2.2.8. VISCOSITY - uspbpep.com

1 EUROPEAN PHARMACOPOEIA Capillary viscometer methodThespecific optical rotationof a liquid is the angleof rotation , expressed in degrees ( ), of the plane ofpolarisation at the wavelength of the D-line of sodium( = )measuredat20 Cintheliquidsubstancetobe examined, calculated with reference to a layer of 1 dmand divided by the density expressed in grams per optical rotationof a substance in solutionis the angle of rotation , expressed in degrees ( ), of theplane of polarisation at the wavelength of the D-line ofsodium ( = nm) measured at 20 C in a solution ofthe substance to be examined and calculated with referenceto a layer of 1 dm containing 1 g/ml of the specific optical rotation of a substance in solutionis always expressed with reference to a given solvent the conventional system adopted by the Pharmacopoeiathe specific optical rotation is expressed by its valuewithout units.

2 The actual units, degree millilitres perdecimetre gram [( ) ml dm 1 g 1] conversion factor from the International System to thePharmacopoeia system is the following:In certain cases specified in the monograph the angle ofrotation may be measured at temperatures other than 20 Cand at other polarimeter must be capable of giving readings to thenearest . The scale is usually checked by means ofcertified quartz plates. The linearity of the scale may bechecked by means of sucrose Determine the zero of the polarimeter and the angleof rotation of polarised light at the wavelength of the D-lineof sodium ( = nm) at 20 C.

3 Measurementsmay be carried out at other temperatures only where themonograph indicates the temperature correction to be madeto the measured optical rotation. Determine the zero ofthe apparatus with the tube closed; for liquids the zero isdetermined with the tube empty and for solids filled withthe prescribed the specific optical rotation using the neat liquids:For substances in solution:wherecis the concentration of the solution in the contentcin g/l or the contentc in per centm/mof a dissolved substance using the following formulae.

4 =angle of rotation in degrees read at 20 C,l=length in decimetres of the polarimeter tube, 20=density at 20 C in grams per cubic the purposes of the Pharmacopoeia, densityis replaced by relative density ( ),c=concentration of the substance in g/l,c =content of the substance in per VISCOSITYT hedynamicviscosity orviscosity coefficient is thetangential force per unit surface, known asshearing stress and expressed in pascals, necessary to move, parallel tothe sliding plane, a layer of liquid of 1 square metre at arate (v) of 1 metre per second relative to a parallel layer at adistance (x) ratio dv/dxis a speed gradient giving therate of shear Dexpressed in reciprocal seconds (s 1)

5 , so that = unit of dynamic VISCOSITY is the pascal second (Pa s). Themost commonly used submultiple is the millipascal second(mPa s).Thekinematic VISCOSITY v, expressed in square metres persecond, is obtained by dividing the dynamic VISCOSITY bythe density expressed in kilograms per cubic metre, of theliquid measured at the same temperature, / .Thekinematic VISCOSITY is usually expressed in square millimetresper capillary viscometer may be used for determining theviscosity of Newtonian liquids and a rotating viscometer fordetermining the VISCOSITY of Newtonian and non-Newtonianliquids.

6 Other viscometers may be used provided that theaccuracy and precision is not less than that obtained withthe viscometers described CAPILLARY VISCOMETERMETHODT hedeterminationofviscosityusingasuitable capillaryviscometer is carried out at a temperature of 20 C, the liquid to drop from one mark to the other is measuredwith a stop-watch to the nearest one-fifth of a second. Theresult is valid only if two consecutive readings do not differby more than 1 per cent. The average of not fewer than threereadings gives the flow time of the liquid to be the dynamic VISCOSITY ( )inmillipascalseconds using the formula.

7 K=constant of the viscometer, expressed in squaremillimetres per second squared, =density of the liquid to be examined expressedin milligrams per cubic millimetre, obtained bymultiplying its relative density () by ,t=flow time, in seconds, of the liquid to be constantkis determined using a suitable viscometercalibration calculate the kinematic VISCOSITY (mm2 s 1), use thefollowing formula:v= (1)applytoallmonographsandothertexts29