PRINCIPLE

Samples are combusted in an oxygen atmosphere at 1350 C, converting elemental carbon, sulfur, and nitrogen into CO2, SO2, NOx, and N2. These gases are then passed through the IR (infrared) cells to determine the carbon and sulfur content and a TC (thermal conductivity) cell to determine N2.

EQUIPMENT

  1. LECO CNS-2000
  2. Balance accurate to 0.1 mg.
  3. Ceramic sampling boats.

REAGENTS

  1. Anhydrone - magnesium perchlorate - Mg(ClO4)2
  2. Lecosorb - sodium hydroxide on an inert base.
  3. Copper sticks.
  4. Copper turnings.
  5. N-catalyst.

GASES

Helium 99.99% carrier gas
Oxygen 99.99% combustion gas
Compressed air pneumatic gas

STANDARDS

%
CNS
Sulfamethazine 51.8 20.1 11.5
EDTA 41.1 9.59 0
Alfalfa* 45.5 2.80 0.259
Barley* 44.5 1.37 0.136
Oat meal* 46.4 2.64 0.209
Soil* 0.77 0.04 0

* These are certified, Nist traceable reference samples. The elemental values listed for them will differ when different lot numbers are used.

PROCEDURE

  1. Touch the blank screen - 6 icons will appear.
  2. Blank Calibration:
    1. Touch the "Analyze" icon.
    2. Touch the "Select ID Code" key.
    3. Using the arrow keys, scroll to "BLANK 01".
    4. Touch "ESC".
    5. Touch "Tare Balance"
    6. Touch "Enter Wt." 6 times.
    7. Touch the "Analyze" key - The instrument will automatically analyze 6 blanks.
    8. After the 6 blanks have been analyzed, touch "ESC" in order to return to the main menu.
    9. Touch "Calibrate"
    10. Touch "Blanks"
    11. Select the elements to be analyzed and touch "OK".
    12. Using the arrow keys, scroll to "Blanks".
    13. Using the "Include Results" and/or "Exclude Results" key, highlight the best 3 blanks (lowest per cent C, N, and S).
    14. Touch "Process Results" (the computer will display values for the new calibration and the last calibration).
    15. Touch "OK" if the results are acceptable (blank calibration values will be automatically printed.
    16. Touch "ESC" in order to return to the main menu.
  3. Standard Calibration
    1. Touch the "Analyze" icon.
    2. Touch "Select ID Code".
    3. Using the arrow keys, scroll to the standard being used.
    4. Touch "ESC"
    5. Place a ceramic sampling boat on the balance (it will be automatically be tared).
    6. Weigh 0.15 to 0.20 g standard sample into the boat and touch "Enter".
    7. Repeat steps e and f 3 times, weighing a total of 4 standard samples.
    8. Touch the "Analyze" key.
    9. When the door opens. Remove any previously used sample boat.
    10. At the "Load Sample into Purge Area" prompt, place the first weighed standard into the opening and touch "OK" (the sample door will close).
    11. At the "Push Boat into Hot Zone" prompt, push the boat completely in and pull the boat pusher completely out.
    12. Repeat steps i, j, k, and l for the next 2 standard samples.
    13. After analysis or the 3 standard samples is complete, touch "ESC" in order to return to the main menu.
    14. Touch the "Calibrate" icon,
    15. Touch "Drift Correction"
    16. Select the elements for correction and touch "OK".
    17. Using the arrow keys, scroll to the selected standards.
    18. Using the "Include Results" key highlight the 3 standards to be used in the calibration.
    19. Touch the "Process Results" key (the instrument will display old and new calibration equations for each element).
    20. If the results are acceptable, touch "OK" (the results will be automatically printed.)
    21. Touch "ESC" in order to return to the main menu.
  4. Curve Verification Sample:
    1. Touch the "Analyze" icon.
    2. Touch the "Analyze" key.
    3. Load the last weighed standard into the furnace following steps j, k, and l in section 3 above. Results will be automatically printed when they are complete.
    4. Touch "ESC" in order to return to the main menu.
  5. Sample Analysis:
    1. Touch the "Analyze" icon.
    2. Touch "Select ID Code".
    3. Touch "Modify ID Code".
    4. Using the on screen keyboard, Identify the first sample.
      1. The instrument will automatically increment sample numbers.
      2. If sample numbers are not consecutive or some other sample identification is used, step 5c will have to be repeated for each sample.
    5. Weigh 0.15 to 0.20 g sample into a sample boat and proceed as in steps i, j, k, and l of section 3 above.
    6. After analysis of samples is complete, touch "ESC" in order to return to the main menu.
  6. Reports:
    1. Touch the "Reports" icon.
    2. Touch the "Results" icon.
    3. Use the "Include Results and/or "Exclude Results" key to highlight those samples to be reported."
    4. Touch "Process Results".
    5. At the computer prompt, touch either "Transfer Results to A:\RESULTS" or "Print Results" or touch both of them (a check mark will appear by the selection).
      1. If "Transfer Results to A:\RESULTS" is selected, place a 3– inch diskette into the instrument.
      2. Touch "OK" (results will be printed).
      3. Touch "ESC" twice.
      4. Touch the "Logoff" icon.

QUALITY CONTROL

  1. Following the last client sample, analyze one duplicate sample, one quality control sample, and one standard calibration sample.
    1. Values on the duplicates must agree within 20% of the average value.
    2. Values on the quality control sample must lie within the limits established for this sample.
    3. Values on the calibration standard must be within 10% of the known values.

REFERENCE

  1. Kirsten, W. J., 1979. Automated methods for the simultaneous determination of carbon, hydrogen, nitrogen, and sulfur, and sulfur alone in organic and inorganic materials. Anal. Chem. 51:1173-1179.