HIRANUMA APPLICATION DATA

Factorstandardization

Automatic Titrator

Data No. O10Feb. 03,
2022

Standardization of EDTA titrant

1. Abstract
Disodium dihydrogen ethylenediamine tetraacetate (hereinafter referred to as EDTA) is a chelating agent
and has the property of forming chelate compounds with many metal ions. It is used as a titrant for achelatometric titration method to quantify metal ions. The chelatometric titration method has a wide range ofapplications, various metal ions could be measured with the use of appropriate indicator reagent and pH.
Factors are indicated on the commercially available standard solution for volumetric analysis. The factor
determination is required when the standard solutions are prepared in the laboratory. Also it is effective tocheck the repeatability by the factor measurement using a standard material to check the performance of titrator
system. Japanese Industrial Standard JIS K 8001 and the Japanese Pharmacopoeia describe that zinc, which isa standard material for a volumetric analysis, should be used for the factor determination of EDTA standard
solution.
In this report, zinc standard solution, which is prepared from standard material for volumetric analysis, isused for standardization of EDTA titrant. 1 mol of zinc and 1 mol of EDTA react quantitatively according toformula (1).
Zn2+ ＋ EDTA → Zn･EDTA ＋ 2Na+ ･･･(1)In this method, an indicator reagent is used to determine the end point based on the color change of thesample solution. The indicator reagent has the property of binding to metal ions unreacted with EDTA, and thecolor changes depending on whether or not they bind with metal ions. The indicator reagent used in this report,Eriochrome Black T (hereinafter, EBT), changes the color of the solution from red to blue before and after theend point. By detecting this color change with a photometric probe, the end point of zinc titration with EDTA
titrant is determined.
1) Japanese Pharmacopoeia Eighteenth Edition
2) Japanese Industrial Standard JIS K8001 General rules for test methods of reagents

2. Configuration of instruments and reagents(1) Configuration of instruments
Main unit: Automatic Titrator

COM Series (with photometric unit, M-type)

Electrodes: Photometric probe (with 650 nm interference filter)
Glass-reference combination electrode GR-501BZ(2) Reagents
Titrant: 0.01 mol/L (0.1 N) EDTA standard solution (Buret No. 1)

Standard material : 0.01 mol/L (0.1 N) zinc standard solution (f = 1.028)
0.6720 g of metallic zinc (purity 100.00%) was dissolved in 20 mL of 20 %hydrochloric acid, dilute to 1 L with DI water.
Factor of zinc standard solution= [weighing amount of zinc (g)／atomic weight of zinc (g/mol)]×[purity(%)／100]／[prepared volume (L)×nominal molar concentration(mol/L)]= [0.6720／65.38]×[100.00／100]／[1×0.01] = 1.028
pH adjuster (1): 100 g/L sodium hydroxide solution

pH adjuster (2): pH 10 ammonia buffer
Dissolve 7 g of ammonium chloride in 30 mL of DI water, add 57 mL of 30 %ammonia solution and dilute to 100 mL with DI water.

Indicator reagent: EBT indicator reagent
Prepared by dissolving 0.5 g of EBT and 4.5 g of hydroxylammonium chloridein 100 mL ethanol.

3. Measurement procedure(1) Take 25 mL of 0.01 mol/L zinc standard solution into a 200 mL tall beaker with a volumetric pipette.
(2) Add 75 mL of DI water and a stirrer bar to the beaker.
(3) Immerse the glass-reference combination electrode to check pH of the solution. Add 100 g/L sodiumhydroxide solution to adjust the pH to about 9.5-10.
(4) Add 2 mL of pH 10 ammonia buffer.
(5) Add 3 drops of EBT indicator reagent.
(6) Immerse the photometric probe and start titration with 0.01 mol/L EDTA titrant. The inflection point
appearing on the titration curve is detected, and the end point is determined by B-Cross detection
method.

4. Measurement conditions and results
Examples of titration conditions
Cndt No.
1MethodB-Cross
ConstantNo.
1Buret No.
1Size
25
Amp No.
2Blank
0D. Unit
T%
Molarity
0.01
S-Timer
5 sec
Factor1.028
C.P. mL
23 mL
K0T Timer
10 sec
L0D.P. mL
1.0 mLEnd Sens
200Unit
Fact1
Over mL
1.0 mL
FormulaS/(D-B)*F
Max.Vol.
40 mL
Digits4*1: The factor of 0.01 mol/L zinc standard solutionmL
mLmol/L*1

Mode No.
Pre Int
Del K
Del Sens
Int Time
Int Sens
Brt Speed
Pulse

2100055280

Measurement results
Measurement
No.
123Samplesize (mL)252525Titrant
volume (mL)

Factor25.80325.76725.7890.99600.9974
0.9966

Factor standardization measurement

Examples of titration curves

Statistical results

Avg.
SDRSD

0.997
0.001
0.07 %secmV
secmV

5. Note(1) About the parameter setting
In this titration, the color change of indicator occurs suddenly and sharply at the end point. To prevent theend point from being passed due to excessive increment volume of the titrant, the volume of each drop should
be constant at 0.1 mL, which is set in the parameter “Pulse”. Setting the parameter “Del K” to zero allows thetitration without dynamic control of the titrant increment volume. For the titrations where the electrode signal
changes rapidly at the end point, this setting will improve the repeatability. The measurement time can beshortened by using the parameter “CP mL”, which set titrant volume 0.5-1.0 mL before the end point.
In addition, since end point of this titration is defined at the point where the color change of the indicator iscompleted, the end point detection is set to “B-Cross” on Method in parameter. If the beginning of color change
should be defined as the end point, such as back-titration method, set the detection method to “F-Cross”.
(2) About selection of interference filter for photometric probe
The photometric probe comes with two types of interference filters, 530 nm and 650 nm. In this report, theEBT indicator reagent is used in the alkaline pH range, and the solution color changes from red to blue at theend point, thus 650 nm was selected for the filter. For chelatometric titration of zinc, there are other titration
method using other indicator reagent and pH range. As shown in Application Data No. G1, when the indicatorxylenol orange is used in the acidic pH, the color change at the end point is from red-purple to yellow and the530 nm filter is used.
In general, when the color of the solution is (orange, red, and red-purple), the transmittance (%T) decreases
relatively large with using a filter at 530 nm, and when the color of the solution is (green, and blue), thetransmittance decreases at 650 nm. If multiple colors are mixed in the solution, it would not be as describedabove. In that case, select the wavelength of filter that can detect the larger change in transmittance.

Keywords：Factor standardization, Chelatometric titration, Photometric titration, EDTA,Disodium dihydrogen ethylenediamine tetraacetate, Zinc, Eriochrome black T, EBT*Some measurement would not be possible depending on optional configuration of system.