8 December 2020
By Laura McGregor (Product Marketing Manager, SepSolve Analytical Ltd)
Those of you who routinely run GC or GC–MS instruments will be all too familiar with the frustrations of retention time drift.
In a perfect world, the retention time (RT) for each compound would remain constant from run to run, assuming that the same experimental conditions were applied. However, this is not always the case.
Retention time drift can be caused by a number of factors, some of which can be controlled (e.g. carrier gas pressure and flow rate), while others, such as column wear or minor leaks, are more likely to impact your analyses, especially when running long-term studies or dealing with very complex samples.
How does RT drift affect comparative analysis?
In comparative analysis, we must ensure that we are comparing like-with-like, so that we don’t generate false positives or negatives because of RT drift. In targeted workflows, this can often be resolved by expanding the RT tolerance windows for each of the compounds of interest, but this isn’t an option for untargeted data analysis, where we don’t know which compounds are important.
Chromatographic alignment is the obvious solution to these difficulties, but many of the reported algorithms rely on time-consuming manual processes, exceptionally complex scripts including a host of user-defined options, or are restricted to shifts of just ±10 seconds, which isn’t helpful in many real cases and has prevented their widespread adoption.
In the new ChromCompare+ chemometrics package, alignment is an essential step in untargeted workflows for both 1D and 2D GC–MS data, to ensure like-with-like comparisons and the discovery of true differences between samples.
Our algorithm uses the available spectral information to automatically align the chromatograms with virtually no user input.
Consequently, you do need multiple compounds in common across the datafiles, but these don’t need to be high-loading peaks nor in the same, or even similar, relative abundances. Chromatograms with few or no common compounds cannot be aligned by any automated alignment algorithm in a meaningful way.
In ChromCompare+, a single datafile is selected as a ‘reference’, allowing alignment to be applied to the entire dataset in a simple, automated manner. In combination with our novel untargeted workflows, this provides fast and confident identification of the significant differences between your chromatograms, regardless of your application or GC–MS platform.
Dr Laura McGregor has a background is in analytical forensic science, and her Ph.D. (at the University of Strathclyde, UK) focused on the chemical fingerprinting of environmental contamination using GC×GC−TOF MS. Following roles in application support and product marketing for Markes International’s TOF MS and software portfolios, she joined SepSolve in October 2017, where she oversees marketing activities across the full product range.