厨房洗涤剂中阴离子表面活性剂含量检测方案(自动电位滴定)

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阴离子表面活性剂含量的测定 应用资料表面活性剂分为阳离子表面活性剂、阴离子表面活性剂、两性表面活性剂和非离子表面活性剂。本应用资料使用两种检测方式(表面活性剂电极和粒子电荷检测器)测量厨房洗涤剂中所含阴离子表面活性剂的含量。京都電子工業株式会社KYOTO ELECTRONICSMANUFACTURING CO.，LTD.APAT-0149er APAT-0149er Application Note Measurement of anionic surfactants in kitchen detergent byusing surfactant electrode and particle charge detector Industry Cosmetics & soapInstrument Automatic potentiometric titratorMeasurement method Potentiometric titration / Ion-association titrationStandards QB/T 4970 1. Scope Surfactant is a compound having hydrophobic and hydrophilic parts in the molecule. Dependingon the properties of the hydrophilic part， surfactant is classified into cationic surfactant， anionicsurfactant， amphoteric surfactant， and nonionic surfactant. In these surfactants， cationic surfactants have a property which the hydrophilic group has apositive electric charge after ionic dissociation， whereas anionic surfactants have a negativecharge. Both of these electric charges react and produce association formation. The producedassociation formation is insoluble and precipitated in water by decreasing ofelectric charge andincreasing of hydrophobicity during the reaction. Potentiometric titration method uses thischemical reaction to directly titrate the ionic surfactant. This Application Note introduces thecase which the anionic surfactants contain in kitchen detergent is measured by using two kindsof detectors (surfactant electrode and particle charge detector). 2. Precautions The sensing part of the surfactant electrode does not have a high resistance to organic solvents.Therefore this part should not be cleaned with organic solvents. After measurement， theelectrode should be rinsed with distilled water and wiped off water with paper towel from thesensing part of electrode. When the particle charge detector is used， immerse the probe in ethanol after eachmeasurement and clean by driving the piston for approximately 1 minute. After that，completely remove the ethanol by rinsing it out with distilled water before starting the nextmeasurement. 3. Post-measurement procedure When the surfactant electrode is used， remove the internal solution and rinse the inside withdistilled water several times by using dropper. After the water from inside， attach the suppliedprotective cap and keep it dry. In the case that the electrode is stored with distilled waterdeterioration of the electrode is accelerated due to elution of the ingredients elements of fromthe sensitive membrane into the solution. When the particle charge detector is used， immerse the probe into ethanol， and rinse by drivingthe piston for approximately 1 minute. Remove the ethanol by rinsing with distilled water， andwipe off away water with a paper towel from the probe and keep the probe dry. 4. Apparatus ·Automatic potentiometric titrator (preamplifier ： STD) ·Combined surfactant electrode (Internal liquid： 3.3mol / L potassium chloride solution) ·Particle charge detector 京都电子工业株式会社-可睦电子(上海)商贸有限公司 上海市徐汇区宜山路333号1201室 电话：021-54488867 电邮： kemu-kem@163.com 网址： http：//www.kem-china.com 5.Reagents Titrant：0.004mol/L benzethonium chloride Solvent ： Distilled water 6. Procedure 1) Take 2.5 g kitchen detergent precisely into a beaker. 2) Add distilled water until 500mL. 3) Take 5mL the sample solution precisely in another beaker， and add 100mL distilled water. 4) Titrate sample solution with 0.004 mol/L of benzethonium chloride solution， and detectinflection point as end-point in titration curve. 7.Calculation Measurement result by using surfactant electrode (%)=EP1xTFxC1xK1/(S/R)Measurement result by using particle charge detector (%)=EP2xTFxC1xK1/(S/R) EP1 ... Titration volume of 1st end point(mL) EP2 ·.Titration volume of 2nd end point (mL) ···Factor of titrant =0.9819*CKSR ...Coefficient of concentration conversion =1.496mg/mL ·..Coefficient of unit conversion =0.1 ..Sam···ple size (g) ·.Purity， dilution factor =100 *The factor was calculated from the mass and the purity of benzethonium chloride solution whenthe titrant is prepared. 8. Example -Titration parameter- *Below parameter was used when measurement by using a surfactant electrode wasperformed. ： Intermit ： EP Stop Number of EP ：1 End Sense ：Auto Gain ：1 Max. Volume ：20(mL) Data Sampling ： Set Channel/Unit(Ctrl.) ：Ch1，mV Data sampling pot. ：999mV Channel/Unit(Ref.) ：Off Data sampling vol. ：0.1mL pH Polarity ： Standard Ctrl. Speed ： Set Titr. Type Check ： No Check Cut-off time ：7s Wait Time ：10(s) Unit volume ：0.1mL Dose Mode ： None Dispense speed ：1s/mL Other Ctrl. ： Standard Auto Int. Mode ： Standard (The above condition is an example. The setting condition depends on the titrator model.) *Below titration curve was obtained by using a surfactant electrode -Titration parameter- *Below parameter was used when measurement by using a particle charge detectorwas performed. ： Intermit ： EP Stop Number of EP ：2 End Sense ： Auto Gain ：1 Max. Volume ：20(mL) Data Sampling ： Set Channel/Unit(Ctrl.) ： Ch2，mV Data sampling pot. ：999mV Channel/Unit(Ref.) ：Off Data sampling vol. ：0.1mL pH Polarity ：： Standard Ctrl. Speed ： Set Titr. Type Check ： No Check Cut-off time ：7s Wait Time ：30(s) Unit volume ：0.1mL Dose Mode ：None Dispense speed ：1s/mL Other Ctrl. ： Standard Auto Int. Mode ： Standard Piston Speed ：7 Stirrer Speed ：4 Stirrer Speed ：4 (The above condition is an example. The setting condition depends on the titrator model. -Titration curve一 *Below titration curve was obtained by using a particle charge detector Table 1 The measurement result of anionic surfactant in kitchen detergent By using Surfactant electrode By using Particle charge detector Sample(g) Titration amount (mL) Conc.(%) Sample(g) Titration amount(mL) Conc.(%) 1 2.5397 2.4231 14.01 2.5397 2.4209 14.00 2 2.5397 2.4361 14.09 2.5397 2.3877 13.81 3 2.5397 2.4418 14.12 2.5397 2.3763 13.74 Mean 一 2.4337 14.08 一 2.3950 13.85 S.D. 一 0.0096 0.06 一 0.0232 0.13 R.S.D(%) 一 0.3938 0.39 一 0.9675 0.97 9. Summary The concentration of the anionic surfactant contained in kitchen detergent was determined bypotentiometric titrator with using two detectors (surfactant electrode and particle chargedetector). These results showed different of potential behaviors on the titration. When thesurfactant electrode is used， single inflection point was detected in the titration curve， whereaswhen the particle charge detector was used， two inflection points were observed in the titrationcurve and the second inflection point was adopted into concentration as the end point.The abovedifference is caused from difference principle of these detectors. The results by using both detectors were obtained with good repeatability which the both RSDvalues were less than 1%. Also， significant difference in these two measurement results werenot observed. The features of these detectors are summarized as follows： the surfactant electrode is reasonablePrice compared to the particle charge detector， but the general lifetime is only from 3 to 6 months.The particle charge detector is expensive than the surfactant electrode， but probe part ischemically stable， and can be continuously used unless the main body of the unit haveelectrical/mechanical failure. Nevertheless， it has measurable limitation depending on somesurfactant structures. To measure surfactants by manual analysis method， chloroform which is categorized inhazardous materials needs to be used. The method is the two-phase titration which requires acomplicated operation procedure. In automatic titration method， the samples are directly titratedwithout using chloroform， which enables simple and quick measurement. 都電子工業株式会社KYOTO ELECTRONICSMANUFACTURING CO，LTD