HPLC Assay Testing: What It Is And Why It’s Important

Introduction to HPLC Assay Testing

When any pharmaceutical company, agrochemical company, or an FMCG (Fast Moving Consumer Goods) company develops or markets any product, it must mention the content of the items or ingredients (% w/w) of that particular product on its product label. This % w/w content test or assay test is an important test before releasing that particular product into the market.

Understanding HPLC Assay

The term “assay” is a quantitative content of a compound and a relative value calculated against its corresponding standard. One technique that supports this objective is the determination of assay by High-Performance Liquid Chromatography (HPLC). One of the strengths of HPLC is that it is an excellent quantitative analytical technique. It is used to quantify primary or major components of a sample for mixtures of many components in a sample and also for trace components present in the sample.

Method Development Requirements

Now, since the “assay by HPLC” test is an important test among all other tests to define the quality of the product, it is required that the HPLC method used to determine assay should be equally good. The development of a good quantitative HPLC method requires an understanding of the critical concepts of accuracy, precision, linearity and specificity. Understanding the complete analytical method lifecycle is essential for successful method development and implementation.

Key Analytical Parameters

Accuracy is the closeness of the measured value to the true value. Precision refers to the reproducibility of multiple measurements of a homogeneous sample. This can include reproducibility of results using different instruments, analysts, laboratories and so on. The linearity of a method is a measure of response vs. concentration that approximates a straight line.

The specificity or selectivity of the HPLC assay method is to show the absence of interference of various other components e.g. product impurities, mobile phase buffer, process solvents and demonstration of stability indicating the nature of the assay method through forced degradation studies. The entire study where the above parameters are checked is termed method validation.

Calculation Methods and Formulas

In the HPLC assay test, the most general method for determining the concentration of an unknown sample is by using an external standard. In this method usually 5 or 6 replicates of standard preparation of a known concentration are injected followed by 2 separate sample preparations of known concentration. E.g. The % w/w assay (ODB) is then calculated using the following formula:                                                                     

Where, A_sa      = Average peak area of the compound in sample preparation; A_{sd A} = Average peak area of standard preparation; W_{sd A} = Concentration of standard preparation in mg/mL; W_sa   = Concentration of sample preparation, in mg/mL; LOD = Loss on drying of the sample (% w/w); P = Potency of standard.

The reporting of the HPLC is either “% w/w As is” or “% w/w on Anhydrous basis” (OAB) or “% w/w on Dried basis” (ODB).

System Suitability Parameters

The common system suitability criteria for an assay by HPLC test are viz. (i) calculation of % RSD (Relative Standard Deviation) of peak area obtained from replicate standard injections. (ii) tailing factor of analyte peak and (iii) theoretical plates obtained for the analyte peak on a particular HPLC column mentioned in the method of analysis. e.g. maximum permitted % RSD for assay of an Active Pharmaceutical Ingredient (API) by HPLC, of 5 consecutive injections of the standard should be NMT 0.73% for a limit of 98.0 % to 102.0 % as per the European Pharmacopoeia chapter on chromatographic separation techniques.

Why HPLC Assay is Important

HPLC assays are essential in chemical/pharmaceutical/agrochemical/FMCG manufacturing to control the quality and yields of every stage of the product.

Pharmaceutical Quality Control

The HPLC assay of pharmaceutical formulation ensures the manufacturer that the formulation in the market has the right amount of active ingredient (API) in it. It is also directly related to the patient’s health. If the formulation has excess or less API in it than required. It could result in either no adverse or no effect on a patient’s health.

It also helps quantification of unwanted compounds (impurities) in either API or formulations to ensure their quality. For detailed information on HPLC impurity analysis techniques, including method development strategies for detecting trace impurities

Cost Benefits and Efficiency

Incorporating HPLC assay in manufacturing allows us to enjoy significant cost reductions over time. Providing accurate content analysis enables the optimisation of products and selecting the most cost-effective raw materials thereby minimizing material waste and production inefficiencies.

Conclusion

HPLC assay testing serves as a critical quality control measure across pharmaceutical, agrochemical, and FMCG industries. By ensuring accurate quantification of active ingredients and impurities, HPLC assays protect patient safety, maintain product efficacy, and support regulatory compliance. The implementation of validated HPLC methods not only guarantees product quality but also provides significant economic benefits through optimized manufacturing processes and reduced waste.

As analytical requirements continue to evolve, HPLC assay testing remains an indispensable tool for manufacturers committed to delivering high-quality, safe, and effective products to the market.

FAQ’s

Reference:

• Snyder, Lloyd R., et al. Practical HPLC Method Development. Wiley-Interscience, 1997, www.wiley.com/en-us/Practical+HPLC+Method+Development%2C+2nd+Edition-p-9780471007036.