JASCO P-2000旋光仪

An emission line of light source such as a sodium lamp or a mercury lamp is usually used to measure the optical rotation of pharmaceutical products. However, the Japanese Pharmacopeia and the European Pharmacopeia only mention the use of a sodium lamp as the light source. A polarimeter using a halogen lamp and a band pass filter (BPF) can also be used, as mentioned in the United States Pharmacopeia. However, the measurement error from the transmission property, that is the difference between the center wavelength of the BPF and the wavelength of emission line, cannot be avoided. Herein, the optical rotation of pirarubicin was measured using a sodium lamp and a halogen lamp, and the measurement error between the results was evaluated.

Optical rotation of Dextromethorphan Hydrobromide in accordance with the U.S. Pharmacopeia, is requested to be measured at 325 nm, however there is no emission line of 325 nm available in the polarimeter using Na lamp or Hg lamp as light source. Therefore, for the measurement of optical rotation of Dextromethorphan Hydrobromide, a polarimeter with halogen lamp as a light source and interference filter (325 nm) has been usually used, but as shown in Fig. 1, the optical rotatory dispersion (ORD) spectrum, there is a very steep slope in the short wavelength range near 325 nm, where even a very small error in the wavelength of interference filter may cause a very large error in the optical rotation measurement, which will makes the accurate measurements very difficult. On the other hand, if the measurement by using 365nm is allowed, since no wavelength error is expected, the measurement of optical rotation can be implemented with much higher accuracy. In this experiment, Dextromethorphan Hydrobromide was measured using polarimeter with Hg lamp (365 nm), polarimeter with Halogen lamp and interference filter (325 nm) and polarimeter with ORD attachment.

Optical rotation is the property of substances, rotating the plane of polarization when linearly-polarized light passes through such substances. This is the property which occurs specifically to optical active substances in which the refractive indices of right and left circularly-polarized light are different. Optical rotation that rotate light in a clockwise direction as viewed towards the light source is defined as dextrorotation (+) and the opposite, levorotation (-).