The operation parameters of the whole chromatographic system can be checked with properly selected SST mixtures. System suitability testing limits are the acceptance criteria that must be met prior to the use of sample analysis.

The system suitability testing limit should conform to criteria provided in guidelines by CDER and other pharmacopeial references like USP and ICH. Some of the parameters which can be checked as SST requirements are:

- Capacity Factor
- Resolution
- Tailing Factor
- Theoretical Plate Number
- Signal to Noise ratio
- Repeatability

Let’s look in to each of the System Suitability parameters :

**Capacity Factor:** The capacity factor is a measure of, where the peak of interest is located with respect to void volume, i.e., elution time of the non-retained components. Generally, the value of K is > 2.

**Resolution**: Resolution is an important HPLC performance indicator. It is used to ensure that closely eluting compounds are resolved from each other as they pass through the column in the given condition. Resolution of > 2 between the peak of interest and the closest potential interfering peak is desirable.

**Tailing Factor**: Tailing factor is a measure of peak symmetry. It is calculated as Tf = (a +b) / 2a, where ‘a’ and ‘b’ are the peak half-widths at 5% of the peak height, a is the front half-width, b is the back. Tailing factor of < 2 is generally recommended.

**Theoretical Plate** **Number(N)**: The theoretical plate number is a measure of column efficiency. H, or HETP, the height equivalent of a theoretical plate, measures the column efficiency per unit length (L) of the column. peak position, particle size in the column, flow-rate of the mobile phase, column temperature, viscosity of the mobile phase, and molecular weight of the analyte are some of the parameters which can affect Plate number.

**Signal to Noise ratio**: The *s*ignal-to-noise (S/N) ratio is often used to measure the sensitivity of a liquid and gas chromatography instrument.

**Repeatability**: The closeness of the agreement between the results of successive measurements carried out under the same conditions of measurement.

**Summary**: Retention time, pressure, and other criteria may be included as system suitability test parameters. The system suitability parameters may not be the same for all the analytical methods. All the parameters mentioned in this article may not be considered for all analytical methods, the minimum system suitability test parameters requirement changes with the purpose of testing.