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小木虫论坛-学术科研互动平台 » 化学化工区 » 分析 » 化学分析 » 请教硬脂酸钠的检测方法
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mllove2222

金虫 (小有名气)

[求助] 请教硬脂酸钠的检测方法

请教各位大神，我想检测硬脂酸钠水溶液的浓度，请问有什么简单易行的检测方法么？谢谢！！！
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1楼 2013-05-31 16:33:21
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lifucheng

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mllove2222: 金币+2, ★有帮助 2013-06-01 09:49:30
加入钙离子或者镁离子，硬脂酸钠会与钙离子或镁离子生成硬脂酸钙过硬脂酸镁沉淀，可以定性的检测。如果要定量的话，还是用离子色谱吧，估计得用离子对模式了。
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2楼2013-05-31 21:00:29
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yugijiang

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mllove2222: 金币+4, ★有帮助, 很详细，请问有简单的化学法么？希望找一种不要仪器分析的方法。 2013-06-01 09:51:46
Sodium Stearate
(soe' dee um steer' ate).

Octadecanoic acid, sodium salt;     
Sodium stearate    [822-16-2].
DEFINITION
Sodium Stearate is a mixture of sodium stearate (C18H35NaO2) and sodium palmitate (C16H31NaO2), which together constitute NLT 90.0% of the total content. The content of C18H35NaO2 is NLT 40.0% of the total. Sodium stearate contains small amounts of the sodium salts of other fatty acids.
IDENTIFICATION
•  A. When heated, it fuses. At a high temperature it decomposes, emitting flammable vapors and the odor of burning fat, finally leaving a residue that, when moistened with water, is alkaline to litmus paper, effervesces with acids, and colors a nonluminous flame intensely yellow.
•  B.
Sample: 25 g
Analysis: Dissolve the Sample in 300 mL of hot water, add 60 mL of 2 N sulfuric acid, and heat the solution, with frequent stirring, until the separated fatty acid layer is clear. Wash the fatty acids with boiling water until they are free from sulfate, collect in a small beaker, and warm on a steam bath until the water has settled and the fatty acids are clear. Allow the acids to cool, pour off the water layer, then melt the acids, filter into a dry beaker while hot, and dry at 105 for 20 min.
Acceptance criteria: The solidification temperature of the fatty acids is NLT 54.
ASSAY
•  Procedure
Standard solution: Transfer 50 mg of USP Stearic Acid RS and 50 mg of USP Palmitic Acid RS into a small conical flask fitted with a suitable reflux attachment. Add 5.0 mL of a solution prepared by dissolving 14 g of boron trifluoride in methanol to make 100 mL; swirl and reflux for 15 min or until the solid is dissolved. Cool, transfer the reaction mixture with the aid of 10 mL of chromatographic solvent hexane to a 60-mL separator, and add 10 mL of water and 10 mL of saturated sodium chloride solution. Shake, allow to separate, then drain and discard the lower, aqueous layer. Pass the hexane layer through 6 g of anhydrous sodium sulfate (previously washed with chromatographic solvent hexane) into a suitable flask.
Sample solution: Transfer 100 mg of Sodium Stearate into a small conical flask fitted with a suitable reflux attachment. Add 5.0 mL of a solution prepared by dissolving 14 g of boron trifluoride in methanol to make 100 mL; swirl and reflux for 15 min or until the solid is dissolved. Cool, transfer the reaction mixture with the aid of 10 mL of chromatographic solvent hexane to a 60-mL separator, and add 10 mL of water and 10 mL of saturated sodium chloride solution. Shake, allow to separate, then drain and discard the lower, aqueous layer. Pass the hexane layer through 6 g of anhydrous sodium sulfate (previously washed with chromatographic solvent hexane) into a suitable flask.
Chromatographic system
(See Chromatography 621, System Suitability.)
Mode: GC
Detector: Flame ionization
Column: 1.5-m × 3-mm, preferably glass; packed with 15% G4 on support S1A
Carrier gas: Helium, passed through a bed of molecular sieve for drying, if necessary.
Injection volume: 1–2 μL
Temperatures
Injection port: 210
Detector: 210
Column: 165
System suitability
Samples: Standard solution and Sample solution
Suitability requirements
Resolution: NLT 2.0 between methyl palmitate and methyl stearate, Sample solution
[NOTE—Locate the peaks by comparison with the chromatogram from the Standard solution. ]
Relative standard deviation: NMT 1.5% for methyl stearate and methyl palmitate for five replicate injections of the Sample solution
Analysis
Sample: Sample solution
Calculate the percentage of sodium stearate (C18H35NaO2) in the portion of Sodium Stearate taken:
Result = (A/B) × 100
A        =        = peak area due to methyl stearate
B        =        = sum of the peak areas of all the fatty acid esters
Calculate the percentage of sodium palmitate (C16H31NaO2) in the portion of Sodium Stearate taken:
Result = (A/B) × 100
A        =        = peak area due to methyl palmitate
B        =        = sum of the peak areas of all the fatty acid esters
Acceptance criteria
Sodium stearate: NLT 40.0%
Sum of sodium stearate and sodium palmitate: NLT 90.0%
SPECIFIC TESTS
•  Acidity
Sample solution: Heat 50 mL of alcohol to the same temperature, ±5, as that attained when the pink endpoint is reached in the titration of the sample specimen. Add 3 drops of phenolphthalein TS and sufficient 0.020 N sodium hydroxide to produce a faint pink color. Add 2.00 g of Sodium Stearate, and dissolve with the aid of a small amount of heat: no pink color is produced.
Analysis: Titrate the solution with 0.020 N sodium hydroxide until a pink color is produced.
Acceptance criteria: 1.00–4.25 mL of 0.020 N sodium hydroxide is required (0.28%–1.2% as stearic acid).
•  Loss on Drying 731
Sample: Tare a beaker containing 1 g of washed sand, previously dried at 105, add 500 mg of Sodium Stearate, and again weigh.
Analysis: To the Sample add 10 mL of alcohol and evaporate at 80 to dryness, and dry at 105 for 4 h.
Acceptance criteria: NMT 5.0%
•  Fats and Fixed Oils, Acid Value of Fatty Acids401
Sample: 1 g of the fatty acids obtained in Identification test B
Acceptance criteria: 196–211
•  Fats and Fixed Oils, Iodine Value of Fatty Acids401
Sample: The fatty acids obtained in Identification test B
Acceptance criteria: NMT 4.0
•  Alcohol-Insoluble Substances
Sample solution: Reflux 1.0 g with 25 mL of alcohol.
Analysis: It dissolves completely, and the resulting solution is clear or NMT slightly opalescent.
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in well-closed, light-resistant containers.
•  USP Reference Standards 11
USP Palmitic Acid RS
USP Stearic Acid RS
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3楼2013-05-31 21:14:56
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fjy135974

金虫 (小有名气)
可以取一定量的溶液，置于烘箱中把水烘干，称取剩余固体的质量，即可得到溶液的浓度。
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我们从不开口那个言语，那一句我爱你，永远像少了勇气…
4楼2014-07-08 15:41:03
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