Exploratory study on chemical compounds related to pulmonary hypertension

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Thermal desorption systems (TDS) are often used in the field of analytical chemistry. Atmospheric pressure ionization mass spectrometers (APIMS) can detect very low levels of gaseous compounds. The combined use of TDS and APIMS has the potential of detecting low levels of metabolites in the body. In the present study, we developed a new TDS for the biological application of APIMS. The developed system consists mainly of mass-flow controllers, gas cleaners and a thermal desorption tube in which the cleaned gases pass through capillary tubes placed within a larger tube packed with a quartz wool heat source. A heat sensor was attached to the surface of the tube, which was surrounded by a coiled heater. The temperature profiles of the carrier gas were controlled by a thermo-regulator at a given pattern. While maintaining a constant mixing ratio, the desorbed gas was diluted with the same carrier gas and introduced into the APIMS. The temperature of the carrier gases were slightly lower tha … More n the temperature setting of the thermo-regulator, but followed it well at a rate of 10 oC /min. We next applied the TDS-APIMS system to the measurement of lactate in solution and in blood. One micro liter of samples was put inside a capillary tube, which was preliminarily baked. The mass spectrum of lactate ions was analyzed using the negative charge mode of the APIMS. Lactate ions was desorbed at a comparatively low temperature, below its boiling point, and easily charged with electrons in the ionization chamber of the APIMS. The peak ion intensity at the m/z of 89 (CH3CHOHCOO-) increased in a concentration-dependent manner, and exhibited a linear relation within the ranges of 10-5 to 10-4 M. The detection limit of lactic acid (anion) was 1.0 x 10-5 M. Rat plasma was also analyzed in both positive and negative ion charges modes. In both ionization states the spectrums were well reproduced. In conclusion, a new type of thermal desorption system was developed for the biological application of an atmospheric pressure ionization mass spectrometer with high sensitivity. The TDS-APIMS system successfully detected free organic compounds with low mass numbers, such as lactic acid in nano-liter volumes of blood. Less