A High Sensitivity Portable

GC for VOC’s & Sulfur

Compounds #Pittcon

Dr. John N. Driscoll

PID Analyzers, LLC

Sandwich, MA 02563

http://www.hnu.com

Pittsburgh Conf. on Anal. Chem., Orlando, FL

Paper # 2210-1

AbstractA new Model 312 portable GC has been developed for the analysis of volatile organic compounds. The GC uses a touch screen display thus making it easy for operator control and familiarity. The GC weighs 27 pounds and can be battery or line operated.

The PID has been redesigned to minimize the dead volume. The electronics have been modified to provide a constant current output for the PID that reduced noise significantly. The electronics uses an integral Pentium PC with Windows XP and PeakWorks software for chromatography. A 16 bit ADC with autoranging is used for signal processing. With these changes and system optimizations, we have achieved nearly an order of magnitude improvement in the detection limit for organic compounds. The detection limit for benzene with no preconcentration is < 0.5 ppb with a dynamic range of nearly 8 orders of magnitude for the PID.

The GC uses wide bore (0.53 mm) and narrow bore (0.32 mm) capillary columns up to 50 meters in length. PLOT and micropack columns are also used for gases. Applications include VOCs in factories, fenceline measurements, hospitals… Typical analyzes involve solvents (aromatics, ketones, chlorinated hydrocarbons, ETO, …) and levels well below current OSHA PELs.

312

Portable

GC

Presentation Objectives

• Describe:

– Features of GC312

– Detectors available

– PeakWorks Software

– Applications with various detectors

What are the features?

• Integral Pentium PC (350 MHz) with embedded Windows XP (2 GB Smart Card)

• 7” Color VGA display with Touch screen

• Windows XP Operating System with PeakWorks Chromatography Software (32 bit)

• Detectors- new & improved

• On-board carrier gas >16 hours

• Weight- < 17 pounds

• Dimensions- 16” L x 12” W x 6” H

• Battery, 12 VDC (30-75 C oven)- >4 hours or

or 8 hoursvext battery; line operation (30-175 C)

312 Portable GC

• Integral Pentium PC with embedded Windows

XP and PeakWorks Chromatography SW

• 2 GByte smart card- no hard drive

• Six detectors to choose from: Specific to

Universal: FPD, PID, FID, COD, FUV, TCD

• Battery (oven= 35-75 C) or 12 VDC/line

operation (35-175 C)

• Syringe or optional automatic sampling module

GC Detectors

• PID- hydrocarbons (>C4), inorganic species H2S, NH3, PH3, etc. at ppb to ppm levels (ppb-%)

• FID- specific for hydrocarbons (ppm-%)

• FPD- specific for S or P (ppb)

• COD- HC, H2, NH3 (high ppm to 100%)

• FUV- nearly universal detector (ppb to%)

• TCD- universal detector ( ppm to %)

What Improvements have been

Made to the GC Detectors

• PID• Mechanical, chromatographic, electronic &

software-results: improved detection limits from 2 ppb to < 0.5 ppb

• FUV– Electronic, chromatographic, & software-

results: improved detetion limits from 1-2 ppm to 25-100 ppb

• FID– Electronic, chromatographic, & software-

results: from 100 ppb to 25-50 ppb

Photoionization Detector

• R + h = R + + e-

• where

•

• R= molecule

• h = a photon with an

• energy > IP of R

• R+ = positive ion

• e- = electron

Process

PID Characteristics

• Linear dynamic range > 5 x107

• Detection limit <0.5 ppb benzene

• Non destructive; other detectors can be run in-series

Sensitivity increases as the carbon number increases (carbon counter)

• For 10.2 eV lamp, responds to carbon aliphatic compounds > C4, all olefins and all aromatics

• The PID also responds to inorganic compounds such as H2S, NH3, Br2, I2, PH3, AsH3, e.g. any compound with an ionization potential of < 10.6 eV

• The PID is more sensitive than the FID; >200 x more sensitive for aromatics, 80 times for olefins, & 30 times for alkanes > C6

• Non destructive detector; other detectors can be run downstream

• Concentration sensitive detector

FUV Characteristics

• Measures absorbance @ 124 nm-log signal

• Nearly Universal Response

• Linear (Log) Range > 105

• Low dead volume < 40 uL- fast response

• Non- destructive

• Concentration sensitive detector

• Environmental applications: freons, landfill

gases, O2, CO2, CH4 at same detection limit as

FID (0.1 ppm), VOCs

FID characteristics

• Linear dynamic range > 2 x 106

• Detection limit 50 ppb

• Sensitivity increases as the carbon number increases

(carbon counter)

• Sensitivity to substituted species depends on the

mass of carbon present and the ability to break the

carbon bonds

• The FID is most sensitive to hydrocarbons

• Detector is destructive since sample is burned; mass

flow rate

• Requires the use of zero grade (high purity) hydrogen

and air to produce the flame

PID FUV FID

Species

C1-C4 alkanes N Y Y

C5+ alkanes Y Y Y

Alkenes Y Y Y

Aromatics Y Y Y

Dynamic Range 5 x 10exp7 1 x 10exp5 1 x 10exp6

Detection Limits

Air

aromatics < 0.5 ppb 25-100 ppb 50-100 ppb

alkenes <5 ppb 25-100 ppb 50-100 ppb

alkanes < 10 ppb 25-100 ppb 50-100 ppb

Water

aromatics < 0.1 ppb 2.5-10 ppb 2.5-10 ppb

alkenes 0.1 ppb 2.5-10 ppb 2.5-10 ppb

alkanes 1 ppb 2.5-10 ppb 2.5-10 ppb

Detectors and Characteristics

GC Signal Schematic

PCRS232

Touch Screen

Digital I/O- valves

Diagnostics

ADC 16 bit

Display

Time clock, data calc & storage on Smart Card or USB

Memory Stick

Detector

AMP

Std TBM & THT in CH4

PID

LNG Stream with TBM &THT

PID

100 ppb BTEX

*10000

-5

0

5

10

15

20

25

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

min

1

2

3

4

5

6 7

PID

5 ppb BTEX

*1000

-15

-10

-5

0

5

10

15

20

25

30

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00

min

1

2

3 4

56

PID

Low Level (ppb) Linearity of PID

Low Level Linearity of Benzene & Ethyl Benzene

y = 972.99x - 16.272

R2 = 0.9999 y = 389.31x - 8.112

R2 = 0.9999

0

5000

10000

15000

20000

25000

0 5 10 15 20 25

ppb Benzene/Ethyl Benzene

Pe

ak

Co

un

ts

Cl2 plant effluent-TCD

TCD

H2S in Cement Plant Effluent

PID

Solvents

FID

Method

On-screen keyboard

PID 10.6 eV

Detector Parameters

PID 10.6 eV- 3 ppb

Calibration

Summary

• The Model 312 is:

– Compact- weighs 27 lbs

– Sensitive- ppb levels for PID, FUV, COD, FID,

FPD

– Has application to the analysis of ppb levels of

aromatics, VOC’s, sulfur compounds,

chlorinated HC’s, hydrides, inorganics …

– Has easy to use PeakWorks chromatography

software

– Can provide rapid “lab type” results in the field