Quantification of Sodium Polyacrylate

Plastic, Rubber Quantification of Sodium Polyacrylate

Acidbase titration by Automatic Potentiometric Titrator

Standard

1.Abstract

Sodium polyacrylate is measured by adding pure water and adjusting pH to pH12 ～12.5 with 1mol/L sodium hydroxide. All carboxyl radical in sodium polyacrylate are made sodium salt by this operation. Afterwards, titrate with 1mol/L Hydrochloric acid. The inflection point is detected 2 points and the first clear inflection point is due to excessive sodium hydroxide. The second unclear inflection point is due to carboxyl radical of sodium polyacrylate. The difference of titration volume of these 2 inflection points corresponds to the volume of sodium polyacrylate.

2.Reference

1) “Experiment and Calculation for Quantitative Analysis” –Vol.2 by Seiji Takagi from Kyoritsu Publishing Company

3.Cautions in measurement

1) Handle with care when you work on chemicals. 2) 2 inflection points are detected automatically with the combination of 2 different detection sensitivity methods, because the differentiation value of second inflection point is small when titrating with Hydrochloric acid.

TII-96004 Ver.01 1/4

4.Post-measurement care

Rinse the electrode with pure water, and keep it dipped in a beaker filled with pure water to refrain its tip from drying up.

5.Test equipment

Main unit ： Automatic potentiometric titrator (Standard preamplifier: STD-） Electrode ： Option Glass electrode Option Ceramic type reference electrode Standard Temperature compensation electrode Option ： Power burette （for pH adjustment）

6.Reagent

Titrant ： 1mo1/L Hydrochloric acid ( f=1.004 ) Additive ： Pure water, 1mo1/L Sodium hydroxide

7.Measurement procedure

―Measurement― 1) Deliver precisely weighed 3g sample to a 200mL beaker. 2) Add 100mL pure water, and stir well. 3) Adjust pH to 12～12.5 with 1mol/L Sodium hydroxide. (Method 10: Auto control) Titrate with 1mol/L Hydrochloric acid to obtain concentration of Sodium polyacrylate. (Method 11: Auto control, Method 12: Auto cut-off)

8.Formula

Sodium polyacrylate ( mg/g ) = ( EP2 － EP1 ) × FA1 × C1 × K1 / SIZE EP1 ： EP1 titration volume ( mL ) EP2 ： EP2 titration volume ( mL ) FA1 ： Factor of titrant (1.004 ) C1 ： Concentration conversion coefficient ( 94mg/mL ) K1 ： Unit conversion coefficient ( 1 ) SIZE ： Sample size ( g )

TII-96004 Ver.01 2/4

9.Example of measurement －Ambient condition－ Room temperature：24 ℃ Humidity：47 ％ Weather：Cloudy

- Titration parameter - ＊Titration parameter＊（Method 10）＊Titration parameter＊（Method 12） pH adjustment up to the second inflection point Titration form ： EP Stop Titration form ： EP Stop Titration burette ： 03 Titration burette ： 01 Reagent name ： 1M-NaOH Reagent name ： 1M-HCl Detector number ： 1 Detector number ： 1 Preamplifier unit ： pH Preamplifier unit ： pH Max. volume of burette ： 20.0 mL Max. volume of burette ： 20.0 mL Auto stirrer ： Off Auto stirrer ： Off Wait time before titration： 0 sec Wait time before titration ： 0 sec Titration direction ： Auto Titration direction ： Auto

＊Control parameter＊（Method 10）＊Control parameter＊（Method 12） EP 1 potential ： 12.0 pH Number of EP(1-3) ： 1 EP 2 potential ： 12.0 pH Auto EP redetection ： Off Over-titration ： 0.0 mL End sense（Potential）： 50.0 Gain ： 1 End sense (Differential）： 20.0 Control speed ： 0.5 Over-titration volume ： 0.0 mL Data sampling potential ： 4.0 mV Gain ： 1 Data sampling volume ： 0.5 mL Data sampling potential ： 4.0 mV Stability sense ： 0.5 mV/sec ＊Titration parameter＊（Method 11） Delay time before stability check ： 15 sec up to the first inflection point Limit time of stability check ： 30 sec Titration form ： EP Stop Data sampling volume ： 0.2 mL Titration burette ： 01 Separate potential setup ： Off Reagent name ： 1M-HCl Separate potential ： 0.0 pH Detector number ： 1 EP potential setup ： Off Preamplifier unit ： pH EP potential ： 0.0pH Max. volume of burette ： 20.0 mL Auto stirrer ： Off Wait time before titration ： 0 sec -Titration curve- Titration direction ： Auto

＊Control parameter＊（Method 11） Number of EP (1-3) ： 1 Auto redetection of EP ： Off End sense （potential）： 50.0 End sense （differential）： 100.0 Over-titration volume ： 0.0 mL Gain ： 1 Control speed ： 0.5 Data sampling potential ： 4.0 mV Data sampling volume ： 0.5 mL Separate potential setup ： Off Separate potential ： 0.0 pH EP potential setup ： Off EP potential ： 0.0 pH

(The above printout data are obtained from titration by AT-410) (Red underline shows the difference from the other method)

TII-96004 Ver.01 3/4 －Measurement results－ Number of test ３ Mean 399.76 mgNaOH/g SD 0.72 mgNaOH/g RSD 0.18 % ＊The above results were obtained by 3 tests of the same sample.

10.Summary

Sodium polyacrylate is a polymer with high water absorbability with main structure of [-CH2-CH(CO2Na)-]n. High water absorbability comes from its gel formation absorbing water molecules into its netted structure. Such feature is made use of dispoable diaper and sanitary goods.

The test result shows a good repeatability with 0.18% relative standard deviation. Precise and reliable measurement is assured by the automated potentiometry.

N-Wissen GmbH

E-Mail: [email protected] | Tel: +49 (0) 69 8900 4008

Ferdinand-Porsche-Str. 2, 63073 Offenbach - Germany

TII-96004 Ver.01 4/4