Micro ph combination electrode

Stock solutions of peptide was prepared by dissolving the peptide at 12 (or 22) wt% R 3 L 12 in hexafluoroisopropanol (HFIP), because R 3 L 12 is a highly hydrophobic peptide. An aliquot 1 ml of 12 (or 22) wt% R 3 L 12 in HFIP was added to 15 ml of ultrapure water (ThermoFisher Barnstead) inside a 1.5 ml Eppendorf. The Eppendorf was then vigorously vortexed while adding 2 Â 145 ml of ultrapure water, 10 mM NaOH, 47 mM NaOH or 100 mM NaOH to obtain 0.04 (0.07) wt% R 3 L 12 at pH 9, 12 or 13 respectively. The pH was measured with a Mettler Toledo FiveEasy pH meter with Sigma-Aldrich micro pH combination electrode (glass body).

Low resolution spectra were recorded on a Bayspec Agility Raman spectrometer equipped with a 785 nm laser working at 300 mW. 10 mM Nb 10 samples were prepared by adding 25 mg of solid Nb 10 to the buffer solutions (1.5 ml, 0.1 M) with the pH already pre-adjusted using dropwise addition of [N(CH 3 ) 4 ] OH (1.0 M) in order to avoid pH shock. The pH value was recorded after the Nb 10 addition. The following buffers and pH were used: MES ( pH 6.13), PIPES ( pH 7.28), HEPES ( pH 8.18), CHES ( pH 9.05), CAPS ( pH 10.08 and pH ∼ 11.12) and [N(CH 3 ) 4 ]OH ( pH ∼ 12.80). The pH was measured with a Sigma-Aldrich micro pH combination electrode calibrated between pH 4.01 and 10.01. The alkaline error is likely to be very significant only for the 0.1 M [N(CH 3 ) 4 ]OH solution ( pH 12.80). The solutions were pressed through 0.2 micrometer membrane filters which diminish, but do not eliminate, the Tyndall effect, as is typical. Spectra were collected after ca. four hours at 293 K. The speciation diagram in Fig. 3 was constructed assuming that the signal intensity of 10 mM Nb 10 was ca. 70 cps.