Microwave Plasma Atomic Emission Spectrometry: A New Method for Measuring ions in paediatric parenteral nutrition bags.

In order to guarantee the quality of our parenteral nutrition bags, several controls are carried out: gravimetric, analytical (osmolality, Na, K), visual. For ion determination, the unit had to acquire in 2018 a new equipment following the shutdown of maintenance and consumables of the photometer flame. We chose a microwave plasma atomic emission spectrometer (MP AES 4210 from Agilent). This new method of determination required several months of validation prior to routine implementation.

For this, we performed the following tests to validate the determination of Na, K, Ca and Mg: repeatability, intermediate fidelity, accuracy, inter-sample contamination, linearity, matrix effect The repeatability determines that the analysis of the same sample gives the same result, intermediate fidelity as critical parameter variation (here operator, standard solutions) do not vary the results, the accuracy validate the fact that the result obtained corresponds to the result expected, the cross-sample contamination demonstrate the absence of contamination that could interfering with the results.

Finally, the method was tested on our samples and compared for Na and K to the results obtained with our method in place. All these tests were made in multi-elementary to be close to the analytical conditions that will be developed in routine.

For each ion, two wavelengths were tested (NA 588.995/589.592 nm ; K 766.491/769.897 nm ; Ca 396.847/422.673 nm ; Mg 517.268/518.360 nm). Our acceptability thresholds have been 5% for repeatability, intermediate fidelity, accuracy (relative bias) ; 1% for inter-sample contamination ; 10% for matrix effect.

The conditions of analysis of the apparatus require a pre analytical work of dilution of the samples, three dilutions are tested (1/500e , 1/250 e and 1/100e ). For each ion and each wavelength, all the tests came back compliant, it means below our acceptability thresholds. Except for calcium where only the wavelength at 422,673 nm has been validated. Dilutions at 1/500e and 1/250e resulted in too many non-compliances on our samples. 1/100e dilution was routinely retained. Na and K assays by MP AES 4210 have been routine since January 2019. The Ca et Mg jwill be implemented in October 2019. We will then study the possibility of dosing the P after agreement of our pediatricians.The number of possible analyses with this new device also opens possibilities to realize some elements determinations to qualify water for hemodialysis, according to the European Pharmacopoeia.

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