Chromatographic response retention time

The most important parameters related to chromatographic response (retention time, peak width, resolution), well known by GC users, are also fundamental in the characterization of GCxGC peaks. However, some of them take in GCxGC a new meaning for instance, resolution or peak capacity must be considered in a different way. Other characteristics, such as orthogonality or structured chromatograms, are specific of GCxGC. 

Another useful standard Is SRM 1647, priority pollutant polynuclear aromatic hydrocarbons (in acetonitrile). It can be used to calibrate liquid chromatographic Instruments (retention times. Instrument response), to determine percent recoveries, and to fortify aqueous samples with known PAH concentrations. Figure 8 Illustrates the HPLC separation and UV detection (fluorescence is also used extensively) for the 16 priority pollutants. 

Moment analysis of chromatographic peaks retention times at peak maximum (Imax), mean retention times (p), separation factors (a), standard deviations of chromatographic response peaks (o) and mass transfer resistances (aV2p ) in pulse chromatographic experiments with a mbtture of octane (n-C8) and iso-octane (2,2,4-TMCs) separated on ZGctab and ZGdtab column at 130°C... 

The calibration solutions, which typically contain a number of analytes at known concentrations, are useful for validating the chromatographic separation step (e.g. retention times and analyte detector response). 

Cech, N. B. Krone, J. R. Enke, C. G. Predicting electrospray response from chromatographic retention time. Anal. Chem. 2001,73,208-213. 

Chromatographic system (See Chromatography <621 >.) The liquid chromatograph is equipped with a 230 nm detector and a 4.6 mm x 30 cm column that contains packing L7. The flow rate is about 2 mL/min. Chromatograph the Resolution solution and the Standard preparation, and record the peak responses as directed under Procedure the resolution, R, between the dibutyl phthalate and miconazole peaks is not less than 5, the tailing factor for the miconazole peak is not more than 1.3, and the relative standard deviation for replicate injections of the Standard preparation is not more than 2%. The relative retention times are about 0.7 for dibutyl phthalate and 1 for miconazole. 

Chromatographic system. (Follow the method described in the general procedure <621 >.) The gas chromatograph is equipped with a flame ionization detector and a 1.2 m x 2 mm column packed with 3% phase G32 on support S1A. The injection port, detector, and column temperatures are maintained at about 250, 300, and 250 °C, respectively, and helium is used as the carrier gas, flowing at rate of about 50 mL/min. The relative retention times for cholestane and miconazole nitrate are about 0.44 and 1, respectively. Chromatograph the Standard preparation, and record the peak responses as directed for procedure The resolution, R, between cholestane and miconazole nitrate is not less than 2 and the relative standard deviation of replicate injections is not more than 3%. 

Procedure Separately inject equal volumes (about 5 pL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times for cholestane and miconazole nitrate are about 0.5 and 1, respectively. Calculate the quantity, in mg, of Ci8H14Cl4N2OHN03 in the portion of topical powder given by the formula ... 

Chromatographic system. The gas chromatograph is equipped with a flamioniza-tion detector and a 2 mm x 1.8 m glass column packed with 10% phase G34 on 80- to 100-mesh support SI A. The column temperature is maintained at about 150 °C, and the injection port and the detector block temperatures are maintained at about 250 °C. Dry helium is used as the carrier gas at a flow rate of about 40 mL/min. Chromatograph the Standard preparation, measure the peak responses, and calculate the ratio, Rs, as directed for procedure the relative retention times are about 0.5 for valproic acid and 1.0 for biphenyl the resolution, R, between valproic acid and biphenyl is not less than 3.0 the relative standard deviation for replicate injections is not more than 2.0%. 

Controlled release epoxy formulations in which tin is chemically anchored as tributyltin carboxylate to the polymer chain are discussed. NMR evidence is presented to establish that rapid exchange exists in tributyltin carboxylates. Consequently, even the interfacial reaction between tributyltin carboxylates and chloride is very fast equilibrium constants are reported for the reaction between tributyltin acrylate in hexane and sodium chloride in water. IR spectra, gas chromatographic retention time, chloride assay, and the complex intensity pattern of the molecular ion peaks in the mass spectrum show that the product of the reaction is tributyltin chloride, suggesting that it is the chemical species responsible for antifouling activity in marine environment. 

Lucic, B., Trinajstic, N., Sild, S., Karelson, M., Katritzky, A. R. J. Chem. Inf. Comput. Sci. 39, 1999, 610-621. A new efficient approach for variable selection based on multiregression Prediction of gas chromatographic retention times and response factors. 

System Suitability. Although method validation is performed once at the end of method development, system suitability tests are performed on a specific system periodically (usually daily) or prior to each batch during validation and sample analysis to determine the system performance (see Chapter 13). During method development or/and upon completion of the validation, system suitability data should be evaluated and used to define acceptance criteria to use before starting sample analysis. System suitability tests include (1) the reproducibility of retention time, (2) adequate sensitivity to quantify LLOQ (minimum detector response), (3) appropriate sensitivity to quantify ULOQ (within range of detector), and (4) chromatographic separation. 

The analogy between spectrophotometric analysis and chemical sensing at multiple wavelengths leads to an even stronger case of third-order analysis. When the spectrum is recorded at the output of a chromatographic column, the components are resolved according to their chromatographic retention times, Ir. The response (Fig. 10.1c) can be shown as... 

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