Volatile organic compounds in the exhaled breath of young patients with cystic fibrosis.

Inflammatory mediators in the exhaled breath are receiving growing medical interest as noninvasive disease markers. Volatile organic compounds have been investigated in this context, but clinical information and methodological standards are limited. The levels of ethane, propane, n-pentane, methanol, ethanol, 2-propanol, acetone, isoprene, benzene, toluene, dimethyl sulphide (DMS) and limonene were measured in repeated breath samples from 20 cystic fibrosis patients and 20 healthy controls (aged 8-29 yrs). Three end-exhaled and one ambient air sample were collected per person and analysed on a customised gas chromatography system. Intra-subject coefficients of variation ranged between 9 and 34%, and hydrocarbon breath levels were influenced by their inspired concentrations. The alveolar gradient for pentane was higher in cystic fibrosis patients than in healthy controls (0.36 versus 0.21 ppb) and inversely proportional to forced expiratory volume in one second; highest values were observed in patients with pulmonary exacerbations (0.73 versus 0.24 ppb). Cystic fibrosis patients also exhibited a lower output of DMS (3.9 versus 7.6 ppb). Group differences were not significant for ethane and the remaining substances. It was concluded that chemical breath analysis for volatile organic compounds is feasible and may hold potential for the noninvasive diagnosis and follow-up of inflammatory processes in cystic fibrosis lung disease.

A new mathematical procedure to evaluate peaks in complex chromatograms.

Automatic peak evaluation in chromatograms and subsequent quantification of compound concentrations is still a challenge in the analysis of complex samples containing hundreds or thousands of compounds. Although a number of software packages for peak evaluation exist, baseline definition and overlapping peaks of different shapes are the main reasons which prevent reliable automatic analysis of complex chromatograms. A new mathematical procedure is presented which uses peak shapes extracted from the chromatogram itself and modified by nonlinear (in fact, hyperbolic) stretching of the peak head and tail. With this approach, the peak parameters are position, height, scale of front, scale of tail, and smoothness of transition from front to tail scaling. This approach is found to give a substantially better fit than traditional analytically defined peak shapes. Together with a good peak finding heuristic and nonlinear optimization of parameters this allows a reliable automatic analysis of chromatograms with a large number of peaks, even with large groups of overlapping peaks. The analysis matches the quality of standard interactive methods, but still permits interactive refinement. This approach has been implemented and tested on a large set of data from chromatography of hydrocarbons in ambient air samples.

Description and characterization of an on-line system for long-term measurements of isoprene, methyl vinyl ketone, and methacrolein in ambient air.

In this work we present a detailed technical description of the system that was set up for long-term on-line measurements of isoprene and two of its major degradation products, methyl vinyl ketone and methacrolein in order to provide a better understanding of the role of forest stands as a complex source of reactive trace gases into the troposphere and to elucidate the role of forests as chemical reactors. Volatile organic compounds (VOCs) are preconcentrated on cartridges containing a package of two solid adsorbents (Tenax TA and Carbopack X). Ozone removal is performed prior to sampling by titration with nitrogen monoxide. For the calibration and characterization of the system, a diffusion source was built to produce standard gas mixtures of up to 16 different compounds with mixing ratios at tens ppt (parts per trillion) level mixing ratios and high accuracy. The developed system allows a reliable quantification of these VOCs (detection limit approximately 10 ppt, reproducibility approximately 5%) with a high temporal resolution (approximately 30 min) and has proven to be stable and run automatically without major maintainence.