The NC2100 soil analyzer is suited to measure major constituents such as carbon and nitrogen
(also sulfur, hydrogen, and oxygen when properly configured). It does this by combusting a
carefully weighed sample in a small tin foil wrapper. The combustion occurs in a stream of pure
oxygen and helium. The resulting gases pass through a set of columns, which convert
(oxidize/reduce) the gases into a single gas (e.g. CO2, N2, SO2). The gas stream is then passed into
a chromatography column (See Instrument Layout below) and eventually arrives at a TCD
(thermal conductivity detector). The peak areas are measured to get a sensitive analysis of the
element in the original sample. Because of different responses for the different elements, a
calibration must first be performed with at least one standard that contains the element(s) of
interest. Usually this calibration is good for a number of samples, but quality control requires
that a known sample or standard be run periodically. Known samples, which have a very similar
composition (relative to your unknowns) will be the best check of proper instrument operation
(e.g. Soil reference material, Peach Leaves, etc.).
Elemental Analyzer (EA2100)
1.
Before running:
Check Instrument Maintenance via Eager software. If maintenance is required follow separate directions for
such. Check uV level within the Eager window: this should be about 1000 uV. If it isn’t then there is probably a
leak somewhere. If it has to be adjusted this is done via removing the panel on the right side of the instrument
and adjusting
the dial at the
bottom.
Left click on the Maintenance Program icon:
Left click Edit; select Set Maintenance; Select Default. This will show you how many samples have been run:
2. Check anhydrous column (central module, small Mg Perch column).
a. If wet it will look dull and clumpy. If the flow drops below 120 ml/min (measured with an external flow
meter as necessary) the Mg Perch is probably wet. If there is any sign of wetness it must be changed or
the chromatography column will be ruined!
b. Add glass wool to the bottom of a clean column to cover the threads. Add Mg Perch up to the top
threads then more glass wool. The Teflon section of the o-ring goes next to the glass.
3. Check for leaks:
a. Turn machine on via the toggle at the back right of the machine.
b. Take machine off standby (SPC FUN -> STBY -> YES)
c. Helium tank should be turned on and flow set to 120 ml/min (SET UP-> “(arrow right)” -> SET FLOW.
d. Screw on the cap to the carrier gas outlet (bottom of central module). If the flow doesn’t drop to below 5
ml/min then there is a leak somewhere in the system. Follow separate instructions for Leak Test.
4. Check purge:
a. Disconnect at autosampler and connect tubing to external flow meter attached at the instrument top.
This should read 60-90 ml/min (= 60-90 SCCM).
b. If 60-90 ml/min flow rate is not achieved, open the central module by sliding the cover backwards (use
some force to release the magnetic hold).
c. Turn the needle valve counterclockwise if low, clockwise if high.
5. If all checks pass, set oven temperature to:
a. LEFT (catalyst): 1000 C
b. RIGHT (copper): 780 C
c. GC (oven): 50 C
d. Air: >62 psi (300-400 kPa needed to move the autosampler). NOTE: The current tank needs to run at 80
psi!
e. Helium: 40 psi
f. Oxygen: 40 psi
6. Record all problems, repairs, and maintenance actions (beyond the normal maintenance of the crucible,
reaction columns, and the adsorption trap) in the CN Logbook. Record the gas levels and the number of samples
being run.
7. Run a bunch of system blanks (no tin cup nor sample) through the instrument until the baseline is less than 0.2
mV differential at the nitrogen peak (about 65-68 seconds retention time).
Program Files -> Thermo -> Eager XPerience for USB -> Methods -> Systemblanks.mth
SAMPLE PREPARATION
1.
Homogenizing the Sample
a. A first coarse homogenizing on sample amounts of a few hundred grams is followed by finer
homogenizing on a few dozen grams, until optimum granulometry (100-200 um) is reached.
b. The resulting sample is dried in an oven: 105C
2. Weighing the sample
a. First ensure that the work area and tools have been thoroughly cleaned with ethanol. Keep the door to
Ag 48 closed to limit air flow that affects the balance.
b. Place one tin in the balance and tare.
c. Remove the tin from the balance and place it into one of the depressions in the wrapping block.
d. Using a spatula place approximately 20 mg sample into the tin. Reweigh to double-check that you have
that amount.
e. Hold the tin above the sample (about half-way) with both forceps. The forceps should be holding the tin
no more than ¼ of the way from the outside.
f.
Perform a “Z-fold”: move one hand slightly backwards while the other hand either stays stationary or
moves slightly forward. You should see a “z” in the fold. Now push the forceps together to tighten the
z-fold.
g. Carefully squish the tin together above the sample using the forceps. Be extremely careful not to
puncture the tin. This can be done by holding with one pair of forceps and squishing with the other.
h. From the top of the tin carefully make one roll downwards to start closing the opening. Make about 3
rolls toward the sample.
i. Hold the tin with one pair of forceps and, using the cylindrical tool, gently press down on the sample to
remove all air.
j. The sample should look like a cubical box. If it is too long and skinny it will not drop correctly into the
autosampler. Pick up the tin and drop slightly onto the wrapping block to ensure that there are no spills.
k. Reweigh and record the weight in milligrams. Place in the appropriate well in a sample plate.
Sample Table: (A sample table is a “Method”)
1. RECALCULATION -> RESET CALIBRATION FACTORS
2. Clear sample table: EDIT -> SAMPLE TABLE -> EDIT SAMPLE -> CLEAR SAMPLE TABLE
3. Fill sample table (*.mth file; parameters are an elemental analyzer method or *.eam file)
a. EDIT -> SAMPLE TABLE -> EDIT SAMPLE -> FILL SAMPLE TABLE
b. Number of samples: use 200 (maximum amount) as your number of samples so that you can add later
as needed.
c. “Add”
d. The system will run until it sees a blank line in the sample table.
e. DON’T DELETE LINES!! Insert the blank as EDIT -> INSERT EMPTY LINE.
f. SAMPLE 1 = System blank (no tin cup).
g. BLANK = tin cup with no standard or sample
i. Blank average (Nitrogen) should be close to zero (possibly as high as 4000).
ii. Carbon blank should be <15000 area counts.
h. BYPASS = a standard that is not weighed. It sets the instrument’s peak identification before other
standards and samples are run. The retention times within the predicted range can be adjusted before
running the calibration.
i. STANDARD = chemical standard such as EDTA. This must be no more than 6 months old. Run 5
standards at the beginning of each test.
j. CHECK STANDARD = a standard run as an unknown to check the calibration. Run at least one CHECK
STANDARD every 10-20 samples to test the calibration.
i.
ii.
iii.
iv.
v.
4.
5.
6.
7.
8.
Setup Instructions for STD-CHECK
Enter the component table.
Enter a minimum and or maximum value for check standard (absolute %).
A dialogue box will open.
If you only want to apply minimum and maximum values to check standards then check first box
on top of page otherwise will be applied to all unknown samples.
vi. Determine action to be taken when check standard is out of range:
1. None (Set flag for custom report) or
2. Stop sequence or
3. Set instrument to standby.
SAVE method before you run anything! Do not save over the original. Make sure you press “Enter” or move to
a new cell before you close out of the sample table otherwise the last item entered will not be registered.
RECALCULATION -> RESET CALIBRATION FACTORS
START ANALYSIS
VIEW SAMPLE BEING ACQUIRED
a. STOP analysis: stops acquiring and saves up to that point
b. ABORT analysis: stops acquiring and does not save
SUMMARIZE RESULTS
a. If something is wrong with the standard it won’t be on the curve. (View -> View Calibration Curve)
i. Right click on a point to get information.
ii. Perform a K-Fit analysis. Write down the numbers in the log book.
iii. Carbon blank should be <15000 area counts; nitrogen blank average should be close to zero.
b. CHECK STANDARDS – standards run as unknowns. These should read at +/- 0.2-0.5% of the tested
values.
c. Soil unknowns should read at +/- 10%.
d. If standards, bypass, blanks, and checks look OK then load your samples.
9. ADD SAMPLES to sample table:
a. This cannot be accomplished via a transfer from Excel.
b. Rename any “sample name” and add the corresponding weights.
c. “Enter” after entering a weight OR move off the cell.
d. Add one blank line after every 6 samples. Add 2-3 blank lines and standard checks after 24 samples.
e. If you have more than 200 samples/standards/blanks/checks you will need to save the excess as another
sample table.
f. SAVE METHOD
10. RUN/START analysis
11. NOTE: “Last Sample Calculated Results” and “Acquiring” windows are the only two that can be left open so as
not to interfere with the sample acquisition.
12. NOTE: Sample Run is at the autosampler marked position when at the beginning of the run. At about 60 sec the
autosampler advances to the next sample and holds it on top of the internal door ready to drop after the
chromatogram is done. The instrument seems to run better when the NEXT sample after a blank line is a system
blank.
13. NOTE: If an “error generating report” occurs, advance the sample table by one line manually and save method.
If this is not done the next sample will rewrite over the previous one.
14. NOTE: “Stop Analysis” stops the sample acquisition and saves up to that point. “Abort Analysis” stop sample
acquisition and does not save.
15. NOTE: With the K-factor analysis the carbon blank should be less than 15000 area counts. The blank averages
should really be close to zero.
16. Summarize Results: if something is wrong with the standard it won’t be on the curve. Right click on the point on
the curve to get information.
a. In the summary table you can group like samples together by assigning the like sample a group number.
(This is done if you have duplicate or triplicate of the same sample so you could see the elemental
average, percent RSD, and Variance of the like samples.)
b. To display the data for a specific group, place the cursor on the group and select the drop-down screen
you are looking for the element that you want averaged.
c. To print your data, select the “Print” drop down menu and select “Print All Groups”. This will bring up
the print screen and select to “Print By Peaks”.
17. Recalculation: Save after integration. If there is a problem with a peak not saving after being added, go through
the recalculation but for that one chromatogram do NOT reintegrate.
18. SHUT DOWN:
a. Flip toggle switch on back of instrument.
b. Turn off all gases.
c. Turn off computer.