Quantitative determination of lead ion | Autotitrator COM-A19 - JM Science

 

HIRANUMA APPLICATION DATA Automatic Titrator Data No. G9 Apr. 5,2019
Metals Quantitative determination of lead ion

1. Abstract

The chelatometric titration is generally used for the determination of lead ion (Pb2+). The pH region the lead ion can be directly titrated is pH 3.5 ~ 10 (stability constant = 17.88).1 However, it generates Pb(OH)2 precipitation at alkaline region. When performing titration under alkaline condition, the auxiliary complexing agent such as ethanolamine, tartaric acid, or citric acid should be added in advance to generate weak chelatometric complex and avoid the generation of lead hydroxide precipitation.

It is titrated at pH around 4 ~ 5 when performing under acidic condition. This report introduces an example that the lead ion in sample solution adjusted to pH 5 by hexamine solution is determined with using XO indicator (red purple →yellow).

Pb²+ + Na₂EDTA  →  Pb-EDTA + 2Na+

2. Configuration of instruments and Reagents

(1) Configuration
  Main unit : Hiranuma Automatic Titrator COM series (Photometric titrator unit type M)
with 530 nm optical filter
  Electrode : Glass – Reference electrode GR-501BZ (for pH confirmation)
(2) Reagents    
  Titrant : 0.01 mol/L EDTA standard solution
  Buffer solution : 5 ~ 10 mL of 20 % hexamine solution
  Indicator : 0.2 mL of XO indicator (0.1 % solution)

3. Measurement procedure

(1) Dispense 1 mL of sample into a 100 mL beaker with volumetric pipette.
(2) Add about 60 mL of DI water.
(3) Add hexamine solution to adjust the pH to 5.
(4) Add 0.2 mL of XO indicator.
(5) Immerse photometric probe into sample solution and titrate with 0.01 mol/L EDTA standard solution.

4. Measurement conditions and results

Examples of titration conditions

Quantitative determination of lead ion Hiranuma Autotitrator COM-A19 from JM Science

Measurement results

Number of
measurement
Size
(mL)
Titrant
volume(mL)
Lead ion
Concentration (g/L)
1 1 9.998 20.737
2 1 9.997 20.735
3 1 9.931 20.598
Statistic
calculation
Avg. 20.69 g/L
SD 0.080 g/L
RSD 0.385 %

 Examples of titration curves

5. Note

(1) Measurement condition
The color of indicator reagent suddenly changes at the endpoint, therefore the minimum increment titration without “Del K” control allows to get good results. The function “CP mL” can reduce the measurement time by continuously adding slightly smaller volume of titrant than the titrant consumption required to the endpoint. The “Method” on condition parameter is set to “B Cross” because the endpoint is defined as the point where the color change of the indicator is completed.
(2) Interfering ions
There is no interference on the measurement even if alkaline-earth metal or Mg is contained in the sample. However, please note that Ni²+, Fe³+, Zn²+, Cd²+, and Co²+ ions are also titrated at the same time.

 

Keywords: Lead ion, Photometric titration, Chelatometric titration

References
(1) K. Ueno, “Chelatometry”, 1989, Nankodo, Tokyo.

*Some measurement would not be possible depending on optional configuration of system.

Hiranuma aquacounter autotitrator com-a19Metals

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