Gas Chromatography Tips
When installing your column into an FID jet, never pass the column through the flame. This will burn the inner (phase) and outer (polyimide) coatings and will cause higher background signals. Purge column with oxygen-free carrier gas for at least 30 minutes before heating GC oven. When storing a capillary column, seal the column ends with a used septum. Remember to cut at least 3cm from each column end before re-installation. If you're having problems with solvent focusing, or early eluting peaks seem broad or lop-sided in splitless injection, then try using a column with a thicker film. Set the FID temperature 20°C above the maximum method temperature, 250°C is usually the recommended temperature. When peak shape deteriorates, replace the liner immediately and cut 30cm from the front end of the column. When changing your column, liner or septum, SGE recommends lowering the injector temperature to <100°C to prevent stripping the liner deactivation. This is especially important for the analysis of trace levels of active compounds. Always re-tighten Graphite / Vespel® ferrules by ¼ to ½ turn after the first 2-3 oven cycles. To prevent increasing retention times in your chromatography, replace the septum daily. Condition column at:
a. 20°C above the method temperature or
b. the recommended maximum column temperature (whichever temperature is lower). If the injection port temperature is not specified in the method, 250°C is usually the recommended temperature. Always use SilTite™ or Graphite/Vespel® ferrules when connecting a column to a GC/MS interface. For maximum FID sensitivity, set the air flow 10 times higher than the hydrogen flow. To extend the lifetime of your packed column, ensure the oven temperature is 50°C, or less, before turning off the carrier gas. Do not use plastic tubing in GC systems. Plastic tubing, when used for general plumbing, can absorb up to 20% moisture allowing external laboratory gases to transpire through the tubing. SGE recommends stainless steel tubing to be used throughout the GC system.
SGE HPLC fittings, guard cartridges and in-line filters are completely compatible with all other manufacturers' HPLC columns and systems. If you are doing any method development with reversed phase HPLC, Wakosil II 5C18 RS columns should be the first columns to try. Always use a guard cartridge to prolong column life. For quick and easy column connections use EasyLOK nuts. If your reversed phase HPLC run is taking too long on a C18 or ODS column try using a SGE Wakosil II 5C8 RS (basic compounds and method development), Exsil C8 (existing method on an older style ODS), or Nucleosil C8 (protein analysis and peptides). SGE Guard cartridges can be used in conjunction with competitors' columns (for those customers with methods validated on other columns). PEEKsil tubing is an excellent alternative to PEEK tubing as its internal bore is unaffected by any organic solvents. Wakosil II 5C18 AR columns have a pH range of 1.4 - 9.4 making it a very TOUGH phase. If you are close to the limit of detection using a standard 4.6mm or 4mm ID HPLC column try using a 2mm ID column. This saves solvent too. For complete loop fill, the syringe capacity should be greater than twice the loop volume. The loop capacity sets the injection volume. For partial loop fill, the injection volume should be no greater than half the loop capacity. The injection size sets the injection volume. If you can't pre-filter samples, make sure to use a low dead volume in-line filter after the injector.
To maximize accuracy and reproducibility, it is recommended that the minimum volume injected from a syringe is 20% of the total syringe capacity. To eliminate carryover between samples, flush the syringe with solvent 15-20 times, remembering to discard the first 2-3 washes. Achieve a 1% RSD instantly by presetting the syringe volume. Large volume injection syringes are ideal for temperature programmable split injection. For best syringe life, ensure your syringe is rinsed 5 to 10 times in clean solvent prior to storage.