GC-MS calibration

The following is an example of GC/MS calibration standard levels. Concentrations other than those shown below may also be prepared and used if necessary. The GC/MS calibration standards may be prepared as set out in Table 3. 

Gas chromatographic-mass spectrometric (GC-MS) calibration standard mixes for quantitation were prepared in ethyl ether at concentrations of 20, 50, and 75 ppm. Internal standard spiking solution containing 1-chlorohexane, 1-chlorododecane, and 1-chlorooctadecane was prepared from individual stock solutions in methanol of each component. Two hundred microliters of each solution were added to ethyl ether and diluted to 2 mL. Forty microliters of this internal standard mix was added to the column extracts before diluting to 2 mL to yield a final concentration of 100 ppm per internal standard component. 

Massold, E., Bahr, C., Salthammer, T. and Brown, S.K. (2001) Determination of VOC/ TVOC by TD/GC/MS-calibration procedures. International Symposium on Thermal Desorption in Occupational, Medicinal and Environmental Chemical Analysis, October 9-10, Birmingham, Alabama. 

TABLE 1 GC/MS Calibration Components (Calibrated Aromatic Components)... 

The next step is to show that the response for the analysis of any target compound is linear. This step is known as the initial calibration and is achieved by the analysis of standards for a series of specified concentrations to produce a five-point calibration curve (Figure 41.2a, b). On subsequent days, a continuing calibration must be performed on calibration check compounds to evaluate the calibration precision of the GC/MS system. 

Because an increase in resolution causes a decrease in sensitivity, it is best to operate at the lowest resolution commensurate with good results. Some instrument data systems will allow calibration with an external reference material such as perfluorokerosene and then use of a secondary reference material for the internal mass reference. Tetraiodothiophene, vaporized using the solids probe inlet, is recommended as the secondary reference. The accurate masses are 79.9721, 127.9045, 162.9045, 206.8765, 253.8090, 293.7950, 333.7810, 460.6855, and 587.5900. For a higher mass standard, use hexaiodobenzene. Because the mass defect for these internal reference ions are so large, a resolution of 2000 is ample to separate these ions from almost any sample ions encountered in GC/MS. 

A procedure involving SPME followed by GC/MS has been developed to determine propanil in water samples. A Carbowax-divinylbenzene SPME fiber is used. Linearity of the calibration curves is attained in the range 0.1-10 ugL in water samples. ... 

GC/MS. GC/MS is used for separation and quantification of the herbicides. Data acquisition is effected with a data system that provides complete instrument control of the mass spectrometer. The instrument is tuned and mass calibrated in the El mode. Typically, four ions are monitored for each analyte (two ions for each herbicide and two ions for the deuterated analog). If there are interferences with the quantification ion, the confirmation ion may be used for quantification purposes. The typical quantification and confirmation ions for the analytes are shown in Table 4. Alternative ions may be used if they provide better data. 

Inject the cleaned up sample into the GC/MS system operated under the same conditions as employed for standardization. Compare the peak areas of the analytical samples with the calibration curve. Determine the concentrations of the At-methyl derivative of flutolanil and At,0-dimethyl derivative of the metabolite M-4 present in the sample. 

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. 

Multiway methods For analyzer data where a single sample generates a second order array (ex. GC/MS, LC/UV, excitation/emission fluorescence), multiway chemometric modehng methods, such as PARAFAC (parallel factor analysis) [121,122], can be used to exploit the second order advantage to perform effective calibration transfer and instrument standardization. 

Petroleum crude and its refinery products have two major component based on distillation. The portion that can be distilled under refinery conditions can be called volatiles and the nondistillables are the nonvolatiles. The volatiles can be analyzed by GC or GC-MS. The crude has both components. The distillate as the names applied, such as naphtha and kerosene contain only volatiles. When GPC is used for analyzing various distillates, the fractions separated by GPC can be characterized by GC or GC-MS. These data can be used to verify the nature of components present in various distillation cuts as a function of GPC elution volume. If the samples such as crude contains both volatiles as well as nonvolatiles, the samples should be separated into volatiles and nonvolatiles. The GPC of both components should be used to calibrate the GPC of the total crude. The parameter that can be obtained from GPC is effective molecular length. It can be used to relate other molecular parameters of interest after calibration. 

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