Foxboro MIRAN 1BX Laboratory

MIRAN Infrared Spectrometry

The MIRAN is a portable (weighs @ 30 pounds) single beam infrared (IR) analyzer. IR of 2.5-14.1 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 4.4liters 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)

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.
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

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

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------

sample 2------***

sample 3---

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. detector1. synchronizes IR beam with detector

b. circular variable filter2. controls resolution of infrared beam

c. nichrome wire source3. prevents IR radiation from scattering

d. sample cell4. converts IR energy to electrical signal

e. fixed slit5. generates IR radiation

f. mirror6. selects wavelength of infrared beam

g. light pipes7. holds gas compounds to be analyzed

h. chopper blades8. 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?