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Particulate organic matter (PN/PC)

 

                1.  Materials:

1.  drying oven

2.  desiccator, desiccant

3.  tin disks

4.  two pairs of fine-tipped forceps

5.  aluminum foil

6.  kimwipes

7.  pelletizer

8.  pellet-holding tray

9.  balance (to 0.  001 mg)

10.  acetanilide  (CHN standard)

11.  ashed 25-mm GF/F filters

12.  spatula

13.     Perkin-Elmer CHN analyzer, manual

14.     Apple leaf (or other) C and N check standard

 

2.  Place filters in the walk-in freezer until ready to analyze.   Also, use the Manual for the Perkin-Elmer CHN analyzer to assist you; most of the steps outlined below are also discussed in the Manual (Currently we are using a PE 2400 Series II CHNS/O Analyzer).  

 

3.  On the day before the filters are to be pelletized, place them in a drying oven at 37C for at least 12 hours.   Then transfer the dried filters to a desiccator.   Pull a vacuum on the desiccator if possible.   If the filters are dried at Toolik at 55 C this isn’t as important especially if Hydrogen values are not important.

 

4.  Take the filters to the instrument room (3rd  floor, Loeb or 3rd floor Starr ).   Tear off a section of aluminum foil to use as a work surface.   Get the tin disks and forceps from the drawers beneath the CHN analyzer and the balance.   Clean the forceps thoroughly with kimwipes.   Use the forceps to handle the tin disks and the filters; do not use your fingers!

 

5.  To pelletize a filter, center the filter on a tin disk, sample side up.   Make sure you have only one tin disk; they're very thin and it's easy to pick up more than one at once.   With the forceps, fold the disk in half so that the filter is on the inside.   Fold the disk again lengthwise (you should now have a long thin strip rather than a quarter-circle; see the manual).  

 

6.  Fold the ends of the strip over, and then roll the burrito up.   If you roll it up too tightly, you may rip the tin, so be careful.   When it is rolled up, no part of the filter inside should be visible.  

 

7.  Place the "burrito" into the pelletizing cylinder.   Put the cylinder in the wide mouth-side of the stage mount.   Pull down the handle part way and line up the press with the opening of the cylinder.   When they are lined up, pull the handle all the way down and press the burrito.  

 

8.  Lift the handle and remove the cylinder.   Flip the stage mount over so that the narrow-mouth side is up.   Put the cylinder back on the stage, line up the press and the opening, and pull the handle down.   The press will knock the pellet into the narrow-mouth opening.  

 

9.  Using the forceps, remove the pellet and place it into a pellet-holding tray (there are several trays in the instrument room).   It is essential that you keep track of which pellet is in which hole in the tray.   The holes in the trays are marked (A1, A2, A3, etc.  ), so use the data sheets provided (titled "AUTO RUN Sample Information (Filters)" or make your own) to record which pelletized sample is in which hole.   Leave the first row (A1-A12) empty; you will put your initial standards and blanks in that row.   About every 10 pellets, skip two holes (a standard blank and a filter blank will go in these holes).  

 

10.  Calibrate the balance in the corner, using the instructions provided in the booklet on top of the balance.   The calibration weights are in the drawer under the balance.   The range setting should be 20 mg.  

 

               11.  Pack standard blanks (also called a K factors):  The K factor Is a standard of known amount of acetanilide

1.  Place an ashed 25-mm GF/F filter on a tin disk, fold them in half with the forceps, and then unfold partially so that there is a crease down the middle of the filter and tin.  

2.  Place a counterweight pellet on the left pan of the balance (there are several counterweights in a small plastic box; however, some were made with more than one tin disk and will cause an error on the scale, so keep trying until you get the counterweight with only one tin disk).  

3.  Place the creased filter and disk on the right pan of the balance, lower the pan arrest, and zero the balance. Raise the pan arrest.  

4.  Using the spatula, place a small amount of acetanilide on the creased filter.   Lower the pan arrest and check the weight.   Add or remove acetanilide until you have between 2 and 3 mg of acetanilide.   Record the weight on a Preliminary Standardization Data Sheet (available in folder on table in the CHN room).  

5.  VERY CAREFULLY, using the two pairs of forceps, roll up the disk into a sausage as described above. Make sure you don't spill any of the acetanilide and that you don't rip the tin.  Start over if you do either of these things, or else the weight in the next step will not be correct.  

6.  Pelletize the sausage and reweigh.   If the weight is greater or less than the original weight by more than about 0.  010 mg, start over.   If not, then record the second weight.  

7.  Still using the forceps, place the pellet in a designated hole in the pellet tray.   The first five K factor pellets will go on row A (in holes A1, A3, A5, A7, and A9).   Subsequent K factor pellets will go within the samples; as you recall, every ten samples or so, you left two holes blank.   The first of these holes is for a K factor.   So, place the K factor pellet in the first of a pair of empty holes and record the hole number and the weight of the acetanilide in the K factor pellet on the data sheet (use the Preliminary Data Sheet if the pellets are going into row A and the Auto Run Sample Inf. data sheet if the pellets are being implanted within the samples).  

 

12.  Pack filter blanks:

1.  Using the forceps, place a blank 25-mm GF/F filter that you brought back from the field onto one of the tin disks.  

2.  Pelletize the blank filter in the same manner as the sample filters (described above); do not add acetanilide.  

3.  Transfer the pelletized blank filter to the pellet tray.   Place in one of the empty holes designated for blanks. The first four blanks will go on row A (in holes A2, A4, A6, and A8).   Subsequent blanks will go within the samples; as you recall, every ten samples or so, you left two holes blank.   The second of these holes is for a blank.   So, place the blank pellet in the second of a pair of empty holes and record the hole number on the data sheet (use the Preliminary Data Sheet if the pellets are going into row A and the Auto Run Sample Inf. data sheet if the pellets are being implanted within the samples).  

 

13.  At this point, you are ready to run your samples.   If, however, the CHN machine is already in use or not ready to run, tape your pellet trays shut, label them, and place them in a desiccator with activated desiccant and draw a vacuum on them until the machine is available.  

 

14.  When the machine is available, check with Don Burnette to make sure that there is enough helium, oxygen, and nitrogen gas, and that the columns are fresh enough to run all of your samples.

 

15.   The PE 2400 must be programmed to run filters and therefore give results in ug of C, H, N.  These values are then converted to ug/L following the formulas below.  Blanks are designated on the analyzer and will be automatically subtracted from the value of any pellet entered as a “sample” and not a blank or K factor.  For additional information regarding the analyzer or procedure contact Chris Crockett (MBL 508 289 7584, ccrockett@mbl.edu) or Don Burnette (MBL 508 289 7764) for CHN availability and costs.

                 

                   Total PN (ug/L)=Mass N * 1000 / amt filtered

 

                   Total PC (ug/L)=Mass C * 1000 / amt filtered

 

 

                  

Please contact arc_im@mbl.edu with questions, comments, or for technical assistance regarding this web site.