USP36 921 WATER DETERMINATION

1、 水分測(cè)定水分測(cè)定 WATER DETERMINATION 很多藥典物品要么是水合物，要么含有處于吸附狀態(tài)的水。因此，測(cè)定水分含量對(duì)于證實(shí)與藥典標(biāo)準(zhǔn)的符合性是很重要的。通常，在各論中會(huì)根據(jù)該物品的性質(zhì)，要求使用下面若干方法中的一個(gè)。偶爾，會(huì)允許在 2 個(gè)方法中任選一個(gè)。當(dāng)該物品含有水合狀態(tài)的水，按照具體各論中的規(guī)定，使用方法 I（滴定法）、方法 II（恒沸法）、或方法 III（重量分析法），在標(biāo)題水分項(xiàng)下給出。Many Pharmacopeial articles either are hydrates or contain water in adsorbed form. As a resul

2、t, the determination of the water content is important in demonstrating compliance with the Pharmacopeial standards. Generally one of the methods given below is called for in the individual monograph, depending upon the nature of the article. In rare cases, a choice is allowed between two methods. W

3、hen the article contains water of hydration, the Method I (Titrimetric), the Method II (Azeotropic), or the Method III (Gravimetric) is employed, as directed in the individual monograph, and the requirement is given under the heading Water. 在加熱時(shí)的失重可能不全是水的情況下，使用標(biāo)題干燥失重（見(jiàn)干燥失重）。The heading Loss on dryin

4、g (see Loss on Drying ) is used in those cases where the loss sustained on heating may be not entirely water.方法方法 I（滴定測(cè)量法）（滴定測(cè)量法）METHOD I (TITRIMETRIC)除各論中另有規(guī)定外，使用方法 Ia 來(lái)測(cè)定水分。Determine the water by Method Ia, unless otherwise specified in the individual monograph.方法 Ia（直接滴定）Method Ia (Direct Titrati

5、on) 原理：水分的滴定法檢測(cè)是基于水與二氧化硫及碘的無(wú)水溶液在緩沖液中與氫離子之間的定量反應(yīng)。Principle The titrimetric determination of water is based upon the quantitative reaction of water with an anhydrous solution of sulfur dioxide and iodine in the presence of a buffer that reacts with hydrogen ions. 在原本的滴定測(cè)量溶液（即卡爾費(fèi)休試劑）中，二氧化硫和碘溶解于嘧啶和甲醇中。供

6、試樣品可以用該試劑直接滴定，或者可以使用剩余滴定程序來(lái)進(jìn)行分析。此反應(yīng)的化學(xué)計(jì)量比不夠準(zhǔn)確，檢測(cè)的重現(xiàn)性取決于某些因素，例如該試劑成分的相對(duì)濃度、用于溶解供試樣品的惰性溶劑的性質(zhì)、測(cè)定所用的具體方法等。因此，需要使用經(jīng)驗(yàn)性的標(biāo)準(zhǔn)化方法，以保證必要的準(zhǔn)確性。該方法中的精密度很大程度上取決于將大氣濕度從該系統(tǒng)中排除的程度。水分滴定通常使用無(wú)水甲醇作為供試樣品的溶劑。在有些情況下，特殊或不常見(jiàn)的供試樣品也可以使用其他合適的溶劑。在此種情況下，推薦加入至少 20%的甲醇或者其他伯醇。USP36In the original titrimetric solution, known as Karl Fis

7、cher Reagent, the sulfur dioxide and iodine are dissolved in pyridine and methanol. The test specimen may be titrated with the Reagent directly, or the analysis may be carried out by a residual titration procedure. The stoichiometry of the reaction is not exact, and the reproducibility of a determin

8、ation depends upon such factors as the relative concentrations of the Reagent ingredients, the nature of the inert solvent used to dissolve the test specimen, and the technique used in the particular determination. Therefore, an empirically standardized technique is used in order to achieve the desi

9、red accuracy. Precision in the method is governed largely by the extent to which atmospheric moisture is excluded from the system. The titration of water is usually carried out with the use of anhydrous methanol as the solvent for the test specimen. In some cases, other suitable solvents may be used

10、 for special or unusual test specimens. In these cases, the addition of at least 20% of methanol or other primary alcohol is recommended. USP36設(shè)備：任何能夠充分排除大氣濕度，并能確定滴定終點(diǎn)的儀器都可以使用。在直接滴定無(wú)色溶液的情況下，可以通過(guò)從金絲雀黃到琥珀色的顏色改變來(lái)觀察此終點(diǎn)。在向供試樣品作殘留滴定的情況下，會(huì)觀察到與此相反的情況。但是，更常見(jiàn)的情況是，使用儀器依靠電勢(shì)確定終點(diǎn)。該向浸沒(méi)在待滴定溶液中的一對(duì)白金電極上施加 200mV 左右的電壓

11、，形成簡(jiǎn)單電路。在滴定終點(diǎn)，略微過(guò)量的該試劑會(huì)使電流提高到 50 和 150 微安培，并維持30 秒到 30 分鐘，具體時(shí)間取決于被滴定的溶液?？扇芙庥谠撛噭┲械奈镔|(zhì)對(duì)應(yīng)的時(shí)間是最短的。在一些自動(dòng)滴定儀上，在該終點(diǎn)出現(xiàn)的電流或電壓的突然變化會(huì)使盛裝滴定液的滴定管的電磁閥關(guān)閉。市場(chǎng)上銷售的儀器通常包含一個(gè)封閉系統(tǒng)，由一個(gè)或兩個(gè)自動(dòng)滴定管、一個(gè)配備了電極和磁力攪拌器的密封的滴定容器組成。系統(tǒng)內(nèi)空氣通過(guò)適當(dāng)?shù)母稍飫┍３指稍铮摰味ㄈ萜骺梢酝ㄟ^(guò)干燥氮?dú)饬骰蚋稍锟諝饬鱽?lái)進(jìn)行凈化。Apparatus Any apparatus may be used that provides for adequate

12、exclusion of atmospheric moisture and determination of the endpoint. In the case of a colorless solution that is titrated directly, the endpoint may be observed visually as a change in color from canary yellow to amber. The reverse is observed in the case of a test specimen that is titrated residual

13、ly. More commonly, however, the endpoint is determined electrometrically with an apparatus employing a simple electrical circuit that serves to impress about 200 mV of applied potential between a pair of platinum electrodes immersed in the solution to be titrated. At the endpoint of the titration a

14、slight excess of the reagent increases the flow of current to between 50 and 150 microamperes for 30 seconds to 30 minutes, depending upon the solution being titrated. The time is shortest for substances that dissolve in the reagent. With some automatic titrators, the abrupt change in current or pot

15、ential at the endpoint serves to close a solenoid-operated valve that controls the buret delivering the titrant. Commercially available apparatus generally comprises a closed system consisting of one or two automatic burets and a tightly covered titration vessel fitted with the necessary electrodes

16、and a magnetic stirrer. The air in the system is kept dry with a suitable desiccant, and the titration vessel may be purged by means of a stream of dry nitrogen or current of dry air. 試劑：按下面方法配制卡爾費(fèi)休試劑。將 125 克碘加入到含有 670mL 甲醇和 170mL 嘧啶的溶液中，放冷。將 100mL 嘧啶置于一個(gè) 250mL 量筒中，冰浴中冷卻，送入干燥的二氧化硫直到體積達(dá)到 200mL。邊振搖邊緩慢

17、將此溶液加入到放冷后的碘混合物中。搖動(dòng)以使碘溶解，轉(zhuǎn)移此溶液至設(shè)備中，并在標(biāo)定之前放置過(guò)夜。新制的 1mL 此溶液相當(dāng)于約5mg 水，但是會(huì)逐漸變差；因此，在使用前 1 個(gè)小時(shí)需對(duì)其標(biāo)定，或在連續(xù)使用時(shí)每日標(biāo)定。使用中需避光。將該試劑的散裝存貨保存于適當(dāng)密閉的玻璃塞容器中，完全避光，并冷藏。測(cè)定痕量的水（小于 1%）時(shí)，最好使用水當(dāng)量因子不小于 2.0 的試劑，以使滴定液的消耗量較為明顯。USP36Reagent Prepare the Karl Fischer Reagent as follows. Add 125 g of iodine to a solution containing 6

18、70 mL of methanol and 170 mL of pyridine, and cool. Place 100 mL of pyridine in a 250-mL graduated cylinder, and, keeping the pyridine cold in an ice bath, pass in dry sulfur dioxide until the volume reaches 200 mL. Slowly add this solution, with shaking, to the cooled iodine mixture. Shake to disso

19、lve the iodine, transfer the solution to the apparatus, and allow the solution to stand overnight before standardizing. One mL of this solution when freshly prepared is equivalent to approximately 5 mg of water, but it deteriorates gradually; therefore, standardize it within 1 h before use, or daily

20、 if in continuous use. Protect from light while in use. Store any bulk stock of the reagent in a suitably sealed, glass-stoppered container, fully protected from light, and under refrigeration. For determination of trace amounts of water (less than 1%), it is preferable to use a Reagent with a water

21、 equivalency factor of not more than 2.0, which will lead to the consumption of a more significant volume of titrant. USP36可以使用市售的卡爾費(fèi)休類型試劑的穩(wěn)定溶液。也可以使用市售的含有除了嘧啶之外的溶劑或堿，或除了甲醇之外的醇類的試劑。這些試劑可以是單一的溶液，也可以是通過(guò)原位混合兩種含有試劑各組分的溶液形成的試劑。如果某些各論中要求使用稀釋后的試劑，則應(yīng)當(dāng)按照生產(chǎn)商的規(guī)定稀釋。可以使用甲醇或其他適當(dāng)溶劑，例如乙二醇一甲醚，作為稀釋劑。A commercially ava

22、ilable, stabilized solution of Karl Fischer type reagent may be used. Commercially available reagents containing solvents or bases other than pyridine or alcohols other than methanol may be used also. These may be single solutions or reagents formed in situ by combining the components of the reagent

23、s present in two discrete solutions. The diluted Reagent called for in some monographs should be diluted as directed by the manufacturer. Either methanol or other suitable solvent, such as ethylene glycol monomethyl ether, may be used as the diluent.供試溶液：除非在各論中另有規(guī)定，精密稱定或量取一定量的供試樣品，其中含水估計(jì)在2 至 250mg 之

24、間。含水的量取決于試劑的水當(dāng)量因子和終點(diǎn)測(cè)定的方法。在大多數(shù)情況下，可以使用此公式估計(jì)供試樣品的最小量（以毫克計(jì)算）：FCV/KF其中，F(xiàn) 是試劑的水當(dāng)量因子，單位為毫克每毫升；C 是滴定管容量中所使用的體積的百分比；V 是滴定管體積，以毫升計(jì)；KF 是樣品中限度或合理預(yù)期的水含量百分比。對(duì)于手動(dòng)滴定，C 值一般在 30%至 100%之間，而對(duì)于儀器方法終點(diǎn)測(cè)定，在 10%至 100%之間。注：計(jì)算中 FCV 的乘積最好大于等于 200，以保證滴定的最小水量大于等于 2mg。Test Preparation Unless otherwise specified in the individua

25、l monograph, use an accurately weighed or measured amount of the specimen under test estimated to contain 2 to 250 mg of water. The amount of water depends on the water equivalency factor of the Reagent and on the method of endpoint determination. In most cases, the minimum amount of specimen, in mg

26、, can be estimated using the formula:FCV/KFin which F is the water equivalency factor of the Reagent, in mg per mL; C is the used volume, in percent, of the capacity of the buret; V is the buret volume, in mL; and KF is the limit or reasonable expected water content in the sample, in percent. C is g

27、enerally between 30% and 100% for manual titration, and between 10% and 100% for the instrumental method endpoint determination. Note It is recommended that the product of FCV be greater than or equal to 200 for the calculation to ensure that the minimum amount of water titrated is greater than or e

28、qual to 2 mg. 如果供試樣品是帶有推進(jìn)劑的氣霧劑，將其存放于冷凍室中不少于 2 小時(shí)，打開(kāi)容器，并檢驗(yàn) 10.0mL 混合均勻的樣品。在滴定該樣品過(guò)程中，在 10或更高的溫度下確定反應(yīng)終點(diǎn)。Where the specimen under test is an aerosol with propellant, store it in a freezer for not less than 2 h, open the container, and test 10.0 mL of the well-mixed specimen. In titrating the specimen, d

29、etermine the endpoint at a temperature of 10 or higher.如果供試樣品為膠囊，使用不少于 4 個(gè)膠囊的混合內(nèi)容物的一部分。Where the specimen under test is capsules, use a portion of the mixed contents of not fewer than four capsules.如果供試品為片劑，在已知不會(huì)影響檢驗(yàn)結(jié)果的溫度和相對(duì)濕度環(huán)境中，使用不少于 4 片磨碎的細(xì)粉末。Where the specimen under test is tablets, use powder f

30、rom not fewer than four tablets ground to a fine powder in an atmosphere of temperature and relative humidity known not to influence the results.如果各論中顯示供試樣品具有吸濕性，精密稱取一份該固體制劑轉(zhuǎn)移至滴定容器中，盡快操作并小心避免其吸收空氣中的水汽。如果樣品量有限例如凍干制劑或瓶裝粉劑，USP36使用一個(gè)干燥注射器，注射經(jīng)過(guò)精確稱量的適當(dāng)體積的甲醇或其他適當(dāng)溶劑至已去皮的容器中，搖動(dòng)以使該樣品溶解。使用同一個(gè)注射器，從該容器中吸出此溶液并轉(zhuǎn)移至

31、按照測(cè)試方法下規(guī)定準(zhǔn)備的滴定容器中。使用精確稱量的第二份甲醇或其他適當(dāng)溶劑重復(fù)該步驟，將此洗液加入至滴定容器，并立刻滴定。取與用于溶解樣品以及洗滌容器和注射器的溶劑同樣體積的一部分溶劑，按照剩余滴定的水溶液的標(biāo)定項(xiàng)下的規(guī)定，測(cè)定溶劑中的水分含量（以 mg 為單位），并從供試樣品滴定的水分含量（以 mg 為單位）中減去此數(shù)值。在100溫度條件下將容器及其蓋子干燥 3 小時(shí)，在干燥器中冷卻，稱重。根據(jù)該容器與其初始重量的差來(lái)確定所測(cè)定的樣品的重量。Where the monograph specifies that the specimen under test is hygroscopic, t

32、ake an accurately weighed portion of the solid into the titration vessel, proceeding as soon as possible and taking care to avoid moisture uptake from the atmosphere. If the sample is constituted by a finite amount of solid as a lyophilized product or a powder inside a vial, USP36 use a dry syringe

33、to inject an appropriate volume of methanol, or other suitable solvent, accurately measured, into a tared container, and shake to dissolve the specimen. Using the same syringe, remove the solution from the container and transfer it to a titration vessel prepared as directed for Procedure. Repeat the

34、 procedure with a second portion of methanol, or other suitable solvent, accurately measured, add this washing to the titration vessel, and immediately titrate. Determine the water content, in mg, of a portion of solvent of the same total volume as that used to dissolve the specimen and to wash the

35、container and syringe, as directed for Standardization of Water Solution for Residual Titration, and subtract this value from the water content, in mg, obtained in the titration of the specimen under test. Dry the container and its closure at 100 for 3 h, allow to cool in a desiccator, and weigh. De

36、termine the weight of specimen tested from the difference in weight from the initial weight of the container.如果合適，水可以通過(guò)和滴定容器相通的外接爐加熱從樣品中脫附或釋放出來(lái)，然后由惰性的干燥氣體例如純氮?dú)鈳氲味ㄈ萜髦小Ｐ枰⒁夂陀?jì)算由載氣導(dǎo)致的漂移。需要小心選擇加熱條件以避免由于樣品成分分解脫水而生成水。這樣會(huì)使此方法失效。USP36 When appropriate, the water may be desorbed or released from the sample b

37、y heat in an external oven connected with the vessel, to where it is transferred with the aid of an inert and dried gas such as pure nitrogen. Any drift due to the transport gas should be considered and corrected. Care should be taken in the selection of the heating conditions to avoid the formation

38、 of water coming from dehydration due to decomposition of the sample constituents, which may invalidate this approach. USP36試劑的標(biāo)定：在滴定容器中加入足以淹沒(méi)電極的甲醇或其他適當(dāng)溶劑，并加入足量的試劑，以產(chǎn)生滴定終點(diǎn)的特征顏色，或者在約 200mV 外加電壓下產(chǎn)生 100 50 微安培直流電。Standardization of the Reagent Place enough methanol or other suitable solvent in the titr

39、ation vessel to cover the electrodes, and add sufficient Reagent to give the characteristic endpoint color, or 100 50 microamperes of direct current at about 200 mV of applied potential.純化水，二水合酒石酸鈉（USP 標(biāo)準(zhǔn)物質(zhì)）或者具有可追溯到國(guó)家標(biāo)準(zhǔn)的檢驗(yàn)合格證明的市售標(biāo)準(zhǔn)物質(zhì)可以被用來(lái)對(duì)試劑進(jìn)行標(biāo)定。試劑的當(dāng)量因子，推薦低定量，滴定管尺寸，以及標(biāo)準(zhǔn)物質(zhì)用量都是考慮使用何種標(biāo)準(zhǔn)物質(zhì)和其用量的參數(shù)i。對(duì)于純化水

40、或水標(biāo)準(zhǔn)品，快速加入相當(dāng)于 2 到 250mg 水的量。計(jì)算水當(dāng)量因子 F，單位為 mg 水每 mL：W/V其中 W(mg)是標(biāo)準(zhǔn)試樣中水分的重量，以 mg 為單位；V(mL)是滴定中消耗試劑的體積。對(duì)于二水合酒石酸鈉，快速加入差量法精密稱定的 20-125mg 二水合酒石酸鈉(C4H4Na2O6 2H2O)，滴定至終點(diǎn)。水當(dāng)量因子 F，單位為 mg 水每 mL 試劑，由下式給出：W/V (36.04/230.08)其中 36.04 是 2 倍的水的摩爾重量，230.08 是二水合酒石酸鈉的摩爾重量。W(mg)是二水合酒石酸鈉的重量，V(mL)是第二次滴定中消耗試劑的體積。注意二水合酒石酸鈉在

41、甲醇中的溶解度，滴定更多的二水合酒石酸鈉可能需要加入更多新鮮的甲醇。Purified Water, sodium tartrate dihydrate, a USP Reference Standard, or commercial standards with a certificate of analysis traceable to a national standard may be used to standardize the Reagent. The reagent equivalency factor, the recommended titration volume, bur

42、et size, and amount of standard to measure are factors to consider when deciding which standard and how much to use.1 For Purified Water or water standards, quickly add the equivalent of between 2 and 250 mg of water. Calculate the water equivalency factor,F, in mg of water per mL of reagent:W/Vin w

43、hich W is the weight, in mg, of the water contained in the aliquot of standard used; and V is the volume, in mL, of the Reagent used in the titration. For sodium tartrate dihydrate, quickly add 20125 mg of sodium tartrate dihydrate (C4H4Na2O6 2H2O), accurately weighed by difference, and titrate to t

44、he endpoint. The water equivalence factor F, in mg of water per mL of reagent, is given by the formula:W/V (36.04/230.08)in which 36.04 is two times the molecular weight of water and 230.08 is the molecular weight of sodium tartrate dihydrate; W is the weight, in mg, of sodium tartrate dihydrate; an

45、d Vis the volume, in mL, of the Reagent consumed in the second titration. Note that the solubility of sodium tartrate dihydrate in methanol is such that fresh methanol may be needed for additional titrations of the sodium tartrate dihydrate standard.檢測(cè)方法：除各論中另有規(guī)定外，轉(zhuǎn)移足夠量的甲醇或其他合適的溶劑入滴定容器中，確保該體積足夠淹沒(méi)電極（

46、約 30-40mL），以試劑滴定至電化學(xué)或目測(cè)終點(diǎn)，以消耗掉可能存在的水蒸氣。（忽略消耗的體積，因?yàn)槠洳贿M(jìn)入計(jì)算當(dāng)中。）快速加入供試溶液，混合，再次用試劑滴定至電化學(xué)或目測(cè)終點(diǎn)。計(jì)算被測(cè)樣品的水分含量，以 mg 為單位：SF其中 S(mL)為第二次滴定中消耗的試劑體積，F(xiàn) 為試劑的水當(dāng)量因子。Procedure Unless otherwise specified, transfer enough methanol or other suitable solvent to the titration vessel, ensuring that the volume is sufficient

47、to cover the electrodes (approximately 3040 mL), and titrate with the Reagent to the electrometric or visual endpoint to consume any moisture that may be present. (Disregard the volume consumed, because it does not enter into the calculations.) Quickly add the Test Preparation, mix, and again titrat

48、e with the Reagent to the electrometric or visual endpoint. Calculate the water content of the specimen taken, in mg:SFin which S is the volume, in mL, of the Reagent consumed in the second titration; and F is the water equivalence factor of the Reagent.方法 Ib（剩余滴定）Method Ib (Residual Titration)原理：見(jiàn)方

49、法 Ia 部分的原理項(xiàng)下信息。在剩余滴定中，過(guò)量的試劑被加入到被測(cè)樣品中，給予足夠的時(shí)間使其反應(yīng)完全。未被消耗的試劑用水在某溶劑（如甲醇）中的標(biāo)準(zhǔn)溶液滴定。剩余滴定的方法普適，且避免了直接滴定中可能遇到的結(jié)合水釋放緩慢的問(wèn)題。Principle See the information given in the section Principle under Method Ia. In the residual titration, excess Reagent is added to the test specimen, sufficient time is allowed for the r

50、eaction to reach completion, and the unconsumed Reagent is titrated with a standard solution of water in a solvent such as methanol. The residual titration procedure is applicable generally and avoids the difficulties that may be encountered in the direct titration of substances from which the bound

51、 water is released slowly.設(shè)備，試劑，樣品溶液：使用方法 Ia。Apparatus, Reagent, and Test Preparation Use Method Ia.剩余滴定中水溶液的標(biāo)定：將 2mL 水用甲醇或其他合適的溶劑稀釋到 1000mL，制成水溶液。用事先如試劑的標(biāo)定項(xiàng)下方法標(biāo)定的試劑滴定 25.0mL 此溶液以標(biāo)定之。計(jì)算所取水溶液中水的含量，以 mg/mL 為單位：VF/25其中 V是消耗試劑的體積，F(xiàn) 是試劑的水當(dāng)量因子。每周測(cè)定水溶液的水分含量，并用其定期按需標(biāo)定試劑。Standardization of Water Solution for

52、 Residual Titration Prepare a Water Solution by diluting 2 mL of water with methanol or other suitable solvent to 1000 mL. Standardize this solution by titrating 25.0 mL with the Reagent, previously standardized as directed under Standardization of the Reagent. Calculate the water content, in mg per

53、 mL, of the Water Solution taken:V F/25in which V is the volume of the Reagent consumed, and F is the water equivalence factor of the Reagent. Determine the water content of the Water Solution weekly, and standardize the Reagent against it periodically as needed.測(cè)試方法：如果各論中規(guī)定水分測(cè)定使用方法 Ib，轉(zhuǎn)移足夠的甲醇或其他合適的

54、溶劑至滴定容器中，確保該體積足夠淹沒(méi)電極（約 30-40mL），以試劑滴定至電化學(xué)或目測(cè)終點(diǎn)?？焖偌尤霕悠啡芤?，混合，加入精確量取的過(guò)量的試劑。放置足夠長(zhǎng)的時(shí)間讓反應(yīng)完全，然后使用標(biāo)定的水溶液滴定未被消耗的試劑至電化學(xué)或目測(cè)終點(diǎn)。計(jì)算所取樣品中的水分含量(mg)：F(X - XR)其中 F 是試劑的水當(dāng)量因子，X (mL) 是引入樣品后加入試劑的體積，X (mL)是用于中和未被消耗的試劑的標(biāo)定過(guò)的水溶液的體積，R 是比例因子，V/25 (mL 試劑/mL水溶液)，由剩余滴定中水溶液的標(biāo)定項(xiàng)測(cè)得。Procedure Where the individual monograph specifies

55、 that the water content is to be determined by Method Ib, transfer enough methanol or other suitable solvent to the titration vessel, ensuring that the volume is sufficient to cover the electrodes (approximately 3040 mL), and titrate with the Reagent to the electrometric or visual endpoint. Quickly

56、add theTest Preparation, mix, and add an accurately measured excess of the Reagent. Allow sufficient time for the reaction to reach completion, and titrate the unconsumed Reagent with standardized Water Solution to the electrometric or visual endpoint. Calculate the water content of the specimen, in

57、 mg, taken:F(X - XR)in which F is the water equivalence factor of the Reagent; X is the volume, in mL, of the Reagent added after introduction of the specimen; X is the volume, in mL, of standardized Water Solution required to neutralize the unconsumed Reagent; and R is the ratio, V /25 (mL Reagent/

58、mL Water Solution), determined from the Standardization of Water Solution for Residual Titration.方法 Ic（庫(kù)侖滴定）Method Ic (Coulometric Titration)原理：庫(kù)侖滴定法水分測(cè)定使用卡爾費(fèi)休反應(yīng)。但是，碘不是由定量試液引入，而是由含碘離子的溶液在陽(yáng)極氧化反應(yīng)中生成。反應(yīng)池通常包含一個(gè)大的陽(yáng)極池和一個(gè)小的陰極池，由隔膜隔開(kāi)。其他合適的反應(yīng)池（例如沒(méi)有隔膜的）也可以使用。每個(gè)電極池都有一個(gè)鉑金電極以讓電流通過(guò)反應(yīng)池。陽(yáng)極氧化生成的碘立刻與電極池中的水反應(yīng)。當(dāng)所有的水杯消耗

59、掉以后，過(guò)量的碘出現(xiàn)，通常由電位計(jì)測(cè)量，以指示反應(yīng)終點(diǎn)。預(yù)先電解以除去系統(tǒng)中的水汽。每次測(cè)定后不需要更換卡爾費(fèi)休試劑，因?yàn)闇y(cè)定可以繼續(xù)在同樣的試劑溶液中進(jìn)行。此方法的要求是被測(cè)樣品的每種成分都互相相容，且測(cè)試中不發(fā)生副反應(yīng)。樣品溶液通常通過(guò)注射的方法透過(guò)隔膜進(jìn)入到樣品池中。氣體可以通過(guò)可以通過(guò)合適的進(jìn)樣管加入樣品池。這個(gè)方法的精密度很大程度上取決于系統(tǒng)與大氣中水汽的隔絕程度。因此，將固體加入到電解池中時(shí)需要某些預(yù)防措施，例如在惰性干燥氣氛的手套箱中操作?？梢愿鶕?jù)基線漂移的程度監(jiān)視系統(tǒng)的控制。但是這并不意味著當(dāng)這樣引入樣品時(shí)可以省略空白校正。USP36 本方法尤其適合于化學(xué)惰性物質(zhì)例如碳?xì)浠衔?/p>

60、，醇類，醚類，等等。相比于卡爾費(fèi)休計(jì)量滴定，庫(kù)侖滴定是一種微量方法。Principle The Karl Fischer reaction is used in the coulometric determination of water. Iodine, however, is not added in the form of a volumetric solution but is produced in an iodide-containing solution by anodic oxidation. The reaction cell usually consists of a la