1' Unilever Research and Development Vlaardingen,

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Tutorial, HTC-10 Bruges, Belgium
High-speed gas chromatography
Hans-Gerd Janssen1,2
1. Unilever Research and Development
Vlaardingen, Foods Research Center, Advanced
Measurement and Imaging, P.O. Box 114, 3130
AC Vlaardingen, the Netherlands. 2.
University of Amsterdam, Polymer-Analysis Group,
Biomacromolecular Separations, van t Hoff
Institute for Molecular Sciences, Nieuwe
Achtergracht 166, 1018 WV Amsterdam the
Netherlands.
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Unilever RD organisation
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Unilever RD organisation
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Unilever RD organisation
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Contents
Introduction Analysis time Definitions Creating
chaos Examples of (un)successful fast
GC Structuring the chaos Strategies and strategy
selection Practical aspects of fast GC Future
developments Conclusion
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Analysis time in chromatography
We have to distinguish 1. Time to
result Sample comes in at t 0, is processed
etc. results are available at t tend.
Relevant e.g. for acceptance checks. 2.
Operator time Hands-on time (so excl. waiting
time). 3. Instrument time For RD use time 1
is generally not relevant. For acceptance control
time 1 is very relevant. For chromatography time
2 is generally the only relevant time. For mass
spec. (quantitative analysis) time 2 and 3 are
important.
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A Chromatographic Analysis
Paperwork


Result
Sample prep.
Chrom. separation
Interpretation
Detection
Assume taken and meeting requirements
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Acrylamide from potatoe chips
MS helps!!! Acrylamide using accurate
mass time-of-flight MS (GC-TOFMS)
TIC
Use of accurate mass MS eliminates need
to derivatize analytes. Excellent selectivity
and sensitivity is obtained.
71 amu,1 Da mass resolution
71.037 amu, 0.01 Da mass resolution
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Methods for faster analysis Literature overview
Hydrogen carrier gas Shorter columns Higher
velocities Faster temperature programming Narrow
-bore columns Pressure programming Vacuum
outlet Selective stationary phases Coupled
columns Multi-capillary columns Selectivity
tuning Turbulent flow . .
C18 1
C20 0
C18 0
C18 1
2.5
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Creating chaos Examples of (un)successful fast GC
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What is faster analysis ? and how to achieve it ?

• In case of
• A fully optimised separation,
• A non-optimised separation,
• All peaks are equally important,
• Only e.g. two peaks are important?

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Generic methods for faster GC
This is not rocket science - Eliminate baseline
(remember baseline is waste time) - Only
separate those peaks that need to be separated
(constant resolution) - The only way to fit more
peaks into a fixed time is by making them
narrower.
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Fast GC Make fair comparisons ! Normal
GC Length 100 m I.D. 240 µm df 0.5
µm Fast GC Length 40 m I.D. 100
µm df 0.2 µm
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Example of what is fast GC (and what is not?)
Faster GC, or too fast GC????
Fast GC, or too slow GC????
It all depends on what you need!
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Separations that can be made faster
Column 320 µm, L15 m, Wax Temp. prog 75C,
10C/min. Carrier gas Helium Velocity 30 cm/s
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Faster GC An example
Let us make it faster by using a shorter column.
Column 320 µm, L 15 m, CP Wax T-progd at 10
C/min Operated at 30 cm/s
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Faster GC through shorter columns
15 m 10C/min
1.5 m, 120C/min
120C/min
5 m
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Faster GC through faster programming
10C/min
900C/min
120C/min
480C/min
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Faster GC An example
Let us make it faster by using a shorter column.
What would be the result??
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Fast PCB separations
ConventionalHP-5 column, 30 m ? 0.25 mm ID. ?
0.25 ?m).
ConventionalHP-5 column, 30 m ? 0.25 mm ID. ?
0.25 ?m). T. program 50?C (1 min), 40?C?min-1 to
150?C , 4?C/min to 270?C. Hydrogen, 51
kPa. Injection Splitless, 1 ?l. Fast GC HP-5
column, 10 m ? 0.1 mm ID ? 0.1 ?m. T. program
50?C (1 min), 40?C?min-1 to 150?C, 14?C?min-1 to
270?C Hydrogen, 177 kPa. Injection Splitless, 1
?l, 250?C, (too) Fast GC DB-1 column, 3 m ?
0.25 mm ID. T. program 100?C, 12.5?C?min-1 to
150?C. Hydrogen, 100 cm?s-1. Injection
Splitless, 1 ?l, with cryofocus
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Oil analysis is not oil analysis.
Diesel characterisation Oil in
water 5 m, 320 µm, programmed at 30C/min 5
m, 320 µm, programmed at 300C/min
Remember 1. Do not over-separate, minimise
resolution. 2. What is the question??
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How to speed up this separation?
Isothermal, 120C 25 m, CP-Sil 5 CB, 530 µm, 0.5
µm Helium at 15 cm/sec.
Shorter column Higher carrier gas
velocity Higher isothermal temp. Convert to
T-prog. Separation Pressure/flow
programming Lower film thickness Use H2
carrier gas Reduce column dc
(These all would work, but what would be your
first choice ??)
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How to speed up this separation?
Isothermal, 120C 25 m, CP-Sil 5 CB, 530 µm, 0.5
µm Helium at 15 cm/sec.
Shorter column Higher carrier gas
velocity (1) Higher isothermal temp. 1 Convert
to T-prog. Separation 1 Pressure/flow
programming Lower film thickness Use H2
carrier gas Reduce column dc
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How to speed up this separation?
Shorter column Higher carrier gas
velocity Higher isothermal temp. Convert to
T-prog. Separation Pressure/flow
programming Lower film thickness Use H2
carrier gas Reduce column dc
Would they all work? What would be your first
choice??
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How to speed up this separation?
Isothermal, 120C 25 m, CP-Sil 5 CB, 530 µm, 0.5
µm Helium at 15 cm/sec.
Shorter column length NO Higher carrier gas
velocity NO Higher isothermal temp. NO Convert
to T-prog. Separation Maybe Pressure/flow
programming Maybe Lower film thickness No Use H2
carrier gas No Reduce column dc Yes
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How to speed up this separation?
Isothermal, 120C 25 m, CP-Sil 5 CB, 530 µm, 0.5
µm Helium at 15 cm/sec.
Shorter column length NO Higher carrier gas
velocity NO Higher isothermal temp. NO Convert
to T-prog. Separation Maybe Pressure/flow
programming Maybe Lower film thickness No Use H2
carrier gas No Reduce column dc Yes
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Speed determining critical pairs
Are these options - Shorter column? - Faster
rate? - Other phase? - Narrow-bore columns?
Column 320 µm, L 25 m, CPSil 5 Temperature
programmed at 10 C/min Operated at 30 cm/s
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Structuring the chaos Strategies and strategy
selection
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16 (or 19) Solutions for faster GC
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Classification of chromatograms I
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Classification of chromatograms II
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Classification of chromatograms III
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Classification of chromatograms IV
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How we help the analyst ...
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Faster GC Method selection Examples
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The table to help you..
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GC-MS Deconvolution
Peak Name Unique mass 1 1-Nonene
56 2 1-ethyl-1,4- 79
cyclohexane
Deconvolution An additional means for fast
GC. But not the starting point!
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Practical aspects of fast GC
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Definitions in fast GC
Definitions somewhat arbitrary
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Instrumental Requirements
Fast Gradients Temp. Prog. Up to
120C/min. Reproducible, linear (sharp), entire
range, up and down, column compatibility,
etc. Detectors Volumetric and electronic time
constants. Peak ? down to a few ms!!!! Data
systems GC Sampling frequencies up to 100-200
Hz!!! Mass spectrometry Examples were 50 scans/s
is not enough! Auto-samplers 1 minute filling no
longer negligible. Overlap injection
technique. Carrier gas Pressures up to 7-12 bar.
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Injection methods in fast GC
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Optimisation of injection in fast GC

• Split
• Work at high split flow (start at 400 ml/min and
  go down)
• Splitless
• Use low liner id. (lt 1 mm)
• Avoid excessive solvent re-condensation (lt 0.5
  µl, high Tstart oven)
• On-column
• Use wide-bore retention gap
• Use dead-volume free connector (press fit)
• Avoid excessive solvent re-condensation (lt 0.5
  µl, high Tstart oven)
• In all modes Use auto-sampler (What is the fill
  speed, purge rate?)

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Column overloading A common problem in
narrow-bore GC
Narrow-bore columns can be overloaded at 10 ng or
less! Observation
Overloading can be seen from Leading or
fronting peaks. and results in Broadened
peaks, loss of resolution, irreproducible
retention times. The solution is Dilute
sample, inject a smaller volume, increase the
film thickness Be careful If dc /(4df) lt
100, speed is lost.
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Detectors for fast GC
FID Close to zero sensing volume, fast
electronics allow up to 200 Hz NPD Low sensing
volume, up to 200 Hz (commercially
available) FPD Limited sensing volume, up to 50
Hz (commercially available) ECD 150 µl, up to
50 Hz (commercially available), TCD nano-liters
!! In all cases optimise Make-up flow
rate Concentration vs. Mass flow sensitive
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Working range fast GC
Short 50 µm column
Multi-capillary column
Lower end Detection limit
Upper end column loadability

• A typical narrow-bore column only contains
  minute amounts of
• stationary phase dc 100 µm, df 0.1 µm, L
  10 m contains
• 0.6 mg of stationary phase.

• Modern GC detectors made it possible to work
  with short
• narrow bore columns !!!!!

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Future developments
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Computerised selectivity tuning
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Principle of Comprehensive Chromatography
Normal Chromatography
Heart-cut Chromatography
Comprehensive Chromatography
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GCGC for Improved Target Compound Analysis
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Comprehensive GCGC for target compound analysis
7.50
6.25
5.00
second dimension relative retention times
(seconds)
3.75
2.50
1.25
0.00
13
25
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50
63
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first dimension retention time (minutes)
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Conclusions

• There are many ways to reduce the analysis time
  in GC
• It is difficult to select the best method for a
  given separation
• Minimise resolution first!
• If more gain is desired, select constant Rs
  option
• A structured approach for strategy selection is
  available
• Faster GC requires
• Faster injection, faster detection, faster
  ovens, higher Pin
• Injection is crucial. Splitless, PTV, on-column
  not trivial (but possible!)
• Fast GC can be coupled with mass spectrometry
• Mass spectrometry offers additional means for
  faster separations