Pulsed Glow Discharge Mass Spectrometry:

An Ionization Source forAerosol Analysis and Laser Sampling

Farzad Fani-Pakdel

Qualifying ExaminationUniversity of Florida - Department of Chemistry

Division of Analytical Chemistry

Outline

Introduction Aerosols Aerosols characterization Glow discharge Research objective

Experimental Instrumental set-up Particle introduction into system

Preliminary Results

Laser Sampling Importance and application

Cathode design

Aerosols

Suspension of fine solid or liquid particles (~3 nm -100m) in a gas.

Biological Aerosols:

• Viruses: 0.01 - 0.3 micron• Bacteria: 0.5 – 10 micron• Pollen: 5-100 micron

• Allergy and sickness

• Contagious diseases

• Biological warfare

Examples:Atmospheric Aerosols:

• Dust• Fog• Haze • Smoke• Sea spray particles

• Air pollution (Acidic rain)

• Atmospheric reactions

• Material transfer

• War generated particles

Significance:

Chemical Characterization of Aerosols

hv

Nano device

Sampling

Spectroscopy: non-destructive, surface onlyNano sensors: non-destructive, selective, surface onlyMass spectrometry: destructive, core and surface both possibleImportance: chemical contamination or bio hazard in core

Ionization

Ideal Ionization Technique

Soft ionizationprovides surface information, at the molecular level

CI

ICP

Intense ionizationProvides surface and bulkInformation, at atomic level

A moderate ionization like EI will result in fragmentation

Pulsed glow discharge is an ionization source capable of ionization at all these levels at the same time.

Glow Discharge Ionization Source

+-

Anode (+)Cathode (-)

e

Negative Glow

Ar

Ar+

ArAr+

Ar *

e

Penning ionization by meta-stable argon, Electron ionization

eCu Cu+

time

V

Pulsed Glow Discharge

High energy electrons (ICP)Pre-peak

Fragmentation

PlateauPenning ionizationSoft, ( CI )After peak

Schematics of a Glow Discharge -Time of Flight Instrument

Majidi, et al., Anal. Chem., 2003, 75, 1983-1996

Research Objectives:

Application of pulsed GD - TOF Mass Spectrometry for characterization of different particlesbulk vs. surface chemical analysis

CdSe / ZnS nano particles

Gold nano particles

with hydrocarbon chains

MgCl2 , NaCl mixed nano particles

Silicanano particleswith peptides

on surface

Experimental Setup

pressure gauge

Ar

exhaust

Needle ValveNebulizer

TOF GD

Figure is modified from the original:Eric Oxley, Ph.D. Dissertation, Department of Chemistry, University of Florida, 2002.

Glow Discharge Source

Cathode

O-ring

Eric Oxley, Ph.D. Dissertation, Department of Chemistry, University of Florida, 2002.

Particle Introduction 1

Particle Introduction 2

Particle Introduction 3

Particle Introduction 2; Cathode Design

1.0

0.5

0.3

0.7

0.3

0.75

0.3

0.1

0.3

0.1

0.8

AnodeInsulator

Cathodebase

Scale in inches

22 24 26

2

4

sign

al: m

v

m/z

Tap water

DI water

Na-Mg solution

Preliminary Results

To examine the sample introduction design, a sodium chloride-magnesium nitrate solution(1000ppm of each) was nebulized to produce particles of about 100nm size

Laser Sampling:

Introduction of particles /atoms into discharge by laser pulse from the sample’s back side.

•Synchronized sample introduction is possible

•Study of non-conductive thin films also possible, surface analysis of thin films (brain slice)

•Sampling yield improves

•Back side sampling (LIFT or LIBA) has the advantage of sampling directionality

Laser

Laser Induced Back Ablation

mirror

Lenz

Sample on a quartz window

Laser

Pulsed Laser Induced Forward Transfer

Summary

Glow discharge time of flight mass spectrometry can be used for surface and core chemical

characterization of particles

Cathode of the source needs to be modified for sample introduction

An orifice in the cathode seems to be a proper way of particle introduction

Laser sampling can be used for synchronized introduction of particles and also analysis of thin

films (useful for non-conductive samples)

References:1. Eric Oxley, “The Microsecond Pulsed Glow Discharge:

Developments in Time of Flight Mass Spectrometry and Atomic Emission Spectrometry.”, Ph.D. Dissertation, Department of Chemistry, University of Florida, 2002.

2. W.W. Harrison, C. Yang and E. Oxley, Anal. Chem., 2001, 73, 480A-487A

3. C.L. Lewis, M.A. Moser, D.E. Dale, Jr., W. Hang, C. Hassel, F.L. King and V. Majidi, Anal. Chem., 2003, 75, 1983-1996

4. A. B. Bullock, P. R. Bolton, Appl. Phys., 1999, 85, No. 1, 460-465

Acknowledgments:

• Dr Omenetto• Dr Harrison • Dr Igor Gornushkin

• Dr Winefordner• Dr Smith• Dr Kevin Turnery

• Committee members• Winefordner-Omenetto- Smith group• Friends from Yost / Martin group• Machine shop• Electronic Shop