Detector response calibration

This is a general procedure and can be used to calibrate detector response in both liquid and gaseous systems The equation describing this exponential dilution in Figure 2 is ... 

Calibration Detector response amount Retention -> molar mass... 

It is important for obtaining precise results that the signals from the samples to be determined should lie on the linear part of the calibration graph as elsewhere within the dynamic range a small change in detector response corresponds to a relatively large range of concentrations. 

The 1000 A column did not show any resolution between 312 nm and 57 nm particle sizes. Shown in Fig.2 are the calibration curves for the 2000 A and 3000 A columns and for their combination. The 57 nm particle standard appears to have been erroneously characterized by the supplier. This was subsequently confirmed by electron microscopy. The 2000 X column exhibited a sharp upturn in its calibration curve close to the exclusion limit. It is to be noted that while data points corresponding to 312 and 275 nm diameter particles appear on individual column calibration curves, they are not indicated for the calibration curve of the combination. This is because these larger diameter particles were completely retained in the packed colimms, generating no detector response. The percentage recovery for these particles from individual columns was considerably less than 100 resulting in their complete retention when the columns were combined in series. 

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). 

Generate a 4-5-point calibration curve with standards of concentrations within an order of magnitude of the estimated detection limit. For this purpose, the detection limit may be estimated as a concentration that would yield a signal three times Ap p. The calibration curve should be generated by plotting detector response (x) vs concentration (c). 

Analytical standards are prepared for two purposes for fortifying control matrices to determine the analytical accuracy and for calibrating the response of the analyte in the electrochemical detector. 

A new nonweighted linear calibration curve is to be generated with every set of samples analyzed. The calibration standards are interspersed among the analytical samples, preferably with a standard between every two analytical samples, and injected into the HPLC/OECD system. The calibration curve is generated by plotting peak height of the detector response against the concentration for each calibration standard of EMA and methylated HEMA. 

Analytical standards are prepared for two purposes for fortifying control matrices to determine the analytical accuracy and for calibrating the response of the analyte in the mass spectrometer detector. The purity of all standards must be verified before preparation of the stock solutions. All standards should be refrigerated (2-10 °C) in clean amber-glass bottles with foil/Tefion-lined screw-caps. The absolute volume of the standard solutions may be varied at the discretion of the analyst, as long as the correct proportions of the solute and solvent are maintained. Calibrate the analytical balance before weighing any analytical standard material for this method. 

Detectors are usually conpued in terns of their operational characteristics defined by the nininvin detectable quantity of standards, the selectivity response ratio between standards of different conpositlon or structure, and the range of the linear portion of the detector-response calibration curve. These terns are wid. y used to neasure the perfomance of different chronatographic detectors and were fomally defined in section 1.8.1. 

The determination of the relationship between detector response and the sample concentration is termed the calibration of the method. There are two types of methods in use for the quantitative analysis of a sample, i.e., the external standard and the internal standard method. An external standard method is a direct comparison of the detector response of a pure compound (standard) to a sample.2 The calibration of the method is performed by preparing standards of varying concentration and analyzing them by a developed method. Method 1 (below) was developed for toluene, and standards of varying concentration were prepared and analyzed. The results obtained are summarized in Table 2 see Figure 3. 

Calibration of an internal standard method is done by preparing standard samples of varying concentration. The same amount of IS is added to each, and the standard samples are analyzed using a developed method. The detector response, area or height, of each standard is determined, and a ratio is calculated. The graph of concentration vs. area ratio is plotted. The method is considered linear if the correlation coefficient is 0.99 or better. The response factor RF is calculated as... 

For the example of toluene given above, the external standard method can be converted into an internal standard method by adding anisole (an appropriate internal standard) to both standard and sample. The retention time of anisole is 4.5 minutes if analyzed by the method above. To calibrate the internal standard method for toluene, toluene standards of concentration 0.3 to 1.5 mg/ml containing 0.5 mg/ml anisole were prepared. The detector response as a function of the amount of sample injected is shown in Figure 4B. 

To allow for this, before the peak areas are normalised we must first correct each area so as to get the area we would have obtained had the detector response been the same for each of the three compounds. We will now use the results from our mixture to determine calibration factors (relative response factors) for the detector, and then use these for the analysis of a commercial tablet. 

O. Vorm and P. Roepstorff. Detector Bias Gating for Improved Detector Response and Calibration in Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry. J. Mass Spectrom., 31(1996) 351-356. 

Calibration, in current Good Manufacturing Practices (cGMP) terminology, refers to instrument qualification or performance verification of the HPLC. Note that neither any internal instrumental adjustment nor detector response curve for quantitation is intended here as in the common usage of the terminology. In most pharmaceutical laboratories. 

Gas (GC) and Liquid (HPLC) Chromatographs These are similar to spectrophotometers in that they are calibrated via a detector response to some property of analyte. The analyte may either be in solution or, in the case of GC (Figure 5.9), in pure form. Again, a calibration (or "standard") curve of detector response vs. either concentration or amount of pure chemical used is plotted and unknowns determined by correlation with the known stan-... 

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