developments in micro-gc: theory and...
TRANSCRIPT
Developments in Micro-GC:
Theory and Practice
Robert E. Synovec Associate Chair, Graduate Program
Faculty Director, CPAC
Department of Chemistry, Box 351700
University of Washington
Seattle, WA 98195
Email: [email protected]
CPAC GC Workshop, Seattle, WA
October 31, 2010
OUTLINE
• 1D Separations and Extra-Column
Peak Broadening
• Recent Modeling for High Speed
Temperature Programmed GC
• Recent Examples with Bench-Top GC and
State-of-the-art GC-on-a-chip
Micro - GC • Fast analysis times…sub-minute to sub-
second… “GC sensor”
• Optimize chemical information per time…. …..Optimize total peak capacity & peak capacity production
– Minimize extra-column peak broadening with analyzer
design
– Implement high speed temperature programming
1D Peak Capacity Definitions
1nc,1D =
1t
1wb
1 1nc,1D
1t 1wb
=
Peak Capacity for a 1D separation @ Rs=1:
Peak Capacity Production* for a 1D separation:
* X. Wang, D. R. Stoll, P. W. Carr, P. J. Schoenmakers, J. Chromatogr. A, 2006, 1125, 177-181
Peaks resolved per separation time
Total number peaks ideally resolved
0 1 2 3
Time (s) Time (s)
0 1 2 3
0
2
4
6
8
10
0 10 20 30
0
20
40
60
80
100
Rela
tive S
ignal (%
) Isothermal (left) versus Temperature Programmed (right) for 1 meter, 100 micron ID column (simulated from real isothermal data)
Unit resolution for adjacent peaks, with constant peak capacity nc = 40
nc / t = 80 per minute nc / t = 800 per minute
Theory Behind Band Broadening Minimization
Plate Height (H): index describing the rate of band broadening along the separation path
eg xtsH= + +u C u+HB
Cu
2 22g,o c f
2 2g,o s
2D jf d uf 2k'd u1+6k'+11k'H= + +
u D j96(1+k') 3(1+k') D
Golay Equation:
Injection Detection Electronics
Dead Volumes
Longitudinal Diffusion
Resistance to Mass Transfer – Mobile Phase
Resistance to Mass Transfer – Stationary Phase
Hcolumn u: average linear velocity of mobile phase
Short Column: Theoretical H vs. ū
0
50
100
150
200
250
0 200 400 600 800 1000 1200
ū, average linear flow velocity (cm/s)
H (m
m)
ūopt = (192)1/2Dg,o j / dc
1 m x 100 mm i.d. column, H2 , 150 °C, Dg,o = 0.6 cm2/s, k’ = 0
Hmin , ūopt
g s exB
H= +C u+C u+Hu
Theory Behind Band Broadening Minimization
2 22g,o c f
2 2g,o s
2D jf d uf 2k'd u1+6k'+11k'H= + +
u D j96(1+k') 3(1+k') D
1/22 3 2 2 2
g,o o c o f ob 2
g,o s
2D jf(1+k') t (1+6k'+11k' )d ft 2k'd tw = 4 + +
L 96D j 3D
Peak Width Detected:
Golay Equation Limited:
Injection
Detection
Electronics
Dead Volumes
1
10
102
103
104
10 100 1000 ū (cm/s)
wb (
mill
iseconds) = Hmin, ūopt
Big challenge for instrumentation development Need to reduce extra-column band broadening from injection, detection, electronics and dead volumes
Peak width ~ a few ms
Theoretical wb vs. ū (for 1 m column)
Dg,o = 0.6 cm2/s, k’ = 0, 100 mm i.d. column, H2 , 150 °C
GC Sensor: Synchronized Dual-Valve Injection
C
Time, milliseconds
C
0 100 200 300 400
0
1
2
3
FID
Sig
na
l, v
olt
s
G.M. Gross, B.J. Prazen, J.W. Grate, R.E. Synovec, Anal. Chem. 76, 2004, 3517 - 3524.
Separation conditions (1 m x 100 micron) •
KEY….Dual-valve based injection (2.5 ms) •
• 7 component mixture injected (retention order: methanol, benzene, octane,
chlorobenzene,anisole, decane, butylbenzene)
Wb = 5 ms
k’ = 0
Modeling Bigger Picture: wb@opt (at Hmin, ūopt) vs. L (and dc)
V. R. Reid and R. E. Synovec, Talanta, 2008, 76, 703-717.
0.1
1
10
100
1000
10 100 1000 10000 L (cm)
wb
@o
pt (m
s) 50 mm
100 mm
180 mm
250 mm
320 mm
530 mm
k = 0, Dg,o = 0.6 cm2/s, h = 1.135 x 10-5 Pa*s,
Po = 1 atm (101325 Pa), H2 carrier gas, 150 °C
Synchronized Dual-Valve Injection
High-Speed FID
Hext 0
Various dc
Hcolumn only
Bigger Picture: wb@opt (at Hmin, ūopt) vs. L (and dc)
V. R. Reid and R. E. Synovec, Talanta, 2008, 76, 703-717.
0.1
1
10
100
1000
10 100 1000 10000 L (cm)
wb
@o
pt (m
s) 50 mm
100 mm
180 mm
250 mm
320 mm
530 mm
k = 0, Dg,o = 0.6 cm2/s, h = 1.135 x 10-5 Pa*s,
Po = 1 atm (101325 Pa), H2 carrier gas, 150 °C
How does standard practice of GC compare ?
Hext 0 Various dc
Hcolumn only
0 5 10
0.2
0.4
0.6
0.8
1.0
1.2
Separation in ~ 14 minutes >2 second wide peaks
Retention Time, min
Sign
al (
FID
, arb
. Un
its)
Typical GC Separation of Gasoline
Zoom – in of box section
658 660 662 664 666 668
0.5
1.0
1.5
Retention Time, seconds
Sig
nal (F
ID, arb
. u
nit
s)
~ 2 s
nc / t 30 peaks/min 10 min for nc ~ 300
wb@opt (at ūopt) vs. L
0.1
1
10
100
1000
10 100 1000 10000 L (cm)
wb
@o
pt (m
s) 50 mm
100 mm
180 mm
250 mm
320 mm
530 mm
Standard Auto-injection / FID or MSD
Peak widths 2 s or more are typical !!
wb@opt (at Hmin, ūopt) vs. L
0.1
1
10
100
1000
10 100 1000 10000 L (cm)
wb
@o
pt (m
s) 50 mm
100 mm
180 mm
250 mm
320 mm
530 mm
Standard Auto-injection / FID or MSD
Peak widths 2 s or more…..
40 m
180 mm
Wb ~ 300 ms possible
4 Component Mixture…with Auto-Injection only (Methanol, Anisole, Octanol, Tridecane Mixture)
80 120 160 200 240
0
1
2
3
4
5
Time (s)
FID
Re
sp
on
se
(V
)
200:1 split, average Wb= 1.6 s
86 90 Time (s)
M A O T
M
245 251 Time (s)
T
nc / t ~ 36 peaks/min
… 8.3 min for 300 peaks
Column: 40 m x 180 mm ID, Rtx-5 0.4 mm film
Oven: 90-250°C @ 40°C/min
Flow Conditions: Constant Flow, 1.3 ml/min
4 Component Mixture – High Speed GC Capillary: 40 m x 180 mm ID, Rtx-5 0.4 mm film Temperature Program: 90-200°C @ 40°C/min
Injection: 15 ms pulse (modified auto-injection) Flow Conditions: pressure ramp 85-115 psi @17.5 psi/min
Time (s) 50 100 150 200
0
1
2
3
4
FID
Response (
V)
43.1 43.5 43.9 0
2
4
250 ms
187 188.5 190
0
0.2
0.4
750 ms
M
A
O
T
Dead Time Optimized Separation
Consistent
With
Theory!
4 Component Mixture – High Speed GC
nc / t 120 peaks/min … 2.5 min for 300 peaks
Capillary: 40 m x 180 mm ID, Rtx-5 0.4 mm film
Temperature Program: 90-210°C @ 40°C/min
Injection: 20 ms (modified auto-injection)
Flow Conditions: pressure ramp 30-100 psig @17.5 psi/min (1.2 – 5.5 mL/min)
100 150 200
0
0.5
1
1.5
2
Time (s)
FID
Response (
V)
81.6 82.0 82.4
0
0.2
0.4
0.6
203.8 204.2 204.6 205
0
0.04
0.08
0.12
450 ms
500 ms
M
A
O
T
M T
Gasoline – High Speed GC
1
1.5 2 2.5 3 0
2
3
4
Time (min)
FID
Response (
V)
Wb= 480 ms
Wb=540 ms
1 s
Capillary: 40 m x 180 mm ID, Rtx-5 0.4 mm film
Temperature Program: 90-210°C @ 40°C/min
Injection: 50 ms pulse (modified auto-injection)
Flow Conditions: constant flow rate using 45-115 psi @17.5 psi/min
High Speed GC with Temperature Programming
at Hmin and uopt
• 100 mm i.d. column as function of column length, L,
… in limit that all peak broadening is due to column only (no Hex)
• Synchronize carrier gas flowrate and temperature programming rate
so all analytes elute with a k’ 0 ….at moment leaving column
• Model analyte boiling point range such that all elute in temperature
program from 50 oC to 350 oC (“typical” van’t Hoff plot applied)
MODELING SOFTWARE DESIGN AND OUTPUTS
• Temperature Programming Rates
• Separation Run Times
• Peak Widths ~ Constant ( ~ unretained peak)
• Pressure Required
• Total Peak Capacity
• Peak Capacity Production Rates
OUTPUTS
T-Prog Modeling Results Overview
Column Length (m) @ 100 mm i.d.
Temp Program Rate (K/min)
Run time (ms)
Dead time (ms)
Peak width (ms)
Maximum Pressure (psia)
Total peak capacity (nc)
Peak capacity production (nc/t) (1/s)
0.1 1 10
380,000 21,000 780
25 84 271
535 100 12
20 44 130
1.4 7 64
14 230 6000
50 840 23,300
Agilent LTM
Software programmable temperature rates
External column heating allows valve and transfer lines to be heated to inlet temperatures
Quoted ramp rates up to 1800 °C/min
Should cover 300 °C in 10 s
23
10 Component Mixture (C6 – C15) Capillary: 20 m x 180 mm ID, DB-5 0.4 mm film Temperature Program: 75-325°C @ 250°C/min Flow Conditions: 75 - 115 psia @ 40 psi/min
0 5 10 15 20 25 30 35 40 45 50
0
1000
2000
3000
4000
5000
6000
7000
8000
Time (s)
FID
Res
po
nse
(p
A)
14.6 15.0
140 ms
300 ms
Gasoline – High Speed GC Capillary: 20 m x 180 mm ID, DB-5 0.4 mm film Temperature Program: 75-325°C @ 250°C/min Flow Conditions: 75 - 115 psia @ 40 psi/min
0 5 10 15 20 25 30 35 40
0
500
1000
1500
2000
2500
3000
3500
4000
Time (s)
FID
Res
po
nse
(p
A)
Diesel – High Speed GC Capillary: 20 m x 180 mm ID, DB-5 0.4 mm film Temperature Program: 75-325°C @ 250°C/min Flow Conditions: 75 - 115 psia @ 40 psi/min
0 10 20 30 40 50 60
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Time (s)
FID
Res
po
nse
(p
A)
• 50 sq. micron
channels x 30 cm
• 30 sec CNT
growth time
• Integrated thin
film resistive
heating:
5 nm Ti
100 nm Pt
A.D. McBrady, B. Dick, V. R. Reid, A. Noy, R. E. Synovec and O. Bakajin, Anal. Chem., 2006, 78, 5639-5644.
Reid, V.R., Stadermann, M., Bakajin, O., Synovec, R.E. Talanta, 2009, 77, 1420-1425.
1 μm
SEM image Back of Chip
Hydrogen
Carrier
Gas
Commercial
GC Injector
Diaphragm
Valve Injection
Voltage/
Grounding
Leads
Variable
AC Power
Supply
(0 - 120 V)
V1 V2
Hydrogen
Carrier
Gas
Commercial
GC Injector
Diaphragm
Valve Injection
Voltage/
Grounding
Leads
Variable
AC Power
Supply
(0 - 120 V)
Vent FID
V
Deactivated
Silica Capillary
Leads
Hydrogen
Carrier
Gas
Commercial
GC Injector
Diaphragm
Valve Injection
Microfabricated SWCNT Column 30 cm, 50 μm x 50 μm
Voltage/
Grounding
Leads
Variable
AC Power
Supply
(0 - 120 V)
FID
V
Deactivated
Silica Capillary
Leads
FID
V
Top of Chip
Microfabricated GC-on-a-chip
with Carbon Nanotube (CNT) Stationary Phase and High-Speed Resistive Heating
collaboration with Lawrence Livermore National Lab (LLNL)
Alkane Mixture: hexane, octane, nonane, decane, undecane
LLNL CNT Chip: 30 cm x 50 mm x 50 mm; Carrier Gas: H2, 10 psi
Isothermal Separations and General Elution Problem
Time, seconds
FID
Sig
nal, v
olts
Time, seconds
FID
Sig
nal, v
olts
0 2 4 6 8 10 0
0.1
0.2
0.3
0.4
0 0.4 0.8 1.2 1.6 2
0
0.2
0.4
0.6
0.8
C11
C11
50 °C 100 °C
No single temperature provides best resolution per time !
C6
C6
Good resolution at front, but too resolved and diluted at end
Short time, but poor resolution at front
Solution to General Elution Problem: Rapid Temperature
Programming via Resistive Heating ~ 1500 °C/min
(Hexane, Octane, Nonane, Decane and Undecane)
Ti = 50 ºC, H2 carrier gas at 10 psi, 15 ms injection pulse
Application of 36 V yields 1560 ºC/min
0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 0
0.2
0.4
0.6
0.8
1
1.2
Time, seconds
FID
Sig
nal, v
olts
50 °C 115 °C
C11
C6
C8 C9
C10
Conclusions
Optimizing 1D-GC peak capacity production
(1) novel injection techniques
(2) enhancements to temperature and pressure programming
technology
(3) fast, low dead volume detection design with high-speed
electronics
(4) implement modeling to direct experimental efforts
(5) explore new commercial instrumentation
Thank You !