Qualitative and semi-quantitative analysis of the non-polar organic fraction of air particulate matter

Detection of nonpolar molecules by means of carrier scattering in random networks of carbon nanotubes: toward diagnosis of diseases via breath samples

Field effect transistors (FETs) based on random networks (RNs) of single-wall carbon nanotubes (CNTs) have several technological advantages. However, the low sensitivity (or no sensitivity) of RN-CNT sensors to nonpolar molecules is a problematic, negative feature that limits their applications in the detection of a wide variety of diseases via breath samples. In this paper, we show experimental evidence for the detection of both individual nonpolar molecules and patterns of nonpolar molecules, even in the presence of polar molecules in the same environment. We do so by preparing RN-CNT FETs and functionalizing them with organic films that exhibit distinctive electrical and physical (or mechanical) characteristics. Exposing the functionalized RN-CNTs to representative nonpolar breath biomarkers, and, for comparison, to polar molecules in the gas phase, and monitoring the changes in conductance, work function, and organic film thickness show sensitivity toward nonpolar molecules. We explain this observation by carrier scattering as a result of swelling of the organic film upon exposure to (nonpolar) chemical agents. Hence, the sensitivity towards nonpolar molecules can be tailored, even in the presence of polar molecules, by controlling the scattering of charge carrier through deliberate functionalization of CNTs. As examples for the technological impact of our findings, we describe ways to detect lung cancer and kidney disease using specially designed RN-CNT sensor arrays.

The application of thermal methods for determining chemical composition of carbonaceous aerosols: a review

Thermal methods of various forms have been used to quantify carbonaceous materials. Thermal/optical carbon analysis provides measurements of organic and elemental carbon concentrations as well as fractions evolving at specific temperatures in ambient and source aerosols. Detection of thermally desorbed organic compounds with thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) identifies and quantifies over 100 individual organic compounds in particulate matter (PM) samples. The resulting mass spectra contain information that is consistent among, but different between, source emissions even in the absence of association with specific organic compounds. TD-GC/MS is a demonstrated alternative to solvent extraction for many organic compounds and can be applied to samples from existing networks. It is amenable to field-deployable instruments capable of measuring organic aerosol composition in near real-time. In this review, thermal stability of organic compounds is related to chemical structures, providing a basis for understanding thermochemical properties of carbonaceous aerosols. Recent advances in thermal methods applied to determine aerosol chemical compositions are summarized and their potential for uncovering aerosol chemistry are evaluated. Current limitations and future research needs of the thermal methods are included.

Application of direct thermal desorption gas chromatography and comprehensive two-dimensional gas chromatography coupled to time of flight mass spectrometry for analysis of organic compounds in ambient aerosol particles

Semivolatile organic compounds (SVOC) associated with ambient particles smaller than 2.5 microm (PM2.5) were determined in the city of Augsburg, Germany. Daily samples were collected at a central monitoring station from late summer 2002 to spring 2005. SVOC were analysed by direct thermal desorption (DTD)-GC and comprehensive 2-D GC coupled to TOF MS (DTD-GC-TOF MS and DTD-GC x GC-TOF MS). Two hundred compounds were quantified and 'semi-quantified' on a daily basis by DTD-GC-TOF MS. n-Alkanes, n-alkan-2-ones, n-alkanoic acid methyl esters, acetic acid esters, n-alkanoic acid amides, nitriles, linear alkylbenzenes and 2-alkyl-toluenes, hopanes, PAH, alkylated PAH and oxidised PAH, and several compounds that are not-grouped in homologous rows or compound classes were determined. Changes in concentration and pattern of several target compounds as well as methodological advantages and restrictions of DTD-GC-TOF MS are briefly discussed. DTD-GC-TOF MS analysis provided data particularly suited for source receptor modelling and epidemiological time series studies on the health effects of ambient PM. GC x GC enhances chromatographic resolution of PM samples and therefore amplifies the peak identification capabilities of the TOF MS.

Determination of polycyclic aromatic hydrocarbons in diesel exhaust particulate matter and diesel fuel oil

Clean-up procedures were developed for a method for determining the amount of polycyclic aromatic hydrocarbons (PAHs) in diesel exhaust particulate matter and in diesel fuel oils using reversed-phase high-performance liquid chromatography (HPLC). They were based mainly on the elimination of insoluble matter and aliphatic compounds that affect the performance of HPLC, from the dichloromethane extracts of particulate matter or from oils, with the aid of a disposable preparation column containing reversed-phase packings (Sep-Pak C18). Using these procedures, it is possible to detect 1 ng of benzo(a)pyrene in 30 mg of particulate matter with more than a 97% recovery or 0.5 ng in 50 microliters of oil with 91% recovery. Examples of analyses are given for particulate matter emitted from a diesel test engine and for diesel fuel oils, such as gas oil, residual oil and coal-liquefied oil.