Characterization of a Non-Characterization of a Non-

radioactive Electron Capture radioactive Electron Capture

Detector Based on the Dielectric Detector Based on the Dielectric

Barrier Discharge Plasma Barrier Discharge Plasma

Advanced Industrial ChemistryAdvanced Industrial Chemistry

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Albuquerque, NM 87114Albuquerque, NM 87114

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Introduction Introduction

� Discussion of the radioactive ECD Discussion of the radioactive ECD

� DBD-ECDDBD-ECD� Principle of operationPrinciple of operation

� Advantages of the DBD Advantages of the DBD

� Data from the DBD-ECDData from the DBD-ECD

� Exemplary applicationsExemplary applications

� Future work Future work

� ConclusionsConclusions

The ECD DetectorThe ECD Detector

� Derived from Lovelock's argon ionization detectorDerived from Lovelock's argon ionization detector

� Uses radioactive source emitting high energy Beta Uses radioactive source emitting high energy Beta � Typically Ni-63 or Tritium Typically Ni-63 or Tritium

� Beta particles collide with heavier gas generating Beta particles collide with heavier gas generating

“thermalized” electrons“thermalized” electrons

� Electrons in detector set up a standing currentElectrons in detector set up a standing current� High background signalHigh background signal

� Constituents of interest enter detector and capture Constituents of interest enter detector and capture

electronselectrons� Results in a decrease in standing current forming the Results in a decrease in standing current forming the

basis of the chromatographic response basis of the chromatographic response

The ECD Detector: AdvantagesThe ECD Detector: Advantages � Highly sensitive to some constituentsHighly sensitive to some constituents

� Halogenated hydrocarbons, especially multiply Halogenated hydrocarbons, especially multiply

substituted (CT, some pesticides, PCBs), predominant substituted (CT, some pesticides, PCBs), predominant

applicationapplication

� Nitro compounds, especially multiply (DNT, TNT, Nitro compounds, especially multiply (DNT, TNT,

etc....)etc....)

� Disulfides, diketonesDisulfides, diketones

� Selective Selective � Take advantage of differences in sensitivity to simplify Take advantage of differences in sensitivity to simplify

the chromatography the chromatography

� Can be very stableCan be very stable � A bit of explanation is in order here... (HIDA bit of explanation is in order here... (HID, comparison , comparison

to TCD?, routine production)to TCD?, routine production)

The ECD Detector: DisadvantagesThe ECD Detector: Disadvantages

� Needs high purityNeeds high purity gases/no leaksgases/no leaks� Oxygen and water suppress signal Oxygen and water suppress signal

� Limited linear rangeLimited linear range

� Widely varying responses (CF vs CT)Widely varying responses (CF vs CT)

� Radioactive source:Radioactive source: � Subject to licensing requirements/shipping restrictions Subject to licensing requirements/shipping restrictions

� In US, subject to annual monitoring for escape In US, subject to annual monitoring for escape � Prevent thermal runaway: migrate Ni into foilPrevent thermal runaway: migrate Ni into foil

� Hydrogen exchange (for tritium foils)Hydrogen exchange (for tritium foils)

� Long term liability (custody, disposal, etc...)Long term liability (custody, disposal, etc...)

� Difficult to get it clean Difficult to get it clean

Dielectric Barrier Discharge (DBD)-ECD Dielectric Barrier Discharge (DBD)-ECD

detector: use DBD to replace radioactive source detector: use DBD to replace radioactive source

� DBD = Dielectric Barrier Discharge plasmaDBD = Dielectric Barrier Discharge plasma� AC discharge across a dielectric barrierAC discharge across a dielectric barrier� Non-thermal dischargeNon-thermal discharge� Low electrode wear/large electrode surfaceLow electrode wear/large electrode surface� Ability to operate without getters/purgingAbility to operate without getters/purging

� Simple design Simple design � Non-radioactive, windowlessNon-radioactive, windowless� Simple, robust power supplySimple, robust power supply� Conventional electrometersConventional electrometers� Low valve disturbance, packed column compatible Low valve disturbance, packed column compatible

Dielectric Barrier Discharge is keyDielectric Barrier Discharge is key

Discharge CycleDischarge Cycle

0 1 2 3 4 5 6

-1.5

-1

-0.5

0

0.5

1

1.5

Discharges

Multiple discharges per ½ cycle; operating at Multiple discharges per ½ cycle; operating at

~30 kHz ~30 kHz

ECD Schematic ECD Schematic

Amp

Bias or ground

Plasma

ColH2

Detector Picture Detector Picture

Helium plasma colorHelium plasma colorInstalled on Varian 3400Installed on Varian 3400

DBD-ECD Evaluation Set Up DBD-ECD Evaluation Set Up

� HP 5890 GC:HP 5890 GC:� 6 port injection valve 250 ul loop 6 port injection valve 250 ul loop � 30 m X 0.25 RTX-VMS, 1.4 film, helium carrier30 m X 0.25 RTX-VMS, 1.4 film, helium carrier� Temp. programmed oven (35-105C)Temp. programmed oven (35-105C)

� Detector Detector � DBD-ECD in constant current modeDBD-ECD in constant current mode

� Standard DBD power supplyStandard DBD power supply� Standard HP 5890 ECD electrometer Standard HP 5890 ECD electrometer � Helium reaction gas, hydrogen dopant Helium reaction gas, hydrogen dopant

� Evaluation StandardEvaluation Standard� F113 (50ppb), Chloroform (80ppb), PCE F113 (50ppb), Chloroform (80ppb), PCE

(60ppb) in compressed air (60ppb) in compressed air

DBD-ECD data, orDBD-ECD data, or

“Being aggressive does not always “Being aggressive does not always

help.” help.”

� Can take the standing current anywhere we want toCan take the standing current anywhere we want to� Does not necessarily help the sensitivityDoes not necessarily help the sensitivity

� PCE considered a dissociative componentPCE considered a dissociative component� Most susceptible to changes in conditions?Most susceptible to changes in conditions?

� For me, easiest to understand to most difficultFor me, easiest to understand to most difficult

Effect of helium flow rate (reaction gas) Effect of helium flow rate (reaction gas)

ECD concentration dependent detector; ECD concentration dependent detector;

nitrogen incursion nitrogen incursion

30 35 40 45 50 55 60

0

1

2

3

4

5

6

FC

CF

PCE

Zero(/100)

rxn flow rate

are

a

Effect of primary power Effect of primary power

3.5 4 4.5 5 5.5 6 6.5

0

1

2

3

4

5

6

7

FC

CF

PCE

Zero (/100)

Vp

Are

a

Ionization; non-thermal electrons?; off Ionization; non-thermal electrons?; off

axis plasma axis plasma

Effect of dopant gas Effect of dopant gas

Change in 0; so muchChange in 0; so much i i(standing)(standing);fundamental difference ;fundamental difference

with Wentworth; tight control of dopant with Wentworth; tight control of dopant

2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

0

1

2

3

4

5

6

FC

CF

PCE

Zero (/100)

Pressure

Are

a

Effect of temperature Effect of temperature

100 120 140 160 180 200 220 240 260 280 300

0

1

2

3

4

5

6

7

8

9

F113

CF

PCE

Temp (C)

Are

a

Most puzzling; dissociative (II); follows Most puzzling; dissociative (II); follows

trend of Wentworth trend of Wentworth

First look at detection limits; 0.5 pg on First look at detection limits; 0.5 pg on

column, FC and CF column, FC and CF

Looked at PCE; want to look at nitrogen Looked at PCE; want to look at nitrogen

dopant dopant

Trihalomethanes in Drinking WaterTrihalomethanes in Drinking Waterheadspace extraction headspace extraction

DBCM

CF

BF

DCBM

CF

DBCM

40 ppb pesticide standard; Varian 3400; HP-1, 40 ppb pesticide standard; Varian 3400; HP-1, 30 m X 0.32 X 0.25 film, 250/27530 m X 0.32 X 0.25 film, 250/275

65/1/14/125/10/265/1065/1/14/125/10/265/10

Carbon Disulfide and Carbon Carbon Disulfide and Carbon Tetrachloride in airTetrachloride in air

(packed columns, multiple valves, 70:1 split, 2 loop (packed columns, multiple valves, 70:1 split, 2 loop volumes, no getters, process GC)volumes, no getters, process GC)

BFBF

CCl4

CS2

Further Work Further Work

� Nitrogen as a dopant source Nitrogen as a dopant source � Compare linearity and detection limits to hydrogen Compare linearity and detection limits to hydrogen

� Continued exploration of physical design Continued exploration of physical design

� Application to heavier components Application to heavier components � In particular, Pesticides and PCBs In particular, Pesticides and PCBs

� Beta prototype in commercial laboratories Beta prototype in commercial laboratories

DBD-ECD effective substitute for DBD-ECD effective substitute for

radioactive ECD radioactive ECD

� Large/Stable/Non-radioactive Metastable SourceLarge/Stable/Non-radioactive Metastable Source

� Able to use common laboratory gases Able to use common laboratory gases � Helium and hydrogen/nitrogen Helium and hydrogen/nitrogen � No extra purification required (no getters) No extra purification required (no getters)

� Able to use existing electrometersAble to use existing electrometers� Simple to implementSimple to implement� Able to take advantage in software integration Able to take advantage in software integration

� Disadvantages Disadvantages � Basically the same as a radioactive ECD Basically the same as a radioactive ECD

(varying sensitivity, two gas supplies, limited (varying sensitivity, two gas supplies, limited linearity, clean gases, leak free system) except,linearity, clean gases, leak free system) except,

� Tight control of dopant necessaryTight control of dopant necessary