01 Jul HPLC, a modular technique that complements NMR

Did you know? SPECIFIC POLYMERS has its own analysis laboratory with a vast array of equipment for studying the structural, thermal and rheological properties of chemicals, resins, paints or varnishes.

At first, it allows us to analyze our own products to assess their quality and purity, thus ensuring that the products we ship meet expectations. In addition, we offer analysis services to support our customers R&D activities and we have the ability to analyze a large range or products.

Based on the specificity of each product, SPECIFIC POLYMERS adapts its analysis methods and has the capacity to develop tailor-made methods.
As for example, in the case study presented below, we highlight the complementarity of  high-performance liquid chromatography (HPLC) – recently acquired at the end of 2023- and nuclear magnetic spectrometry (NMR) for the in-depth analysis of a multi-component’s formulation.
This will enable us to conclude on the advantages and limitations of the 2 methods, and prove their complementarity.

Study context: analysis of a formulation

HPLC separation and quantification techniques

How does HPLC work?

After leaving the column, the analytes pass through a UV detector whose response is proportional to the analyte concentration.

In this study, the eluent used is a mixture of acetonitrile (apolar) and water (polar). By adjusting the composition of the mobile phase, HPLC can be adapted to the different matrices to be analyzed, demonstrating a great flexibility.

a. External calibration method

The HPLC external calibration method involves the use of known standards of controlled purity. To establish a calibration curve, standard solutions of precise concentrations are injected and their UV responses measured. The unknown samples are then analyzed, and their concentrations determined by comparing their responses with the calibration curve obtained. This method enables precise quantification of analytes based on the linear relationship between standard concentration and UV response.

Conclusion: if you have a series of samples to analyze, this method is recommended and is more reliable. On the other hand, when you have a sample matrix effect, this method becomes less reliable.

b. Addition method

The HPLC  addition method involves adding known quantities of a standard of known concentration to the sample to be analyzed, and then measuring the responses before and after addition. By comparing the increase in response due to the addition of standard, the initial concentration of analyte in the sample can be determined.

Conclusion: This method is particularly useful for compensating for matrix effects and obtaining more accurate results. For a series of samples to be analyzed, it is more time-consuming.

Comparison of HPLC vs NMR techniques

Case 1: consistent results between the 2 techniques: NMR and HPLC

Case 2: different results between NMR and HPLC techniques

Conclusion

Both methods have their limitations, but these can be overcome by combining the two methods.

– Cross-validation: Results obtained by HPLC can be validated and extended by NMR. For example, an impurity detected by HPLC can be structured and confirmed by NMR.
– Complete analysis: Combined use enables complete analysis of a sample, ensuring separation, quantification and structural identification of components.
Combining HPLC and NMR provides an exhaustive understanding of the sample, maximizing the precision and reliability of the analysis.