System Suitability in HPLC Analysis

HPLC, short for High-performance liquid chromatography is a technique used for separating the components in a mixture. In the HPLC technique, a liquid sample is passed over an absorbent material to test its efficacy.
HPLC chromatography technique is used in pharmaceutical industries for research and testing purposes. Most of the pharmaceutical companies follow a three-step approach to check the functioning of their High performance liquid chromatography systems- Initial System Qualification, Method Validation and Suitability Testing (SST).

System Suitability Test (SST)
Selecting a proper System Suitability Testing mixture is essential to check the specifications of a liquid chromatographic system. System Suitability Testing limits are acceptance criteria that must be met prior to sample analysis. Some of the common chromatographic systems used in pharmaceutical sample analyses are:

• Active ingredient assays
• Impurity determinations
• Dissolution testing

The System Suitability Testing limits should conform to the guidelines provided by CDER (Center for Drug Evaluation and Research). Other sources for referencing about the System Suitability Testing are the USP (United States Pharmacopeia) and the ICH (The International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use). Especially, one of the ICH’s guidelines has a section dealing entirely with the System Suitability Testing. Some parameters which can be checked using the System Suitability Testing are:

• Resolution
• Retention time
• Pressure
• Column efficiency
• Repeatability
• Plate Number
• Tailing factor
• Signal-to-noise ratio

Let us look at some of these parameters.
Resolution: One of the most important parameters. Resolution is used to check whether the critical separation is feasible under the given conditions.
Retention time: Retention time is one of the easy-to-identify parameters. The resolution should be fairly constant. This is because values outside the retention-time window might go unreported by the system under test.
Pressure: The suitability testing must be carried out within set pressure limits. This is to ensure that wearing of system components is reduced.
The column is efficiency-Also known as band broadening.
Repeatability: Successive measurements taken under the same measurement conditions should give the same results.
Plate number: The Plate number is a theoretical plate index(N) used to determine column efficiency. The plate number is arrived at by using the plate theory. Plate number changes depending on the type of analysis carried out.
Tailing factor: This is also called as Symmetry factor. Tailing factor becomes important if the peak tailing has chances of affecting the method’s performance. Similar to Plate number, the Tailing factor also depends upon the type of analysis.
Signal-to-Noise Ratio: S/N ratio is a measure of the system’s performance at the lower end.
It is not enough to perform System Suitability Testing at the beginning of the assay alone. For the purpose of periodic monitoring, it is necessary to do the System Suitability Testing at regular intervals. This is because the performance of the system under test may change due to continuous use.

Summary
The System Suitability Tests mentioned in this article are not exhaustive. The System Suitability Tests to be performed are decided by the pharmaceutical scientists or analysts, considering various factors of the system under test. Pharmaceutical scientists use statistical analyses to set realistic System Suitability Testing limits. An optimum system should provide the maximum information out of a minimum number of tests. The System Suitability Tests should be designed such that the requirements are met easily when the system is functioning correctly and fails if there is a problem.