USP37称量要求
USP37<1251>使用分析天平称量（中英文）
2013-12-31 15:08:35| 分类：USP|举报|字号订阅
<1251> WEIGHING ON AN ANALYTICAL BALANCE
使用分析天平称量
（本文件来自USP37-NF32，目前尚未实施，信息仅供参考）INTRODUCTION 介绍
Weighing is a frequent step in analytical procedures, and the balance is an essential piece of laboratory equipment. The general information described here applies directly to electronic balances used in analytical procedures. Although many portions of the chapter are applicable to all balances, some are applicable only to analytical balances. This chapter should not be considered all-inclusive, and other sources of information (e.g., the US National Institute for Science and Technology and balance manufacturers) may be useful and applicable when analysts perform a weighing operation or implement a weighing procedure[i][ii].The information given in this chapter is applicable not only to balances used for materials that must be accurately weighed (see Balances 41 ) but also to balances used in all analytical procedures.
称重在分析程序中是一个很频繁的操作，天平是化验室的基本设备。这里的一般信息适用于在分析过程中使用的电子天平。尽管本章节的一部分也适用于所有天平，一些仅适用于分析天平。本章不应作为包括所有的文件，一些其它来源的信息（例如，美国国家科学技术研究所和天平生产商）可能也很有用，适用于化验员进行称量操作，或实施称重程序。本章中给出的信息不仅适用于必须精密
称定的物质（参见<天平41>），同时也适用于所有分析过程中使用的天平。
QUALIFICATION 确认
Users should consult Analytical Instrument
Qualification 1058 , standard operating procedures, and recommendations from manufacturers when they devise qualification plans.
用户在设计其确认计划时，应参考<分析仪器确认1058>，标准操作规程，和生产商的推荐。
Installation 安装
The balance's performance depends on the conditions of the facility where it is installed. Analysts should consult information provided by the manufacturer before they install a balance.
天平的性能取决于其安装所处的环境。在安装天平前，化验员应参考供应商给出的信息。
Support surface: The balance should be installed on a solid, level, nonmagnetic surface that minimizes the transmission of vibration (e.g., a floor-mounted, granite weigh bench). If a metallic support surface is used, the surface should be grounded in order to prevent the buildup of static electricity.
支持台面：天平应安装在坚固、水平、无磁场的平面，尽量减少震动传递（例如，安装在地板，花岗岩称重台）。如果采用了金属的支持台面，表面应接地，以避免静电聚积。
Location: If possible, the balance should be located in a room that is temperature and humidity controlled. The location should have a clean, consistent electrical power supply. The location should be free of drafts and should not be near ovens, furnaces, air conditioner ducts, or cooling fans from equipment or computers.
位置：如果可能，天平应安装在一个温湿度可控的房间。位置应清洁，具有持续的电力供应。位置应不会产生波动，不靠近烘箱、马弗炉、空调送回风罩，或设备、空调的冷却风扇。
The balance should be positioned away from outside windows so that direct sunlight does not strike the balance. The balance should not be installed near sources of electromagnetic radiation such as radiofrequency generators, electric motors, or hand-held communication devices (including cordless telephones, cellular telephones, and walkie-talkies). The balance should not be located near magnetic fields induced by laboratory instrumentation or other equipment.
天平位置应远离窗户，以避免直接阳光照射。天平安装不应靠近电磁辐射源，如无线频率发向射源，电子马达，或手动通话设施（包括无绳电话、手机、手提无线电话机）。天平不应安装在化验室设备或其它设备产生的磁场区域附近。
The performance of the balance should be assessed following installation and before use in order to demonstrate adequate performance. In some situations, it may not be possible to position the balance in an optimum environment. Examples of potential facility issues include the following:
天平的性能在安装后使用前应进行评估，以证明其性能符合要求。在某些情况下，可能无法将天平安装在一个理想的环境。潜在的设施问题包括以下：
1. Air currents sometimes are present in the laboratory.
化验室中有时会有气流
2. Temperatures in the laboratory vary excessively (check the manufacturer's literature about temperature sensitivity).
化验室温度有时会快速波动（检查供应商关于温度敏感性的说明）
3. Humidity is either very low or very high. Either condition may increase the rate at which the sample weight varies because of pickup or loss of water. Low humidity increases the buildup of static electricity.
湿度可能会很低或很高。由于失水或吸水，太高或太低都会影响样品重量变动的速度。低湿度会增加静电积聚。
4. Adjacent operations are causing vibration.
邻近操作产生震动
5. Corrosive materials are used nearby or are routinely weighed.附近使用腐蚀性材料，或常规称量腐蚀性物料
6. The balance is located within a fume hood because it is used to weigh corrosive or hazardous materials.
由于天平用于称量腐蚀性或危险性物料，因此安装在排烟罩内
7. The balance is adjacent to equipment that produces a magnetic field (e.g., a magnetic stirrer).
天平邻近产生磁场的设备（例如，电磁搅拌器）
8. Direct sunlight strikes the balance.
天平有直接太阳光照
In situations when the balance is located near equipment or systems that induce vibration, drafts, electromagnetic radiation, magnetic fields, or changes in temperature or humidity, the assessment should be conducted with those systems operating in order to duplicate a worst-case scenario.
如果天平位置接近产生震动、摆动、电磁辐射、磁场或温湿度变化的设备，则需要对这些系统在操作状态下进行评估，以重复最差情况环境。
Operational Qualification 运行确认
An operational qualification should be performed either by the user or by a qualified third-party vendor after the equipment has been installed.
在天平安装后，应由用户或第三方供应商进行运行确认。
As a minimum, the power should be turned on and the balance should be allowed to equilibrate according to the manufacturer's instructions (1–24 h, depending on the type of balance) before use. Depending on the balance, analysts should include the following procedures in the operational qualification:
最低要求，要打开电源，根据生产商的要求，在使用前让天平平衡（1-24小时，根据型号不同而不同）。根据天平型号，化验员应在运行确认中包括以下程序：
1. Mechanical mobility of all moveable parts
所有可移动部件机械动态
2. Control of stable indication
稳定指示的控制
3. Manually triggered or automatic adjustment by means of
built-in weights
内置砝码的手动或自动调节
4. Operation of ancillary equipment
辅助设备的操作
5. Tare function
去皮功能
6. Initial calibration
初始校正
Several types of electronic analytical balances use built-in weights for manually triggered or automatic adjustment. This
adjustment usually is applied to reduce the drift of the balance over time and to compensate for drifts caused by variations in the ambient temperature.
一些电子分析天平使用内置砝码，可以进行手动或自动调节。这种调节一般用于减少天平随时间的漂移，对由于周围产生震动引起的漂移进行补偿。
Calibration normally is performed as part of the operational qualification, but it also can be performed periodically thereafter. Calibration should be performed at the location where the balance is used in normal operation.
校正一般作为运行确认的一部分实施，但也可以在之后进行周期性校正。校正应在天平所正常操作的原位进行。
Performance Qualification 性能确认
Table 1 provides a list of the most important balance properties that should be assessed during performance qualification. Depending on the risk of the application and the required weighing process tolerance, some of these tests may be omitted. Tests also can be omitted if there is evidence that the property in question has only minimal effect on the weighing performance. Any procedures used should be consistent with in-house standard operating procedures, applicable for the specific balance, and adequately justified. Performance qualification should be performed periodically as described in standard operating procedures, and the frequency of each of the individual tests can vary depending on the criticality of the property.
表1提供了一个天平最重要属性的清单，在性能确认中应该进行评估。根据应用的风险不同，要求的称重允差不同，有时该类测试可以省略。如果有证据表明该属性仅对称量性能形成很小的影响，则也可以省略对其进行的测试。任何所用的程序均应与公司内部，适用于该特定天平的标准操作规程一致，并应进行充分判定。性能确
认应按标准操作规程的描述周期实施，各测试的实施频率可能根据属性的关键程度不同而不同。
The weights that are used to perform the tests should be stored and handled in a manner that minimizes contamination. Before executing the tests, the analyst should place the weights in the vicinity of the balance for an appropriate time to reach sufficient thermal equilibrium. If possible, all tests should be carried out with a single test weight in order to minimize handling errors, but multiple test weights are permitted.
用于测试的砝码存贮和使用过程应能尽量减少污染。在进行测试前，化验员应将砝码放置在天平附近一段时间，以使其温度达到与环境温度平衡。如有可能，所有测试均应采用同一个砝码，以尽可能减少操作误差，但使用多个砝码也是允许的。
The tests should be recorded in such a manner that the data can be used to easily track balance performance and to assist in laboratory investigations as needed. Meaningful acceptance criteria can be set depending on the required weighing tolerance, i.e., the maximum allowed deviation permitted by specifications, regulations, etc., of a quantity to be weighed from its target value. Procedures should be in place to address test results that are outside acceptable ranges and to provide assurance that balance cleanliness and environment have not affected the result. Also, a procedure should be in place for removing a balance from operation when observed results fall outside acceptable ranges.测试过程要进行记录，数据应能很容易地追踪到天平性能，帮助化验室进行必要的调查。根据要求的称重误差，即质量标准、法规等允许的与目标重量值的最大允差，可以设定实际的可接受标准。应有程序说明测试超出可接受范围的结果，并保证天平的清洁和环境不会对结果产生影响。应有程序说明如果观察到结果超出可接受标准，则天平则不能继续使用。
Organization for Standardization, this concept is referred to as trueness. Because deviations are largely independent from each other, it is not likely that all deviations occur simultaneously and have the same algebraic sign.
灵敏度、线性和偏心率均为系统性误差，即它们会局限天平的精密度（基于<药典方法的验证1225>精密度定义，和ICH Q2）。在国际计量词汇（VIM）中，和国际标准化组织文件中，本根据被引用为真实性。因为偏差很大程度上相互独立，因此不可能所有偏差同时产生，并具有同向性（即同时正负）。
Therefore the arithmetic addition of all individual deviations to assess the balance accuracy would constitute a rather conservative approach. A quadratic addition of the individual deviations is a more realistic approach. By allocating 50% of the weighing tolerance budget to the acceptance criteria of the individual properties, e.g., sensitivity, linearity, and eccentricity, analysts ensure adherence to the required weighing tolerance. Therefore, the acceptance criteria for the individual properties that account for the systematic deviations are set to weighing tolerance divided by 2. These properties—or a subset of them—also can be taken to fulfill the accuracy requirement described
in 41 . In this case the acceptance criteria thus allow a maximum deviation of 0.05% for sensitivity, linearity, and eccentricity. Repeatability preferably is tested with a test weight of a few percent of the balance capacity. At the lower end of its measurement range, the performance of laboratory balances is limited by the finite repeatability, and limitations induced by systematic deviations normally can be neglected. Therefore, the whole weighing tolerance budget can be allocated to the acceptance criterion of the repeatability test.
因此，采用所有单个误差的算术加和，来评估天平的准确度是一种较为保守的方法。采用单个偏差的二次加和是一种更现实的方法。将各单个属性的可接受标准置为称量允差的50%，如，灵敏度、线
性和偏心率，化验员可以保证达到所需的称量允差。这样，单个属性的可接受标准作为系统误差设定为称量允差除以2。这些属性-----或属性的子集----也可以认为是满足<41>中描述的精密度要求。在这种情况下，可接受标准允许最大偏差为灵敏度、线性和偏心率的0.05%。重复性最好采用一个天平最大载重量百分之几重量的砝码测试。在测量范围的低值端，化验室天平的性能由有限次数重复性所限度，由系统误差引入的限度一般可以忽略。因此，整个称量允差可以直接作为重复性测试的可接受标准。
For the sensitivity and linearity tests as described above, the analyst should use certified weights with an appropriate weight class (e.g., according to International Organization of Legal Metrology R111 or American Society for Testing and Materials
E617, available from https://www.360docs.net/doc/ea13585531.html, and https://www.360docs.net/doc/ea13585531.html,, respectively). [NOTE—If a differential method is used for the linearity test, certified weights may not be required.]
对于上述灵敏度和线性，化验员应使用具有适当重量分类（例如，根据国际法定计算组织R111或美国材料试验协会E617，可分别从上述网址获得）且认证过的砝码。【注----如果使用了不同方法进行线性测试，认证过的砝码，可能不需要认证过的砝码】Depending on the acceptance criterion, it may be sufficient to consider only the nominal weight value of the test weights. If the nominal value of the test weight is considered, analysts should ensure that the maximum permissible error does not exceed
one-third of the acceptance criterion. Alternatively, if the certified value of the test weight is considered, its calibration uncertainty should not exceed one-third of the acceptance criterion. If more than one weight is used to perform the test, the calibration uncertainties of the weights must be summed and the sum should not exceed one-third of the acceptance criterion. For tests such as eccentricity or repeatability, the use of certified weights is optional, but analysts must ensure that the mass of the weight does not change during the test.
根据可接受标准的不同，可能只需要考虑测试所用砝码的名义重量。如果考虑的是名义值，化验员应保证最大允差不超过可接受标准的1/3。相应的，如果考虑的是测试用砝码的校正值，则校正不确定度应不超过可接受标准的1/3。如果使用了不止一个砝码，则校正砝码不确定度必须要进行加和，和值应不超过可接受标准的
1/3。对于偏心率或重复性，可以使用认证过的砝码，但化验员必须保证砝码的重量在测试期间不产生变化。
The tests described above also can be included in formal periodic calibration in order to fulfill applicable cGMP requirements.
上述测试也可以包括在正式的周期性校正中，以满足所实施的cGMP的要求。
Balance Checks 天平检查
A balance check using an external weight helps ensure that the balance meets weighing tolerance requirements. The balance check is performed at appropriate intervals based on applicable standard operating procedures. The frequency of the balance check depends on the risk of the application and the required weighing tolerance. Checks with external weights can be replaced partially using automatic or manually triggered adjustment by means of built-in weights. When analysts perform the balance check with an external weight, the same acceptance criteria may apply as described in the sensitivity test above.
对天平采用外部砝码进行检查，可以保证天平符合称重允差要求。根据所要求的标准操作规程，可以采用适当的间隔进行天平检查。检查频率取决于使用的风险，以及称重允差要求。采用外部砝码进行检查可以部分采用自动或手动内置砝码调节功能代替。如果化验室采用外部砝码进行检查时，适用上述灵敏度测试相同的可接受标准。
Minimum Weight 最小称样量
The minimum net sample weight, mmin, of a balance can be expressed by the equation:
天平的最小称样净重，mmin，可以用以下等式表达：
mmin = k ×s/required weighing tolerance
mmin = K X s/所要求的称样误差
where k is the coverage factor (usually 2 or larger) and s is the standard deviation (in a mass unit, e.g., in mg) of not fewer than 10 replicate measurements of a test weight. The minimum weight describes the lower limit of the balance below which the required weighing tolerance is not adhered to. The equation above takes into account that the performance of laboratory balances at the lower end of the measurement range is limited by the finite repeatability.
这里，K是包含因子（一般取2或更大），s是对一个测试用砝码进行不少于10次重复称量所得的标准偏差（质量单位，例如mg）。最小称样量描述的是天平可以用于称量的低限，如果样品量低于该限度，则不能满足要求的允差。上述公式考虑了化验室天平的称量范围内较低称样量的性能，其采用的是有限重复性方法。
For materials that must be accurately weighed, 41 stipulates that repeatability is satisfactory if two times the standard deviation of the weighed value, divided by the nominal value of the weight used, does not exceed 0.10%. For this criterion the equation above simplifies to:
对于必须精密称定的物质，<41>中说明了如果所称数值的标准偏差乘以2，除以所用砝码的名义质量，不超过0.10%，则认为重复性满足要求。对此标准，上述公式简化为：
mmin = 2000 ×s
If not subject to the requirements of 41 , the minimum weight value may vary depending on the required weighing tolerance and the specific use of the balance.
如果不需要满足<41>的要求，则最小称量值可能会依据所要求的称重允差不同和天平用途不同而不同。
To facilitate handling, the test weight that is used for the repeatability test does not need to be at the minimum weight value but can be larger because the standard deviation of repeatability is only a weak function of the test weight value.
为便于操作，用于重复性测试的砝码重要不需要是最小重复值，可以更大，因为重复性的标准偏差只是所测试重量值的一个很弱的功能。
In order to satisfy the required weighing tolerance, when samples are weighed the amount of sample mass (i.e., the net weight) must be equal to or larger than the minimum weight. The minimum weight applies to the sample weight, not to the tare or gross weight.
为了满足所要求的称重误差，样品称重量（即净重）必须等于或大于最小称重量。最小重量是指样品净重，不是指皮重或毛重。Factors that can influence repeatability while the balance is in use include:
在天平使用中可能影响重复性的因素包括：
1. The performance of the balance and thus the minimum weight can vary over time because of changing environmental conditions.
天平性能，因为环境条件变化在不同时间可能会变化的最小重量
2. Different operators may weigh differently on the balance—i.e., the minimum weight determined by different operators may be different.
不同操作人员在天平上操作可能会不同-----即，最小称样量由不同操作者来测试可能会有不同结果
3. The standard deviation of a finite number of
replicate weighings is only an estimation of the true standard deviation, which is unknown.
有限次数重复称量的标准偏差仅是真实标准偏差的估计，而真实标准偏差是不可知的
4. The determination of the minimum weight with a test weight may not be completely representative for the weighing application.
一个测试砝码进行最小称样量的测试可能不能完全代替实际称量
应用
5. The tare vessel also may influence minimum weight because of the interaction of the environment with the surface of the tare vessel.
盛装样品容器也可能会对最小称样量形成影响，因为环境与样品容器的表面可能会有相互作用
For these reasons, when possible, weighings should be made at larger values than the minimum weight.
由于这些原因，如果可能，称样量应尽可能大于最小称样量。OPERATION OF THE ANALYTICAL BALANCE 分析天平的操作
Select the appropriate balance for the quantity and performance needed. General chapter 41 provides requirements for balances used for materials that must be accurately weighed. The balance user should check the balance environment (vibration, air currents, and cleanliness) and status of calibration before use.
根据数量和要求的性能选用适当的天平。通论<41>中提供了用于必须精密称定的物质的天平要求。在使用前，天平使用者应检查天平的环境（震动、气流、洁净度）和校正状态。
Receivers 受器
To ensure suitable performance in measuring the weight of a specimen, analysts should consider selection of a proper receiver for the material.
为保证在对样品重量的称量过程中有适当的表现，化验员应考虑选择适合于物料的容器
General characteristics: All receivers must be clean, dry, and inert. The total weight of the receiver plus the specimen must not exceed the maximum capacity of the balance. With a properly maintained and adjusted laboratory balance, weighing uncertainty for small samples, i.e., net weights with a mass not exceeding typically a few percent of the capacity of the balance, essentially is determined by the repeatability. However, repeatability depends on the size and surface area of the weighed object. For this reason large or heavy receivers introduce a deviation from the conditions under which the repeatability was determined without considering the receivers. Therefore, either receivers of a low mass and small surface should be used (especially in cases when specimens of low weight are being measured) or the repeatability test should be performed with the receiver placed on the weighing pan as a preload. Receivers should be constructed from nonmagnetic materials in order to prevent magnetic interference with electronic balance components. Receivers should be used at ambient temperature in order to prevent the formation of air currents within the weighing chamber.
一般特性：所有称量容器均必须清洁、干燥、惰性。称样器加上样品的总重量应不超过天平的最大载重量。如果一个化验室使用的天平维护良好、调整适当，在称定较小数量的样品时，例如，样品净重不超过天平最大载重量的百分之几时，其称量不确定度基本是应该由重复性来决定的。但是，重复性取决于所称对象的尺寸和表面积。因此，如果重复性测试时未考虑样品容器，则较大的或较重的
样品容器会引入条件偏差。因此，应采用较小质量或较小表面积的样品容器（特别是如果需要称量很小重量的样品时），或将样品容器放置在称样盘上作为预置重量来测试重复性。样品容器应采用非磁性材料制成，以避免磁力对天平部件的干扰。样品容器应在室温下使用，以避免称量空间内形成气流。
Solid samples: Receivers for weighing solid materials include weighing paper, weighing dishes, weighing funnels, or enclosed vessels, including bottles, vials, and flasks. Hygroscopic papers are not recommended for weighing because they may have a detrimental effect on the observed results.
固体样品：固体样品用的容器包括称量纸、称量盘、称量漏斗或气密容器，包括瓶、小瓶、锥瓶。不建议采用吸湿性的纸用于称重，因为这些纸可能会对结果产生不利影响。
Weighing dishes typically are constructed from a polymer or from aluminum. Antistatic weighing dishes are available for measuring materials that retain static electricity. Weighing funnels typically are constructed from glass or from a polymer. The design of this type of receiver combines attributes of a weighing dish and a transfer funnel, which can simplify the analytical transfer of a weighed powder to a narrow-necked vessel such as a volumetric flask. For solid samples that are volatile or deliquescent, analysts must weigh the material into an enclosed vessel. Where practical, analysts should use an enclosed vessel with a small opening in order to reduce sample weight loss from volatilization or weight gain from the adsorption and absorption of atmospheric water.
典型的称量盘采用聚酯或铝制成。称量吸附静电物质时，可以采用抗静电称量盘。典型的称量漏斗采用玻璃或聚酯制成。该类称样容器的设计结合了称量盘和转移漏斗的特性，可以简化将称量好的粉末转移至细颈容器，如容量瓶的操作。对于挥发性或溶解性的固体样品，化验员必须将物质称至一个密闭的容器。如果可行，化验员
应采用一个气密性容器，仅有很小的开口，以减少由于挥以带来的样品失重，或由于吸收空气中的水分而增重。
Liquid samples: Receivers for liquid samples typically are inert, enclosed vessels. For liquid samples that are volatile or deliquescent, analysts should use an enclosed vessel with a small opening, and the enclosure should be replaced rapidly following material transfer. Special precautions should be taken to be certain that the receiver and the enclosure are constructed from a material that is compatible with the liquid sample. The receiver and enclosure must have a seal that is sufficient to prevent leaks from a liquid that is of low viscosity or has low surface tension or a low boiling point.
液体样品：典型的液体样品的容器为惰性，可以密闭的容器。对于挥发性或溶解性液体样品，化验员应使用一个带盖的气密性容器，只有很小的开口，容器应在物料转移后迅速替换密封盖。特别要确认容器和盖子所用材质与液体样品应相容。容器和密封器必须密合，能够防止低粘度、或低表面张力、或低沸点液体泄漏。Types of Weighing 称量类型
Weighing for quantitative analysis: The initial step for many quantitative analyses is to accurately weigh a specified amount of a sample. Section 6.50.20 in the General Notices stipulates that solutions for quantitative measures must be prepared using accurately weighed analytes: i.e., analysts must use a balance that meets the criteria in 41 . Errors introduced during the weighing of a sample can affect the accuracy of all subsequent analytical measurements.
定量分析用的称量：很多定量分析的第一步即是精密称定一定数量的样品。在通则<6.50.20>中阐述了用于定量检测的溶液必须使用精密称定的样品来制备，即，样品必须使用符合<41>要求的天平。在样品称量过程中引入的误差，会对之后的所有分析测量的准确度产生影响。
Addition weighing: Addition weighings typically are used for solid samples or liquid samples for which volatility is not an issue. The receiver is placed on the balance. After the balance display stabilizes, the analyst should tare the balance; add the desired amount of material to the receiver; allow the balance display to stabilize; record the weight; and quantitatively transfer the material to an appropriate vessel or, if it cannot be guaranteed that the entire amount has been transferred, weigh the receiver again and note the weight difference.
增量称量：增量称量典型地用于没有挥发问题的固体样品或液体样品。样品容器应放置在天平上，等天平显示稳定后，化验员应将天平去皮，将需要的重量的样品加入至容器内，等天平显示稳定，读取重量值，将样品定量转移至适当的容器，或，如果无法保证所有样品均能被转移，则将称量用容器重新称量，记下前后重量差异。Dispense weighing: Dispense weighing typically is used for weighing emulsions or viscous liquids such as ointments. In these situations it is not practical to weigh the material into a typical receiver. Accordingly, the analyst should tare the balance; place the sample on the balance in a suitable container (e.g., a bottle, tube, transfer pipet, or syringe) that has been wiped clean on the outside; record the weight after the balance display stabilizes; transfer the desired amount of sample to an appropriate receiving vessel, such as a volumetric flask; and place the pipet or syringe back onto the balance. The difference in the two weighings is equal to the weight of the transferred specimen.
分配称量：分配称量典型地用于乳状液体或粘性液体称量，如膏剂。在这种情况下，将样品在常用的容器中进行称量不实际。因此，化验员可以先将天平去皮，将样品放置在外表清洁的适当的容器中（例如，瓶、管、移液管或移液针），等天平显示稳定后，记录读数，转移想要的数量的样品至适当的接收容器中，例如，容量瓶，再将移液管或移液针放回天平。两次称量值的差值，即为所转移的样品的重量。