verified on the Thermo Scientific™ TSQ Quantiva™ triple-stage quadrupole mass
spectrometer. The resulting routine was embedded into the instrument control
software.
Results: Method ensures sufficient signal in the uncalibrated polarity upon completion
of EMGC in the opposite polarity by updating the EMGC parameters for uncalibrated
polarity using the predictive routine described below. This protects the instrument from
becoming inoperative in a polarity with a “lagged” or outdated EMGC.
wh
of
fun
vo
the
sce
ha
In detection systems, a flux of incident ions hits the conversion dynode producing
secondary particles which are received by the electron multiplier and amplified into a
measurable signal. For positive ion polarity, the flux of secondary particles consists
mostly of electrons, however, in negative ion polarity, these particles are positive ions.
The difference in secondary particles necessitates an independent EM gain calibration
1
for negative and positive polarities1.
Silivra , Harald
Oser 1, ,Joshua
Maze , Terry
Olney 2, Terry Olney
Oleg Silivra1,Oleg
Harald
Oser
Joshua
Maze
Thermo Fisher Scientific, San Jose, CA; Thermo Fisher Scientific,
Austin, TXsignificant aging and the calibration was maintained in only one
If the EM experienced
1Thermo Fisher Scientific, San Jose, CA; 2Thermo
polarity, the “lagged”
EMGC parameters
for the opposite polarity
may result inTX
a weak
Fisher
Scientific,
Austin,
or absent signal which makes running the EM gain calibration impossible and prevents
1
1
1
2
1
2
the use of the instrument in the affected polarity.
Overview
Purpose: To protect instrument from becoming inoperative because of weak or absent
signal from the electron multiplier (EM) which experienced significant aging while EM
gain calibration (EMGC) was maintained in only one polarity.
Methods: Analytical model and automated “calibration” routine were created and
verified on the Thermo Scientific™ TSQ Quantiva™ triple-stage quadrupole mass
spectrometer. The resulting routine was embedded into the instrument control
software.
Results: Method ensures sufficient signal in the uncalibrated polarity upon completion
of EMGC in the opposite polarity by updating the EMGC parameters for uncalibrated
polarity using the predictive routine described below. This protects the instrument from
becoming inoperative in a polarity with a “lagged” or outdated EMGC.
Introduction
In detection systems, a flux of incident ions hits the conversion dynode producing
secondary particles which are received by the electron multiplier and amplified into a
measurable signal. For positive ion polarity, the flux of secondary particles consists
mostly of electrons, however, in negative ion polarity, these particles are positive ions.
The difference in secondary particles necessitates an independent EM gain calibration
for negative and positive polarities1.
Results
Methods
Analytical
Model
The
proposed
method resolves the aforementioned problems by employing the
automated update of EMGC parameters for the polarity opposite to the one being
For analytical description of the problem, we assume that EM gain, G, can be
calibrated.
described by the following function:
Mass Spectrometry
(1)
G  A exp{BU }
Analytical model and automated routine were developed and verified on a TSQ
Quantiva triple-stage quadrupole mass spectrometer.
where A and B are calibration parameters and U is a voltage applied to the first stage
Data Analysis
of EM. Please note that the proposed formalism can be generalized to a class of
functions
of the
form G
B*U), where
is aannormalization
factor and
is a
The
method
consists
of =
anG(A,
analytical
model A
and
automated routine.
TheBautomated
voltageruns
scaling
factor.
for completion
the purposes
weinwill
only use
routine
every
timeHenceforth
the EMGC though,
runs. After
of of
theclarity,
EMGC
a given
the explicit
of gain
function
given by
Eq.(1)
of two
possible
polarity,
the form
routine
builds
an analytical
model
forand
the consider
opposite one
polarity
using
the
scenarios: the
EMGC for
negative
polarity isThe
outdated,
EMGC the
in positive
polarity
parameters
it obtained
from
the calibration.
routinethe
compares
modeled
and
has justparameters
been completed.
current
for the non-calibrated polarity. If a specified update condition is
met, the calibration parameters are updated using the rules specified in the model.
For two chosen points of this calibration, say, LowGain and HighGain, the following
Updating the non-calibrated polarity ensures the signal will be sufficient for operation
equalities hold:
or any necessary calibration procedures.
C
C that the
CL slope of the EMGC curve for the
In developing the method,itGwas (assumed
POS APOS , BPOS , U POS )  LowGain
(2) polarity is not
non-calibrated
important and can be set equal to the slope from
 critically
C
C
CH
(
,
,
G
A
B
U
 HighGain
the polarity being calibrated.
A
second
assumption
made about differences in
 POS POS POS POS )was
positive and negative polarities in generation of flux of secondary particles from the
dynode and
conversion into electron current. It is proposed here that the difference
where UCLPOS , UCHPOS are EM voltages corresponding to low gain and high gain,
can be minimized
by appropriately setting the voltage offsets of the EM and the
superscript C stands for “calibrated” (recently) and subscripts POS and NEG denote
conversion dynode relative to ground potential.
positive and negative polarity, correspondingly.
If the EM experienced significant aging and the calibration was maintained in only one
polarity, the “lagged” EMGC parameters for the opposite polarity may result in a weak
or absent signal which makes running the EM gain calibration impossible and prevents
the use of the instrument in the affected polarity.
The difference between positive and negative polarities in generation of primary flux of
secondary particles and converting them into electron current can be minimized by
appropriately setting the voltage offsets of the EM and the conversion dynode relative
to ground potential. The residual difference shows itself as different potentials applied
to the first stage of EM in positive and negative polarities, both recently calibrated. We
will denote its difference as a “shift” voltage, US . This voltage was estimated at the
gain normally used for mass and resolution calibration and at the beginning of EMGC.
Methods
FIGURE 1. Results of positive mode calibration and corresponding “ideal” and
updated gain functions derived for negative polarity. The shift voltage was
taken equal to US = –100 V. The signal target for updated function was ~50%.
The proposed method resolves the aforementioned problems by employing the
automated update of EMGC parameters for the polarity opposite to the one being
calibrated.
Mass Spectrometry
Analytical model and automated routine were developed and verified on a TSQ
Quantiva triple-stage quadrupole mass spectrometer.
Data Analysis
The method consists of an analytical model and an automated routine. The automated
routine runs every time the EMGC runs. After completion of the EMGC in a given
polarity, the routine builds an analytical model for the opposite polarity using the
parameters it obtained from the calibration. The routine compares the modeled and
current parameters for the non-calibrated polarity. If a specified update condition is
met, the calibration parameters are updated using the rules specified in the model.
Updating the non-calibrated polarity ensures the signal will be sufficient for operation
or any necessary calibration procedures.
In developing the method, it was assumed that the slope of the EMGC curve for the
non-calibrated polarity is not critically important and can be set equal to the slope from
the polarity being calibrated. A second assumption was made about differences in
positive and negative polarities in generation of flux of secondary particles from the
dynode and conversion into electron current. It is proposed here that the difference
can be minimized by appropriately setting the voltage offsets of the EM and the
conversion dynode relative to ground potential.
Poste r N ote 6 4 4 0 2
Automatic Update of Electron
Multiplier Gain Calibration
Parameters in PolarityIntroduction
Opposite
the One
Being Calibrated
AutomatictoUpdate
of Electron
Multiplier Gain Calibration Paramete
Fo
eq
wh
su
po
Th
se
ap
to
to
wil
ga
FIG
Th
up
fun
tak
As
slo
ca
Fig
Th
co
lin
co
co
wh
is
in
the
Ine
wh
(6
ar
At
as
en
up
Fo
vo
wh
va
so
un
(G
Results
Thus,
Thus, an
an “ideal”
“ideal” gain
gain function
function for
for outdated
outdated negative
negative polarity
polarity EMGC
EMGC is
is just
just the
the gain
gain
function
function for
for recently
recently completed
completed positive
positive polarity
polarity calibration
calibration shifted
shifted by
by U
USS ::
Analytical
Analytical Model
Model
For
For analytical
analytical description
description of
of the
the problem,
problem, we
we assume
assume that
that EM
EM gain,
gain, G,
G, can
can be
be
described
described by
by the
the following
following function:
function:
(1)
(1)
G
G  AAexp{BU
exp{BU}}
where
where AA and
and BB are
are calibration
calibration parameters
parameters and
and U
U is
is aa voltage
voltage applied
applied to
to the
the first
first stage
stage
of
of EM.
EM. Please
Please note
note that
that the
the proposed
proposed formalism
formalism can
can be
be generalized
generalized to
to aa class
class of
of
functions
of
the
form
G
=
G(A,
B*U),
where
A
is
a
normalization
factor
and
B
is
a
functions of the form G = G(A, B*U), where A is a normalization factor and B is a
voltage
voltage scaling
scaling factor.
factor. Henceforth
Henceforth though,
though, for
for the
the purposes
purposes of
of clarity,
clarity, we
we will
will only
only use
use
the
the explicit
explicit form
form of
of gain
gain function
function given
given by
by Eq.(1)
Eq.(1) and
and consider
consider one
one of
of two
two possible
possible
scenarios:
the
EMGC
for
negative
polarity
is
outdated,
the
EMGC
in
positive
polarity
scenarios: the EMGC for negative polarity is outdated, the EMGC in positive polarity
has
has just
just been
been completed.
completed.
For
For two
two chosen
chosen points
points of
of this
this calibration,
calibration, say,
say, LowGain
LowGain and
and HighGain,
HighGain, the
the following
following
equalities
equalities hold:
hold:
(2)
(2)
CC
CC
CL
CL )  LowGain
G
,,BBPOS
,,U
GPOS ((AAPOS
UPOS
POS )  LowGain
 POS CCPOS CCPOS CH
CH
( A POS,,BBPOS
,U POS ))  HighGain
GPOS
HighGain
G
POS ( APOS
POS , UPOS
CL
CH
where
, UCH
are EM voltages corresponding to low gain and high gain,
where U
UCLPOS
POS , U POS
POS are EM voltages corresponding to low gain and high gain,
superscript
superscript C
C stands
stands for
for “calibrated”
“calibrated” (recently)
(recently) and
and subscripts
subscripts POS
POS and
and NEG
NEG denote
denote
positive
positive and
and negative
negative polarity,
polarity, correspondingly.
correspondingly.
The
The difference
difference between
between positive
positive and
and negative
negative polarities
polarities in
in generation
generation of
of primary
primary flux
flux of
of
secondary
secondary particles
particles and
and converting
converting them
them into
into electron
electron current
current can
can be
be minimized
minimized by
by
appropriately
appropriately setting
setting the
the voltage
voltage offsets
offsets of
of the
the EM
EM and
and the
the conversion
conversion dynode
dynode relative
relative
to
to ground
ground potential.
potential. The
The residual
residual difference
difference shows
shows itself
itself as
as different
different potentials
potentials applied
applied
to
the
first
stage
of
EM
in
positive
and
negative
polarities,
both
recently
calibrated.
to the first stage of EM in positive and negative polarities, both recently calibrated. We
We
will
will denote
denote its
its difference
difference as
as aa “shift”
“shift” voltage,
voltage, U
USS .. This
This voltage
voltage was
was estimated
estimated at
at the
the
gain
normally
used
for
mass
and
resolution
calibration
and
at
the
beginning
of
EMGC.
gain normally used for mass and resolution calibration and at the beginning of EMGC.
FIGURE
FIGURE 1.
1. Results
Results of
of positive
positive mode
mode calibration
calibration and
and corresponding
corresponding “ideal”
“ideal” and
and
updated
updated gain
gain functions
functions derived
derived for
for negative
negative polarity.
polarity. The
The shift
shift voltage
voltage was
was
taken
equal
to
U
=
–100
V.
The
signal
target
for
updated
function
was
~50%.
taken equal to USS = –100 V. The signal target for updated function was ~50%.
(3)
(3)


Fo
Fo
fol
fo
ii
C exp B CC U  U 
G
 ACPOS
GNEG
exp BPOS
NEG  APOS
POS U  USS 
As
As we
we are
are further
further interested
interested in
in calculations
calculations for
for one
one gain
gain value
value only,
only, we
we assume
assume that
that the
the
slope
(G) is not important and can be taken equal to the one from gain
slope of
of log
log10
10 (G) is not important and can be taken equal to the one from gain
calibration
calibration in
in positive
positive mode.
mode. The
The resulting
resulting “ideal”
“ideal” gain
gain function
function is
is presented
presented in
in
Figure
Figure 1.
1.
The
The next
next step
step is
is to
to calculate
calculate ifif the
the outdated
outdated calibration
calibration needs
needs to
to be
be updated.
updated. In
In the
the
course
course of
of calculations,
calculations, itit is
is assumed
assumed that
that signal
signal intensity
intensity for
for outdated
outdated calibration
calibration is
is
linearly
linearly proportional
proportional to
to the
the then
then current
current gain
gain value.
value. This
This allows
allows substitution
substitution of
of signal
signal
comparison
comparison with
with gain
gain value
value comparison,
comparison, which
which allows
allows to
to formulate
formulate the
the following
following
condition
condition for
for updating
updating gain
gain function:
function:
(4)
(4)
ii
Cold)   LowGain
G
(U Cold
GNEG
NEG (UNEG
NEG )   LowGain
Th
Th
Fo
Fo
ou
ou
in
in
where
where αα << 11 defines
defines the
the fraction
fraction of
of the
the nominal
nominal gain
gain triggering
triggering the
the update
update and
and the
the LHS
LHS
Cold
is
– the voltage corresponding to low gain
is the
the ideal
ideal gain
gain function
function estimated
estimated at
at U
UColdNEG
NEG – the voltage corresponding to low gain
in
outdated
calibration
in
negative
polarity.
In
explicit
form,
the
update
condition
takes
in outdated calibration in negative polarity. In explicit form, the update condition takes
the
the form:
form:
(5)
(5)
 

CC
Cold
old  U CC  U
exp
U CNEG

exp BBPOS
 UPOS
POS UNEG
POS  USS  
Th
Th
Inequality
Inequality (5)
(5) may
may be
be expressed
expressed as
as aa condition
condition for
for voltage
voltage of
of the
the outdated
outdated calibration:
calibration:
(6)
(6)
CCold
THR
old
THR
U
 U
UNEG
UNEG
NEG
 NEG
ln( )
 THR
THR  U CC  U  ln( )
UNEG
U
NEG  UPOS
POS  USS  B CC
BPOS

POS
THR
where
is a threshold voltage triggering the update. When obtaining expression
where U
UTHRNEG
NEG is a threshold voltage triggering the update. When obtaining expression
C
ColdNEG
(6),
and calibrated voltage UCold
(6), itit was
was accounted
accounted that
that calibration
calibration parameter
parameter BBCPOS
POS and calibrated voltage U
NEG
are
are negative
negative values.
values.
At
At the
the next
next step,
step, we
we calculate
calculate the
the parameters
parameters which
which update
update the
the outdated
outdated calibration
calibration to
to
aa state
state satisfying
satisfying two
two main
main conditions.
conditions. First,
First, update
update must
must deliver
deliver aa signal
signal which
which is
is good
good
enough
to
see
the
calibrant
peaks
and
to
run
mass
or
gain
calibration.
Second,
the
enough to see the calibrant peaks and to run mass or gain calibration. Second, the
update
update must
must provide
provide such
such aa signal
signal without
without multiplier
multiplier overload.
overload.
THR
Following
, the target EM
Following the
the ideology
ideology for
for finding
finding the
the update
update threshold
threshold voltage,
voltage, U
UTHRNEG
NEG , the target EM
TRG
voltage,
, for satisfactory signal may be written as:
voltage, U
UTRGNEG
NEG , for satisfactory signal may be written as:
(7)
(7)
ln(  )
TRG
TRG  U CC  U  ln(  )
U
UNEG
NEG  UPOS
POS  USS  B CC
BPOS
POS
where
where β,
β, (β
(β << 1)
1) is
is the
the ratio
ratio of
of acceptable
acceptable signal
signal to
to expected
expected nominal
nominal signal.
signal. Then
Then the
the
UPD
UPDNEG can
and BUPD
be found when
values
values for
for updated
updated calibration
calibration parameters
parameters AAUPDNEG
NEG and B
NEG can be found when
solving
solving the
the equation:
equation:
(8)
(8)
UPD
UPD(U TRG
TRG )  LowGain
G
GNEG
NEG (UNEG
NEG )  LowGain
UPDNEG )) is
under
(GUPD
equal to the slope of log
under assumption
assumption that
that the
the slope
slope of
of log
log10
NEG is equal to the slope of log10
10 (G
10
ii
(G
). Here and forward the superscript UPD stands for “updated.”
(GNEG
NEG ). Here and forward the superscript UPD stands for “updated.”
2 Automatic Update of Electron Multiplier Gain Calibration Parameters in Polarity Opposite to the One Being Calibrated
Th
Th
res
re
FIG
FI
up
up
eq
eq
For the explicit form of gain function given by Eq.(3), one immediately finds the
following solutions for the case of outdated calibration in negative polarity:
(9)


UPD
UPD
11 C
C
C
C
GNEG
NEG   APOS
POS exp BPOS
POS U  U SS 
 UPD
UPD
11
C
C
C
C


A
exp
B
U

 NEG
NEG
POS
POS SS APOS
POS
UPD
C
C
 BUPD

B
NEG
POS
POS
 NEG


The resulting updated gain function for β ~ 50% is plotted in Figure 1.
Following the same method, the update condition and updated gain function for
outdated calibration in positive polarity can be derived from results of recent calibration
in negative polarity. The update condition gets the form:
(10)
C
Cold
old
THR
THR
U POS
 U POS
POS
POS

ln( )
 THR
THR
C
C
POS  U NEG
NEG  U SS 
C
C
U POS
BNEG
NEG

(11)


UPD
UPD
11 C
C
C
C
GPOS
POS   ANEG
NEG exp BNEG
NEG U  U SS 
 UPD
UPD
11
C
C
C
C
exp  BNEG
 APOS
POS  
NEGU SS ANEG
NEG
UPD
C
C
 BUPD
POS  BNEG
NEG
 POS

In the current experimental setup, the potential difference between the conversion
dynode and the first stage of the EM comprised about +10 kV in positive ion polarity
and about –14 kV in negative ion polarity. Multiple calibrations confirmed that in
negative ion polarity, the first stage of the EM is usually set 100V to 200V more
negative as compared to positive ion polarity. Therefore, the “shift” voltage USS = ±100
V (sign depends on polarity) was used in building the simulated EM gain function for
the non-calibrated polarity and used in calculation of the update condition.
In one implementation, the update engaged if the simulated gain estimated using the
old calibration parameters fell below 10% of nominal gain. In this case, the new values
for calibration parameters were calculated to set gain value at 50% of expected
nominal gain.
The robustness of the method was confirmed by artificially changing the EM calibration
parameters in the calibration file. The change resulted in a 1000-fold decrease of EM
gain in the affected polarity and consequently in a weak signal, insufficient for mass or
EM gain calibration. Performing EMGC on the artificially modified calibration file
confirmed that the MS instrument was set into a state with well detected signal
allowing the successful EM or mass and resolution calibration without overloading the
multiplier and attached electronics.
Conclusions
The corresponding updated gain function is expressed as:

Experimental Verification
 The developed analytical model allows for quantitative estimate of EM gain
calibration parameters for polarity opposite the one being calibrated.
 The elaborated automated routine which runs every time the EM is calibrated
compares modeled gain parameters with the then current ones for the opposite
polarity, and updates them if the specified update condition is met.
The results for simulation of updated gain function for positive polarity judging from
results of recently completed EMGC in negative polarity are presented in Figure 2.
FIGURE 2. Results of negative mode calibration and corresponding “ideal” and
updated gain functions derived for positive polarity. The shift voltage was taken
equal to USS = –100 V. The signal target for updated function was ~50%.
 The described method protects the instrument from becoming inoperative in a
polarity with “lagged” EMGC because of weak or absent signal.
 The method ensures that the MS instrument will be set into a state with well
detected signal without overloading the multiplier and attached electronics.
 The general nature of the developed analytical model assumes that upon
appropriate tailoring of parameters entering the model, the method may be
applicable to EM based detection systems of different design.
References
1. Schoen, A.; John Syka, S. private communication, March 1989.
Acknowledgements
We would like to thank Dr. Alan Schoen from Thermo Fisher Scientific for fruitful
discussions on the processes of generation of secondary particles in detection
systems.
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