Analytical validation of a cation assay in binary parenteral nutrition with capillary electrophoresis

Introduction
Individualised binary parenteral nutritions (PN) are daily prepared in our pharmacy for extremely preterm babies. Control process include determination of cations concentration. This control is carried out by enzymatic method in the biochemistry laboratory. Several issues related to this analysis technique have been identified: sodium detection limit (Na+) of 20mM and a lower quality control of 80mM while the majority of the binary mixtures producted have a theoretical Na+ concentration between 15 and 40mM. Moreover an interaction between calcium (Ca2+) and magnesium (Mg2+) leads to an overestimation of the Mg2+ concentration particularly during high amont of Ca2+ (Chouaou et al. GERPAC 2020). In order to have an appropriated method to our specific condition, we acquired a capillary electrophoresis (Wynsep^®) that we wish to qualify for the determination of cations.

Objective
To study the feasibility and to carry out the validation of cations assay (Na+, K+, Ca2+ et Mg2+) in binary mixtures of parenteral nutrition with capillary electrophoresis according to ICH Q2 (R1) criteria.

Material and method
The selected performance criteria were: linearity, repeatability, intermediate precision, accuracy, lower quantitation limit and matrix effect. The linearity was evaluated from five concentrations for three days. To evaluate repeatability and intermediate precision, three concentrations were chosen and repeated six times.

Results
For each cation, the response is linear over the interval studied (Na+[50-300µM], K+[20-200µM], Ca2+[10-100µM], Mg2+[5-50µM]) with a R²>0,99. All the coefficients of variation (CV) for repeatability and the intermediate precision are <5 %; Accuracy of the method seems correct (biases <5%). Lower quantification limits are as follows: 10µM for Na+ and K+; 5µM for Ca2+ and Mg2+. No matrix effect was observed (binary mixture was compared to a sample with the same cations concentrations in sterile water.

Discussion/conclusion
These results allowed us to validate the assay method.. The analysis time is the same with the two methods. CE will allow us to overcome the enzymatic method problems. Thus, this technique allows us to improve the security of control process.

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