旋光度
2.2.7. OPTICAL ROTA TION
旋光是手性物质的特性，即能使偏振光的平面旋转。
Optical rotation is the property displayed by chiral substances of rotating the plane of polarisation of polarised light.
右旋物质的旋光度为正的（+），即右旋物质可以使偏振光平面顺时针方向旋转；左旋物质的旋光度为负的（-）。
Optical rotation is considered to be positive (+) for dextrorotatory substances (i.e. those that rotate the plane of polarisation in a clockwise direction) and negative (−) for laevorotatory substances.
精确的旋光度αmλt是指，在温度下，波长为λ的光透过长1m或含1kg/m3旋光活性物质的液体，所发生的旋转，用弧度(rad)表示。实际操作中，旋光度常用mrad﹒m2﹒kg-1表示。The specific optical rotation αmλt is the rotation, expressed in radians (rad), measured at the temperature t and at the wavelength λ given by a 1 m thickness of liquid or a solu tion containing 1 kg/m3 of optically active substance. For practical reasons the specific optical rotation αmλt is normally expressed in milliradians metre squared
per kilogram (mrad²m2²kg−1).
本药典采用以下常规定义
The Pharmacopoeia adopts the following conventional definitions.
纯液体旋光度α：旋光度α以角度(°)表示，即20℃下，1dm长测定管的纯液体使钠光谱D 线（λ＝589.3nm）的偏振光平面所旋转的角度；对于溶液，按专论规定方法制备。polarised
The angle of optical rotation of a neat liquid is the angle of rotation α, expressed in degrees (°), of the plane of polarisation at the wavelength of the D-line of sodium (λ = 589.3 nm) measured at 20 °C using a layer of 1 dm; for a solution, the method of preparation is prescribed in the monograph.
液体旋光度αD20：测定即20℃下，1dm长的测定管的含待测液体的溶液使钠光谱D线（λ＝589.3nm）的偏振光平面所旋转的角度(°)，即溶液旋光度α。溶液中液体旋光度，由溶液旋光度α除以溶液中被检测液体的密度（g/cm3）计算得出。
The specific optical rotation αD20of a liquid is the angle of rotation α, expressed in degrees (°), of the plane of polarisation at the wavelength of the D-line of sodium (λ = 589.3 nm) measured at 20 °C in the liquid substance to be examined, calculated with reference to a layer of 1 dm and divided by the
density expressed in grams per cubic centimetre.
固体物质的旋光度αD20：测定20℃下，1dm长测定管的含被测物质1g/ml的溶液使钠光谱D线（λ＝589.3nm）的偏振光平面所旋转的角度，即溶液旋光度α。溶液中固体物质的旋光度由溶液的旋光度α计算得出。溶液中某物质的旋光度与溶剂和浓度有关。
The specific optical rotationαD20of a substance in solution is the angle of rotation α, expressed in degrees (°), of the plane of polarisation at the wavelength of the D-line of sodium (λ = 589.3 nm) measured at 20 °C in a solution of the substance to be examined and calculated with reference to a layer of 1 dm containing 1 g/mL of the substance. The specific optical rotation of a substance in solution is always expressed with reference to a given solvent and concentration.
按本药典采用的惯例，旋光度不标注单位；它的实际单位为(°)﹒ml﹒dm-1﹒g-1。
In the conventional system adopted by the Pharmacopoeia the specific optical rotation is expressed by its value without units ; the actual units, degree millilitres per decimetre gram [(°) ²ml²dm−1²g−1 ] are understood.
本药典的旋光度同国际标准单位旋光度的换算关系如下：
The conversion factor from the International System to the Pharmacopoeia system is the following:
αmλt=αλt×0.1745
如果专论有特别要求，按要求选择温度（可能不是20℃）和波长。
In certain cases specified in the monograph the angle of rotation may be measured at temperatures other than 20 °C and at other wavelengths.
旋光计的读数必须精确到0.01°。测量范围通常由鉴定用石英片检查；测量范围内线性由蔗糖溶液检查。
The polarimeter must be capable of giving readings to the nearest 0.01°. The scale is usually checked by means of certified quartz plates. The linearity of the scale may be checked by means of sucrose solutions.
方法
Method.
20±0.5℃下，旋光计调零，用钠光谱的D线（λ＝589.3nm）测定，或者按专论要求的温度测定旋光度。测定液体的旋光度，测定前放入封闭的空测定管，调零；测定固体的旋光度，测定前放入盛有所用溶剂测定管，调零。
Determine the zero of the polarimeter and the angle of rotation of polarised light at the wavelength of The D-line of sodium (λ = 589.3 nm) at 20 ± 0.5 °C, unless otherwise prescribed. Measurements may be carried out at other temperatures only where the monograph indicates the temperature correction to be made to the measure doptical rotation. Determine the zero of the apparatus with the tube closed; for liquids the zero is determined with the tube empty and for solids filled with the prescribed solvent
按下式计算旋光度：
Calculate the specific optical rotation using the following formulae.
纯液体旋光度：
For neat liquids :
αD20=α
l∙ρ20
溶液中物质的旋光度：c为浓度，单位g/l。
For substances in solution: where c is the concentration of the solution in grams per litre.
αD20=1000α
l∙c
按下式计算以g/l为单位的溶解物质的浓度c，或以m/m 百分比为单位的浓度c′：Calculate the content c in grams per litre or the content c′in per cent m/m of a dissolved substance using the following for mulae :
c=1000α
l∙αD20c‘=1000α
l∙αD20∙ρ20
α= 20 ±0.5°C下，旋光度读数，单位度（°）
l = 测定管长度，单位dm。
ρ20= 20 °C 下溶液密度，单位g/cm3，本药典在2.2.5节中以相对密度代替密度。
c = 溶解物质的浓度，单位g/l。
c′= 溶解物质的浓度，单位g/l。
α= angle of rotation in degrees read at 20 ± 0.5°C;
l = length in decimetres of the polarimeter tube;
ρ20= density at 20 °C in grams per cubic centimetre. For the purposes of the Pharmacopoeia, density is replaced by relative density (2.2.5).

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