Validation test with water standard KF Coulometry – Heat evaporation method | Karl Fischer titrator AQ-300/MOICO-A19/EV-2000 - JM Science
HIRANUMA APPLICATION DATA Karl Fischer Titrator Data No. KF18 Nov.29. 2018
Water contents Validation test with water standard KF Coulometry – Heat evaporation method

1. Abstract

 A heat evaporation method using Karl Fischer titrator combined with solid evaporator is suitable for insoluble sample in anode solution, such as plastics and inorganic compounds. The measurement of with the heat evaporation method is carried out by heating the sample while a carrier gas is blown into the evaporation chamber and introducing the evaporated moisture together with the carrier gas into the electrolysis cell.
 This application introduces an example of measurement of solid water standard for validation of titrator system with solid evaporator.

2. Apparatus and Reagents

(1) Apparatus for heat evaporation method
    Titrator : HIRANUMA Karl Fischer Coulometric titrator AQ-series or MOICO-A19
    Evaporator : Hiranuma Solid Evaporator EV-2000
    Electrolytic cell : Standard Cell
Fritless Cell (No cathode solution required)
       
(2) Reagents    
    Anode solution : HYDRANAL Coulomat AG
    Cathode solution : HYDRANAL Coulomat CG
    Dehydrated methanol : HYDRANAL Methanol
    Carrier gas : Nitrogen gas (Dew Point : -65 ℃ or less)
       
(3) Water standard material
 (i) HYDRANAL- Standard sodium tartrate dihydrate (Honeywell)
   CoA : 15.64 %(*¹), Permissible range of recovery rate : ± 5 %(*²), Heat temperature : 160 °C
 (ii) HYDRANAL- Water Standard KF-Oven, 140-160°C (Honeywell)
   CoA : 5.04 %(*¹) , Permissible range of recovery rate : ± 4 %, Heat temperature : 140 – 160 °C
 (iii) Water Standard Oven 1 % (Merck)
   CoA : 0.99 %(*¹) , Permissible range of recovery rate : ± 3 %, Heat temperature : 140 – 400 °C

 (*1) CoA values described in the test report are different with each production lot.
 (*2) Permissible range of standard material (i) is set to our own criterion for inspection of evaporator, not described on the document of this standard.

3. Procedure

(1) Fill 100 mL of anode solution and 50 mL of dehydrated methanol into anode compartment. Fill one ampoule of cathode solution into cathode compartment (Fig.3.1). When fritless cell is used, cathode solution is not necessary.
(2) Start blanking to attain stable background.
(3) Flow N2 carrier gas with flow rate 200 mL/min.
(4) Set the formed aluminum foil into the evaporation chamber of EV-2000 (Fig.3.2).
(5) Connect electrolytic cell and evaporation chamber with tube (Fig.3.3).
(6) Blanking become stable and then start pre-heating at set temperature.
(7) After the pre-heating procedure finished, confirm blanking stable with carrier gas flowing.
(8) Make formed aluminum foil to use balance dish.
(9) Weigh the sample on the aluminum foil. Weighing amounts are approximately 0.05 g for standard material (i), 0.1 g for standard material (ii) and 0.2 g for standard material (iii).
(10) Put the sample with aluminum foil into evaporation chamber from stopper of the chamber.
(11) Start titration. Measurement parameter is shown in Table 4.1.
(12) Blank measurement is also performed with same procedure except for sample addition.


Fig.3.1. Preparation of the reagents. (Standard Cell)



Fig.3.2. Forming the aluminum foil.




Fig.3.3. Schematic diagram of heat evaporation method.

4. Parameters and results

Table 4.1 Parameters for heat evaporation method.

Condition File    
Cal Mode 0:Sample weight(net)  
  X=(H₂O-BLANK)/SIZE  
Interval Time 30 sec
Current MEDIUM  
Min.Timer 5 min
Blank Value 0 µg
Unit Mode AUTO  
Auto Interval 0 g
Minimum Count 5 µg
Back Ground ON  
Sample Size Input Every Time  
*Cell Type Stadard/Fritless  
EV.File    
     
* Step 1 Temp. 160
Time 0 min
Step 2 Temp. 0
Time 0 min
Step 3 Temp. 0
Time 0 min
Pre. Heat End Time 5 min
End B.G. 0 μg
Cooling Time 5 min
B.G. Count 60  
Back Purge Time 5 sec

(* Set the electrolytic cell and heating temperature appropriately.)

 

Table 4.3 Results of water content measurement of water standard.

Water
Standard
Temp.
(°C)
Cell No. Sample
Size (g)
Water
(μg)
Water
Content(%)
Statistics Results Recovery
rate(%)
(i) 160 Standard 1 0.0529 8149.4 15.4053 Avg. 15.418 % 98.6
15.64%     2 0.0615 9506.1 15.4571 SD 0.035 %
      3 0.0527 8110.6 15.3901 RSD 0.23 %
    Fritless 1 0.0216 3327.3 15.4042 Avg. 15.436 % 98.7
      2 0.0378 5853.4 15.4852 SD 0.043 %
      3 0.0577 8896.3 15.4182 RSD 0.28 %
(ii) 150 Standard 1 0.1426 7242.6 5.0790 Avg. 5.083 % 100.8
5.04%     2 0.1406 7181.3 5.1076 SD 0.023 %
      3 0.1180 5973.0 5.0619 RSD 0.45 %
    Fritless 1 0.1430 7294.1 5.1008 Avg. 5.088 % 100.9
      2 0.1011 5143.9 5.0879 SD 0.013 %
      3 0.1080 5479.9 5.0740 RSD 0.26 %
(iii) 300 Standard 1 0.1236 1240.1 1.0033 Avg. 1.007 % 101.7
0.99%     2 0.1223 1230.4 1.0061 SD 0.004 %
      3 0.1523 1539.0 1.0105 RSD 0.36 %
    Fritless 1 0.2661 2668.6 1.0029 Avg. 1.005 % 101.6
      2 0.2372 2391.3 1.0081 SD 0.003 %
      3 0.2419 2431.8 1.0053 RSD 0.26 %

5. Note

(1) Validation test of titrator with solid evaporator is evaluated from the recovery rate of the result with respect to the CoA value written in the test report of the water standard. Permissible range of recovery rates differed depending on the type of water standard materials. The recovery rate of standards (i), (ii) and (iii) should fall within the range of ± 5 %, ± 4 % and ± 3 % respectively.
(2) Select the type of water standard that is close to the water content or heating temperature of your actual sample.
(3) The optimized electrolysis control for fritless cell of AQ series released after 2009 improves the measurement accuracy of fritless cell. It can be used with the evaporator as well. Suitable reagent for fritless cell is required. For example, Hydranal coulomat AG and AG-Oven are compatible with fritless cell.
(4) When nitrogen gas for carrier gas is not available, optional a dry air pump for EV-2000 can be used to supply air carrier gas. When using air as a carrier gas, pay attention to the following points.
i) Background moisture tends to be higher than nitrogen gas.
ii) When the sample has tendency of thermal decomposition, it wouldl be promoted in the air.

Keywords: Karl Fischer, Coulometric titration, Heat evaporation, Water standard, Validation, Fritless cell
Hiranuma aquacounter aq-300 coulometric karl fischer titratorHiranuma aquacounter coulometric karl fischer titrator moico-a19Hiranuma aquacounter ev-2000 solid evaporatorWater contents

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