Precision related substances

System Suitability Tests. The appropriate system suitability tests should be defined before method validation (e.g., precision, resolution of critical related substances, tailing, detector sensitivity). These system suitability tests should be performed in each method validation experiments. System suitability results from the method validation experiment can be used to determine the appropriate system suitability acceptance criteria. 

Intermediate precision is to determine method precision in different experiments using different analysts and/or instrument setup. Similar to that of repeatability, one should evaluate the results of individual related substances, total related substances, and the consistency of related substance profiles in all experiments. The percent RSD and confidence level of these results are reported to illustrate the intermediate precision. 

Typically, linearity and accuracy determination covers a wide concentration range (e.g., 50% of the ICH reporting limit to 150% of specification). However, the concentration range for precision will be limited by the availability of sample of different related substance levels. Therefore, to ensure an appropriate method validation range with respect to precision, it is critical to use samples of low and high levels of related substance in precision experiments (e.g., fresh and stressed samples). 

Other Considerations. Typically, the variations in robustness results are compared to the intermediate precision results to demonstrate that robustness is not affected significantly within normal day-to-day variation. When the related substance results are affected by some critical experimental parameters, a precautionary statement needs to be included in the procedure to ensure that this parameter is tightly controlled between experiments. For example, if percent organic of mobile phase affects the results significantly, the procedure should indicate the acceptable range for percent organic (e.g., 50% organic 2%)... 

Clearly, all of the related substances, with the exception of hGH dimer, exhibited full biopotency as compared to hGH monomer. Further investigation of hGH dimer demonstrated that traditional immunoassays could not distinguish it from hGH monomer, although an immunoradiometric (IRMA) assay using two monoclonal antibodies could distinguish the two forms (8). As expected, size exclusion HPLC was also able to distinguish monomeric and dimeric forms of hGH. Further studies revealed that the IRMA assay precision was approximately 5-6% RSD, whereas size exclusion HPLC exhibited a precision of 1-2% RSD. Therefore, size exclusion HPLC was selected as the most useful candidate for replacement for the in-vivo bioassay. 

The above statement has lot of details in reference to what is a SIM The statement starts with method validation (refer to Chapter 9). Next, most methods need to be specific (specificity, resolution of active from related substances, peak purity), reproducible (precision), quantitative (recovery, linearity, LOD, LOQ), and able to monitor a change in chemical, physical, and/or microbiological properties of drug products over time (refer to sections on stability testing and mass balance). 

GC-MS has found wide application in studies of monoamines in both animal models and in human neuropharmacology [452]. Interest has centred on the use of selected ion monitoring in the determination of trace amounts of the amines, their metabolites and related substances with a possible function as neurotransmitters. The SIM approach complements established assay methods such as gas chromatography with electron capture detection (ECD), fluorimetry or enzymic assay. A check on specificity is afforded and in many cases enhancement in sensitivity and precision of measurement can be obtained. Method development, principally relating to estimation of central amine turnover, is noted in this Section and an outline of work on human depression serves to illustrate the potential of GC-MS to the study of CNS dysfunction. 

HPLC provides reliable quantitative precision and accuracy, along with a linear dynamic range (LDR) sufficient to allow for the determination of the API and related substances in the same run using a variety of detectors, and can be performed on fully automated instrumentation. HPLC provides excellent reproducibility and is applicable to a wide array of compound types by judicious choice of HPLC column chemistry. Major modes of HPLC include reversed phase and normal phase for the analysis of small (<2000 Da) organic molecules, ion chromatography for the analysis of ions, size exclusion chromatography for the separation of polymers, and chiral HPLC for the determination of enantiomeric purity. Numerous chemically different columns are available within each broad classification, to further aid method development. 

Another recent innovation deals with the chemistry of the capillary wall. For example, capillaries have been improved by coating their inner surfaces with novel chemistries, or by adding a replaceable dynamic coating solution, allowing better resolution of analytes (109-114). Carrier solutions or background electrolytes can be enriched with a variety of additives, permitting the separation of closely related substances at baseline resolution (see Refs. 115-118 and Sec. II). These improvements have lead to better precision, selectivity, and accuracy of separated analytes. Precision and accuracy is improved for both peak migration and peak area counts for the simple and complex analytes. 

Despite the qualitative validity of such comparisons, the precise relation between polarization and the electronic structure of a substance has been found only within the spectroscopic approach, which has permitted to determine separately the atomic Pa) and electronic (P ) polarization and also the effective charges of atoms by measuring the intensities of infrared (IR) absorption bands in molecules. Evidently, the ratio Pa/Patomic charges are also approximate owing to the neglect of anharmonism and changes in the orbital overlaps during vibrations of atoms. 

The method development by MEEKC is useful for the determination of active and excipient compounds as well as related substances of drugs, with very high precision and accuracy. The application of MEEKC in pharmaceutical analysis offers a powerful tool in quality control of pharmaceutical laboratories. 

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