropriate ions for each isomer. Measurements are not made from total ion current profiles. 

Figure 3. LC/MS selected ion current profiles of a low standard containing 0.5 ng/ml 13-cis, 0.5 ng/ml all trans and 20 ng/ml tetradeuterated 13-cis retinoic acid. Stationary phase Diol column (1 x 250 mm) mobile phase 15% toluene...

ENDOGENOUS I EVELS IN HUMAN PLASMA. Figure 4 is the selected ion current profile of endogenous retinoic acid extracted from the plasma of a male volunteer. No differences were noted in the profiles between male and female volunteers. All profiles were quite similar in appearance. Table III lists the individual concentrations of endogenous plasma cis and trans retinoic acid of... 

GC-MS runs were stored as files by the data system on discs FORTRAN routines were written to compare selected parameters in file sets and to reduce the data to summary tables for hard copy output. These routines facilitated the determination of peak areas of components in extracted ion current profiles (EICP) for both total and selected ion chromatograms, calculated the removal of components of interest (e.g., those containing halogen isotopes) by treatment processes (GAC, CI2) or derivatization, summarized the occurrence of new components of interest in treatment or derivatization, and calculated the percent of the total ion current represented by a given component. The programs allowed operator discrimination between major and minor components in a file set by preselection of an ion current threshhold for data reduction. For data summarized herein, components were >4000 ion counts, which corresponds to a level >5 of the internal standard (decachlorobiphenyl) response. 

Two aspects of this experiment deserve emphasis. Firstly, the ion current profiles are remarkably free from interfering coipounds the urinary purification procedure was sufficiently selective to enable even the endogenous (mlabeled) PGF-M to be detected with no chrematography of the samples prior to GC-MS. Secondly, the experiment dononstrates that the method can be applied to the analysis of other tetranor metabolites. n fact there are other prostaglandin-related catpounds which should be amenable to purification fcy this procedure. These include tetranor PGD and PGE carpounds (after borohydride reduc-... 

FIGURE 18.3 Extracted ion current profiles of the water-soluble vitamins detected in a green kiwi extract (see reference [138] for the details). The LC—SRM (standard reference material) chromatogram was acquired by a high-flow ESI source (TurboIonSpray source). Each analyte was identified on the basis of the retention time, the two selected SRM transitions and their relative abundance. Only the most intense SRM ion current is reported in the figure. 

In the process of SNMS analysis, sputtered atoms are ionized while passii through the ionizer and are accelerated into the mass spectrometer for mass analysis. The ion currents of the analyzed ions are measured and recorded as a function of mass while stepping the mass spectrometer through the desired mass or element sequence. If the purpose of the analysis is to develop a depth profile to characterize the surface and subsurface regions of the sample, the selected sequence is repeated a number of times to record the variation in ion current of a selected elemental isotope as the sample surfiice is sputtered away. 

GC/MS separation of mixtures of the compounds are usually performed on capillary columns with low and mid polarity and a length in the range of 30 50 m, with a total separation time of20 40 min, and temperature ramping from 40 to 300 °C. Total ion current (TIC) profiles are often obtained using ion trap or quadrupole analysers. Quantification is performed by selected-ion monitoring (SIM) detection using calibration curves. 

True profile analysis requires scanning over the whole mass range for the acquisition of all data on excreted compounds. Quantitation has been more challenging on a quadrupole instrument because total ion current peaks are seldom a single component and extracted-ion chromatograms (EICs) when recovered from scanned data are of poor quality due to the lower sensitivity of scanning GC-MS. Thus, we developed profile analysis based on SIM of selected analytes but tried to ensure the components of every steroid class of interest were included. For ion traps the fundamental form of data collection (in non-MS/MS mode must be full -scans). Thus, the quantitative data produced are EICs obtained from scanned data. The EICs are of the same ions used for SIM in quadrupole instruments and the calibration external standards are the same. 

The capillary HPLC separation from a selected protein spot provides a base-peak profile shown in Figure 6.2A. The base-peak profile is similar to a total ion current (TIC) profile, but it contains only the most abundant mass spectral peak in each scan. The chromatogram is simplified and the contributions from background ion abundances are eliminated, resulting in an enhanced signal-to-ion ratio for an improved visualization of data. The molecular mass for each component is labeled along with corresponding amino acid residues. This format provides a comprehensive approach for peak selection and peptide identification. 

Figure 55-8 Partial urine organic acid profiles 15-23 minute portion of a 33 minute run) of two patients with tyrosinemia type i. A, Acutely III patient with markedly elevated excretion of succiny[acetone, pre-NTBC treatment.The insert shows the selected ion chromatogram of the [M-15] ion of succinylacetone O-TMS-oxime TMS ester, m/z 212 B, Fifteen month old patient, succinylacetone was not detected by either total ion current (orrow) or selected ion chromatogram in three different urine specimens.This patient was later shown to be compound heterozygote for the French Canadian common splice mutation (IVS12+5G>A) and another previously unreported mutation. Peak legend I, Succinylacetone (oxime, peak I) 2, succinylacetone (oxime, peak II) 3, 4-hydroxy phenyllactic acid 4, 4-hydroxy phenylpyruvic add (oxime).The symbol marks the internal standard (pentadecanoic acid), signal abundance is normalized to the intensity of the internal standard peak.

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