ELEMENTAL ANALYSIS FOR DUMMIES
E
LEMENTAL
A
NALYSIS
F
OR
D
UMMIES
(for ECS 4010)
).......................................................................................... 2
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I. BASICS
How does the Darn Thing Work? (The non-scientific version)
Here is the basic principle of how this system works.
This EAS system is called a dynamic system because helium is constantly pumping through the machine. Helium is used to keep the gases moving through the machine as combustion occurs and for analysis. It’s an easy, non-corrosive, relatively cheap gas, plus it makes people’s voice sound funny – so it was an optimal choice for this machine.
The sample is dropped from the autosampler ( in fuchsia ) down into the combustion tube ( in red ).
The combustion tube is already heated up by the left furnace, but when the sample is dropped in, oxygen is rushed into the tube and the sample is combusted at an extremely high temperature
(reaching 1600-1800
C). Now that our little sample has been turned into gas, helium gas that is flowing through the entire system moves the combusted sample into the reduction tube ( in peach ).
The reduction tube is filled with chopped up pieces of copper wire. When the gases from our combustion move through this tube, excess oxygen is removed from the gases to avoid messing with our nitrogen readings later on. From here the gases move through a water trap (in
), which absorbs all water from the sample. Then the gases move through the column ( in green ), which is really more of a circular tube (but still called a column to confuse you). The gases move at different rates, which is how they can be analyzed. Nitrogen comes through first creating a peak ( the blue one ) on your computerized chromatogram (the graph on your computer, dummy), then comes your carbon peak ( the brown one ).
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What are these Different Gases For?
Helium: Helium is constantly being pumped through the system. It keeps all the gases moving.
Oxygen: Oxygen is used to combustion. Our samples are wrapped in tin. The tin/oxygen combustion reaction creates the über hot temperatures. Yaow!
Air: Air spurts through the autosampler to rotate it in order to drop samples into the machine.
II. SAMPLE PREPARATION
Before you start throwing samples into the autosampler and firing up the elemental analyzer, make sure to follow the instructions below in order to properly prepare your samples. This ensures that our elemental analyzer is happy and you (or other folks in the lab) won’t have to spend a ton of time troubleshooting or redoing the analysis.
Bypasses and Standards
Before you run your samples, you have to set up the machine by running 2 bypass samples and at least 4 standard samples. Bypass samples or conditioners are 1-2 mg of a typical sample that you will analyze (plant material, soils, etc.). The exact weight of the bypasses isn’t too important so you don’t need to record it. What the sample does is that it allows you to check to see the machine is running smoothly. Also be sure to run 1 quality control sample (it can be either Acetanilide or another known standard) every 10-12 unknown samples.
Standards (e.g. Acetanilide, Orchard Leaves, etc.) are chemicals or compounds with a known concentration of nitrogen and carbon. They’re used to create a calibration curve for the unknown plant or soil samples that you will analyze. The weights of the standards are important since this helps the computer calculate the calibration. The standards should cover a range of weights as well.
This range depends on which standard you’re using and the estimated expected levels of carbon and nitrogen in your plant/soil samples. Please use standards in the small vials in the desiccator – NOT the ones in the bottles in the drawers.
Standard
Acetanilide
Atropine
BBOT
LECO Orchard
Leaves
LECO Soil
%Nitrogen %Carbon
10.36%
4.84%
6.51%
≈51%
≈2%
Range of weights
0.1 to 1.1 mg for analyzing samples with low nitrogen and carbon (like plant litter, stems, and
71.09% soil, etc.)
0.4 to 3 mg for analyzing samples with higher nitrogen and carbon (like plant leaves, peat, etc.)
0.4 to 3 mg for analyzing samples with low
70.56% nitrogen and high carbon (like soil)
72.53%
This also contains 7.44% Sulfur, if of interest
≈2%
Actual content various by lot. Good for plant samples (leaves, stems, roots).
≈0.2%
Actual content varies by lot. Good for soils.
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Drying and Grinding Samples
First, the samples have to be dried, ground, and dried again before weighing them for analysis.
Only a small amount (about 2-4 mg for plant samples, up to 10 mg for soil samples) is needed for analysis so you must make sure that the sample is homogenized and that the amount is representative of the whole sample. Generally, you want to use the smallest amount possible because larger samples will use up the quartz insert more quickly. You should consult your advisor, standard methods, and/or other literature to determine the appropriate drying and splitting methods for your study.
Plant material can be dried in a convection oven and then ground up using a Wiley mill with the finest mesh insert (#1). If you have concerns about sample homogeneity, you can take multiple portions of the original sample for grinding and analysis.
After grinding, the samples should be dried overnight at 60°C an oven. After drying, place samples in desiccators and allow them to cool to room temperature (usually for about 1 hour). Once the samples are cooled, they are ready to be weighed.
Weighing the Samples
Materials: o balance (set to read at microgram level with 3 decimal places = 0.000 mg) o 2 pair of forceps o squirt bottle of ethanol o lab gloves o microspatula o sample containers (lightweight tin capsules) o log book and pen to record sample and standard weights o dried and ground samples o calibration standard in desiccators (Acetanilide = white powder) o well plate for samples o well plate for standards and blanks o sample preparation block o brush
1) Before starting, make sure the area and tools are clean. Put on gloves to avoid crosscontaminating the samples and to avoid contact with the standards. (They can be toxic) Use ethanol to clean microspatula, forceps, and sample preparation block. Use the brush to clean off dirt and particles on balance pan and area inside sliding doors of the balance.
2) Use clean forceps to take out a tin capsule from the plastic container from Costech labeled:
Pressed Tin Capsules, 3.5 x 5mm. These are located in the drawer underneath the elemental analyzer labeled “Elemental Analyzer Supplies.” DO NOT TOUCH capsules, forceps, microspatula, or samples with your fingers.
3) Slide door on the side of balance. Place the empty tin capsule on balance pan, and close the door. Press “Tare” and wait for balance to tare off weight of boat (reading should be 0.000 mg).
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4) Remove the tin capsule from the balance pan, place it on the sample preparation block, and put a small amount (¼-2 scoops) of sample into the capsule. Depending on sample density, this should be about 2 mg. Adjust scoop size and number depending on sample density and desired weight. This takes a bit of practice. If you spill any of the sample material onto the balance or sample preparation block, clean up the area with a brush before proceeding.
5) Put the tin capsule with the sample in it back on the balance to get an idea of the rough weight.
If it is not in range, remove sample and either add or take out sample as needed and repeat step
5.
6) If the weight is in range, remove and place the sample and container on the sample preparation block. Use the forceps to close the capsule top by squeezing the sides together. Grab the capsule on the top at either end, push the ends toward the middle, forming a “Z” shaped fold.
Holding the capsule at the bottom with one set of forceps, fold down the top with the other set of forceps. Form the capsule into a roughly cubical shape by firmly pressing the sides together with one forceps while pressing down on it with the other. Avoid flattening the capsule as this can cause jamming in the autosampler. If the tin capsule is punctured, discard and start over.
7) Place folded and compressed capsule in well plate and record position (well number) in the
Excel spreadsheet (see below for Example of Spreadsheet Layout ). Repeat for all standards and unknowns. During the weighing process, minimize the time of exposure outside the desiccator for all standards and unknowns.
Example of Spreadsheet Layout
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8) When the data entry is completed, save the file into your EAS working folder. You may save a copy of the XLS spreadsheet file (a good idea) and you must save a text version of the data using the Save As… option. Select “Text (Tab Delimited)” as the file type and name your file.
Answer OK to the warnings issued about saving as a text file. This is the file you will import into the EAS system. See below.
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III. MACHINE PREPARATION
Be sure to read the “ EAS Quick Start Guide”
posted on the machine before you start using the elemental analyzer.
The machine has to be in “Work” mode before you can run the analysis. To do this, press the
“work” button on the elemental analyzer and press “enter.” The machine takes a while to warm up so you might want to do this as you do the Machine Preparation procedures.
Before running any samples, all three lights on the top left hand corner of the keypad (“left”,
“right,” and “oven”) must be steady green (not flashing).
Checking for Leaks
Before making any runs, it is of paramount importance to check for leaks! Make sure the machine is in “Work” mode before checking.
Take a cap located in the same compartment on the elemental analyzer as the water trap, and screw it onto the helium vent valve (bottom right on the machine, labeled “V
He
”). Be careful not to screw on the caps too tightly otherwise this will damage the rubber seals inside the caps. Wait 10-15 seconds for the pressure to stabilize then turn the helium gauge down (counter clockwise). If the pressure remains the same for about 30-45 seconds, then there are no leaks. Turn the helium gauge back up until the needle twitches slightly. Unscrew the cap from the vent. IMPORTANT: Be sure to turn the gauge back up before removing the cap.
Remember to place the caps back into the compartment so they don’t get lost!!
If there is a leak, please go to VII. TROUBLESHOOTING .
Entering Data into the Machine
1) Open the EAS Clarity software and log in as a user. Select the method (generally you will leave it as is). Select the Data Table icon to open the data table then select Import from the file menu.
Select the data file you saved as text in the dialog window that appears. The file should preview with your data and column headings as shown. Click Finish to import the data from the file to the data table. See below for clarification.
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2) Alternatively, you may enter data directly into the sample table. The sample table works similar to an Excel spreadsheet. Remember that you must have 2 bypasses and at least 4 standards before each run so enter those into the first 6 rows of the table like so: a) “ Row No.
”: The row number
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b)
“
Sts.
”: The sequence state lets you know if the sample has not yet been analyzed (green), is currently being analyzed (red), or has already been analyzed (blue). c)
“
Run
”: All rows that are checked will be run. This column must be checked before the sample will be analyzed. d)
“
Sample
”: Type in sample names here to keep track e)
“
Weight [mg]
”: All weights must be in milligrams. Remember, the weights of the bypasses don’t matter so you can leave those at 0.0000. The weights of the standards and the unknown samples you are analyzing are important , however, so make sure you enter those in. f) “ File Name ”: All the samples must have a different file name so that the data doesn’t get written over. The “%3r” ensures that each filename has a unique number attached to it. g)
“
Sample type
”: You can leave this as “Unknown” for both bypasses samples and any unknown samples, but it must be set at “Standard” when the entry is a standard so the program knows to use these particular entries to calculate the calibration curve. h)
“
Lvl
”: This only applies to standards. Each standard must have a different level number
(e.g. 1, 2, 3, 4) or else the calibration curve will not be calculated correctly. i) “ Standard Name ”: This only applies to standards as well. Specify a standard name from the dropdown menu when you click on the right corner of the cell. j)
“
Nitrogen [%]
” and “
Carbon [%]
”: The percent nitrogen and carbon should automatically appear as soon as you select a Standard Name.
3) Always remember to save the data table in the AS system when you’re done! You will need to recall it when you run the analysis.
IV. RUNNING THE ANALYSIS
Loading the Autosampler
Remove the clear plastic cover of the autosampler. Using a pair of clean forceps (clean with 70% ethanol), place the samples into the autosampler in the same order that they appear on the sample table file that you just saved. The number you start putting samples in doesn’t
matter. Just make sure that the order of the samples in the autosampler matches the order in the sample table . After you’ve loaded the autosampler, replace the clear cover.
The autosampler can fit 50 samples at once, but you can analyze more than 50 samples in one run by refilling the autosampler between analyses.
Remember to clean the autosampler at the end of the run with an air compressor (next to the elemental analyzer. DO NOT load samples that have been punctured or are leaking. This may allow dirt to get stuck under the autosampler and scratch the Teflon plate.
Checking the Detector Signal
1) Go to the “Data Acquisition” window by clicking on the “Detector Signal” button button.
2) Make sure the baseline mV is above zero:
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3) If the baseline mV is negative, remove the metal covering under the keypad (where the water trap is). There should be a dial labeled “Zero” on the upper right hand corner, below the “Gain” dial.
Turn it clockwise to increase the baseline mV.
Setting the Calibration
Whenever you create a new sample table, a calibration file with the exact same name as the sample table should be created automatically by clicking the “Calibration Window” button or going to the menu bar and selecting Window > Calibration.
After running the standards (see Running the Machine ), you should check the calibration by clicking on the “Nitrogen” and “Carbon” tabs at the bottom. Look at the “Correlation Factor” on the bottom left hand corner of the screen. It should be very close to 1 if the correlation curve is a good fit (i.e. 0.9999). If not, you may need to weight out more standards and run them. Once the calibration curve is calculated and it is a good fit, save the calibration by click on the “Save” button
or by going to the menu bar and selecting File > Save.
Running the Machine
1) After you have loaded the bypasses, standards, samples, you are ready to run the machine.
2) Make sure the elemental analyzer is in “Work” mode, and the lights on the top left hand corner of the key pad (“left”, “right,” and “oven”) are green (and not flashing). Press “remote” and
“enter” and this will allow the elemental analyzer to accept commands from the computer.
3) On the computer, make sure all the samples you want to run have a check mark in the “Run” column of the sample table.
Note: If this is your first time running samples on an elemental analyzer, run bypasses and standards only first to confirm that the instrument is working and the calibration curve is a good fit before running the rest of your samples. First, set the sample stop time to 25 seconds then observe the window for a bright white glow. Once the machine has finished running the bypasses and standards, switch the sample stop time back to 15.
Please ask the lab manager for help on this step!
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4)
Click on the “Run” button
or go to the menu bar and select Sample Table > Run.
5)
When you click on the “Detector Signal” button
, a Data Acquisition window will appear with the chromatogram of the sample being run. The first, smaller peak is nitrogen and the second, larger peak is carbon.
6) After a sample has been analyzed, the “Sts.” Column will turn blue. If you click on the
“Summary Table” tab at the bottom of the Sample Table window, you can see the % nitrogen,
% carbon, and nitrogen-to-carbon ratio. This information can then be copied and pasted into an
Excel spreadsheet.
7) While the samples are being analyzed, you can still save your work. Remember to save often!!
8) After all the samples have been analyzed, you can copy all the information from the “Summary
Table” tab on the Sample Table window to an Excel spreadsheet for further analysis.
Remember to save your sample table file.
9)
To exit “remote” mode, hit “Abort” and “enter”.
Shutting Down the Machine
1) After saving your sample table file and calibration file, you can close the EAS Clarity program.
2) Go to the key pad on the elemental analyzer and press “abort” and “enter” to bring the machine out of “Remote” mode. Then press “St-by” and “enter” to bring the machine to “Stand-by” mode and allow the ovens to cool down.
V. MACHINE MAINTENANCE
(Usually preformed by lab manager or instrumentation specialist)
General
The gas pressure regulators on the gas tanks should be:
Air = 35 psi
He = 40 psi
O
2
= 28-30 psi
The pressure valves on the elemental analyzer should be:
Air = 2 bars
He = 1 bar
O
2
= 1 bar
The flow rates of the gases should be (these should be checked while the machine is in work mode):
Purge = 100 ml/min
He = 100 ml/min or ~20 ml/12s
O
2
= 25-30 ml/min or ~10 ml/20s
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The temperature of the ovens should be (in standby and in work mode):
Left Right GC Oven
Standby
800ºC 450ºC 65ºC
Work
1000ºC 650ºC 65ºC
Note: If the machine will be in standby for several weeks/months, set the temperature for both furnaces lower (~600ºC) to preserve the life of the thermocouple or candleheaters.
The machine parts need to be changed as follows (remember to record how many samples it takes before each part is changed since this may vary):
Quartz insert: after running about 200 samples (fewer if the samples are large)
Combustion columns: after running about 1000 samples
Reduction tube: after running about 800 samples
Water trap: after running 100 moist samples or 300 drier samples
The autosampler should also be cleaned with compressed air after running about 100 samples.
The helium tank may need to be replaced after running about 1200 samples or every 2-3 months.
Changing the Quartz Insert
1)
Make sure the machine is set at “Standby” before changing the quartz insert.
2) Unscrew the top bolt over the combustion tube.
3) Remove the insert by sticking a Sharpie marker into the combustion tube and pulling the insert out. Remember, the bottom of the insert is HOT. Even at “Standby,” the furnace is still at 800
C so handle the insert carefully. Use garden gloves if necessary.
4) Place the insert – the bottom end should have slits – in the metal beaker beside the elemental analyzer, and let it cool. Once it has cooled down to about room temperature, throw out the old insert.
5) Pack some quartz wool at the bottom of the new insert and carefully place it inside the combustion tube.
6) After insert replacement, check that the flow rates of the gases match the ones listed above.
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Changing the Combustion Column
1)
Make sure the machine is set at “Standby” and the gases are turned off (by pressing F3) before changing the combustion column.
2) Carefully remove the used combustion column from the CN Machine.
3) Obtain either a new column, or reuse an old one that has been cleaned.
4) Using a pair of forceps, place a wad of quartz wool into the bottom of the column, taking time to make sure there is no air space between the
2 mm Chromium oxide catalyst on top of
1 cm Quartz wool inside Quartz insert bottom of the wad and the opening of the column.
Use a wooden dowel to gently pack the wool so that it’s roughly 4 cm thick. Not too tightly, as
5) the helium flow needs to be able to pass through the system.
6) Next, pour in the silvered cobaltous oxide (dark blue compound) until they stand approximately 6 cm high.
7) Place a smallwad of quartz wool over the silvered cobaltous oxide and use the wooden dowel to gently pack the wool so that it’s roughly 1 cm thick.
8) Then, pour in the chromium oxide (dark green compound) until they stand approximately 11 cm high.
9) Place a small wad of quartz wool over the chromium oxide, and use the wooden dowel to gently pack the wool so that it’s roughly 1 cm thick.
10) Before placing the quartz insert into the combustion column, place a wad of quartz wool into the bottom of the insert and use a wooden dowel to gently pack the wool so that it’s roughly 1 cm thick. Add 2 mm of chromium oxide to the insert. Gently place the insert into the combustion tube. The top of the insert should be a few millimeters above the top of the combustion tube. Be sure to test that the quartz insert fits inside the column before placing the column in the furnace.
11) Clean off all wool particles from the lip of the column using a Kim wipe, (excess particles will allow air to enter the system). Place an O-ring on the top of the column down about 5-10 mm or
1/4 of an inch from the top. Place the column into the left furace and once it is in position, slide a thermal collar up and hold it in place with an O-ring. Next, place a metal nut up the bottom of the column followed by a washer (inside the nut). Finally, roll an O-ring onto the bottom to hold the nut and washer in place. (See image below.)
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12) Slide the threaded (male) fitting up onto the tube gently seating the quartz tube. Screw the nut hand tight.
Changing the Reduction Column
The procedure for changing the reduction column is similar to the procedure for changing the combustion column except after packing 4 cm of quartz wool, the reduction column has about 40 cm of copper wire shavings and 1 cm of quartz wool at the top. After packing everything in the tube, place the reduction column into the right furnace the same way you would place the combustion column into the left furnace.
Changing the Water Trap
1) Make sure the machine is set at “Standby.”
2) Unscrew the water trap from its holder. Be careful not to lose the silicone seal or the black seal when unscrewing the water trap.
3) Empty out the used magnesium perchlorate, and rinse out the water trap tube.
4) Make sure the water trap is COMPLETELY dried before refilling it. You can do this by oven drying, for example.
5) Seal off the bottom of the tube with a small piece of quartz wool.
6) Carefully use a dry funnel and sprinkle magnesium perchlorate granules into the tube. DO NOT
TO GET ANYTHING WET AND DO NOT INHALE ANY DUST GENERATED FROM
POURING PROCESS.
7) Seal off the tube using another piece of quartz wool.
8) Clean the silicone and black seals for the water trap with a bit of ethanol before placing them on the water trap.
9) Screw the water trap back into its holders.
Cleaning the Autosampler
At the end of a run, the autosampler must be cleaned, especially if the last batch of samples was treated with acid. It is easiest to clean out each slot using compressed air.
Changing the Helium Tank
1) When the helium tank is used up, turn the top valve on the tank clockwise to completely turn off the gas tank. Also turn the open/close dial on the regulator clockwise to seal off the regulator.
2)
Use a wrench (1 1/8”), and loosen the gas regulator from the tank by turning it counterclockwise. (Take the wrench and push up – it is counterclockwise if you look at the gas tank from the valves’ side.)
3) Remember to put the cap over the valve of the old, used tank in order to protect the valve. Keep the tank chained to the wall until it is ready to be picked up. All tanks must be chained to the wall.
4) When the new tank arrives, make sure that it is also chained to the wall before you hook it up to the machine.
5) Remove the valve-protection cap on the new gas tank. Make sure the gas tank is off, and use a wrench to attach the gas regulator to the tank. Tighten the regulator by turning the nut
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clockwise. You can’t use Teflon tape on a gas regulator so make sure the regulator is completely tightened.
6) Open the gas tank by turning the valve counterclockwise. The primary dial (the one on the right) should read about 2500 psi. Check for any leaks between the gas tank and the regulator by putting soapy water in the connection between the tank and the regulator. If the bubbles expand, this means that there is a leak and you must tighten the regulator more.
7) While the open/close valve on the regulator is still closed, turn the increase/decrease dial on the regulator clockwise until the pressure as indicated on the secondary dial (the one on the left) is at 40 psi. To do a second gas regulator leak check, close the top valve on the tank. If there is no leak, the needle on the primary dial should remain at 2500 psi. If there is a leak, tighten the regulator onto the gas tank more.
8) Once the regulator is on the tank properly, turn the open/close valve on the regulator counterclockwise to open it and allow gas to flow to the Elemental Analyzer.
9) Adjust the helium pressure on the machine by turning the top dial until it is at 1 bar.
10) Check if there are any leaks between the gas regulator and the Elemental Analyzer by closing the gas and regulator valve. The helium pressure on the machine should remain at 1 bar. If there is a leak, tighten the connections between the gas regulator and the Elemental Analyzer.
11) Do a regular leak check as described in III. MACHINE PREPARATION and also check the flow rates of the gases (listed at the beginning of this section) with bubble flow meter.
12) Remember to call Environmental Health and Safety (x7-5445) to pick up the empty helium tank.
Elemental Analyzer Logbook
Keep track of when you change/clean the elemental analyzer in the black logbook beside the machine. Also keep track of when you run samples, the type of samples, and how many there are.
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VI. ADVANCED ANALYSES
Increasing the sensitivity of the Elemental Analyzer
For samples with low nitrogen content, there are two ways to increase the sensitivity of the
Elemental Analyzer.
Option one:
1) Weigh out samples that are around 10-12 mg.
2) Increase the gain from 3 to 4 or 5. (The gain can be adjusted by turning the dial at the top righthand corner of the chamber where the water trap is; this amplifies the signal transmitted.)
Option two:
1) Decrease the temperature of the GC column to around 50-55ºC.
2) Make sure the helium flow rate is still at 100 mL/min otherwise the sample will not get enough oxygen.
CO
2
-only or nitrogen-only analyses
For samples with very low nitrogen content compared to carbon dioxide, it may be necessary to analyze nitrogen and carbon dioxide content separately.
1) First, analyze only the nitrogen content.
2) Change the setting on the machine so that it is now on the macro loop. The “M” or macro loop button is on the keypad of the Elemental Analyzer, right beside the “μ” (micro) and “Sμ” (semi-micro) button.
3) Set the gain to 4 or 5. (The gain can be adjusted by turning the dial at the top right-hand corner of the chamber where the water trap is; this amplifies the signal transmitted.)
4) Set the range to high. (The range can be adjusted by flipping the switch below the gain dial from L to H.)
5) Clean out the system by running 5 samples of 1 mg acetanilide.
6) Change the oxygen pressure to 1.5 bar by turning the black dial below the purge valve.
7) Pack the CO
2
trap according to the diagram above.
8) The CO
2
trap inlet should be connected to the water trap using Teflon tubing. The outlet side of the CO
2
trap should be connected back to the machine.
9) Run samples that are no larger than 20 mg.
10) Remember to check the insert more often since the sample size is larger.
11) After running all the samples for N analysis, change the settings so that the machine can analyze the carbon dioxide content. Remember to take out the CO
2
, set the machine back to semi-micro loop (Sμ), set the gain back to 3, and set the range back to low.
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12) Weigh out samples of the same material again, but decrease the sample weight to 3-4 mg. This should reduce the nitrogen signal but provide enough carbon dioxide for analyzing the carbon content.
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VII. TROUBLESHOOTING
How to fix a leak
If the pressure level on the helium falls after the gauge is turned, then there is a leak in the system.
In order to fix this, go through the following checklist:
Are the connectors on the combustion column, reduction column, and water trap tightened?
If not, unscrew and re-tighten the connectors.
Do the o-rings on the combustion column, reduction column, and/or water trap need to be cleaned? If they do, remove them, clean them with a bit ethanol and put them back in place.
Do the o-rings on the combustion column, reduction column, and/or water trap need to be changed? If they do, put the old o-ring aside in a bag for old o-rings. Take a new o-ring, clean it with ethanol and put it back in place.
Missing peaks when running the standards
Occasionally, the Elemental Analysis Software may not be able to recognize peaks in the chromatogram of the standards so they must be entered in manually.
1) Go to the Calibration window , and click on the “General” tab.
2) Depending on which standard is missing, change the level to the appropriate number. For example, if this was the first standard that was run, change the level to 1. If this was the second standard, the level should be 2 and so on. (See image below.)
3) Go to File > Open Standard to open the chromatogram that corresponds with the standard that is missing its peak.
4)
Click on the “Add Peak” button
. Two vertical lines will show up on the chromatogram.
Move them to the appropriate peak and click on it to add the peak.
5)
If there is more than one peak missing, click on the “All Peaks” button, and the program will recognize all peaks shown.
6) If the computer still can’t recognize the peak, change the retention time (“Reten. Time”) to match the retention time of the chromatogram. Or you can also change the “Left Window” or
“Right Window”.
Please ask one of the technicians in the lab for help on this step!
7) If the missing peak is from a unknown sample, please see the next section.
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Missing peak when running unknown samples
1) Go to the chromatogram window
, and click on the “Integration” tab.
2)
Change the “Threshold” value to 0.2, and the computer should be able to recognize the peaks.
If this doesn’t work, you can try decreasing the value, or change the value for “Peak Width”.
Note that “threshold” refers to the slope that is recognized.
3) Save to update the table.
4) If the missing peak is from a standard, please see the previous section.
Combustion Tube or Quartz Insert
If there is a problem in the results, it is probably your insert or your combustion tube (more likely the insert). After running about 200 samples, the insert could accumulate a lot of combusted material that could mess up the analysis. Change the insert by following the instructions in V.
MACHINE MAINTENANCE . Remember to check the flow rates of gases after changing the insert as well!!
Reduction Tube
If the reduction tube is not working, oxygen will be getting into your results. The nitrogen peak will start to get substantially larger over 2-3 samples. Replace the reduction tube. After the tube replacement, test the flow rates of the gases.
Water Trap
If the water trap fails, the baseline will drift up slowly over time. (See image below.) Empty the used up magnesium perchlorate and quartz wool, wash out the tube, pack it again, and reuse it.
If a Sample is Caught in the Autosampler, What Do You Do?
Reverse the blue tubing on the left side of the autosampler. This will pneumatically push the piston forward. Take the main pin out from the left side of the autosampler. Remove the 3 screws from the front plate of the autosampler. Use a kimwipe to clean out the piston. Re-lube the black plastic
O-ring on the front piston with a tiny amount of silicone vacuum grease. Put everything back and change the blue tubing back to the way it was before.
Any other problems, call Bruno at Costech!
Bruno Lavettre ( bruno@costechanalytical.com
) or Sandy (available from 12 – 3 pm EST)
(661) 297-2395
Whatever you do, don’t turn off the machine and for the love of god, don’t use a wrench on it!!
Last updated: 5/03/2010
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