Automated Tuning of a Single Quadrupole MS Systemfor User-Supplied Calibrants

Overview: Instrument Voltages to be Tuned

Summary:

Introduction:

Ben Trumbore, Simon Prosser, Nigel SousouAdvion, Inc. 30 Brown Rd, Ithaca, NY 14850

A mass spectrometer tuned to speci�c compounds can produce more intense and accurate signals for those compounds than when it is tuned using a generic calibrant mixture. It is challenging to achieve this bene�t while maintaining e�ciency, robustness and ease of use.

The presented algorithm requires users to declare the masses of the compounds that are to be targeted by the algorithm. It also ensures that the initial voltages and mass calibration are such that peaks can be seen at these masses. The ensuing auto-tuning process is described below. After the instrument’s voltages have been tuned, a mass calibration is performed to complete the auto-tuning process.

This algorithm was implemented in Advion’s Mass Express software for controlling the Advion expression Compact Mass Spectrometer (CMS).

The auto-tuning process described here operates only on voltages that are applied within the instrument’s chambers. Voltages used to optimize the behavior of an ion source are not included, allowing multiple ion source optimizations to be used with a single set of tuned instrument voltages. Detector gain is also not auto-tuned.

Compounds Used to Produce Sample Data

An algorithm is presented that allows a single quadrupole mass spectrometer to be automatically tuned to any user-supplied calibrant containing one or more compounds. Its run-time is proportional to the number of masses targeted by the user. The algorithm incorporates di�erent analysis techniques as appropriate for the voltage(s) being tuned.

A robust and e�cient software algorithm is presented that automatically optimizes the performance of a single quadrupole mass spectrometer for any user-supplied calibrant.

Auto-tunable ParametersExtraction ElectrodeHexapole BiasHexapole RF RampIon Energy RampResolution Ramp

Ion Source ParametersIon source voltageIon source gas temperatureCapillary voltageCapillary temperatureSource voltage ramp

Name m/z Chloride 34.97 Nitrite 46.1 Nitrate 62.1 Bromide 78.92 Sulfate 96.96 Tetra (butyl) ammonium bromide 242.28 Tetra (hexyl) ammonium bromide 354.41 Tetra (octyl) ammonium bromide 466.53 Tetra (decyl) ammonium bromide 578.66

Extraction Electrode & Hexapole Bias

These voltages mainly a�ect signal intensity and are inter-dependent: Extraction Electrode must be ≥ Hexapole Bias. Using Extraction Electrode of 9.0 V, �nd the best Hexapole Bias voltage using an average response for all masses. Then �nd the best Extraction Electrode voltage using an average response for all masses, selecting the lowest voltage that raises intensity to the plateau.

Signal Intensity for Several Masses:Hexapole RF only a�ects signal intensity, is independent of other voltages, and behaves very consistently between instruments, so we use an explicit ramp instead of tuning for each instrument. The voltage range for good performance is very tight for low masses, and the ramp that �ts through that window is not ideal for higher masses.

Hexapole RF

Ion Energy & ResolutionThese highly inter-dependent voltages a�ect peak intensity, resolution and shape, and poor settings make peaks disappear. They are tuned by �rst de�ning a function for evaluating peak “quality”, which multiplies peak intensity by evaluators for peak resolution and shape. Then, for each target mass, �nd a voltage pair that optimizes this function. Finally, �nd parameter ramps that most closely �t the best voltage pairs for all target masses.

R e s o l u t i o n function appraises peak width at half height such that 0.6 evaluates to 1.0 and below 0.45 or above 0.75 evaluate to 0.0.

Shape function appraises peak symmetry about its centroid by comparing the peak’s front and tail partial-widths at half height, evaluating a width imbalance of 0 to be 1, and an imbalance of 0.2 to be 0.

• Green is desirable, blue and red are not.• Combining evaluation functions reduces the number of candidate voltage pairs.

Dark green region is best voltage combination for this mass.

expression CMS

Quadrupole AnalyzerHexapole Detector

~2 mbar ~5 x 10-3

mbar ~5 x 10-6mbar

Heated Capillary Inlet

Electrospray Probe

Compact Mass Spectrometer

ESI Voltage

HexapoleRFHexapole

Bias

Extraction Electrode

CapillaryVoltage and

Temperature

SourceVoltage

Ion Energy

Pole Bias(fixed)

Resolution adjusts RF/DC ratio

Detector Gain

Dynode

Electron

Heated Desolvation GasNebulization Gas

multiplier

Simultaneous Selection of Resolution and Ion Energy Voltages to Produce Best Peak Resolution, Symmetry and Intensity

Application of Evaluation Functions for m/z 242.28:

Evaluation Functions:

0.1

0.2

0.3

0.4

0.5

-3.0

-2.6

-2.2

-1.8

-1.4

-1.0

-0.6

-0.2

0.2

0.6

1.0

1.4

1.8

2.2

2.6

3.0

Reso

lutio

n (v

olts

)

Ion Energy (volts)

Intensity 0E+0-1E+8

1E+8-2E+8

2E+8-3E+8

3E+8-4E+8

4E+8-5E+8

5E+8-6E+8

6E+8-7E+8

7E+8-8E+8

0.1

0.2

0.3

0.4

0.5

-3.0

-2.6

-2.2

-1.8

-1.4

-1.0

-0.6

-0.2

0.2

0.6

1.0

1.4

1.8

2.2

2.6

3.0

Reso

lutio

n (v

olts

)

Ion Energy (volts)

Peak Shape -0.2--0.15

-0.15--0.1

-0.1--0.05

-0.05-0

0-0.05

0.05-0.1

0.1-0.15

0.15-0.2

0.1

0.2

0.3

0.4

0.5

-3.0

-2.6

-2.2

-1.8

-1.4

-1.0

-0.6

-0.2

0.2

0.6

1.0

1.4

1.8

2.2

2.6

3.0

Reso

lutio

n (v

olts

)

Ion Energy (volts)

Resolution 0.4-0.45

0.45-0.5

0.5-0.55

0.55-0.6

0.6-0.65

0.65-0.7

0.7-0.75

0.75-0.8

Over-resolved

Under-resolved

Fronting

Tailing

PoorIntensity

0.1

0.2

0.3

0.4

0.5

-3.0

-2.6

-2.2

-1.8

-1.4

-1.0

-0.6

-0.2

0.2

0.6

1.0

1.4

1.8

2.2

2.6

3.0

Reso

lutio

n (v

olts

)

Ion Energy (volts)

Intensity, Resolution and Peak Shape 0E+0-1E+8

1E+8-2E+8

2E+8-3E+8

3E+8-4E+8

4E+8-5E+8

0.1

0.2

0.3

0.4

0.5

-3.0

-2.6

-2.2

-1.8

-1.4

-1.0

-0.6

-0.2

0.2

0.6

1.0

1.4

1.8

2.2

2.6

3.0

Reso

lutio

n (v

olts

)

Ion Energy (volts)

Resolution and Peak Shape 0.0-0.1

0.1-0.2

0.2-0.3

0.3-0.4

0.4-0.5

0.5-0.6

0.6-0.7

0.7-0.8

0.8-0.9