The purpose of today's lab work is to:
- Remake the AuNP fiber solutions that failed to produce fibers yesterday
- Practice making buffers by making a Tris and a phosphate buffer
We followed the protocol that Dr. Hartings left in his lab notebook for today.
- Our 5mL AuNP fibers from yesterday were successful, so we did not remake these. However, our 1mL solutions were unsuccessful, so we remade all 16 of these samples.
- We then made our Tris buffer:
- We used the | science gateway calculator to determine how much dry Tris we needed for 500mL of a 10mM solution
- In the calculator, we checked off the Tris option from the list of common reagents in order to enter in the molecular weight of Tris
- We then entered in the volume (500mL) and the concentration (0.010M)
- The calculator gave us the result of 0.6057g of Tris needed
- We measured out 0.5079g Tris and diluted it in HPLC water to a final volume of 500mL using a 500mL volumetric flask
- Next, we made our phosphate buffer:
- We used the | phosphate buffer calculator to determine how much dry monosodium phosphate and disodium phosphate were needed to make 500mL of a 10mM solution of phosphate with a pH of 7
- We entered 7.0 for the pH and 10.0mM for the buffer strength
- We entered the molecular weight of monosodium phosphate as 174.18D and disodium phosphate as 137.99D
- The calculator gave us the result of needing 1.00518g/L of monosodium phosphate and 0.58357g/L of disodium phosphate
- Since we only needed 500mL, or 0.5L, of the phosphate buffer, we divided 1.00518g by two in order to determine the mass of monosodium phosphate needed for our buffer. We did the same for disodium phosphate. Our results were 0.52059g for the monosodium phosphate and 0.291785g for the disodium phosphate.
- We measured out the monosodium and disodium phosphates and diluted both in HPLC water to a total volume of 500mL in one 500mL volumetric flask.
- Note: I did not make note of the exact mass of each phosphate that was actually weighed out
- We calibrated our pH probe by using ph=4, 7, and 10 standards. The pH probe was rinsed with HPLC water in between each standard.
- We then measured the pH of our Tris buffer. The buffer was initially too basic, so we adjusted the pH to 9.04 by adding HCl.
- Next, we measured the pH pf our phosphate buffer. The pH was 7.4, indicating that the buffer was close, but not exactly, what we were aiming for. In order to adjust the pH of this buffer, we would have had to add more monosodium phosphate, which would have changed the conductivity of the buffer. We decided against doing this as the pH was close to the target of 7.0.
- We then measured the conductivity of our Tris buffer using the conductivity probe. The conductivity of the buffer was 281.2µS/cm.
- Finally, we measured the conductivity of our phosphate buffer. The conductivity was 1655µS/cm.
Data and Results
Half of our 1mL AuNP fiber syntheses were successful in forming fibers. Interestingly, there seemed to be a physical divide between the half that formed fibers and the half that did not. All 16 samples were in the same test tube holder in the oven; the tubes on the left half of the rack were successful in forming fibers, while the tubes on the right half of the rack failed.
A description of the buffers that we made is below. The buffers were not perfect, but they were reasonably close to the target pH and conductivity.
- Mass of Tris used: 0.5079g
- Molarity: 10mM
- Final volume: 500mL
- Final pH: 9.05
- Conductivity: 281.2µS/cm
- Mass of monosodium phosphate used: about 0.5206g
- Mass of disodium phosphate used: about 0.2918g
- Molarity: 10mM
- Final volume: 500mL
- Final pH: 7.4
- Conductivity: 1655µS/cm
Matt Hartings What were the results of your syntheses?