Introduction

- Paper Spray (PS) mass spectrometry (MS) has become an important tool in the analysis of

complex and unpurified mixtures

- PS-MS is ideal for use with portable mass spectrometers because nebulizer gases are not

required, but there are still some aspects of the PS experiment that need improvement

- For example, the use of high DC voltage (>3kV) to in PS-MS to generate stable ion signal

poses safety concerns

- High wicking rates generated at high voltage conditions causes the time for analysis to be

narrow and requires large volume of the spray solvent (>10 µL)

- A new hydrophobic paper spray ionization method is developed that allows the use of low

spray voltages (0.3 kV). No spray solvent is required

Approach

Significance

- Reduction in spray voltage and solvent during PS-MS is important in the creation of

miniature, handheld mass spectrometers for on-the-spot chemical

- Decrease in power and other resources needed for mass analysis means a reduction

in battery size, cost and weight; all allowing for easy, widespread use of miniature

mass spectrometers

- Longer window of analysis is essential for accurate chemical characterization,

especially in complex mixtures where extra time is needed for tandem MS (MS/MS)

Experimental Procedure

Mechanistic Consideration

- The mechanism of hydrophobic paper

spray ionization is not clear, but we rule

out the possibility of inlet ionization

- The application of high DC voltage is

essential in the ionization process

(Figure 5)

- Ions are formed possibly via a typical

electrospray mechanism

- Dry paper conducts electricity through

an electron tunneling process

Summary

- The use of hydrophobic paper

decreased the adhesion forces between

the sample being analyzed and the

paper by forming a droplet

- New capabilities include controllable

wicking rate, and lower limit of

detection

- Graphite pencil line provides a simple

means to increase conductivity of a

non-wetting hydrophobic paper

Acknowledgement

This research was supported by The

Ohio State University start-up funds

References1. Badu-Tawiah, A.K., Thou M.M., Whitesides,

M.G. US Patent 2013

2. Wang, H., Liu, J., Cooks, R.G., Ouyang, Z.

Angew. Chem. Int. Ed. 2010, 49(5), 877-80

Hydrophobic Paper Spray Ionization Mass SpectrometryKathryn M. Davis and Abraham Badu-Tawiah*

Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210

Results and Discussion

We hypothesized that by using hydrophobic paper:

- Adhesive forces between paper and analyte, due

to entrapment of analyte in paper pores, can be

minimized to allow the use of low voltages for

sample desorption and ionization

- Wicking rates can be minimalized to allow

smaller volume of liquid to be analyzed over a

longer period of time.

Lower Spray Voltage: Conductivity of hydrophobic paper

was increased by applying a thin line of graphite pencil on its

surface

The graphite line creates less electrical resistance, and enables

the use of 0.3 kV DC spray voltage (Figure 4)

Untreated Paper

Treated Paper

- Filter paper was cut into triangles using a laser cutter, and

was then treated with trichloro(3,3,3-trifluropropyl) silane

vapor under vacuum (~20 torr) to create a thin hydrophobic

layer only on the surface of the paper (Scheme 1)

- Slow salinization (with no heating) over a period of four

hours ensures that only the exposed surface hydroxyl (OH)

groups were derivatized, while most of the internal OH

groups involved in intermolecular hydrogen bonding within

the fiber core were left unaltered

RSiCl3- H2O- HCl

Figures of Merit: Hydrophobic surface allows the formation

of a droplet that sits on top of the paper surface

This enables (1) lower limit of detection (Figure 3), lower

wicking rate (2), and (3) longer time frame for analysis (Figure

1) for a smaller volume of the target mixture

Scheme 1

50

100

(A) 100% = 1.53E6

0 0.3 0.6 0.9 1.2 1.5 1.8

Time (min)

0

50

100

(B) 100% = 1.54E8

0

Rela

tive

Ab

un

da

nce

Figure 1. Extracted ion chromatogram for methamphetamine

(m/z 150) obtained from paper spray ionization at 3 kV using

(A) untreated hydrophilic paper (B) hydrophobic paper

(A) Time = 0 – 0.8 minutes; 100% = 2.17E5

70 120 170 220 2700

50

100

Re

lative

Ab

un

da

nce

245150

15787

(B) Time = 0 – 0.8 minutes; 100% = 3.70E7

70 120 170 220 270

m/z

0

50

100

Re

lative

Ab

un

da

nce

150

91

Figure 2. Mass spectra recorded at 3 kV using (A) conventional paper spray

and (B) hydrophobic paper spray. Figures 2A and B were obtained from

0 - 0.8 minute time range of Figures 1A and B, respectively

Comparison: Hydrophilic versus hydrophobic paper spray ionization - in

terms of analysis time (Figure 1) and

signal intensity (Figure 2) when using 2

µL of 5 ppm methamphetamine and 3

kV

80 100 120 140 160 180

m/z

0

50

100

Rela

tive

Ab

un

da

nce

119

132

15091MW 149

Methamphetamine

m/z 150

Figure 3. Tandem MS spectrum for methamphetamine at the

detection of 1 ppb in methanol/water (1:1, vol/vol) solution

Figure 4. Analysis of 5 ppm methamphetamine at 0.3 kV using

hydrophobic paper having a thin graphite line at its surface

100% = 1.05E7

80 120 160 200 240 280

m/z

0

50

100

Re

lative

Ab

un

da

nce

150

91

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

Time (min)

0

50

100

Re

lative

Ab

un

da

nce

3 kV 0 kV

Figure 5. Total ion chromatogram showing the

effect of DC high voltage on hydrophobic

paper spray. Signal is observed only after the

application of 3 kV