Date Published: July 24, 2017
Publisher: Springer Berlin Heidelberg
Author(s): Hwanmi Lim, Trifa M. Ahmed, Christoffer Bergvall, Roger Westerholm.
An online two-dimensional (2D) liquid chromatography/2D gas chromatography system with two mass-selective detectors has been developed on the basis of a previous system with two flame ionization detectors. The method translation involved the change of carrier gas from hydrogen to helium, column dimension and detectors. The 2D system with two mass-selective detectors was validated with use of polycyclic aromatic hydrocarbon (PAH) standards and two standard reference materials from air and diesel exhaust. Furthermore, the system was applied to a real sample, wood smoke particulates. The PAH values determined correlated well with the previous data and those from the National Institute of Standards and Technology. The system enhanced the benefits of the previous system, which were limited by the low detectability and lack of mass selectivity. This study shows an automated 2D system that is valid for PAH analysis of complex environmental samples directly from crude extracts.
Multidimensional chromatography (MDC) has been an alternative to single chromatography for analysis of environmental samples which may contain various compounds of interest as well as complex matrices . Especially, multidimensional gas chromatography (MDGC) has had the main role because of its high separation capacity with the help of capillary gas chromatography (GC) columns . A classic MDGC approach used so-called heart-cut via a flow switching device (GC–GC) located between the two columns to direct a fraction of the compounds from the first column to the second for further separation . Another mode in MDGC is comprehensive GC × GC, which was introduced later, where a modulator continuously collects and transfers small effluents from the first column to the second column . Both modes are complementary and intended to maximize the peak capacity . GC–GC is more applicable for identifying and studying known compounds, whereas the latter mode is used more extensively for characterization and classification of known and unknown compounds [6, 7].
We developed an automated 2D-LC/2D-GC system with two MSDs based on the previous system with two FIDs to improve the detectability and selectivity of PAHs in complex environmental matrices. The detector change involved the use of helium as the carrier gas, resulting in decreased column efficiency. Hence the method translation involved not only the carrier gas but also the column dimension to improve the separation. Two SRMs from the NIST, urban dust (SRM 1649a) and diesel particulate extract (SRM 1975), and a wood smoke particulate sample were used to validate the system developed. The results showed good correlation with those reported previously, especially greater agreement with the values obtained with the previous 2D system and from the NIST than those obtained by 1D-LC–GC/MS. The crude extracts originally prepared in the previous study and stored at -20 °C until analysis showed acceptable stability except for anthracene and indeno[1,2,3-cd]fluoranthene, possibly due to their chemical stability or the influence of the matrix during storage.