Chromatographic response

Identifications in terms of gas chromatographic responses, infrared data, and colorimetric tests... 

Figure 1 presents the gas chromatographic responses obtained from a pyrethrum concentrate. Peak I has been identified as cinerin I, peak II as a cinerin-type compound, peak III as pyrethrin I, peak... 

If SIM is being carried out in conjnnction with chromatography, a further consideration is that an adequate number of cycles of measurement must be made to define the shape and intensity of the chromatographic response exactly, or otherwise inaccurate and imprecise measnrements will be made (Fignre 3.12). 

This sometimes complicates the extraction of molecular weight data as it is not always immediately clear which ions in the spectrum originate from each component. This can be determined by the use of equation (4.6). An example of this is shown in Figure 4.18, which shows the electrospray spectrum from what is apparently a single chromatographic response, while Table 4.3(a) displays the results of applying equation (4.6) to the major ions found in that spectrum. As... 

Figure 4.18 Electrospray spectrum from a single chromatographic response in the LC-MS analysis of a tryptic digest. From applications literature published by SCIEX, Concord, Ontario, Canada, and reproduced by permission of MDS SCIEX, a division of MDS Inc.

The digestion of the protein, after heme removal, using Glu-C endoproteinase was also carried out. This enzyme cleaves the polypeptide backbone on the carboxyl terminus of a glutamic acid residue and in this case yielded twelve chromatographic responses. Despite two of these arising from unresolved components, molecular weight information was obtained from 15 polypeptides, one of which was the intact protein, covering the complete sequence, as shown in Table 5.10. 

The complexity of the traces is such that the differences between them are not immediately obvious and this is not an unusual situation, particularly as the molecular weight of the parent protein increases. A detailed examination of the spectra associated with each of the chromatographic responses may therefore be necessary before the information required by the analyst is obtained. 

The electrospray spectrum from the corresponding chromatographic response in the LC-MS analysis of the tryptic digest of the protein after reaction with the inhibitor is shown in Figure 5.24. In addition to the three species found in the digest of the parent protein, two additional polypeptides, with molecular weights of 2439.36 zb 0.07 and 2457.43 zb 0.02 Da, i.e. 70 and 88 Da above... 

Equation 4.32 expresses the difference between the retention parameters Ai p of two solutes as a chromatographic response function ... 

For manual optimization methods the peak separation function, P, is easy to determine and can be calculated as shown in Figure 4.30 (479). The chromatographic response function for the chromatogram is then simply the sum of the In P values for the n adjacent peak pairs. 

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], ... 

Fig. 9-17. Chromatographic response to a feed pulse. Comparison between experimental (points) and model (lines) results. (Pulse during 7.5 min flow rate 5 mL min-1.)...

Fig. 9.9 Gas-chromatographic response of a standard mixture of brominated anilines derived from A monoLinuron B Fenuron C, Linuron and D, chlorobromuron (R=14min). Amount applied, 0.5ng. Perkin-Elmer, Model 452, gas chromatograph Sdurce Reproduced with permission of the Royal Society of Chemistry [138]...

Fig. 9.10 Gas-chromatographic responses of extracts from soils (10g) containing Diuron after hydrolysis and bromination (a) 0.04ng standard (Rt=7min) (b) application of 2pl from 10ml of an extract of soil containing 0.04mg kg-1 and (c) recovery of Diuron added to soil at 0.8mg kg-1, 6pl being applied from a 50-fold dilution of (b). Pye 104 gas chromatography.

We will describe an accurate statistical method that includes a full assessment of error in the overall calibration process, that is, (I) the confidence interval around the graph, (2) an error band around unknown responses, and finally (3) the estimated amount intervals. To properly use the method, data will be adjusted by using general data transformations to achieve constant variance and linearity. It utilizes a six-step process to calculate amounts or concentration values of unknown samples and their estimated intervals from chromatographic response values using calibration graphs that are constructed by regression. 

General Analytical Plan. A six step process is described to calculate the amount or concentration values of unknown samples using chromatographic response values and calibration graphs that were constructed by regression. The steps are ... 

In the calibration problem two related quantities, X and Y, are investigated where Y, the response variable, is relatively easy to measure while X, the amount or concentration variable, is relatively difficult to measure in terms of cost or effort Furthermore, the measurement error for X is small compared with that of Y The experimenter observes a calibration set of N pairs of values (x, y ), i l,...,N, of the quantities X and Y, x being the known standard amount or concentration values and y the chromatographic response from the known standard The calibration graph is determined from this set of calibration samples using regression techniques Additional values of the dependent variable Y, say y., j l,, M, where M is arbitrary, are also observed whose corresponding X values, x. are the unknown quantities of interest The statistical literature on the calibration problem considers the estimation of these unknown values, x, from the observed and the... 

Inserting tolerance intervals of the chromatographic responses in this equation results in rugged intervals for the factors. By comparing these intervals with the inaccuracy of the settings of the experimental conditions a statement about the ruggedness of the method is made. The tolerance intervals of the responses are defined by the experimentator, e.g. 2.5% difference in the area response between two independent analyses is considered acceptable in reference [16], i.e. a value of 0.025 0.307=0.0076 for the above mean response. The rugged interval for the injection temperature is then obtained from equation (29) ... 

Chromatographic response and optimization functions Experimental variables Optimization method Ref... 

A good initial approach is to study the behavior of known synthetic precursors, drug analogs or degradates. In our previous example, dexamethasone acetate, one can readily purchase compounds such as cortisone, cortisone acetate, dexamethasone alcohol, dexamethasone-17-keto analog, prednisolone alcohol, and so on. Their chromatographic responses, relative to the compound of interest, will indicate which structural modifications are detec-... 

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