Impact of the analytical optimization of a cation quantification method by capillary electrophoresis using the RGB tool

Introduction
Our pharmacy produces parenteral nutrition (PN) bags for patients in neonatology. The liberatory quantification method of cations (K⁺, Ca²⁺, Na⁺ and Mg²⁺) by capillary electrophoresis with conductimetric detection (CE) takes 8 min per bag. During high throughput production sessions, this can cause delays in the delivery of the PN bags. Our aim was to reduce the analysis time, while maintaining analytical performance, and to study the ecological and economic impact of the modifications.

Materials and methods
The CE method uses a neutral capillary column, MES hydrate/histidine/ether-18-crown-6 buffer with a potential differential of 20 kV. The initial method (M1) involved diluting samples with water for injections, followed by a 2 min rinse after each analysis. Method optimization (M2) involves diluting the sample with a 5 mg/mL histidine solution, switching to a 1 min rinse and adding peak smoothing with a Savitzky-Golay (SG) filter. M1 and M2 were compared using Nowak and Kościelniak’s RGB tool (1) according to three items: analytical performance (red = R), environmental friendliness (green = G) and method productivity (blue = B). The criteria chosen for performance were: intermediate precision, accuracy, minimum resolution (MR) and average peak asymmetry (AM). For the environmental impact: annual energy consumption of the computer and the EC. For productivity: analysis time per bag and theoretical total quantification time for 1144 bags produced in 2023. The overall results produced by the tool are characterized by the brilliance (MB) and colors obtained.

Results
The analysis time varied from 8.1 to 5.5 min, MR from 1.39 ± 0.02 to 1.53 ± 0.03 and AM from 0.31 ± 0.02 to 0.42 ± 0.01 for M1 and M2 respectively. The RGB tool assigned the color gray to M1 (MB at 37.5%) and cyan to M2 (MB at 67.9%). Using M2 would save 47 h per year or 65.9kWh. Despite comparable accuracy and intermediate fidelity, the LOQ of Mg²⁺ increased from 5 to 9 µM, enabling only 35.5% of the bags to be quantified by M2 compared with 93% for M1 in 2023.

Discussion and conclusion
The superiority of M2 was demonstrated according to RGB. However, application of the SG filter increased the LOQ of Mg²⁺, thus reducing the number bags eligible for Mg²⁺ quantification. Combining M2, for high Mg²⁺ values, with M1 for low values, would enable us to quantify all our bags and save 17h per year or 23.07 kWh, which could be increased for centers preparing adult NP with higher Mg values²⁺. Although the evaluation by the RGB tool remains subjective, and that in our case the methods were similar, it allowed us to illustrate that the optimization of analytical methods influence the environment and hospital productivity and environmental impact.

Reference : (1) Nowak et Kościelniak, Anal. Chem. 2019, 91, 10343−10352

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