Relative response factor

The relative response factor (RRF) of 1 defines that an impurity and active at identical concentrations have the same analytical response. Generally, no corrections for RRF need to be performed if the RRF of particular impurities are between 0.8 and 1.2. If the relative response factors are outside this region, the impurities can be overestimated or underestimated. For example, if impurity X has an RRF of 0.5 compared to the active, then it would be underestimated and if impurity Y has an RRF of 1.5 compared to the active, then it can be overestimated. In these cases the RRF must be taken into account when determining the percent of related substances during evaluation of the purity of the DS or the DR The following equation could be used. 

if the there are two actives in the drug product and the impurities in the drug product from one active are being quantitated versus the other active 

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This result can be used to prepare a synthetic mixture to obtain relative response factors. 

Using the peak area method, prepare a standard solution in which the amounts of each component will approximate the amounts found in the sample being analyzed. From the standard solution, obtain the GC peak areas for each component. Assign to one of the major components a relative response factor (RF) of 1.0. This component is the reference. The response factors for the other components are obtained in the following manner. 

Where SA R is the specific area of the reference peak, and SA is the specific area of component x. AR is the GC peak area of the reference, Ax is the GC peak area of component x, WR is the weight of the reference, and Wx is the weight of component x. The weight percent of component x can be obtained from the sample chromatogram by using the relative response factors in the following equation ... 

It is crucial in quantitative GC to obtain a good separation of the components of interest. Although this is not critical when a mass spectrometer is used as the detector (because ions for identification can be mass selected), it is nevertheless good practice. If the GC effluent is split between the mass spectrometer and FID detector, either detector can be used for quantitation. Because the response for any individual compound will differ, it is necessary to obtain relative response factors for those compounds for which quantitation is needed. Care should be taken to prevent contamination of the sample with the reference standards. This is a major source of error in trace quantitative analysis. To prevent such contamination, a method blank should be run, following all steps in the method of preparation of a sample except the addition of the sample. To ensure that there is no contamination or carryover in the GC column or the ion source, the method blank should be run prior to each sample. 

Establish control charts of instrumental performance. Day-to-day variations in pump flow rate, relative response factors, absolute response to a standard, column plate counts, and standard retention times or capacity factors are all useful monitors of the performance of a system. By requiring that operators maintain control charts, troubleshooting is made much easier. The maintenance of control charts should be limited to a few minutes per day. 

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... 

It is being recognized increasingly that regulation can have a positive impact on laboratory productivity.36 System suitability testing has been proposed as superior to and supplemental to calibration in the UV-VIS detector.37 Large variations in both response factor and in relative response factors were observed on different instruments. Even on the same instrument, UV-VIS spectra can be extremely dependent on solution conditions, as was observed in a separation of hypericin, the antidepressant extract of St. John s wort.38... 

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. 

Using the relative response factors that you calculated in the last Section, correct each peak area by dividing by the appropriate response factor. For each injection, calculate the amount Of aspirin and caffeine present, expressing the results as mg per tablet. 

H. Wang, G.J. Provan and K. Helliwell, HPLC determination of catechins in tea leaves and tea extracts using relative response factors. Food Chem. 81 (2003) 307-312. 

The truncated peptide analogs were used to demonstrate the specificity of the method and to evaluate the limit of quantitation of potential impurities. Potential impurities were spiked into a solution of IB-367 at 0.05%, 0.1%, 0.2%, 0.5%, and 1% to assay the linearity of potential impurities at low concentrations. The method exhibited acceptable linearity for impurities from 0.05 to 1%. The relative response factors of these analogs were assessed to determine area normalization feasibility. 

Determined by GC on an HP-5 or a Supelco Simplicity 1 fused-silica capillary column. The percentage compositions were obtained from electronic integration measurements, without taking into account relative response factors. 

Further discussion of method validation can be found in Chapter 7. However, it should be noted from Table 11 that it is frequently desirable to perform validation experiments beyond ICH requirements. While ICH addresses specificity, accuracy, precision, detection limit, quantitation limit, linearity, and range, we have found it useful to additionally examine stability of solutions, reporting threshold, robustness (as detailed above), filtration, relative response factors (RRF), system suitability tests, and where applicable method comparison tests. 

Use Normalized Area Percent analysis for impurities and related substances testing. Index the area % to the parent drug (where parent = 100%). Apply a correction for relative response factors (RRF) if those are known. 

Where the specific impnrity is unavailable or is too costly, the use of composite or degraded samples is possible. This approach involves the nse of a dirty sample of a drug substance or the creation of a mixture of impurities through the in situ forced degradation method. Both of these approaches are best nsed for qualitative uses. In each of these mixtures, the impurities are present in unknown quantities. The real benefit of this type of impnrity standard is the low cost and the ability to unequivocally identify the peak loci of the impurities. When these mixtures are used in conjunction with a compendial standard and a well-developed set of relative response factors the resnlts will meet most analytical needs. 

Sensitivity and linearity problems. Incorrect quantification of impurities. Inaccurate use of relative response factor (s)... 

Note that all the desired properties depend directly or Indirectly on the ratio A/n and therefore, on the relative response factors and signal to noise ratios of the spectrophotometer and the differential refractometer. In general, spectrophotometers are more sensitive than differential refractometers, therefore, the ratio A/n at the tails of the chromatogram, that is, the refractometer signal will be zero while there still be a signal from the spectrophotometer. In addition, equations 9 and 10 are hyperbolic functions of the concentration. Thus, as the concentration decreases the apparent values of Mw and [n] will increase, increasing the uncertainty in the estimates of the molecular weights and the intrinsic viscosities (see Appendix I and references 26-29). In the limit when A/n - (or n/A 0), the polymer... 

Isomeric Group and PCB Number Structure (chlorine-filled) Relative Retention Time Relative Response Factor Log... 

Relative response factor the ratio of the response factor of individual related substance to that of a drug substance to correct for differences in the response of related substances and that of the drug substance. It can be determined using the following equation ... 

If a linearity curve (Figure 3.1) is constructed for both the related substance and the drug substance by plotting the response versus the concentration, the relative response factor can also be determined by... 

Response Factor. The response factors of the related substances should be similar to that of the drug substance (i.e., relative response factors close to unity). Otherwise, a response factor correction must be used in the calculation. 

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