CRDS Water Isotope Analysis - δD δ18O
Dr DeSoto is a Picarro L2120i liquid water cavity ring-down spectroscopy (CRDS) laser. dD and d18O of water are derived from absorption of specific spectral lines in the near-infrared range. Water vapor is introduced into an optical measurement cavity with an effective path length of up to 20 kilometers. We have two other Picarro liquid water isotope analyzers, Gorky, a L1102i that also measures dD and d18O and Phoenix, a L2140i that measures dD, d18O, and d17O.
Currently, each injection takes approximately 8 minutes and 30 seconds. A full tray of 54 vials with 10 injections each, then, will take about 3 days and 5 hours.
Users use be careful with syringe needles and vials. If either of these items are no longer useful (i.e. broken), they must be discarded into the broken glass container. The vaporizer is 110 *C and the septum nut can be hot to the touch.
- Clean up previous run – Close Coordinator, empty the existing tray, throw caps in trash, discard water down sink, vials go in beaker in drying oven.
- Load new waters - load 200 uL of water into 300 uL fused insert vials
- Take notes - Write the tray description and any other notes in the notebook while loading waters into vials.
- Prepare autosampler - Put vials in tray, clean syringe, modify job, don’t change the septum yet
- Fill out the daily log (DrDeSoto_DailyLog.ods)
- Start Run – open Coordinator Launcher, select High Precision, Start Autosampler, click Change Septum, wait for first injection to complete
- Take more notes – write down time and date of run start, what you did with the syringe, septum etc.
- Change Septum – when coordinator indicates the first injection is complete, press “Septum Changed” when done
- File management – make sure a directory has been created on the server for these samples (e.g. S:\data\projects\...).
- Tray Description – create tray description file in newly created folder, use excel, save as yymmdd_TrayDescription.csv
- Data - use matlab and the gorky script to reduce data from DeSoto
Clean up previous run
Close the Coordinator...be patient, it will close eventually. Remove vials from the previous run and take them to the wet lab. Open each vial, throw caps in trash, and discard the water down the sink. If the vials contained dirty or salty samples, they must be soaked in DI water. You will likely have to pipette DI water into each vial. Once vials are clean, gently place vials in beaker and put them into the drying oven.
If the instrument was not previously running AND the water backgrounds are currently in the 10,000 to 20,000 range, the valve on the back of the vaporizer is allowing room air to flow into the instrument. Rotate the valve 180° to allow dry air to flow into the instrument. You should see the water backgrounds begin to drop. Ideally, the water background is below 100 ppm before you start.
Load new waters
Load 200 uL of water into 300 uL fused insert vials. Use the pipette, pipette tips, and trays in 303B drawers labeled ‘Laser’. Vials are located on the lab bench above these drawers. Should you wish to load 1 mL of water, old vials are located in a drawer labeled ‘Laser – extras’. Use one full tray of dry clean pipette tips and also have one empty pipette tray available. For each distinct water, use a clean dry pipette tip, discarding the wet tips into the tray that started out empty. In this way, you will have one pipette tip tray with dry clean tips and one tray to receive the wet tips. If the pipette itself becomes wet, either on the inside or outside, ensure it is dry before proceeding. Use wipes or paper towels and / or compressed air to dry it out. Make sure the caps are just tight enough but not too tight. If the cap septum is overly concave, it is too tight. Put all standard waters and all sample waters back in the refrigerator when loading is complete. Put the wet pipette tip tray in the drying oven. As you are loading waters, write the water type or sample ID in the notebook.
Write the date, your name, sample set id, and the complete tray description as well as any other notes you desire in the notebook (Dr DeSoto) while loading waters into vials.
Place the tray of samples and standards onto the tray-holder into either the rear or front position. Make certain the tray is properly seated in one of these two positions. Visually check the caps one last time; no cap should be overly concave.
Modify the autosampler job according to your current number of vials and your preferred number of injections per vial. From the home screen on autosampler controller, turn the wheel to highlight the appropriate job and center click. 'First' should be 1, 'Last' should be the last vial in your tray (e.g. 54), 'Increment' should be 1, 'Count' should be the number of injections per vial you wish to have (e.g. 10). To change any of these values, rotate the wheel until the value is highlighted, center click, and turn the wheel to edit the number. Center click again when you are done editing. Press 'Home' (the F4 button) when you are finished editing the job.
The lab uses a daily log for each instrument or preparation line to allow users a first glance at the readiness of the instrument. By comparing the current state of the instrument to historical states, you are more informed about the instrument and whether or not it is functioning properly and ready to run your samples.
Each daily log is web based and browser accessible. No link is provided here by design. Open the browser on the controlling computer and you should see at least two tabs already open. One tab is this SOP and the other is the daily log. If the browser has more than two tabs open, it may have additional SOPs. Use the bookmark toolbar as needed if tabs have been closed.
Work through each cell of the daily log. If you are uncertain where to find certain information, hover over the column header tip, denoted by a question mark (?).
Make certain to press the 'save to log' button when you are finished entering data.
You are welcome to make notes if you have observed something with or done something to the instrument and would like to document that information. Use the "insert note" link at the top of the daily log to make a note. You may enter notes at any time.
Open the Coordinator Launcher, select High Precision or High Throughput, Start Autosampler (F4 from Home screen). Assuming you are running only one tray, rotate wheel until 'selected' is highlighted and center click. If you have two trays, select 'All' with a center click. Click "Change Septum" (upper right corner of Coordinator window) and wait for first injection to complete.
While waiting for Dr DeSoto to be ready to have its septum changed, type in tray description, use C:\DrDeSoto\TrayDescriptions\_Rear_TrayDescription.csv (or *\_Front_* if you are loading a tray for the front position) and save it as yymmdd_TrayDescription.csv.
Load Sample Description by clicking ‘Load Sample Descriptions’ in the Coordinator software and then browse to the tray description you just typed in (c:\DrDeSoto\TrayDescriptions\). Note the software expects you to enter two tray descriptions, one for the front tray and one for the rear tray. The first window prompt is for the front tray ("frnt") and the second window prompt is for the rear tray ("rear"). If you have two tray descriptions, great, otherwise, you can cancel the "frnt" window prompt, then select your rear tray description when prompted.
Change Vaporizer Septum
After the first injection is complete the coordinator will indicate when its appropriate to change the septum. Remove the magnetic cover and use the slotted wrench side of this cover to loosen the nut. Remove the nut with your fingers taking care as it is hot. The septum should be stuck inside the nut. Use the large-gauge needle that is in the syringe cleaning kit to extract the septum. Discard the old septum into the trash. Place the new septum into swage-lok nut using the blunt end of large-gauge needle. Place the nut back onto the vaporizer taking care not the allow the septum to fall out when you turn the nut over. Hand tighten the nut; you should feel the nut bottom out. Press “Septum Changed” which is the same button you pushed to begin changing septum in Coordinator window.
Take more notes
Write down the time and date of run start. This is essential as files are named within the instrument based on time. Also write down what you did with the syringe, the septum, etc.
Make sure a directory on the server has been created (e.g. S:\Data\projects\[YOUR PROJECT]\) and then create ‘raw’, ‘reduced’, and 'traydescriptions' folders within there. Copy the data from C:\IsotopeData\ to the 'raw' folder. Your file will have the date and time you started it as part of the filename (e.g. HBDS2213_IsoWater_20160223_151837.csv) where HBDS2213 is the instrument serial number and the time is so lovingly put in GMT, thanks Picarro. Also copy the TrayDescription file you created on DeSoto to the 'traydescriptions' folder.
Type 'gorky' into matlab command prompt. Browse to raw file you just transferred from DeSoto and open it / select it. Follow prompts in matlab. In the end, a reduced txt file is created
- The syringe has died - You come in to find the syringe mangled while the autosampler and instrument continue to run. Scroll up in the upper Coordinator window to find where the injections stopped work and note that vial number. Close the Coordinator. Replace the syringe with a new one. Discard dead syringe into broken glass. Modify the autosampler job to start on the vial you noted above. Start the instrument as normal but don't worry about changing the septum.
- The water background is way to high - Check the valve on the back of the vaporizer to ensure it is pointing towards dry air (see photo at top of this page.)