Planar microfluid concentrators based on silagerm 8040 for sampling and sample preparation for the analy-sis of gas media

Abstract

Exhaled air is a matrix with a complex molecular composition, including more than 3,500 components of various origins, the content of which can indicate the normal or pathological state of human health.

One of the selective markers of diabetes formed in exhaled air is acetone. Its increased content (more than
2.54 mg/m³) in exhaled air indicates excessive levels of glucose in the blood. To carry out a diagnostically reliable quantitative analysis of acetone in exhaled air, it is necessary to minimize random errors at all stages of sampling, concentration and calibration. The proposed MFC allow to carry out sample preparation and calibration under identical conditions, while combining the stages of sampling and concentration.

The sample was concentrated using microfluidic systems based on Silagerm 8040 filled with a sorbent. Porapak-Q was chosen as the sorbent, which was pre-treated with ethyl alcohol vapour before filling into the channels.

Sorption concentration in dynamic mode using an MFC was carried out by passing the resulting model gas mixture “acetone in air” with a concentration of 2.54 mg/m³ at t = 0^oC until breakthrough appears.

Desorption using the MFC based on Porapak-Q was carried out at temperatures of 50°C, 60°C, 70°C in dynamic mode by passing purified air at a rate of 0.5 ml/sec (desorption time is one second). The effluent was analysed by gas chromatography. The main advantage of this system is the ability to include it in a gas microchromatograph. The resulting analytical complex is mobile, which allows the usage for non-invasive diagnostics in non-laboratory conditions. Optimal concentration conditions using the MFC filled with Porapak-Q sorbent at which the maximum concentration coefficient of 43 was achieved have been established (t_sorb=0^oC; t_des=70^oC, V_sorb=45 ml, t_des=1 sec).

In a comparative analysis of the standard sampling method (using a Tedlar bag) and the method proposed using the MFC, it was found that the use of Tedlar bags for sampling exhaled air resulted in significant decrease in the accuracy characteristics (more than 30-65%) within 12 h, which is not applicable for diagnostic purposes. This fact was due to the sorption of the analyte on the walls of the bag and to eliminate undesirable effects it is necessary to use an additional step of sample drying. When the MFC was used for sampling, such a tendency was not observed, the accuracy characteristic did not decrease by more than 6-10% within 8 hours and no additional stages of drying the sample of exhaled air were required.