What are the differances and applications of HRGC/HRMS and GC-MS/MS instruments

Ask the Expert Question:

What is the difference between the HRGC/HRMS and GC-MS/MS instruments?
What are its major applications?

Experts Response:

By definition HRGC/HRMS stands for “High Resolution Gas Chromatography/High Resolution Mass Spectrometry” and GC-MS/MS stands for “Gas Chromatography/Tandem Mass Spectrometry”.

Starting with the GC-MS/MS, this equipment is fitted with what can be described as a dual mass spectrometry and are generally triple quads (or 3 quadrupoles).  Using a triple quad versus a standard GCMS give greater sensitivity (i.e. allows for lower detection limits from sub part per billion to sub part per trillion) and give greater resolution than a standard GCMS.  For example a standard GCMS can resolve masses 1 atomic mass unit apart.  A triple quad can resolve masses ~1000 atomic mass units apart.  Using GC-MS/MS resolution increase allows for much greater selectivity than standard GCMS.  Another feature of the GC-MS/MS is the dynamic range is much greater than a normal GCMS. 

HRGC/HRMS is a completely different type of instrument for very specific applications.  This instrument is fitted with a huge magnet and has electric sectors, lens and a 6 to 8 foot flight tube.  Using this type of configuration jumps the resolution to 10,000 atomic mass resolutions.  You can separate molecules that may have the same retention time but different masses 0.0001 amu apart.  Also the HRGM/HRMS allows for sensitivity to sub parts per quadrillion level and below and you can easily see 0.5fg on column of 2,3,7,8-TCDD (which is difficult to impossible for a standard GCMS or GC-MS/MS to see).  The dynamic range for the HRGC/HRMS is greater than 2000 times the low point so there is a lot of room to see the low end and the high end without saturating the detector.

There are many methods written for both types of instruments and you can use them for specific needs.  If you are looking for gross contamination then a GCMS is the way to go for general screening and for analytes with little public health risk.  GC-MS/MS is perfect for confirmation of low level GCMS results.  If you are looking to confirm low level results of analytes with high public heath risk then the HRGC/HRMS may be a better option.