MIRAN Infrared Spectrometry
The MIRAN is a portable (weighs @ 30 pounds) single beam infrared (IR) analyzer. IR of 2.514.1 μm are generated by a nichrome wire. The path length is variable from 0.75 – 20 meters, by
the use of gold coated mirrors. The sample cell is 4.4 liters in volume. Molecules will absorb
specific wavelengths of IR depending on bond type, bond length and functional groups. It has a
library of calibration curves for 115 OSHA regulated chemicals and additional curves can be
added. The instrument uses a single wavelength to quantify the compound of interest. Any
compound that also absorbs IR of that wavelength is a potential interferent. Water and carbon
dioxide are common interferents, so the instrument must be zeroed with air of similar humidity
and CO2 concentrations. This is accomplished by zeroing the instrument in the atmosphere to be
tested using filters to remove contaminants to be quantified. Particles, water, acids and bases
degrade the optics (cell windows made of AgBr and mirrors). The detection limit varies 1-10
ppm.
Foxboro MIRAN 1BX Laboratory
General Gas Analysis Using the MIRAN (Semi-Quantitative Analysis)
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Review infrared spectroscopy. See pages 200, 287-289 and 292-295 in OEEC&M (2003) or
Chapter 17, pages 17-19 and pages 22-25 in OEEC&M (2011) and the MIRAN Instruction
Manual.
Note: Page numbers listed in this lab refer to pages in the MIRAN Instruction Manual
Handout (MIMH).
Follow the Instrument Turn-on Procedure given on page 8 of the MIMH. Allow the MIRAN
to warm up. Find the alphanumeric name for the chemical of interest by following the
detailed procedure listed in Table 3 of the MIMH (page 9).
Set the Analysis Parameters by following the steps listed in Table 4 of the MIMH (page 10).
For your first series of measurements enter the following parameters:
Concentration Range OK? - High Range
Readout OK? - Readout in ppm
Display Mode OK? - Read bar graph at end of analysis
Alarm Type OK? - Set alarm to Geiger-counter mode
Once you have entered the analysis parameters you are ready to zero the instrument and
analyze your samples.
Follow the series of operator responses listed in Table 5 of the MIMH (page 12-13) to zero
the MIRAN and analyze your sample.
Be sure to use the appropriate filters for zeroing, usually the activated carbon filter for
organic compounds, and the HEPA for analyzing the gas.
You will be analyzing “airborne” concentrations of acetone, toluene, ethanol and/or
methanol.
Analyze the airborne concentration of the sample following the procedure given in Table 5.
Holding the wand in the proximity of an open vial is usually sufficient to get a meter
response.
Record the concentration values, number of dashes on the bar graph, and % of alarm limit.
Make observations regarding the stability of the readings and the length of time it takes for
the instrument to equilibrate.
Experiment by changing at least two of the parameters and rerun the analyses.
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Record the values.
Gas Identification Using MIRAN and Spectra/Match (Qualitative Analysis)
Using the Spectra/Match software you will obtain spectra of a known chemical, then identify an
unknown.
Instrumentation Start-up
Turn on the converter
Turn on the MIRAN
Turn on the computer with the boot disk in the b: drive
At the C:\ prompt type cd spmatch
Hit the <enter> key
At the C:\spmatch directory type spm
The Main Menu will appear
Running the Background Scan
Move the cursor to SCAN and hit the <enter> key
Move the cursor to Background and hit the <enter> key
Type standby and hit the <enter> key
ENTER COMMAND
Type scan and hit the <enter> key
SET SCAN PARAMETERS?
Type Y and hit the <enter> key
SCAN TYPE OK?
Type S and hit the <enter> key
SPECTRA GAIN OK?
Type 8 and hit the <enter> key
PATH LENGTH OK?
Type 6.75 and hit the <enter> key
GAS SAMPLE READY?
Put on the zero filter
Type Y and hit the <enter> key
INTRODUCING GAS
This step will take several minutes
INITIALIZING SCAN
This step will take several minutes
START SPECTRA SCAN?
Type Y and hit the <enter> key
This step will take several minutes
Running the Sample Scan
The Main Menu will appear
Move the cursor to SCAN and hit the <enter> key
Move the cursor to Sample and hit the <enter> key
Type standby and hit the <enter> key
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ENTER COMMAND
Type scan and hit the <enter> key
SET SCAN PARAMETERS?
Type Y and hit the <enter> key
SCAN TYPE OK?
Type S and hit the <enter> key
SPECTRA GAIN OK?
Type Y and hit the <enter> key
PATH LENGTH OK?
Type Y and hit the <enter> key
GAS SAMPLE READY?
Put on the HEPA filter
Type Y and hit the <enter> key
INTRODUCING GAS
Place 1-2 ml of sample on a piece of paper towel and place it very close to the wand
without touching it.
This step will take several minutes
INITIALIZING SCAN
This step will take several minutes
START SPECTRA SCAN?
Type Y and hit the <enter> key
This step will take several minutes
Spectra Analysis
The Main Menu will appear
Move the cursor to Calculate and hit the <enter> key
This step will take several minutes
Move the cursor to Match and hit the <enter> key
Select Current Spectra
This step will take several minutes
DO YOU WANT TO PRINT SPECTRA?
Type N and hit the <enter> key
DO YOU WANT TO SAVE SPECTRA?
Enter the filename as “filename.BIN” (for example Group11.BIN).
Use a unique code (otherwise it will tell you that the file already exists).
Do not try to enter a drive designation since the software can only save to the hard drive
(C:\).You can always go to DOS and copy the files from the hard drive to a floppy .
If you want to check if your spectra has been saved
Move the cursor to Match and hit the <enter> key
Select Current Spectra and look for your filename then press the esc key to get out.
If you want to see the hit list
Move the cursor to Display and hit the <enter> key
Select HQI and look at the computer hits
If you want to look at the spectra
Move the cursor to Display and hit the <enter> key
Select Spectra and look at the computer hits
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Repeat procedure with the unknown and record the data.
Questions
1. Assume that you have set the MIRAN read out to ppm and the display mode to bar graph
prior to analysis. You measure several gas samples of ethane (alarm limit = 500 ppm). You
observe the following bar graphs for the samples.
sample 1
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sample 2
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sample 3
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Give the ppm reading that corresponds to each bar graph.
2. Why should you not analyze concentrations of ammonia greater than 500ppm?
3. Is the MIRAN designed to perform qualitative or quantitative analysis? Discuss some
advantages and limitations of the instrument. Additionally, discuss how interferences during
zeroing and gas analysis may affect your interpretation of the data you receive from the MIRAN.
4. The MIRAN has two audible alarm settings (upper limit alarm and the geiger counter alarm).
Give examples of situations where each type of alarm is appropriate and when there is a distinct
disadvantage to using a given alarm type.
5. Match the component of the MIRAN 1B analyzer and its corresponding function
a. detector
b. circular variable filter
c. nichrome wire source
d. sample cell
e. fixed slit
f. mirror
g. light pipes
h. chopper blades
1. synchronizes IR beam with detector
2. controls resolution of infrared beam
3. prevents IR radiation from scattering
4. converts IR energy to electrical signal
5. generates IR radiation
6. selects wavelength of infrared beam
7. holds gas compounds to be analyzed
8. determines pathlength of infrared beam
6. What are the two most common interfering gases in IR spectrometry and the way to reduce
these interferences?
7. What is the Beer-Lambert Law and its application in analytical methods?
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