This document describes the method of using GC/MS for sample screening and the importance of using the RTL mass spectral database for confirmation. It also provides detailed information on when and how to lock methods.
Retention Time Locking (RTL) is a feature in Agilent Technologies' MSD Productivity ChemStation that allows users to match retention times on one GC or GC/MS system to those of another like system. This process compensates for variations caused by routine maintenance, such as column trimming, or differences between instruments running duplicate methods.
The guide details the procedure for establishing and maintaining a locked method. It covers selecting an appropriate standard compound, acquiring calibration data using five specific inlet pressures, calculating the Retention Time vs. Pressure (RT vs. P) curve, and saving the resulting RTLock method to ensure consistent peak identification across different instruments.
You should lock or relock your methods whenever you make changes to the chromatographic system, such as changing or trimming a column, installing the method on a new instrument, using a detector with different outlet pressure, validating system performance, or troubleshooting problems.
The target peak should be easily identifiable, symmetrical, and elute in the most critical part of the chromatogram. Very polar compounds or those subject to degradation should be avoided.
Multiple (five) injections of a standard at predefined inlet pressures are used to calculate the retention times for the RT vs. P calibration curve.