Polarimeter adjustment

Detailed instructions for using the polarimeter and the temperature-regulating bath will be provided in the laboratory. After determining the path lengths of the cells to be used, fill a cell with pure solvent and zero-adjust the instrument. Next, rinse and fiU a cell with the polymer solution.f... 

Kinetics of Racemization of Amino Acids. Phosphate was used to buffer solutions of the L-amino acids at pH 7.6. Solutions of L-aspartic acid were buffered at the various pH values by either hydrochloric acid, oxalate, succinate, phosphate, borate, or NaOH. The pH values of the buffered solutions at the elevated temperatures were estimated as described previously (38). Sodium chloride was added to the solutions to adjust the final ionic strength to 0.5. The solutions were degassed and sealed under vacuum in borosilicate glass ampules. The ampules were sterilized immediately after being sealed by heating at 100 °C for 15 to 20 minutes. The rates of racemization were determined from measurements of the rate of change of optical rotation (a) of the solutions. The measurements were made on a Perkin-Elmer 141 polarimeter at 365 nm. With the exception of the aspartic acid solutions at pH values less than 2 and the phenylalanine solutions, all samples were diluted in 1M HC1 before measuring the rotation. 

In [9] it was shown that instrumental polarization for the polarimeter installed at the 60-cm telescope of the observatory near Tarija (Bolivia), had statistical error 0.024 % and the mean square was 0.023%. Investigations have shown that instrumental polarization in Newton and Nesmith focus can reach 5%, whereas it is less than 0.05% in a well adjusted Cassegrain. In the former case, values of Pi increase with wavelength whereas they decrease in the latter. 

System precision was determined using six consecutive injections of the target concentration of the analyte and comparing the percent relative standard deviations (%RSDs). The target concentration was 0.5 mg/mL, which was adjusted based upon higher or lower detector sensitivity. The CD detector yielded the best precision across all compounds studied and for 63% of the experiments, showed a %RSD of less than 5. The Chiralyzer showed a slightly better response over the PDR polarimeter, with the ORD showing the worst precision data. 

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