á231ñ HEAVY METALS This test is provided to demonstrate that the content of metallic impurities that are colored by sulfide ion, under the specified test conditions, does not exceed the Heavy metals limit specified in the individual monograph in terms of the percentage (by weight) of lead in the test substance, as determined by concomitant visual comparison (see Visual Comparison in the section Procedure under Spectrophotometry and Light-Scattering á851ñ) with a control prepared from a Standard Lead Solution. [NOTE—Substances that typically will respond to this test are lead, mercury, bismuth, arsenic, antimony, tin, cadmium, silver, copper, and molybdenum.] Determine the amount of heavy metals by Method I, unless otherwise specified in the individual monograph. Method I is used for substances that yield clear, colorless preparations under the specified test conditions. Method II is used for substances that do not yield clear, colorless preparations under the test conditions specified for Method I, or for substances that, by virtue of their complex nature, interfere with the precipitation of metals by sulfide ion, or for fixed and volatile oils. Method III, a wet-digestion method, is used only in those cases where neither Method I nor Method II can be utilized.Special Reagents Lead Nitrate Stock Solution— Dissolve 159.8 mg of lead nitrate in 100 mL of water to which has been added 1 mL of nitric acid, then dilute with water to 1000 mL. Prepare and store this solution in glass containers free from soluble lead salts. Standard Lead Solution— On the day of use, dilute 10.0 mL of Lead Nitrate Stock Solution with water to 100.0 mL. Each mL of Standard Lead Solution contains the equivalent of 10 µg of lead. A comparison solution prepared on the basis of 100 µL of Standard Lead Solution per g of substance being tested contains the equivalent of 1 part of lead per million parts of substance being tested. Method I pH 3.5 Acetate Buffer— Dissolve 25.0 g of ammonium acetate in 25 mL of water, and add 38.0 mL of 6 N hydrochloric acid. Adjust, if necessary, with 6 N ammonium hydroxide or 6 N hydrochloric acid to a pH of 3.5, dilute with water to 100 mL, and mix. Standard Preparation— Into a 50-mL color-comparison tube pipet 2 mL of Standard Lead Solution (20 µg of Pb), and dilute with water to 25 mL. Adjust with 1 N acetic acid or 6 N ammonium hydroxide to a pH between 3.0 and 4.0, using short-range pH indicator paper as external indicator, dilute with water to 40 mL, and mix. Test Preparation— Into a 50-mL color-comparison tube place 25 mL of the solution prepared for the test as directed in the individual monograph; or, using the designated volume of acid where specified in the individual monograph, dissolve in and dilute with water to 25 mL the quantity, in g, of the substance to be tested, as calculated by the formula: 2.0 / (1000L),in which L is the Heavy metals limit, in percentage. Adjust with 1 N acetic acid or 6 N ammonium hydroxide to a pH between 3.0 and 4.0, using short-range pH indicator paper as external indicator, dilute with water to 40 mL, and mix. Monitor Preparation— Into a third 50-mL color-comparison tube place 25 mL of a solution prepared as directed for Test Preparation, and add 2.0 mL of Standard Lead Solution. Adjust with 1 N acetic acid or 6 N ammonium hydroxide to a pH between 3.0 and 4.0, using short-range pH indicator paper as external indicator, dilute with water to 40 mL, and mix. Procedure— To each of the three tubes containing the Standard Preparation, the Test Preparation, and the Monitor Preparation, add 2 mL of pH 3.5 Acetate Buffer, then add 1.2 mL of thioacetamide–glycerin base TS, dilute with water to 50 mL, mix, allow to stand for 2 minutes, and view downward over a white surface *: the color of the solution from the Test Preparation is not darker than that of the solution from the Standard Preparation, and the intensity of the color of the Monitor Preparation is equal to or greater than that of the Standard Preparation. [NOTE—If the color of the Monitor Preparation is lighter than that of the Standard Preparation, use Method II instead of Method I for the substance being tested.] Method II pH 3.5 Acetate Buffer— Prepare as directed under Method I. Standard Preparation— Prepare as directed under Method I. Test Preparation— Use a quantity, in g, of the substance to be tested as calculated by the formula: 2.0 / (1000L),in which L is the Heavy metals limit, in percentage. Transfer the weighed quantity of the substance to a suitable crucible, add sufficient sulfuric acid to wet the substance, and carefully ignite at a low temperature until thoroughly charred. (The crucible may be loosely covered with a suitable lid during the charring.) Add to the carbonized mass 2 mL of nitric acid and 5 drops of sulfuric acid, and heat cautiously until white fumes no longer are evolved. Ignite, preferably in a muffle furnace, at 500 to 600, until the carbon is completely burned off. Cool, add 4 mL of 6 N hydrochloric acid, cover, digest on a steam bath for 15 minutes, uncover, and slowly evaporate on a steam bath to dryness. Moisten the residue with 1 drop of hydrochloric acid, add 10 mL of hot water, and digest for 2 minutes. Add 6 N ammonium hydroxide dropwise, until the solution is just alkaline to litmus paper, dilute with water to 25 mL, and adjust with 1 N acetic acid to a pH between 3.0 and 4.0, using short-range pH indicator paper as external indicator. Filter if necessary, rinse the crucible and the filter with 10 mL of water, combine the filtrate and rinsing in a 50-mL color-comparison tube, dilute with water to 40 mL, and mix. Procedure— To each of the tubes containing the Standard Preparation and the Test Preparation, add 2 mL of pH 3.5 Acetate Buffer, then add 1.2 mL of thioacetamide–glycerin base TS, dilute with water to 50 mL, mix, allow to stand for 2 minutes, and view downward over a white surface*: the color of the solution from the Test Preparation is not darker than that of the solution from the Standard Preparation. Method III pH 3.5 Acetate Buffer— Prepare as directed under Method I. Standard Preparation— Transfer a mixture of 8 mL of sulfuric acid and 10 mL of nitric acid to a clean, dry, 100-mL Kjeldahl flask, and add a further volume of nitric acid equal to the incremental volume of nitric acid added to the Test Preparation. Heat the solution to the production of dense, white fumes, cool, cautiously add 10 mL of water and, if hydrogen peroxide was used in treating the Test Preparation, add a volume of 30 percent hydrogen peroxide equal to that used for the substance being tested, and boil gently to the production of dense, white fumes. Again cool, cautiously add 5 mL of water, mix, and boil gently to the production of dense, white fumes and to a volume of 2 to 3 mL. Cool, dilute cautiously with a few mL of water, add 2.0 mL of Standard Lead Solution (20 µg of Pb), and mix. Transfer to a 50-mL color-comparison tube, rinse the flask with water, adding the rinsing to the tube until the volume is 25 mL, and mix. Test Preparation— If the substance is a solid— Transfer the quantity of the test substance specified in the individual monograph to a clean, dry, 100-mL Kjeldahl flask. [NOTE—A 300-mL flask may be used if the reaction foams excessively.] Clamp the flask at an angle of 45, and add a sufficient quantity of a mixture of 8 mL of sulfuric acid and 10 mL of nitric acid to moisten the substance thoroughly. Warm gently until the reaction commences, allow the reaction to subside, and add additional portions of the same acid mixture, heating after each addition, until a total of 18 mL of the acid mixture has been added. Increase the amount of heat, and boil gently until the solution darkens. Cool, add 2 mL of nitric acid, and heat again until the solution darkens. Continue the heating, followed by addition of nitric acid until no further darkening occurs, then heat strongly to the production of dense, white fumes. Cool, cautiously add 5 mL of water, boil gently to the production of dense, white fumes, and continue heating until the volume is reduced to a few mL. Cool, cautiously add 5 mL of water, and examine the color of the solution. If the color is yellow, cautiously add 1 mL of 30 percent hydrogen peroxide, and again evaporate to the production of dense, white fumes and a volume of 2 to 3 mL. If the solution is still yellow in color, repeat the addition of 5 mL of water and the peroxide treatment. Cool, dilute cautiously with a few mL of water, and rinse into a 50-mL color-comparison tube, taking care that the combined volume does not exceed 25 mL. If the substance is a liquid— Transfer the quantity of the test substance specified in the individual monograph to a clean, dry, 100-mL Kjeldahl flask. [NOTE—A 300-mL flask may be used if the reaction foams excessively.] Clamp the flask at an angle of 45, and cautiously add a few mL of a mixture of 8 mL of sulfuric acid and 10 mL of nitric acid. Warm gently until the reaction commences, allow the reaction to subside, and proceed as directed under If the substance is a solid, beginning with “add additional portions of the same acid mixture.” Procedure— Treat the Test Preparation and the Standard Preparation as follows: Adjust the solution to a pH between 3.0 and 4.0, using short-range pH indicator paper as external indicator, with ammonium hydroxide (a dilute ammonia solution may be used, if desired, as the specified range is approached), dilute with water to 40 mL, and mix. To each tube add 2 mL of pH 3.5 Acetate Buffer, then add 1.2 mL of thioacetamide-glycerin base TS, dilute with water to 50 mL, mix, allow to stand for 2 minutes, and view downward over a white surface*: the color of the Test Preparation is not darker than that of the Standard Preparation.

谢谢MSD2PhD ，要是有中文版的就更好了。

重金属该文提出了特定测定条件下，重金属杂质与二价硫离子起显色反应，显示其含量，通过与标准铅溶液的对照物作同步视觉比较，确定其含量不超过专论里以待测物里铅含量（百份含量）为标准的重金属限，（在分光光度法与光散射下面的方法部分可以看到视觉比较）。[注释：方法可以检测到铅、汞、铋、锑、银、铜和钼]除另有规定外，用方法Ⅰ测定重金属含量。方法Ⅰ适用于那些在特定测试条件下，可以得到清晰、无色的溶液。方法Ⅱ适用于那些在方法Ⅰ无法得到清晰、无色的溶液，或适用于这些物质：由于络合性质，而受到与二价硫离子起反应的金属影响，或是固定的挥发性油类。方法Ⅲ湿蒸煮法适用于既不能用方法Ⅰ也不能用方法Ⅱ的情况。 特定的溶液硝酸铅储备液——将159.8mg硝酸铅加入含有1ml硝酸的100ml水里，然后用水稀释到1000ml。制备、保存此溶液的玻璃瓶均不得含可溶性重金属。标准铅溶液——使用当天，用水将10.0 ml的硝酸铅储备液稀释到100.0ml，既得。（每ml标准铅溶相当于10mg的铅）在100 ml标准铅溶液基础上配制的对照液，每g待测物相当于待测物百万分之一的铅含量。方法ⅠPH3.5醋酸盐缓冲液——在25ml水里溶解25.0醋酸铵，加入38.0ml 6N 盐酸。如果需要，用6N氢氧化铵调节PH为3.0—4.0，加水至100 ml，混匀。标准液——移入50ml的比色管2ml标准铅溶液（含有20ug 铅）加水至25ml。用1N乙酸或6N 氢氧化铵调节PH为3.0—4.0，用精密PH试纸作为外指示剂。加水至40ml，混匀。供试液——将专论里规定的25 ml待测液加入50 ml的比色管；或用专论里说明的标定的酸，用水溶解、稀释到25ml待测物质的含量，单位g，用下式来计算2.01（1000L）其中，L是重金属的百份含量限，用1N乙酸或6N氢氧化铵调节PH为3.0—4.0，用精密试纸作为外指示剂，用稀释到40 ml，混匀。监控液——在第三个50 ml的比色管里加入25 ml供试液和2ml标准铅溶液。用1N乙酸或6N氢氧化铵调节PH为3.0—4.0，加水至40 ml，混匀。操作步骤——在盛有标准溶液，供试液和监控液的三个试管里，个加入2 ml PH为3.5的醋酸盐缓冲液，然后加入1.2 ml硫代已酰胺—甘油 平衡试液，加水至50ml，混匀，静止2分钟。置于白色背景上，依上而下观察：供试管呈色不得深于对照管，监控管呈色应深于或相同于对照管。[注释：如果监控管呈色浅于对照管，用方法Ⅱ代替方法Ⅰ来测供试品]方法ⅡPH3.5醋酸盐缓冲液——同方法Ⅰ标准液——同方法Ⅰ供试液——待测物的含量，单位g，用下式来计算：2.0/（1000L）其中L是重金属的百分含量限，将所称量的物质移到合适的坩埚，加入足量的硫酸湿润，在低温下小心燃烧直至完全炭化。（在炭化过程中，可以用合适的盖子松松地盖住坩埚）。加入炭化堆2ml硝酸和5滴硫酸，缓缓加热直至不产生烟雾。最好在500 – 600于马弗炉燃烧，直至完全炭化。冷却，加6N盐酸盐4ml，加盖在气浴上煮15分钟，掀盖，在气浴上慢慢蒸发至干。用1滴盐酸湿润残渣，加10ml热水，煮2分钟。逐滴加入6N氢氧化铵，直至溶液对湿润试纸是碱性的，加水至25ml，用1N乙酸调至PH值3.0 – 4.0 间，用精密PH试纸作为外指示剂。必要的话可以过滤，用水冲洗坩埚和过滤器，将滤液与冲洗液加入50ml比色管，加水至40ml，混匀。方法步骤——在盛有标准液，供试液的试管里各加入2mlPH3.5的醋酸盐缓冲液，然后加入1.2ml硫代乙酰胺-甘油 平衡溶液，加水至50ml，混匀，静止2分钟，置于白色背景上，以上而下观察：供试管呈色不得深于对照管。方法ⅢPH3.5的醋酸盐缓冲液——同方法Ⅰ标准液——将8ml硫酸和10ml硝酸加入干净，干燥的100-ml凯氏瓶，再加入与加入供试液中的硝酸体积相等的硝酸。加热溶液到粘稠产物，有白烟，冷却，小心加入10ml水，如果处理拱试品时，需要氢氧化铵用30%氢氧化铵其体积等于制备供试品所用的氢氧化铵的量，缓慢加热到粘稠产物，有白烟。再次冷却，小心加入5ml水，混匀，煮至粘稠，有白烟，2-3ml。冷却，用少量的水稀释，加2ml标准铅溶液（含有20ug铅），混匀。移入50ml比色管里，用水冲洗烧瓶，将冲洗液加入比色管至25ml，混匀。供试液——如果是固体——将专论里指定的供试品量加入干净、干燥的100ml凯氏瓶。[注释——如果反应泡沫特别多，可以用300ml烧瓶]。让烧瓶成45℃斜置，加8ml硫酸和10ml硝酸来充分湿润物质。缓缓加热至反应开始，反应可以减缓下来，并加入相同的酸混合物。每次加入后就加热，直至加入18mL酸混合物。升高加热温度，并缓慢地煮至溶液成黑色。继续加热，另外可以加硝酸直至无黑色物质生成，然后强热至生成粘稠产品，有白烟。冷却，缓缓加5ml水，轻轻煮沸成粘稠的，有白烟的产品，继续加热至体积变成几ml。冷却，缓缓加5ml水，1检查溶液的颜色。如果是黄色，缓缓加入1ml 30%的氢氧化铵，并蒸发成体积为2-3ml，粘稠状，具有白烟的产品。如果溶液还是黄色，再次加入5ml水，和过氧化物处理。冷却，缓缓地用一些水稀释，并冲洗到50mL比色管里，注意总体积不能超过25ml。如果是液体——将专论里指定的供试品量加入干燥、干净的100-mL凯氏瓶。[注释：如果反应泡沫特别多，可以用300ml烧瓶]让烧瓶成45℃斜置，缓缓加入8ml硫酸和10ml硝酸的混合酸。缓慢加热至反应开始，反应可以减缓下来，且可以象固体那样“从加入相同的混合酸”进行下去。操作步骤——处理供试液和标准液的方法如下：用氢氧化铵将溶液的PH值调至3.0-4.0，用精密PH试纸作为外指示剂，（如果想达到特定的范围，也可以用稀释的氨溶液），加水至40ml，混匀。在每个管里加入PH为3.5的醋酸盐缓冲液，然后加入1.2ml硫代乙酰胺-甘油 平衡试液，加水至50ml，混匀，静止2分钟，置于白色背景上，以1上而下观察：供试管呈色不得深于对照管。

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