【求助】请各位帮忙

取本品1.0g溶于25ml水中,振摇,滤过.加1N醋酸2ml,再加入2ml氯化钡试液.

下面一句话的意思我不太理解.因为化学学的不好,我不知道是待测物与氯化钡反应生成的沉淀不得比氯化钡与0.20ml0.020N的硫酸反应生成的沉淀更多还是别的什么.在我看来这是规定了待测物中硫的限度.

我的理解是:待测物所配成的溶液加入过量的氯化钡,产生的沉淀不得超过0.20ml硫酸(0.020N)与过量氯化钡反应所生成的沉淀.

先谢谢楼上的了。 它这里有没有象中国药典中那样“与上同法处理”的意思，要不怎么比较？这里应该是通过溶液的混浊程度来比较吧！

有上下文吗?

全文：
Acetaminophen

C8H9NO2 151.16

Acetamide, N-(4-hydroxyphenyl)-.
4¢-Hydroxyacetanilide [103-90-2].
» Acetaminophen contains not less than 98.0 percent and not more than 101.0 percent of C8H9NO2, calculated on the anhydrous basis.
Packaging and storage— Preserve in tight, light-resistant containers, and store at controlled room temperature.
USP Reference standards 11— USP Acetaminophen RS.
Identification—
A: Infrared Absorption 197K.
B: Ultraviolet Absorption 197U—
Solution: 5 µg per mL.
Medium: 0.1 N hydrochloric acid in methanol (1 in 100).
C: It responds to the Thin-layer Chromatographic Identification Test 201, a test solution in methanol containing about 1 mg per mL and a solvent system consisting of a mixture of methylene chloride and methanol (4:1) being used.
Melting range 741: between 168 and 172.
Water, Method I 921: not more than 0.5%.
Residue on ignition 281: not more than 0.1%.
Chloride 221— Shake 1.0 g with 25 mL of water, filter, and add 1 mL of 2 N nitric acid and 1 mL of silver nitrate TS: the filtrate shows no more chloride than corresponds to 0.20 mL of 0.020 N hydrochloric acid (0.014%).
Sulfate 221— Shake 1.0 g with 25 mL of water, filter, add 2 mL of 1 N acetic acid, then add 2 mL of barium chloride TS: the mixture shows no more sulfate than corresponds to 0.20 mL of 0.020 N sulfuric acid (0.02%).
Sulfide— Place about 2.5 g in a 50-mL beaker. Add 5 mL of alcohol and 1 mL of 3 N hydrochloric acid. Moisten a piece of lead acetate test paper with water, and fix to the underside of a watch glass. Cover the beaker with the watch glass so that part of the lead acetate paper hangs down near the pouring spout of the beaker. Heat the contents of the beaker on a hot plate just to boiling: no coloration or spotting of the test paper occurs.
Heavy metals, Method II 231: 0.001%.
Free p-aminophenol— Transfer 5.0 g to a 100-mL volumetric flask, and dissolve in about 75 mL of a mixture of equal volumes of methanol and water. Add 5.0 mL of alkaline nitroferricyanide solution (prepared by dissolving 1 g of sodium nitroferricyanide and 1 g of anhydrous sodium carbonate in 100 mL of water), dilute with a mixture of equal volumes of methanol and water to volume, mix, and allow to stand for 30 minutes. Concomitantly determine the absorbances of this solution and of a freshly prepared solution of p-aminophenol, similarly prepared at a concentration of 2.5 µg per mL, using the same quantities of the same reagents, in 1-cm cells, at the maximum at about 710 nm, with a suitable spectrophotometer, using 5.0 mL of alkaline nitroferricyanide solution diluted with a mixture of equal volumes of methanol and water to 100 mL as the blank: the absorbance of the test solution does not exceed that of the standard solution, corresponding to not more than 0.005% of p-aminophenol.
Limit of p-chloroacetanilide— Transfer 1.0 g to a glass-stoppered, 15-mL centrifuge tube, add 5.0 mL of ether, shake by mechanical means for 30 minutes, and centrifuge at 1000 rpm for 15 minutes or until a clean separation is obtained. Apply 200 µL of the supernatant, in 40-µL portions, to obtain a single spot not more than 10 mm in diameter to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Similarly apply 40 µL of a Standard solution in ether containing 10 µg of p-chloroacetanilide per mL, and allow the spots to dry. Develop the chromatogram in an unsaturated chamber, with a solvent system consisting of a mixture of solvent hexane and acetone (75:25), until the solvent front has moved three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Locate the spots in the chromatogram by examination under short-wavelength UV light: any spot obtained from the solution under test, at an RF value corresponding to the principal spot from the Standard solution, is not greater in size or intensity than the principal spot obtained from the Standard solution, corresponding to not more than 0.001% of p-chloroacetanilide.
Readily carbonizable substances 271— Dissolve 0.50 g in 5 mL of sulfuric acid TS: the solution has no more color than Matching Fluid A.
Organic volatile impurities, Method V 467: meets the requirements.
Solvent— Use dimethyl sulfoxide.
Residual solvents 467: meets the requirements.
(Official January 1, 2007)
Assay— Dissolve about 120 mg of Acetaminophen, accurately weighed, in 10 mL of methanol in a 500-mL volumetric flask, dilute with water to volume, and mix. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix. Concomitantly determine the absorbances of this solution and of a Standard solution of USP Acetaminophen RS, in the same medium, at a concentration of about 12 µg per mL in 1-cm cells, at the wavelength of maximum absorbance at about 244 nm, with a suitable spectrophotometer, using water as the blank. Calculate the quantity, in mg, of C8H9NO2 in the Acetaminophen taken by the formula:
10C(AU / AS),
in which C is the concentration, in µg per mL, of USP Acetaminophen RS in the Standard solution; and AU and AS are the absorbances of the solution of Acetaminophen and the Standard solution, respectively.
Auxiliary Information— Staff Liaison : Clydewyn M. Anthony, Ph.D., Scientist
Expert Committee : (MDCCA05) Monograph Development-Cough Cold and Analgesics
USP29–NF24 Page 18
Pharmacopeial Forum : Volume No. 31(4) Page 1024
Phone Number : 1-301-816-8139

原来是对乙酰氨基酚啊，那我的理解是对的。CP2005版上有APAP硫酸盐的测定，是用比色法。把标准硫酸钾溶液作为对照溶液，待测溶液和对照溶液分别加入氯化钡然后置黑色背景上观察，待测液也对照液比较不得更浓。以后遇到这种情况你可以先看一下中国药典。