Response factor, chromatographic

Purity. Gas chromatographic analysis is performed utilizing a wide-bore capillary column (DB-1, 60 m x 0.32 mm ID x 1.0 //m film) and a flame ionization detector in an instmment such as a Hewlett-Packard 5890 gas chromatograph. A caUbration standard is used to determine response factors for all significant impurities, and external standard calculation techniques are used to estimate the impurity concentrations. AHyl chloride purity is deterrnined by difference. 

Calibration curves generated for each analyte from the chromatographic standards should be linear (correlation coefficient R > 0.99) with negligible intercepts so that either linear regression or a response factor method may be used for residue calculations. 

The flame ionization detector Is the most popular of the flame-based detectors. Apart from a reduction in sensitivity compared to expectations based on gas chromatographic response factors [138] and incompatibility with the high flow rates of conventional bore columns (4-5 mm I. 0.), the flame ionization detector is every bit as easy to use in SFC as it is in gas chromatography [148,149]. It shows virtually no response to carbon dioxide, nitrous oxide and sulfur hexafluoride mobile phases but is generally incompatible with other mobile phases and mixed mobile phases containing organic modifiers except for water and formic acid, other gas chromatographic detectors that have been used in SFC include the thermionic ionization detector (148,150], ... 

Standards and blanks are the usual controls used in analytical HPLC. Standards are usually interspersed with samples to demonstrate system performance over the course of a batch run. The successful run of standards before beginning analysis demonstrates that the system is suitable to use. In this way, no samples are run until the system is working well. Typically, standards are used to calculate column plate heights, capacity factors, and relative response factors. If day-to-day variability has been established by validation, the chromatographic system can be demonstrated to be within established control limits. One characteristic of good science is that samples... 

HBCD can be determined by GC-MS, using methods similar to those developed for PBDE determinations. As the response factors of the three diastereomers do not appear to differ very much, HBCD can be quantified as total HBCD. However, the different isomers have not so far been separated by this technique. Moreover, because isomers of HBCD are thermally labile (it is known that HBCD decomposition takes place between 240°C and 270°C), elution from a GC column usually results in a broad, diffuse peak. In addition, a number of chromatographic peaks corresponding to different breakdown products were detected. These peaks could interfere with some BFR congeners (e.g., BDE-99) [102,110]. TBBPA can be also determined by GC-MS however, a derivatization step must be carried out prior to injection on the GC system. 

A mixture of methyl esters of fatty acids was chromatographed on a Carbowax 20 M column giving the following peak areas and detector response factors ... 

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. 

The same chromatographic parameters were used in determining the molar response of the individual PCB isomers except, that the area responses were determined with a flame ionization detector. The flow rates of the hydrogen and air combustion gases were 30 and 300 mL/min, respectively. Response factors needed to... 

Note (1) The number of equilibria in Case II is manifold compared to Case I and the equilibrium constants arc quite different, however, they are kinetic terms and thus also responsible for chromatographic efficiency. (2) Selectivity factor x becomes oc when A approaches 0 a becomes 1 when B(S) or B(f ) approaches 0. 

When an assay method is performed repeatedly to analyze a high volume of samples, the instability of the calibration curves or an apparent change in response factor often indicates that some conditions of the assay are drifting, are no longer stable, and need to be evaluated. Reasons for the instability of the calibration curves can include variation of the extraction procedures, deterioration of the efficiency of a chromatographic column, or decline of the efficiency of the detection system (28). 

To calculate the response factor Kt of a compound t, it is essential, according to equation (4.7), to know the injected quantity. However, it is difficult to know precisely the injected volume, which depends on the injector or injection loop or the precision of the syringe. Moreover, the absolute response factor K, (not to be confused with the partition coefficient) depends on the tuning of the chromatograph. This factor is not an intrinsic property of the compound. This is why most chromatographic methods for quantitative analyses, whether they are pre-programmed into an integrating recorder or software, do not make use of the absolute response factor, Kj. 

Leggett et al (Refs 22 23) used a similar technique, except that their apparatus was static . TNT samples were placed in a 125ml vial equipped with silicone rubber septum cap. The vial was thermostatted and the sample and its vapor were allowed to equilibrate for 2—4 weeks. Vapor was withdrawn from the head-space with a stainless steel syringe and injected into a gas chromatograph. The concn of TNT in the headspace vapor was determined by manual triangulation of the peak, giving peak area/ volume, and dividing by the detector response factor (peak area/mass), as determined by injection of known quantities of TNT dissolved in benzene... 

J. R. Troost and E. Y. Olavasen [ Gas Chromatographic/Mass Spectrometric Calibration Bias, Anal. Chem. 1996,68, 708] discovered that a chromatography procedure from the U.S. Environmental Protection Agency had a nonlinear response on a variety of instruments. The assumption of constant response factor led to errors as great as 40%. 

The major disadvantage of this technique is that the entire mixture must be separated and detected in the chromatographic system. All peaks must be standardized via response factors whether their analysis is needed or not. Internal normalization also requires that a detector be used that responds somewhat uniformly to all components. This technique cannot be used with electron capture and flame photometric detectors, for instance. 

Since the mass chromatograph provides molecular weight data, the instrument is ideally suited for quantitative gas chromatography. Considerable time and uncertainty are saved using the system compared with flame ionization and thermal conductivity detectors which require response factors for each and every compound. 

The changes in concentrations of the reactants and products were followed by GC. Prior to running the reactions, response factors of the pure silanes were determined vs. mesitylene. At time intervals, the reaction vial would be quickly opened, 0.5 /A of solution would be removed by syringe and injected into the chromatograph. Once the reaction was complete, the concentrations of all species were calculated. 

Finally, these relative heights or areas are compared with equivalent values obtained from standards curves prepared from known amounts of target compounds to yield values for the amount of each target compound present in the chromatographic injection. Unknowns in the chromatogram can be identified with relative retention times, areas, and heights, but the amount of each present cannot be determined until they are identified, standard curves run, and response factors calculated for each compound. 

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