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(23) Toward a stable electrospray 1
Toward a
Stable Electrospray
Ioan Marginean, Ryan T. Kelly, Jason S. Page,
Ioan Marginean, Ryan T. Kelly, Jason S. Page,
Keqi Tang, and Richard D. Smith
Keqi Tang, and Richard D. Smith
Pacific Northwest National Laboratory
Pacific Northwest National Laboratory
Electrospray Stability
Electrospray Stability
Is the electrospray unstable?
Is the electrospray unstable?
ES displays several regimes, some of them chaotic.
ES displays several regimes, some of them chaotic.
Good stability at relatively large flow rates (jetting).
Good stability at relatively large flow rates (jetting).
Why work at low flow rates if the electrospray is
Why work at low flow rates if the electrospray is
potentially unstable?
potentially unstable?
Higher sensitivity
Higher sensitivity
Lower detection limits
Lower detection limits
Minimized matrix effects.
Minimized matrix effects.
How can we stabilize it?
How can we stabilize it?
Spray image processing.
Spray image processing.
Valaskovic
Valaskovic
et al.
et al.
J Am Soc Mass
J Am Soc Mass
Spectrom
Spectrom
2004
2004
, 15, 1201.
, 15, 1201.
Spray current measurements.
Spray current measurements.
Evans et al.
Evans et al.
Rev
Rev
Sci
Sci
Instrum
Instrum
1972
1972
, 43, 1527.
, 43, 1527. 2
2 mm
2 mm
stainless
stainless
steel
steel
union
union
ESI
ESI
emitter
emitter
1
1
Counter
Counter
electrode
electrode
Bertan
Bertan
205B
205B
-
-
03R
03R
HV Power Supply
HV Power Supply
NI PCI
NI PCI
-
-
MIO
MIO
-
-
16E
16E
-
-
1
1
DAQ board
DAQ board
Computer
Computer
LabVIEW
LabVIEW
program
program
Instrumental Setup
Instrumental Setup
HPLC gradient for
HPLC gradient for
proteomics analyses:
proteomics analyses:
Solvent A: 0.2%
Solvent A: 0.2%
AcOH
AcOH
+ 0.05% TFA in water
+ 0.05% TFA in water
Solvent B: 0.1% TFA in
Solvent B: 0.1% TFA in
90:10
90:10
acetonitrile:water
acetonitrile:water
1
Kelly et al. Anal Chem 2006, 78, 7796.
Voltage (kV)
1.0
1.2
1.4
1.6
1.8
Spray
C
u
rr
ent (
n
A
)
0
100
200
300
400
30 nL/min
Characteristic Curves
Characteristic Curves
1
1
Dripping
Pulsating
Cone-jet
2
20
20
m
m
i.d
i.d
. emitter
. emitter
15% organic
15% organic
1
Jackson et al. Anal Chem 1999, 71, 3777.
2
Nemes et al. Anal Chem 2007, 79, 3105.
Breakdown 3
Voltage (kV)
1.0
1.2
1.4
1.6
1.8
Spray
Curr
ent (
n
A
)
0
100
200
300
400
30 nL/min
50 nL/min
Characteristic Curves
Characteristic Curves
Pulsating
Dripping
Astable
1
Cone-jet
Breakdown
1
1
Marginean et al.
Marginean et al.
Phys Rev E
Phys Rev E
2007
2007
, submitted.
, submitted.
20
20
m
m
i.d
i.d
. emitter
. emitter
15% organic
15% organic
Voltage (kV)
1.0
1.2
1.4
1.6
1.8
Spray
C
u
rr
ent (
n
A
)
0
100
200
300
400
50 nL/min
100 nL/min
Characteristic Curves
Characteristic Curves
Pulsating
Dripping
Astable
Breakdown
20
20
m
m
i.d
i.d
. emitter
. emitter
15% organic
15% organic 4
Voltage (kV)
1.0
1.2
1.4
1.6
1.8
Spray
Curr
ent (
n
A
)
0
100
200
300
400
100 nL/min
200 nL/min
Characteristic Curves
Characteristic Curves
Pulsating
Dripping
Breakdown
Astable
20
20
m
m
i.d
i.d
. emitter
. emitter
15% organic
15% organic
Voltage (kV)
1.0
1.2
1.4
1.6
1.8
2.0
Sp
ray
Cu
rrent (
n
A
)
0
50
100
150
200
80 nL/min
70 nL/min
60 nL/min
50 nL/min
40 nL/min
30 nL/min
20 nL/min
Cone
Cone
-
-
jet Breakdown Region
jet Breakdown Region
U
U
t
t
= 1.27 kV
= 1.27 kV
R = 3.94 G
R = 3.94 G
20
20
m
m
i.d
i.d
. emitter
. emitter
5% organic
5% organic 5
Flow Rate (nL min
-1
)
20
30
40
50
60
Volt
ag
e (k
V)
1.00
1.25
1.50
1.75
Effect of Flow Rate
Above a critical flow rate:
Above a critical flow rate:
The cone
The cone
-
-
jet regime cannot
jet regime cannot
be established.
be established.
Jetting regime:
Jetting regime:
The characteristic curves are
The characteristic curves are
practically identical.
practically identical.
A central stream of droplets
A central stream of droplets
becomes increasingly visible.
becomes increasingly visible.
Drops form on the counter
Drops form on the counter
electrode.
electrode.
0
100
200
300
400
1.0
1.5
2.0
0
30
60
90
S
p
ray

C
urr
e
n
t (n
A
)
Volt
age
(kV
)
Flow Rate (nL min
-1
)
cone-jet
pulsating
astable
dripping
15% organic
15% organic
Flow Rate (nL min
-1
)
20
30
40
50
60
C
h
a
r
ge
s a
v
ail
a
bl
e /
ana
l
y
t
e m
o
lec
u
le
*
225
250
275
300
325
350
Flow Rate:
The Lower the Better
* based on an
* based on an
analyte
analyte
concentration of 10
concentration of 10
-
-
5
5
M
M
0
100
200
300
400
1.0
1.5
2.0
0
30
60
90
S
p
r
ay
C
u
r
ren
t

(
n
A)
Volta
ge (k
V)
Flow Rate (nL min
-1
)
Flow Rate (nL min
-1
)
20
30
40
50
60
Spra
y C
u
rr
ent
(nA
)
100
150
200
250 6
Distance (mm)
2
3
4
5
6
Voltage
(k
V)
1.1
1.2
1.3
1.4
1.5
Distance to the Counter
Electrode
Observations:
Observations:
Constant cone
Constant cone
-
-
jet current
jet current
Changing voltage threshold
Changing voltage threshold
Astable regime domain
Astable regime domain
0
100
200
300
1.00
1.25
1.50
0
2
4
6
S
p
ray

C
urr
e
n
t (n
A
)
Voltage
(kV)
Distance (mm)
cone-jet
pulsating
astable
20
20
m
m
i.d
i.d
. emitter
. emitter
20
20
nL
nL
/min
/min
15% organic
15% organic
Flow Rate (nL min
-1
)
20
30
40
50
60
1.00
1.25
1.50
1.75
2.00
Flow Rate (nL min
-1
)
20
30
40
50
60
Vo
lta
g
e (kV
)
1.00
1.25
1.50
1.75
2.00
20
30
40
50
60
Vo
lt
a
g
e (
k
V
)
1.00
1.25
1.50
1.75
2.00
Effect of Eluent Composition
Observations:
Observations:
Changing voltage thresholds
Changing voltage thresholds
Astable regime domain
Astable regime domain
Would passive control work?
Would passive control work?
5% organic
5% organic
45% organic
45% organic
60% organic
60% organic
cone-jet
pulsating
astable
dripping
cone-jet
astable
pulsating
cone-jet
astable 7
Operation at Constant Voltage
Time (hours)
0
2
4
6
8
10
12
14
Cu
r
r
e
n
t (n
A
)
0
50
100
150
200
V
o
ltage (
k
V
)
0.00
0.25
0.50
0.75
1.00
1.25
Spray

C
u
r
r
en
t CV %
0
1
2
3
4
5
6
Operation with
Feedback Control
Time (hours)
0
5
10
15
20
25
Cu
r
r
e
n
t (n
A
)
0
50
100
150
200
V
o
ltage (
k
V
)
0.00
0.25
0.50
0.75
1.00
1.25
Spray

C
u
r
r
en
t CV %
0
1
2
3
4
5
6 8
Conclusions
Proof of principle provided:
Proof of principle provided:
Spray current measurements can be used as
Spray current measurements can be used as
feedback to stabilize the
feedback to stabilize the
nanoelectrospray
nanoelectrospray
in the
in the
cone
cone
-
-
jet regime.
jet regime.
Working at the lowest possible flow rate improves
Working at the lowest possible flow rate improves
the figures of merit.
the figures of merit.
Compromises to be aware of:
Compromises to be aware of:
Cone
Cone
-
-
jet regime: best sensitivity
jet regime: best sensitivity
but challenging to maintain.
but challenging to maintain.
Jetting regime: inherently stable
Jetting regime: inherently stable
but lower sensitivity.
but lower sensitivity.
0
100
200
300
400
1.0
1.5
2.0
0
30
60
90
S
p
ray

C
u
rre
n
t

(
nA
)
Volt
age
(kV
)
Flow Rate (nL min
-1
)
Acknowledgements
R. D. Smith group
R. D. Smith group
PNNL Instrument Development Lab
PNNL Instrument Development Lab
PNNL Machine Shop
PNNL Machine Shop
Funding:
Funding:
NIH National Center for Research Resources
NIH National Center for Research Resources