A Modified Direct Sample Analysis (DSA) Ionization Source for the Direct Analysis of Thin-Layer Chromatography (TLC) Plates

Gregory T. Winter; Joshua A. Wilhide; William R. LaCourse

Molecular Characterization and Analysis Complex, University of Maryland, Baltimore County, Baltimore, MD 21250

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2 Previous Strategies

Introduction 5

Conclusion

Figure 1. A) Schematic of the DSA ionization source. B) Overall view of the DSA

attached to the AxION TOF. C) Close up view of the DSA with covers off

D) Close up view of the DSA sample tray inlet to the AxION TOF.

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Mesh Sample Tray

Nebulization Gas Inlet

Liquid Inlet

Auxiliary Gas Inlet

Corona Needle

Capillary

Extender

Heater

N2(g)

N2(g)

N2(g)

Commercial Setup A

D

C B

Figure 4. A) Modified source B) Nozzle adapter front view C) Nozzle adapter side view D) Adapted glass

nozzle E) Capillary extender side view F) Capillary extender front view G) Capillary extender, nozzle and

TLC plate on sample carrier H) Capillary extender, nozzle, TLC plate, camera I) Instrument schematic J)

Camera view and computer software control

Modified Source

Figure 6. A) TLC plate under white light 1) Victoria Blue dye from a blue Sharpie 2) Caffeine ( spot not

visible under white light) 3) Acetaminophen 4) Salicalymide B) TLC plate under UV (254nm) light C)

Extracted ion chromatogram of analyzed TLC plate. D) Mass spectra of each compound from the TLC plate

Presented here is a DAPCI source for the direct analysis of TLC plates and other surfaces. The

source was modified from a commercial DSA (Direct Sample Analysis) source made by

PerkinElmer. Modifications were made to the heater and nozzle assemblies as well as the capillary

extension. While only one application is shown, this source configuration has far reaching utility.

While TLC plates offer rapid analyte separation, detection can often be time consuming and

non-specific. Strategies include retention factor comparison with a standard, specific reagent

binding or spectroscopy. Additionally, spots of interest can be scraped off the plate and dissolved in

a solvent for separate analysis. Ambient mass spectrometry has the potential to improve the analysis

of TLC plates by offering direct sampling strategies. The goal of this project was to create an

automated system to analyze TLC plates using a modified DSA source.

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Figure 2. A) Schlieren experimental setup

B) Nozzle internal diameter 1) 4.8 mm 2) 3.2 mm 3) 1.5 mm 4) 0.5 mm

TLC Plate Analysis B

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Mirror

Nozzle

Heater

Nebulizer Gas Inlet

Solvent/Reagent

Inlet

Auxiliary Gas Inlet

Corona Needle

Solvent/Reagent

Probe

Razor

Blade

MS Inlet

A

Figure 3. Schlieren photographs and corresponding water cluster mass spectra produced by

each nozzle. A) Nozzle 1 B) Nozzle 2 C) Nozzle 3 D) Nozzle 4

Decreasing nozzle internal diameter produced higher intensity water clusters.

Despite this trend the intensity decreased with the smallest nozzle. This decrease is

attributed to gas leaks within the system (circled in red above).

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Mass spectrometry has been applied previously to the analysis of TLC plates. The

techniques are divided into two categories, direct and indirect. Indirect techniques involve the

removal of the spot in question for separate analysis. Ambient mass spectrometry falls into the

direct category where the plate remains intact.

Indirect Direct

MALDI MALDI

FAB AP-MALDI

ESI-MS LD-APCI

APCI-MS LIAD-ESI-MS

GC-MS DESI

LC-MS DART

A B

C D

E F

G H

Capillary Extender

Mass Spectrometer Inlet Capillary

Nitrogen Gas Inlet

TLC Plate

X

Motor Y

Motor

High Voltage

Line

Corona Pin

I J

Figure 5. Complete assembly

The initial desire to better understand the DSA led to a study using schlieren

photography. This study illustrated how nozzle size can affect reagent ion spectra and gas

flow patterns. The knowledge gained from the study assisted us in constructing a

multidimensional platform for the analysis of TLC plates.

The new prototype platform successfully combines an automated sample stage with the

modified source. TLC plates as well as other samples have successfully been studied using

this configuration. The improvements to the heater and nozzle assembly reduce the amount

of gas leaks and improves gas flow. The smaller nozzle provides more precise sampling

over the stock design.

To fully utilize the potential of this system additional developments are required.

These developments include:

• More efficient heat transfer to the nitrogen gas

• Improve the gas flow path to further reduce leaks

• Develop more compact design

• Develop computer program to integrate all aspects of the software controls

• Improve capillary extension design to better capture desorbed ions

• New more rugged heater assembly

• Heater provides more gastight fit

• Smaller nozzle

• Improved spatial resolution

• Made of glass to prevent

electrical arching

• Automated sample xy stage

• Manual vertical source adjustment

• Camera to monitor sample position

• 254/365nm UV lamp

• External high voltage and nitrogen

control

• Longer capillary extension

Modifications made to Commercial Source

Patent Pending

2014-015WL

Schlieren Study