In order to cater to the needs of the regulated markets and to address the safety and quality of of the drugs, the pharma industry is adopting a number of sophisticated instruments and techniques. One such effective tool, which is helpful for the industry to meet the demands of the regulatory authorities, is the polarimetry technique.
For any instrument calibration & validation is most important. A NIST traceable quartz control plate, which is known as a calibration tool of the first order available with some of the instrument manufacturer’s adhere to the latest FDA’s position on measurement bracketing. It says instrument has to be calibrated with NIST Traceable QCP for levo, dextro & also for combined rotation and must be validated for all the wavelength’s and the rotational values specified, with three NIST certificates i.e. levo, dextro & combined rotations.It should also have validation for 589.44nm ( USP ) & 589.3 nm ( EP ).This alternative tool avoids using of sucrose solution which is a cumbersome process of drying the sucrose, weighing it etc.
Recent samples involve solvents like HCL which are corrosive in nature and handling should be done cautiously. Somee manufacturers have 6M acid resistance sample cells with Hastelloy & Peek materials which can address these issueseasily. These cells come with NIST Traceable certificate certifying optical path length. Some of the suppliers supply silco steel coating sample chambers by which one can avoid corrosion due to 6M HCl solvent spillage.
Accuracy plays a vital role in selecting the polarimeter, as per the EP 2.2.7 (01/2008) optical rotation chapter. Polarimeter must be capable of reading accurately 0.01deg.
To measure specific rotation between +19 and +24 degrees on certain samples, USP strongly recommends 200mm sample tube.
For addressing the issues for darker samples a instrument should have minimum of 10nm bandwidth to permit high energy throughput & sensitivity for sample transmittance should be 0.01% ( O.D = 4 ), while minimizing the effects of sample ORD & colour.
The USP<781> specifies OR measurements at 25 deg C +/- 0.5 deg C & EP <2.2.7 > at 20deg C +/- 0.5 deg C. To satisfy these norms manufacturers employ Peltier heating & cooling where the sample temp is controlled and also validated with temp cell along with the NIST traceable certificate. And the peltier should reside in the instrument permanently for ease of use. Some manufacturers club peltier system with sample cell with a wire attachment which is cumbersome to use and has chances of recurring expenditure in case of sample spillage on the wire, which is often likely to get damaged.
Some of the manufacturer’s offer various features like touch screen with spill protection,wavelength selection automatic with the press of a lambda button with all the filters built in the system, memory cards for data storage & 21 CFR part 11, & automatic moisture correction.
-The author is associated with Agaram Industries, Hyderabad and can be contacted at umesh@agaramindia.com