Embedded Files
PROCEDURAL VIDEOS TO WATCH:
PROCEDURAL VIDEOS TO WATCH:
REQUIRED CHEMICALS (FOUND ON SHELF UNLESS OTHERWISE NOTED):
REQUIRED CHEMICALS (FOUND ON SHELF UNLESS OTHERWISE NOTED):
REQUIRED VOLUMETRIC GLASSWARE:
REQUIRED VOLUMETRIC GLASSWARE:
100-mL volumetric flasks (5)
50-mL volumetric flasks (5)
25-mL volumetric flasks (4)
10-mL glass pipets (4)
5-mL glass pipets (3)
2-mL glass pipet (1)
SPECIAL EQUIPMENT (FOUND ON SHELF UNLESS OTHERWISE NOTED):
SPECIAL EQUIPMENT (FOUND ON SHELF UNLESS OTHERWISE NOTED):
MARSXpress vessels for microwave digestion (4; on the MARS6 cart)
Carrying rack for Xpress vessels (on the MARS6 cart)
PROCEDURE:
PROCEDURE:
A. Preparation of Steel Samples (NOTE: The MARS 6 microwave oven requires a minimum of eight samples for a single digestion run, but can hold any even number of samples up to 24. You will only be preparing four separate steel samples for analysis. So you must either load your samples with those of one or more other groups, or prepare your cereal samples for the AA lab at the same time as your steel samples since the cereal and steel samples require the same digestion procedure. You can store the digested cereal samples until you are ready to complete that experiment at a later date.)
The steel samples will be digested in Teflon-lined MARSXpress vessels. The components of these vessels are shown in the figure below. Obtain four clean, dry Xpress vessels, stoppers, and caps, along with a tightening tool and a carrying rack.
2. Use an analytical balance to accurately weigh ~0.12 g of steel powder into an Xpress vessel using a plastic weighing funnel (found in the container above the balances) and the "weighing by difference" method shown in this video. Record the mass of steel and repeat for three more steel samples - each in a separate Xpress vessel. Place the vessels in the carrying rack, using the markings on the carrying rack to keep track of the vessels. (Don't write on the Xpress vessels themselves.)
3. Take the carrying rack to a fume hood. In the hood, use a 10-mL graduated cylinder to carefully add ~10 mL of concentrated HNO3 (trace-metal grade) into each of the Xpress vessels. Make sure that all of the steel powder is at the bottom of the vessels since anything stuck to the sides may "superheat" and cause permanent damage to the vessel.
4. For each vessel, insert a tapered stopper (with the tapered end down so that it fits securely), screw on the cap, and tighten using the tightening tool. Make sure the tool is seeded all the way down on the cap, then turn the tool until you hear the click. This ensures that the cap is sealed to the correct tightness. (VIDEO) Place each vessel back in its original location in the carrying rack.
5. Take the carrying rack with all four samples to the MARS6.
6. Open the oven door and remove the turntable. Place each of the vessels into the turntable using the proper configuration. Use the diagram below to load your samples. Make sure all vessels are placed into the Kevlar tubes and that each vessel is pushed all the way down. (VIDEO)
7. Turn on the power to the MARS 6. (The power switch is located on the lower right-hand side of the instrument toward the rear.) It will take 1-2 minutes to boot up. Make sure the vent tube from the back of the MARS 6 is secured under the glass sash of the fume hood and that the fume hood is turned on and running. (VIDEO)
8. Carefully lift the turntable and place it inside the MARS 6 in the proper orientation (with the Xpress logo facing you). The turntable should be locked in place and not able to rotate freely. Close the door and make sure the handle is securely latched. (VIDEO)
9. When the instrument is ready, the display screen will give you two options. Choose the "One-Touch" button. Scroll down the list of methods and find the method called Chem 330. To look at information about the method, hold your finger on the icon for a few seconds. A bar will appear in the upper right-hand corner. Press the lower case "i" to display information.
10. To run the method, simply touch the Chem 330 icon. To start the digestion, press the "Start" button in the lower right-hand corner of the screen. While your samples are running, you can monitor the temperature and time (and other parameters) by clicking on the different graphs on the display screen. The entire process will take ~45 minutes to complete.
11. While your samples are running, begin parts B and C below. (You'll need the solution from part B to dilute your samples when the digestion is complete.)
12. When the digestion is complete, open the microwave door. Remover the turntable and place it on the lab bench. Making sure to grab the individual Xpress vessels by the top, place each of them back in the carrier in their original location and take them back to the analytical lab.
13. Take the vessels to the hood and put on gloves. Bring a squirt bottle of ultrapure water and a beaker of ultrapure water to the hood as well. The contents of the vessels are under high pressure, so open each vessel by pointing it away from you INTO THE HOOD and using the tightening tool to remove the cap. You should hear the depressurization as you open each vessel. Quantitatively transfer the contents of each vessel into separate (labeled 1-4) 100-mL volumetric flasks, dilute each to the mark with ultrapure water, and mix well. You'll probably see some solution on the stoppers, so you'll want to use tongs to rinse them into the flask. (WATCH THIS VIDEO!! Note the video doesn't show the flasks being mixed, but be sure to invert the flask 20-30 times to mix the solution.)
14. Obtain four 50-mL volumetric flasks and label them 1, 2, 3, and 4. Using separate 10-mL glass pipets, accurately transfer 10-mL of steel samples 1-4 into the corresponding 50-mL flask. Dilute each 50-mL flask to the mark with the 2% HNO3 created in part B below. These are your sample solutions.
15. Wash the Xpress vessels with soap and water, rinse 2-3 times with DI water, and leave them to dry.
Sample Prep Summary
B. Preparation of of 2% HNO3 Solution
1. Obtain a 1-L plastic bottle and cap from your lab drawer and label the bottle "2% HNO3". Fill it approximately 3/4 full with ultrapure water.
2. In the hood, use a graduated cylinder to carefully measure 20 mL of trace-metal grade concentrated nitric acid (HNO3). Slowly add this to the water in the plastic bottle, and swirl gently to mix.
3. Fill the bottle to the fill line with ultrapure water as shown in the figure below. Screw the cap on tight, and shake to mix. You will use this solution for many of the sample dilutions outlined below.
C. Preparation of Standard Solutions
1. Using two clean 5-mL glass pipets, pipet 5 mL of the 1000 µg/mL Mn standard solution and 5 mL of the 1000 µg/mL Ni standard solution into a single clean 100-mL volumetric flask and dilute to the mark with the 2% HNO3 you created in part B. Then pipet 5 mL of this solution into a clean 50-mL volumetric flask and dilute with 2% HNO3 and invert 20-30 times to mix well. This is your standard stock solution.
2. Obtain four clean 25-mL volumetric flasks and label them 1-4. Using a single 2-mL glass pipet, add 2 mL, 4 mL, 6 mL, and 8 mL of standard stock solution into flasks 1-4, respectively. Dilute to the mark with the 2% HNO3 created in part B and invert 20-30 times to mix well. These are now your standard solutions.
3. You are now ready to perform the ICP analysis, but it is important that you first calculate the Mn and Ni concentrations (in mg/L) in each of your four standard solutions since you'll need to enter these values in the instrument software. Show these calculated values to me or a TA before continuing.
Standard Prep Summary
D. Instrument Preparation
1. Bring all eight of your volumetric flasks (your four standards plus your four sample solutions) to the ICP instrument. You’ll also need to bring the remainder of your 2% HNO3 solution (in a 250-mL Erlenmeyer flask) to use as the blank. Bring a second 250-mL Erlenmeyer flask filled with 200 mL of RO water to use as a rinse solution. (Be sure to label the flasks so you don’t mix them up.)
2. Check the argon gas cylinder. (WATCH THIS VIDEO) The main valve on the tank should be open (turned all the way counterclockwise) and the small black valve should be open as well. Check the tank pressure. It should be above 200 psi or you'll be in danger of running out of argon in the middle of your analysis. (Let me know if the tank pressure is too low.) The argon regulator pressure should in the range of 80 psi. (Again, let me know if it is not.)
3. Attach the tubes of the peristaltic pump on the ICP by stretching the tubing so that the tabs fit into the slots on the holders as shown below. The pump spins in a clockwise direction. One of the tubes must draw sample into the instrument, and the other sucks excess sample out of the instrument and out to waste. Once this is set up correctly, flip the pressure bars up so they rest against the tubing, then clamp them down. (WATCH THIS VIDEO). CHECK WITH ME OR A TA TO MAKE SURE YOU'VE DONE THIS CORRECTLY BEFORE PROCEEDING!
4. Make sure the ICP instrument power is turned on. The green LED indicator should be lit.
5. Log on to the instrument with USERNAME: CHM4499\chemstu and PASSWORD: C6H12O6.
6. Open the ICP Expert II software by clicking on the desktop icon.
7. Place the input tube (see diagram in the introduction) into your flask of RO water. Start the water flow through the tubing by clicking the Pump Fast button from the menu bar.
8. Watch the bubbles coming from the nebulizer through the drain tube and make sure they move smoothly with no jerky motion. (If needed, adjust the tension on the pressure bars by turning the knobs on the back of the pressure clamps to create an even flow of liquid.) (VIDEO) Now click the Pump Off button to stop the water flow.
9. Make sure the exhaust fan switch under the instrument is in the "ON" position (pushed away from you as in the image below). Hold a Kim-wipe under the exhaust hood above the instrument to make sure the hood is operating correctly.
10. Turn on the cooling unit behind the computer. (The power switch is on the back.) The plasma torch will not light if the cooling unit is not on.
E. Setting up the Software
Click the Worksheet icon to begin creating your method, then select New. Select a file path for your worksheet (C:\Data\), then enter a name for the worksheet and click Ok.
2. When the worksheet opens up, you’ll notice three tabs at the top: Method, Sequence, and Analysis. You’ll want to begin developing your method under the Method tab. Click the Edit Method button on the left. The Method Editor screen will appear (shown below). This screen has four tabs: Element, Conditions, Standards and Notes. You will start in the Element tab.
3. Select the elements Ni and Mn (not Mg) by clicking on each symbol on the periodic table. Your editor screen should now look like the image below.
4. Go to the Conditions tab and replicate the values shown in the figure below. (You may only have to change the Replicate read time and the Instrument stabilization time.)
5. Now move to the Standards tab (shown below). Enter the number of standards (4) in the No of standards box. Next you will enter the concentrations of each element in your standards (in mg/L). Be sure to change the units to mg/L by clicking on the Units box. Finally, change the max % error for all elements to 20%.
6. At this point you have finished creating your method (the Conditions and Notes tabs remain unchanged). Go to File and Save your method, then Exit the Method Editor box.
7. Now you are ready to edit your sequence, so click the Sequence tab from the top of the worksheet screen. Check the Manual button for the Sample Source.
8. Click the Sequence Editor button on the right. The following screen will appear. All you need to do is change the Sample count to 4, make sure the other settings are the same as in the image below, and click Ok.
F. Acquiring the Data
Click the Analysis tab.
Make sure the door to the torch compartment on the instrument is closed and that the sample tube is in the acid solution.
Now it is time to start the plasma. Click the Plasma On button on the computer screen (see below). While the plasma is igniting make sure you or your partner is watching the plasma compartment while keeping a finger on the plasma kill switch (see picture in step D4 above). It should take 30-60 seconds to ignite the plasma. Warning: Be ready to press the kill switch in case the plasma tries but fails to light (you'll hear a popping sound). (VIDEO)
4. Allow the plasma to run for ~10 min before starting the analysis.
5. After 10 min, press the Start Analysis button which should now be green.
6. You should be prompted to "Present" the blank solution. With the sample tube in the 2% HNO3 solution, click the button to begin measuring the blank.
7. Now follow the instructions as they appear on the screen, making sure to wipe off the sample tube before putting it into a new solution. You can follow the process on the computer screen. Pay close attention to the spectra (as in the image below). These are the emission peaks measured for each element. First, note how small the x-axis is. Each measurement is made three times, so you should see an almost perfect overlap of each of the three spectra. Also notice that you can see the calibration curve as each point is added by clicking on the line icon. If anything looks strange, make sure to check with me or a TA.
8. Once the entire run is complete, turn off the plasma by clicking the Plasma Off button shown below.
9. Under the File menu, click Report Settings... and configure the window to look like the following:
10. Print your report by again going to the File menu, clicking Print..., choosing CutePDF Writer as your printer, and clicking OK. Save the printed pdf file to a flash drive, take it to networked computer, and upload it to the Data section of your LabArchives notebook.
11. Show me your data before shutting down the instrument.
G. Shutting Down the Instrument
Place the sample tube in the DI water and click the Pump Fast button. Allow water to be pumped through the system for 1-2 min.
Lift the sample tube out of the DI water and allow the pump to pump air until there is almost no liquid emerging from the nebulizer to the waste container. Then click the Pump Off button.
Close all windows and exit the software.
Unclamp the pressure bars on the ICP peristaltic pump and unhook the tubing. (Leaving the tubing stretched over the rollers will cause them to permanently deform).
Turn off the cooling unit.
H. Waste Disposal / Clean Up
Collect all unused solutions, including leftover standard solution, in a single container (I recommend a large Erlenmeyer flask). Put the container on a stir plate and drop a magnetic stir bar in the solution. Add ~2 mL of universal indicator and begin stirring, then neutralize the solution with sodium carbonate or sodium hydroxide (found in the hood) until the color is green or yellow. Pour the solution down the drain to dispose.
Rinse any used sample or standard containers and place them in the labeled bin in the prep hood.
Place all used pipets in the "Pipets to Be Washed" bin.
Rinse all volumetric flasks 5-6 times with tap water and then 2-3 times with RO water, and return to the shelf. (Use acetone to wash off any markings.) Similarly rinse all glassware from your drawer and return it to your drawer.
Use the sponge in your drawer to clean your bench area.
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