System suitability parameters resolution

In the System Suitability section, different parameters are described which can be applied in order to check the behavior of the CE system. The choice of the appropriate parameters depends on the mode of CE used. The system suitability parameters include retention factor (k) (only for MEKC), apparent number of theoretical plates (N), symmetry factor (Af), resolution (Rs)> Rtea repeatability, migration time repeatability, and signal-to-noise ratio. Practical equations to calculate different system suitability parameters from the electropherograms are presented, which are also included in Table 3. 

Other results obtained from the ruggedness test are the definition of optimized method conditions for the factors and of system suitability criteria for a number of responses. System suitability parameters [6,17] are defined as an interval in which a response can vary for a rugged method. The system suitability criteria are the range of values between which a response (e.g. retention time, capacity factor, number of theoretical plates, resolution) can vary without affecting the quantitative results of the analysis. For instance, a design is performed and the retention time of the main substance varies between 200 s and 320 s without affecting the quantitative determination of the substances. The system suitability criteria for the retention time is then defined as the interval 200 s - 320 s. 

System suitability parameters [6,17] are defined as an interval in which a response (e.g. retention time, resolution, number of theoretical plates) are allowed to vary for a robust method. They can be derived from the minimal and maximal result for the considered response as seen with a design in which the quantitative results of the method were found to be rugged. 

System suitability parameters with their respective acceptance criteria should be a requirement for any method. This will provide an added level of confidence that the correct mobile phase, temperature, flow rate, and column were used and will ensure the system performance (pump and detector). This usually includes (at a minimum) a requirement for injection precision, sensitivity, standard accuracy (if for an assay method), and retention time of the target analyte. Sometimes, a resolution requirement is added for a critical pair, along with criteria for efficiency and tailing factor (especially if a known impurity elutes on the tail of the target analyte). This is added to ensure that the column performance is adequate to achieve the desired separation. 

In addition to validation of the automation, full validation of the chromatographic procedure, as described in Chapter 12, should be conducted for late-phase methods. This should include specification of system suitability parameters to ensure that the performance obtained during method development and validation is maintained during routine use. The system suitability parameters may include specification of acceptable injection repeatability, criteria for resolution between critical pairs, maximum allowable tailing factors, and a means of verifying that the requisite sensitivity is obtained. As recommended by Vander Heyden et al., system suitability limits are best set following robustness tests. 

The USP definition of robustness equals that of the ICH (3) The robustness of an analytical procedure is a measure of its capacity to remain unaffected by small, but deliberate variations in method parameters and provides an indication of its reliability during normal usage. A robustness test is the experimental setup used to evaluate method robustness. It quantifies the insensitivity of the results for a method transfer to another laboratory or instrument. The ICH guidelines also state that One consequence of the evaluation of robustness should be that a series of system suitability parameters (eg., resolution tests) is established to ensure that the validity of the analytical procedure is maintained whenever used (3). 

Figure 5.12. A summary report for system suitability testing documenting result i.d., precision, and other system suitability parameters (S/N ratio, tailing factors, plate count, and resolution). Note that means and precision of each table column can be automatically calculated.

System suitability refers to a unique set of performance specifications that is directly linked to a method. These specifications are not accuracy, precision, linearity, etc., which are measures of method performance and are used to support product release. These data are generated after the analysis set is complete. Conversely, a system suitability parameter directly ties the immediate performance of the method for a specific portion of an analytical sequence. Some parameters that are commonly used as system suitability parameters include theoretical plates aaA/oc peak symmetry for the analyte peak Ifl), resolution or a for multiple analyte peaks in a determination), or check sample results (analysis of a previously analyzed sample). 

Additional system suitability parameters Other parameters for system suitability testing can be considered (e.g., capacity factor, number of theoretical plates, etc.). Capacity factor can be especially important in methods used for stability testing, where adequate resolution of the peak of interest from the solvent front is required so that any degradation products are suitably resolved. 

System suitability errors often include profiles that are not consistent with historical data such as (1) excessive peak tailing, poor resolution of critical components or noisy baseline (2) peak spikes due to micro bubbles or electric shock and (3) integration parameters such as percent main peak area out of range for the assay reference control sample. 

Having optimised the efficiency of a chromatographic separation the quality of the chromatography can be controlled by applying certain system suitability tests. One of these is the calculation of theoretical plates for a column and there are two other main parameters for assessing performance peak symmetry and the resolution between critical pairs of peaks. A third performance test, the peak purity parameter, can be applied where two-dimensional detectors such as diode or coulometric array or mass spectrometry detectors are being used. The reproducibility of peak retention times is also an important parameter for controlling performance. 

System suitability should be based on criteria and parameters collected as a group that will be able to define the performance of the system. Some of the common parameters used include precision of repetitive injections (usually five or six), resolution (R), tailing factor (T), number of theoretical plates (N), and capacity factor ( ). 

Considering the importance of system suitability in determining the accuracy and reliability of method results, it is improper to set an RSD requirement of < 2% for a method that consistently yields values of < 1%. If peak tailing is always < 1.5, then a requirement of < 2.0 does not provide feedback to notify the chemist of a poor or failing column. Resolution requirements must be required for the critical pair of components where a loss of resolution would impact method performance. By addressing these parameters with a more critical eye, the suitability of the analysis system can be accurately determined. 

For system suitability smdies, five replicate injections of mixed standard solutions were injected and parameters such as relative standard deviation of peak area, column efficiency, resolution, and tailing factors of the peaks were calculated. Results are shown in Table 3. 

System suitability testing is an integral part of many analytical procedures. The tests are based on the concept that the equipment, electronics, analytical operations and samples to be analysed constitute an integral system that can be evaluated as such. System suitability test parameters that need to be established for a particular procedure depend on the type of procedure being evaluated, for instance, a resolution test for an HPLC procedure. 

The responses of main interest also are different in method development and robustness testing. In development, the considered responses are related to the quality of the separation (l),such as, for electrophoretic methods, migration times, peak shapes, and the resolutions between neighboring peaks. When the separation is optimized and the method is validated, thus also in robustness testing, the responses of main interest are related to the quantitative aspects of the method, such as contents, concentrations, or recoveries. The responses considered during development occasionally are considered in a second instance, for example, as system suitability test (SST) parameters. 

System suitability is guaranteed if both apparatus test and validation match their requirements. It is best performed on a routine basis and can be done very easily if the HPLC apparatus is equipped with a computer data system. Then during each run or in well-defined intervals a number of parameters are acquired plate number, resolution, precision, retention time, relative retention time (i.e. k value) and peak asymmetry-also if necessary linearity and limits of quantification. The results are followed by statistical tools, including easy-to-monitor graphical documentation with control charts. ... 

These parameters can be ranges (both upper and lower control limits) as in the case of an analyte level in a check standard maximum values (upper control limit only) as in the case of peak asymmetry or minimum values (lower control limit only) as is the case of resolution or plate number. Parameters that do not directly monitor the actual performance of the method (e.g., mobile phase pH, flow rate determination), although functionally important, are inadequate and inappropriate for system suitability determinations. 

The system suitability test is carried out to test critical instrument and method related parameters. In HPLC system suitability us determined ahead of running a method and checks that the parameters which can influence the outcome of the analysis are within specification. This normally includes reproducibUity, peak shape and tailing and resolution of the ingredients. 

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