Number range CHAPTER**FACT SHEET FOR TRACE LEVEL CO MONITORING**

**Principle of Operation**

The current recommendation for the measurement of Carbon Monoxide (CO)
is the use of Non-dispersive Infrared (NDIR) with a gas filter
correlation wheel. This procedure is identical to the current
methodology used to measure CO, however, the trace level version must
have a detector that is more sensitive, have tighter bench temperature
control, be able to remove water and be able to adjust the baseline.

**Trace Level Modifications**

A number of modifications are made to the standard CO monitor to improve
the detection limit for trace gas monitoring. Depending on the
particular make, modifications should include the following:

1.  Required sample stream dried using permeation or Nafion Dryer;

2.  Analyzer baseline determined and corrected using heated palladium or
    hopcalite catalyst;

3.  Frequent auto-zero, at a minimum of once per hour, through the
    catalyst.

**Issues with the Method**

*1) Stable Detector*

It is important for the detector to be operated at a very stable
temperature in order to measure in the ppb range. The detector and
optical bench should be operated within +/- 1.0 degree Celsius to get a
stable baseline.

*2) Water interference*

Water is known to absorb in many wavelengths in the Infrared spectrum.
Therefore, water must be removed from the sample stream before it is
allowed to enter the optical bench. This is performed using Nafion or a
permeation dryer.

*3) CO~2~ interference*

Carbon Dioxide has been shown to be an interferent for CO. It is
important that a narrow wavelength band be used to minimize these
interferents. The current instruments are using 4.6 - 4.8 *u*m, which is
selective for Carbon Monoxide.

**Literature Search**

OAQPS has performed a literature search via the Internet and was able to
find five vendors that claim to have trace level CO instruments: Horiba
LTD., Teledyne-Advanced Pollution Instrumentation (TAPI) Inc., Thermo
Electron Corp., Ecotech Inc. and Environment-SA. An instrument matrix
can be found in Table 1. Of these vendors, the Teledyne-API, Thermo
Electron and Ecotech are the only vendors that currently have
instruments with all three options available. Teledyne-API sells a model
300EU, when equipped with option 53, includes internally mounted
auto-zero switching solenoid system that works in conjunction with a
heated palladium catalyst. API uses this option to adjust the baseline
on an hourly basis. Thermo Electron Inc, who markets the TECO 48C-TLE,
is in the last phases of their development of a trace level CO
instrument with the above mentioned configuration. The zero air scrubber
uses a hopcalite scrubber instead of palladium. Ecotech offers the
9830T, which has the above mentioned configuration and also uses a
hopcalite scrubber instead of palladium. The price of the Teledyne and
Thermo instruments is in the range of \$10,000 to \$15,000. Please see
the Internet web-sites below where you can get information on these
instruments and vendors contacts in your area.

Internet Addresses:

<http://www.environnement-sa.com/index2.html>

<http://www.thermo.com/eThermo/CDA/BU_Home/BU_Homepage/1,,156,00.html>

<http://www.teledyne-api.com/products/index.asp>

<http://www.hii.horiba.com/>

[http://www.ecotech.com.au/newproductframeset.htm]{.underline}

**Calibration and Zero**

Calibrations are performed with commercially available standard mass
flow calibration devices and cylinders containing CO as a stand alone
gas or in multi-blend mixture. Once per hour, sample air is routed
through a heated palladium or hopcalite scrubber, which converts all
CO~2~ to CO. This "scrubbed" air is allowed to enter the optic chamber
and baseline is automatically adjusted once per hour.

**Table 1. Trace Carbon Monoxide Instrument Matrix**

<table>
<colgroup>
<col style="width: 10%" />
<col style="width: 7%" />
<col style="width: 4%" />
<col style="width: 8%" />
<col style="width: 7%" />
<col style="width: 9%" />
<col style="width: 6%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 10%" />
<col style="width: 9%" />
</colgroup>
<tbody>
<tr class="odd">
<td><strong>Instrument Make/Model</strong></td>
<td><strong>Lowest Range</strong></td>
<td><strong>LDL</strong></td>
<td><p><strong>Response</strong></p>
<p><strong>Time</strong></p></td>
<td><strong>Z. Drift</strong></td>
<td><strong>S. Drift</strong></td>
<td><strong>Auto Ranging</strong></td>
<td><strong>Precision</strong></td>
<td><strong>Linearity</strong></td>
<td><strong>Auto zero solenoid</strong></td>
<td><strong>Heated Palladium or Hopcalite zero scrubber
option</strong></td>
<td><strong>Nafion or Permeation Dryer option</strong></td>
</tr>
<tr class="even">
<td><p>Teco</p>
<p>48C-TLE*</p></td>
<td>1000 ppb</td>
<td>40 ppb</td>
<td>30 sec</td>
<td>100 ppb/ day</td>
<td>1% FS/day</td>
<td>Yes</td>
<td>1% FS</td>
<td>1% FS</td>
<td>Yes</td>
<td>Yes</td>
<td>Yes</td>
</tr>
<tr class="odd">
<td>TAPI 300-EU*</td>
<td>1000 ppb</td>
<td>40 ppb</td>
<td>60 sec</td>
<td><p>100 ppb/</p>
<p>day</p></td>
<td>0.5% FS/day</td>
<td>Yes</td>
<td>0.5% FS</td>
<td>1% FS</td>
<td>Yes, option 53</td>
<td>Yes, option 53</td>
<td>Yes, internally mounted on request</td>
</tr>
<tr class="even">
<td><p>Horiba</p>
<p>GA-360E</p></td>
<td>1000 ppb</td>
<td>10 ppb</td>
<td>180 sec</td>
<td>20 ppb/day</td>
<td>2 % FS/day</td>
<td>NA</td>
<td>1% FS</td>
<td>1% FS</td>
<td>No</td>
<td>No</td>
<td>Yes, as an option</td>
</tr>
<tr class="odd">
<td>Environment- SA CO12M</td>
<td>10 ppm</td>
<td>50 ppb</td>
<td>30 sec</td>
<td>100 ppb/day</td>
<td>1% FS/day</td>
<td>NA</td>
<td>NA</td>
<td>1% FS</td>
<td>No</td>
<td>No</td>
<td>No</td>
</tr>
<tr class="even">
<td>Ecotech 9830T</td>
<td>3000 ppb</td>
<td>25 ppb</td>
<td>300 sec</td>
<td>25 ppb/day</td>
<td>0.5% FS/day</td>
<td>Yes</td>
<td>5% for range 0-3 ppm</td>
<td>5% FS</td>
<td>Yes</td>
<td>Yes</td>
<td>Yes</td>
</tr>
</tbody>
</table>