Transcript
Astrid M. Mueller
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Dynamic Light Scattering (DLS) Room BI-018D GLA: Edgardo Garcia,
[email protected], x2713 Remarks: • Centrifuged Toluene is the instrument standard. • All solvents should be centrifuged; MilliQ water and filtered solvents are OK too • There should be a ~30min warm-up period between switching on the 3 boxes and the first measurement, which is usually given until everything is aligned and prepared. Turn-on and Measurement Procedure: 1) Reserve instrument time on the MMRC website. 2) Sign the Composition Book logbook (date, name, experiment, angle). 3) Turn on the cooler (Make sure water pump has the required amount of water. 4) Turn on the detector (PD4043). 5) Turn on the box under the monitor. 6) Log onto the computer as DLS, pwd: bi018d. The computer is usually on. 7) Open the software PrecisionElucidate. 8) Click on Measurement -> System Defaults Shutter 1: 90° (variable), if different change the angle. Hardware: PD4043 (stays) Intensity control: 20% (Unchangeable) Limit: 6 millions photons / sec (Unchangeable) Temperature control: enabled, 25°C (room temperature is default). 9) Wear gloves, open the instrument. 10) Put the detector into the 90°position if it isn't there yet. This means that you need to unbolt the two screws with an Allen wrench at the bottom platform of the detector head, move the detector head assembly to the 90° position, set it down so that the aligning pins fit into the holes, and bolt it down tightening the screws very symmetrically, i.e. tighten one bolt lightly, then the other and go back and forth until the detector head assembly is bolted down tightly. 11) Put ~5 drops of toluene into the center hole of the xy-translation stage. 12) Take a disposable glass test tube from the box in the DLS instrument, try if it fits into the center hole of the xy-translation stage. If it doesn't fit, open the setscrew (allen key) on the side of the xy-translation stage slightly until the test tube slides in. 13) Fill your sample into the test tube so that the liquid fills ~75% of the test tube. 14) Clean the outside of the test tube with a Kimwipe. 15) Mount the test tube in the center hole of the xy-translation stage. Put it carefully all the way into the hole so that it touches the bottom, pull it ~1/2 cm up and tighten the setscrew carefully so that the test tube is held in place. Beware that you do not break the test tube by over-tightening the setscrew. If you break the test tube, call Edgardo. 16) In the software PrecisionElucidate at Measurement -> System Defaults click on Laser enable √ Alignment laser enable √ Dim the room lights, then you should see the red laser light scattering off the test tube. 17) Align the position of the test tube with the two knobs on the xy-translation stage so that the laser beams are centered on the two 1/2" mirrors (use a white card to identify the laser and centering it on the mirrors); you will see a round laser spot on mirror 1, and a more
Astrid M. Mueller
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horizontal-line shaped spot on mirror 2. mirror 2
mirror 1
laser sample
18) Place the black round plastic lid on the sample mount. 19) Close the instrument, take off your gloves. 20) Turn the Alignment laser off in the software (Measurement -> System Defaults) 21) You should see an intensity not higher than 6x106 photons/sec. It it’s higher dilute your sample until is lower than the 6x106 photons/sec. ~2x106 photons seconds works great! If it is below 105 photons/sec align better or increase the laser power slightly; the laser power setting depends on the scattering efficiency of your sample. Larger particles (1 um in diameter) scatter a >90 degree angles. Larger particles may require a laser power setting of ~1% and smaller ones ~75% or even higher. Small particles (~2-50 nm) require the detector to be at <90 degree angles. Click OK to exit. 22) Click on Measurement -> Start Experiment 23) Browse until you find your folder under DLSusers, type in a file name and fill in all sample information 24) The default setting for the refractive index and viscosity is for water. If you measure your particles in a different solvent you need to type in the correct values. 25) The laser wavelength default setting is at 658nm, don't change it. 26) Set the scattering angle at 90° (or whatever position the detector head assembly is placed at) 27) Set the (thermal) equilibration time at 300s (is sufficient for most temperatures) 28) Set the runtime at 2 29) The number of accumulations and experiment repetitions determine the signal-to-noise ratio in your data. For initial screening of particle size, use 10 repetitions and ~60 accumulations, this gives you 10 output files that are automatically saved as your filename with a number at the end. Once you know from roughly analyzing your data which peaks are real, take data with 500 accumulations and 2 experiment repetitions. 30) Press start. You should see four windows. You can change the axis scaling with a right-click on the respective axis. Exponential decay indicates good data
Detection A Black fit should follow green data points
Instrument status log Shows when laser is on (in red), intensity etc.
Detection B (= A)
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31) While the experiment acquires the second experiment repetition, you can start looking at your data with the software PDI. 32) Open PDI. Click File -> Open ->
-> select files -> Open You should see 3 windows. To generate an output file select a peak by dragging the mouse cursor from right to left over the desired peak and click from the menu File -> Print -> Preview Then write the diameters and abundances into your lab book. You may need to do statistics with the results.
data, fit (red and black) fit residue (green)
abundance vs. diameter histogram
Even if the fit appears to match the data reasonably well you may see a peak at 0.01nm that is a fit artifact and not real. Delete it by right-clicking to the right of the peak (you do not want this artifact peak to contribute to your abundance results); right-clicking to the left of a peak makes it reappear again. Whenever you have reason to believe that a displayed peak is not real you should delete it to get proper abundance vs. diameter results. Also, temporarily deleting large peaks provides you with a means to "zoom into" the smaller ones and get more precise values for their abundance. 33) Check that you get real abundance values by enabling MW normalization, which accounts for the fact that larger particles have higher scattering efficiencies than smaller ones. In the PDI program click Setup -> Data View: Choose Distribution over Diameter Show 4 or 5 decades Click MW normalization √ 34) If you do not know what size particles your sample contains, start with a scattering angle at 90°. Depending on particle size you can increase the resolution of the instrument by changing the detector head assembly position and the value in the software. As a rule of thumb, small particles (~1nm) should be measured at ~25-40°, medium particles (~20-50nm) at ~60-75°, and large µm-sized particles at ~120-130°. Shutdown Procedure: 1) Close the PDI program 2) In the software PrecisionElucidate at Measurement -> System Defaults click on Laser enable off 3) Close the software PrecisionElucidate 4) Log off from the computer 5) Turn off the box under the monitor 6) Turn off the detector (PD4043)
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7) Turn off the cooler 8) Wearing gloves, take your sample out and leave the empty test tube upside down in the orange rack with other used test tubes on the lab bench
