Measuring Samples with Large Optical Rotation

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March 18, 2026

Introduction

Some pure liquids* cannot be measured with a polarimeter and a normal 100-mm-path-length cell because their optical rotation exceeds 90 degrees. JASCO offers cells with short path lengths that enable measurements of samples with a large optical rotation. This application note describes optical rotation measurements for orange oil with a 50-mm-path-length cell.

*Pure liquid: a liquid substance composed of only one type of molecule

Experimental

Fig. 1 P-4200 polarimeter

Sample

Orange oil (research use)

System

Instrument:      P-4200 polarimeter

Cell:                  RQC-451 8.5-mm rectangular quartz cell (path length: 50 mm)

Fig. 2 Rectangular cell

Parameters

Light source:  Na lamp

Wavelength:   D line

D.I.T.:                5 sec

Repetition:      1 time

Keywords

Polarimeter, short path length, pure liquid, orange oil

Results

The measurement results are shown in Table 1. The blank measurement was performed using a dry empty cell.1 The use of a 50-mm-path-length cell allowed the optical rotation for orange oil to be measured without dilution, as the measured value remained within 90 degrees.

Table 1. Results

Optical rotation / °Temperature / °C
49.10720.4
Fig. 3. Measurement screen. Top: The current optical rotation and temperature are displayed in the monitor. Bottom: Sample names can be added to the list for future measurement.

Conclusion

Using a short-path-length cell, samples with a large optical rotation can be measured without dilution.

References

  1. United States Pharmacopeial Convention: “USP-NF 2024 Issue 3”, (2024).
  2. Ministry of Health, Labour and Welfare: June 7, 2021, MHLW Ministerial Notification No. 220, “The Japanese Pharmacopoeia 18th edition”, (2021).
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