Retention-time locked methods in gas chromatography

Retention time is one of the most important chromatographic features for analytical chemists since it is the key parameter to separate, identify and quantify compounds of interest from complex mixtures. Although detectors with higher-dimensional signals ease the identification of many components, there are demanding requirements on the retention time, particularly when high-throughput methods are considered. In addition to this, gas chromatographic elution shows significant run-to-run variations due to fluctuations in temperature and pressure, column degradation or matrix effects. In this sense, different approaches have been developed to minimise those variations: the introduction of electronic pneumatic control (EPC) systems, which allow a very efficient control of the flow of the carrier gas, the use of peak alignment algorithms to treat the chromatograms, or the use of retention-time locking (RTL). The RTL is a feature of the Agilent ChemStation software available for those GC instruments equipped with EPC systems. Originally it was developed to assure method translation but it has extended to fix the retention time and to implement peak deconvolution algorithms and database building and searching facilities. In this manuscript, the RTL basis and practical aspects are summarised together with a brief description of some applications.