USP35 <781> OPTICAL ROTATION
Many pharmaceutical substances are optically active in the n that they rotate an incident plane of polarized light so that the transmitted light emerges at a measurable angle to the plane of the incident light. This property is characteristic of some crystals and of many pharmaceutical liquids or solutions of solids. Where the property is possd by a liquid or by a solute in solution, it is generally the result of the prence of one or more asymmetric centers, usually a carbon atom with four different substituents. The number of optical isomers is 2n, where n is the number of asymmetric centers. Polarimetry, the measurement of optical rotation, of a pharmaceutical article may be the only convenient means for distinguishing optically active isomers from each other and thus is an important criterion of identity and purity.
许多药物具有光学活性，也就是说，它们使入射的偏振光发生旋转，使得透射光与入射光呈一可测量的角度。某些晶体与许多药物液体或固体的溶液具有此性质。如果是一液体或溶液中的溶质具有此性质，一般来说存在一个或多个不对称中心，通常一个碳原子具有4个不同的取代基。光学异构体的数量为2n，在这里n是不对称中心的数量。药物的旋光分析可能是唯一的，用来区分光学异构体的一种方便的手段，因此是鉴别与纯度的一项重要的标准。
梦见别人杀蛇
Substances that may show optical rotatory power are chiral. Tho that rotate light in a clockwi direction as viewed towards the light source are dextrorotatory, or (+) optical isomers. Tho that rotate light in the opposite direction are called levorotatory or (–) optical isomers. (The symbols d- and l-, formerly ud to indicate dextro- and levorotatory isomers, are no longer sanctioned owing to confusion with D- and L-, which refer to configuration relative to D-glyceraldehyde. The symbols R and S and and are also ud to indicate configuration, the arrangement of atoms or groups of atoms in space.)
花叶艳山姜表现旋光的物质具有手性特征。那些与与光源呈顺时针旋转的物质为右旋的或（+）光学异构体。那些呈相反方向旋转的物质被称为左旋或（-）光学异构体。
（以前用来表示右旋与左旋异构体的符号d-与l-，因为常与代表D-甘油醛结构的D-或L-相混淆而不再被允许使用，符号R与S和与也被用来表示原子或取代基在空间的排列结构）。
The physicochemical properties of nonsuperimposable chiral substances rotating plane polarized light in opposite directions to the same extent, enantiomers, are identical, except for this property and in their reactions with other chiral substances. Enantiomers often exhibit profound differences in pharmacology and toxicology, owing to the fact that biological receptors and enzymes themlves ar
e chiral. Many articles from natural sources, such as amino acids, proteins, alkaloids, antibiotics, glycosides, and sugars, exist as chiral compounds. Synthesis of such compounds from nonchiral materials results in equal numbers of the enantiomers, racemates. Racemates have a net null optical rotation, and their physical properties may differ from tho of the component enantiomers. U of stereolective or stereospecific synthetic methods or paration of racemic mixtures can be ud to obtain individual optical isomers.
不重叠的手性物质，即对映异构体，可向相反的方向旋转平面偏振光，但旋转的程度相同，除此性质以及与其它手性物质反应外，两者其它的物理化学性质是相同的。由于生物学的受体与生物酶本身也是手性的缘故，对映异构体在药理与毒理方面常常表现极大的不同。许多天然来源的药物，例如氨基酸，蛋白质，生物碱类，糖苷类以及糖类，以手性化合物的形式存在。从非手性的原料合成这些化合物导致得到相同数量的对映异构体：外消旋体。外消旋体的净旋光为零，并且它们的物理性质可能不同于那些对映体的组分。可使用消旋混合物的立体选择性的或立体特异性的合成方法或分离技术得到单独的光学异构体。Measurement of optical rotation is performed using a polarimeter.* The general equation ud in polarimetry is:
可使用旋光计来测量旋光度，在旋光分析时通用的方程是：可乐雪碧
where [] is the specific rotation at wavelength , t is the temperature, a is the obrved rotation in degrees (), l is the pathlength in decimeters, and c is the concentration of the analyte in g per 100 mL. Thus, [] is 100 times the measured value, in degrees (), for a solution containing 1 g in 100 mL, measured in a cell having a pathlength of 1.0 decimeter under defined conditions of incident wavelength of light and temperature. For some Pharmacopeial articles, especially liquids such as esntial oils, the optical rotation requirement is expresd in terms of the obrved rotation, a, measured under conditions defined in the monograph.
考试前妈妈的鼓励
在公式中[]是在波长为时的比旋度；t是温度；a是所观察到的旋转角度，单位是()；l是光路长度，单位是dm；c是待分析物的浓度，单位是g/100ml。因此对于浓度为1g/100ml的溶液来说，用光路长度为1dm的旋光池，在规定的入射光的波长与温度下测量，[]是其测量值的100倍，单位是()。对于某些药用原料来说，尤其是液体，例如挥发油，旋光度要求用在正文中规定的条件下测量而观察到的旋转a来表示。
Historically, polarimetry was performed using an instrument where the extent of optical rotation is estimated by visual matching of the intensity of split fields. For this reason, the D-line of the sodium l
阎立本代表作
amp at the visible wavelength of 589 nm was most often employed. Specific rotation determined at the D-line is expresd by the symbol:
五经博士
and much of the data available are expresd in this form.
历史上，用这样的仪器装置来进行旋光分析：旋光的程度通过目测分离视场的强度来估计。因此，最常使用在可见波长589nm处的钠灯的D线。在D线下所测
得的比旋度用符号来表示，并且得到的许多数据用这种形式来表达。
U of lower wavelengths, such as tho available with the mercury lamp lines isolated by means of filters of maximum transmittance at approximately 578, 546, 436, 405, and 365 nm in a photoelectric polarimeter, has been found to provide advantages in nsitivity with a conquent reduction in the concentration of the test compound. In general, the obrved optical rotation at 436 nm is about double and at 365 nm about three times that at 589 nm. Reduction in the concentration of the solute required for measurement may sometimes be accomplished by conversion of the substance under test to one that has a significantly higher optical rotation. Optical rotation is also affected by the solvent ud for the measurement, and this is always specified.
已发现使用较短的波长（例如借助于滤镜分离所得到的汞灯线的波长，大约在光电偏振计的578，546，436，405 以及365nm处具有最大的透光度）在灵敏度方面具有优势，从而可降低供试化合物的浓度。一般来讲，在436nm处所观察到的旋光大约是589nm的2倍，在365nm处所观察到的旋光是589nm处的3倍。测量所要求的溶质的浓度的降低有时可通过将供试品转换为一具有较强旋光的物质来实现。旋光可被测量所用的溶剂所影响，因此所用的溶剂总是有规定的。
威海游记
It is now common practice to u other light sources, such as xenon or tungsten halogen, with appropriate filters, becau the may offer advantages of cost, long life, and broad wavelength emission range, over traditional light sources.
现在使用具有适当滤镜的其它的光源非常普遍，例如，氙或钨卤素，因为这些光源在价格方面，长的使用寿命方面以及宽的波长发射范围方面，与传统的光源正比，具有很大的优势。
Specific Rotation— The reference Specific rotation 781S in a monograph
signifies that specific rotation is to be calculated from obrved optical rotations in the Test solution or Sample solution USP35obtained as directed therein. Unless otherwi directed, measurements of optical rotation are made at 589 nm at 25. Where a photoelectric polarimeter is ud, a single measurement, corrected for the solvent blank, is made. Where a visual polarimeter is employed, the
奥尔夫律动average of no fewer than five determinations, corrected for the reading of the same tube with a solvent blank, is ud. Temperature, which applies to the solution or the liquid under test, should be maintained within 0.5of the stated value. U the same cell for sample and blank. Maintain the same angular orientation of the cell in each reading. Place the cell so that the light pass through it in the same direction each time. Unless otherwi specified, specific rotation is calculated on the dried basis where Loss on drying is specified in the monograph or on the anhydrous basis where Water is specified.
比旋光—个论正文中参照比旋光（781S），是指按照其中所述的方法，用供试品的实测旋光度来计算比旋度。除另有规定外，在589nm处，25℃下测量旋光度。如果使用光电偏振计，单次测量，用空白溶剂进行校正。如果使用目测的旋光计，取不少于5个测量值的平均值，用空白溶剂校正相同的旋光管的读数。供试溶液或供试液体所使用的温度应保持在规定值的±0.5℃的范围之内。对于样品与溶剂来说，使用相同的旋光池。在每次读数时保持相同的观察角度。每次放置旋光池时，使光沿相同的方向通过旋光池。除另有规定外，比旋度根据干燥物进行计算（如果在正文中规定了干燥失重），或根据无水物进行计算（如果规定了含水量）。
Optical rotation of solutions should be determined within 30 minutes of preparation. In the ca of substances known to undergo racemization or mutarotation, care should be taken to standardize the
time between adding the solute to the Solvent and introduction of the solution into the polarimeter tube.
溶液的旋光度应在配制后的30分钟内测量。如果已知供试品有消旋或变旋现象，应注意使向溶剂中加入溶质与将溶液倒入旋光管中之间的时间进行规定。
