Soil and Water Conservation Labo by fjwuxn


									                   Soil and Water Conservation Laboratory
                        Standard Operating Procedure
        Sherman 230, Soil and Water Conservation Laboratory, UH Mānoa

Mid Infra Red (MIR) Diffuse Reflectance Spectroscopy (DRS) of Ball Milled Soil
Samples with the Varian 2000 FT-IR

To scan soil samples in the mid infrared wavelengths to create spectral libraries and for
chemometric analyses.

Soil Sample Preparation
1. Soil samples need to be oven dried for at least 24 hours at 105 oC and then passed
through a 2 mm sieve to remove rocks and coarse organic debris.
2. The dried and sieved soil samples then need to be ball milled to a fine,
homogeneous powder. See SOP on Ball Milling of Soil and Plant Tissue Samples for
more details on this process.

Reference Material Preparation
1. The reference spectra for the MIR is Potassium Bromide (KBr). Unlike the VNIR
which uses Spectralon, the MIR uses KBr. The KBr needs to be oven dried for 24 hours
at 105oC and then ball milled to a fine, homogeneous powder. KBr is a respiratory,
skin, and eye irritant so always use gloves while dealing with this chemical.

2. KBr is stored in the desiccator cabinet next to the new drying oven.

Sample Holder Preparation
1. In the drawer below the FTIR labeled FTIR Parts, there are 2 sample holders. These
are thin black metal bars, with 4 removable sampling cups. The sampling cups are
considerably smaller than those for the VNIR so care must be taken to prepare a
homogeneous sample. Get the sample holders set them up on the lab bench.
2. In position 1, carefully add the dried and ball milled KBr. Fill the cups completely and
then gently smooth the surface with a spatula. In positions 2-4 carefully add soil
samples to be scanned and smooth the surface with a spatula. Try not to tap the cups
on the bench surface as this can lead to particle sorting and artifacts in the scans. The
second sample holder can also be filled with additional soil samples. Keep track of

which samples are added to which cup holder position. Samples should ALWAYS be
scanned in a random order, even for a small set of samples.

Instrument Operation and Scanning
1. The Instrument itself is left running all the time to avoid problems associated with
heating and cooling.

2. Open the Varian Resolutions Pro software package.
       Start → All Programs → Varian Resolutions → Varian Resolutions Pro

3. Open a file where you will save the new spectra.
       File → Open (Use the Soil Test Samples file to start)
       File → New → Multi-Spectral Document → OK

4. Move sample cup 1 (with the KBr) into position. You may hear a click when it is
position. If not, look down from the top of the chamber to see if cup is in position.

5. Collect a background scan with KBr
       -Hit ‘Collect Background’ button
       -Observe background spectrum
       -Repeat and compare this scan to previous background scans.
       -If this looks good (i.e. comparable to previous scans), then proceed to step 6.

6. Collect a sample scan with the KBr.
       -Hit ‘Collect Sample’ button
       -Wait- it averages 32 scans to get final scan

      -Check the spectrum- The spectrum should read about 100%
      transmittance/reflectance across all the wavelengths and will be slightly noisy.
      *If there is a lot of noise, or there are major dips in reflectance, it probably means
      your KBr has taken on moisture, and it needs to be redried, re ball milled, and
      repacked. Do not proceed with scanning soil samples until you have a good KBr
      white references. Remember that there will be more noise with the KBr white
      reference on the MIR than there will be with the Spectralon on the AgriSpec.
      **Even though this plot says % Transmittance on the Y-axis, % relfectance is
      actually what you are measuring- they’re not the same, it’s just an artifact of the
      -Change sample name to your naming convention in the spreadsheet.

7. Move sample cup 2 into position and collect a sample scan.
      -Hit ‘Collect Sample’ button
      -Wait- it averages 32 scans to get final scan
      -Change sample name to your naming convention in the spreadsheet.

8. Repeat this process with the rest of the samples on the rack, then insert second rack
and repeat for those samples.

9. Repeat KBr background after every two racks measured,if you are measuring more
      - prepare and load samples in the rack with KBr and repeat the background
      collection and scanning of KBr as you did before in steps 5 & 6.

10. When done measuring, make sure file is saved.

11. To export spectra:
      File → Export Spectrum
      -pick what/where you want to export and save
      -for now each spectrum must be exported separately

12. Exit program

13. Put KBr back in dessicator

14. Make sure all sample cups and racks are clean, along with the counters.


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