Training - Fast GC analysis
What is a fast GC column?
A fast GC column has a much smaller internal diameter than a standard GC column. It is also much shorter and more flexible.
- Standard GC column dimensions: 30 m x 0.25 mm ID x 0.25 μm film thickness
- Fast GC column dimensions: 10 m x 0.1 mm ID x 0.1 μm film thickness
- ◄Definitions for fast, very fast and ultra fast GC
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- Fast GC: run times in 5-10 minutes
- Very fast GC: run times in a few minutes
- Ultra fast GC: run times less than one minute (usually several seconds)
- ◄How to achieve faster analysis
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Faster analysis can be achieved in any of the following ways
- A fully optimized separation
- A non-optimized separation
- All peaks are equally important
- Only a small number of peaks are important
- ◄Advantages of fast GC
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- Shorter run times
- Greater sample throughput
- Cheaper columns
- Higher signal to noise ratio
- Lower bleed (thinner films)
- ◄Disadvantages of fast GC
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- Difficult to use for conventional GC/ MS
- Easy to overload the phase (less sample capacity)
- Careful attention required for splitless injections
- Conventional Van Deemter curves don’t apply (high pressure drop)
- ◄Methods for faster analysis
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- Shorter columns
- Higher velocities
- Temperature program rates
- Pressure programming
- Vacuum outlet
- Selectivity
- Narrow bore columns
- Carrier gas selection
- Turbulent flow
- ◄Why such thin film?
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A less thick film is required when the Column ID is reduced, in order to retain the same phase ratio. Phase ratio = column ID (μm) / (4 x film thickness (μm))
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Film thickness (μm)
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0.10
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0.25
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0.50
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1.0
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Column ID (mm)
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Phase ratio
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0.10
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250
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100
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50
|
25
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0.25
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625
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250
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125
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63
|
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0.32
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800
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320
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160
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80
|
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0.53
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1325
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530
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265
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133
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- ◄Why use narrow ID inlet liners?
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The low carrier gas flow rates used with fast columns can cause band broadening in the injection port, especially during splitless injections.
If a liner with a small internal volume is used, the velocity of the carrier gas through the liner will be increased. This reduces the amount of time the sample spends in the injection port minimizing band broadening.
A liner with an internal diameter of 2 mm or less needs to be used in splitless mode to reduce mass discrimination.
- ◄Fast GC theory
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This calculation is only good for isothermal analysis, but use as a guide.
There are two options
- Reduce the number of plates – lose resolution, faster analysis times
- Keep the number of plates constant – maintain resolution, longer run time
- If Beta and Total Plates are the same – chromatography can be identical
Conditions to reduce analysis time by a factor of 2 to 3
- HP 5890 GC
- Fast GC capillary column
- Manual pressure regulator (30 psi max)
- Helium carrier gas
- 20 Hz FID data acquisition
- 30°C/min max oven program rate
Chromatogram comparison of fast and standard GC analysis
- ◄Fatty acid methyl esters (FAMEs)
- ◄Organochlorine pesticides
- ◄Organophosphorous pesticides (OPs) using BPX5
- ◄Organophosphorous pesticides (OPs) using BPX50
- ◄Polycyclic aromatic hydrocarbons (PAHs)
- ◄Polychlorinated biphenyls (PCBs)
- ◄Total recoverable petroleum hydrocarbons (TRPH)
Fast GC columns
- ◄Examples of fast GC columns with part numbers
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Part number
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Phase
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Description
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054022
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BP1
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10 m x 0.1 mm x 0.1 µm
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054099
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BPX5
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10 m x 0.1 mm x 0.1 µm
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054405
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BP20
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10 m x 0.1 mm x 0.1 µm
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054600
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BPX70
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10 m x 0.1 mm x 0.2 µm
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054690
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HT8
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10 m x 0.1 mm x 0.1 µm
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054699
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BPX35
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10 m x 0.1 mm x 0.1 µm
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0547100
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SolGel-WAX
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10 m x 0.1 mm x 0.1 µm
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054740
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BPX50
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10 m x 0.1 mm x 0.1 µm
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054777
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BPX1
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10 m x 0.1 mm x 0.1 µm
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This calculation is only good for isothermal analysis, but use as a guide.
