Parenteral nutrition mixtures controls by inductively coupled plasma optical emission spectrometer: influence of proteins on electrolyte assay

Context
Acquisition of an inductively coupled plasma optical emission spectrometer (ICP-OES), ICAP 7400 duo (ThermoFisher), to carry out analytical control of parenteral nutrition mixtures, led us to determine optimal conditions for validating electrolytes dosing method.

Objective
Aim of this study is to determine influence of proteins during analytical control of binary parenteral nutrition mixtures by ICP-OES in sodium, potassium, calcium and magnesium.

Methods
Five bags of 5 standards binary formulas and 15 nominatives bags were produced with qualified automated compounding system, BAXA EM 2400. A sample of each bag was taken after homogeneization. The matrix effect was studied by comparing 2 ranges of calibration: with or without proteins and by analyzing the Na+, K+, Ca2+ and Mg2+ concentrations of each sample according to these 2 ranges. Results of correlation coefficients were compared with Fischer transformation.

Results
The matrix effect has not been statistically demonstrated (U <1.96). Correlation coefficients obtained are greater than 0.999 for the 4 analytes and the coefficients of variation obtained are the same whatever range used. For standard bags, relative error (RE) averages are lower on Mg2+ concentrations with protein range (<3% vs. <5%). For the other 3 analytes, RE means are the same or even higher with the protein range and one bag has an RE greater than + 10% for calcium. For nominatives bags, REs are on average lower with the non-protein range.

Discussion-conclusion
This study showed that presence of proteins in the calibration range didn’t influence accuracy of the results obtained except for magnesium. Thus, protein range will not be used to validate the dosing method of parenteral nutrition mixtures by ICP-OES.

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