Optimisation of the conditions for the saturation and preparation of chromato-desorption microsystems for the production of acetone gas mixtures

Abstract

The analysis of exhaled breath is an actively developing area of non-invasive medical diagnostics. This approach helps to study the dynamics of physiological processes in the human body and detect patholo-gies at early stages of their development. However, the approach is not widely used due to the imperfections in sampling and sample preparation techniques leading to significant errors in the obtained results.
The aim of our study was to develop devices, methods, and a methodology that would enhance the accuracy of the non-invasive quantitative determination of acetone in exhaled breath used in non-invasive diagnostics of diabetes mellitus. The object of our study were devices which, when used during the calibra-tion and preparation of samples, reduce the overall error of the analysis.
We used medical needles filled with a sorbent as containers for the chromato-desorption microsys-tem (CDmS). The sorbents were an inert carrier Chromaton N-AW modified with 25% sorption-active inor-ganic salt CoCl2, and an intert fibre covered with 25% polyethylene glycol (PEG-20M). The CDmS was satu-rated in the flow and drop regimes at the temperatures of 25 and 50°С. The desorption of the analyte was performed at 70 and 100°С by means of discrete blowing with a 0.5 ml inert gas (nitrogen) through the CDmS placed in a thermal desorption unit connected to the vaporiser of a gas chromatograph.
The results of the study of the prepared CDmS demonstrated the advantages of the drop method over the flow saturation, since it allows a greater number of discrete inputs within a single cycle and thus ensures a constant concentration of the analyte in the gas mixture. The article demonstrates that by regulating the con-ditions for the preliminary preparation of the system (the choice of the saturation and desorption technique) we can obtain gas mixtures with preset concentrations of acetone. The article also proves the possibility of using multiple-point calibration when using CDmS. Various concentrations of calibration gas mixtures can be obtained by changing the desorption temperature and by regulating the conditions for the preliminary preparation of the system, i.e. the amount of the inert gas or acetone gas mixture. The experiments demon-strated that the optimal method of CDmS saturation is the drop method (with 1 μl dosage), while the prelimi-nary preparation of the systems should be performed discretely at 25°С at the speed of 0.5 ml/min. The de-sorption temperature may vary from 70 to 100°С while the blowing time depends on the desorption stage. When using systems with CoCl2 it is inadvisable to set the temperature above 100°С.
The experiments demonstrated that with discrete dosing the stability error Δ of the obtained gas mix-tures varies from 10 to 15%, which enhances the accuracy of the analysis performed using the devices with CDmS. The obtained dependencies and developed techniques can be used to design a device for express quantitative determination of acetone in exhaled breath and to increase its sensitivity to this biomarker as well as to others.