Effect of Ph on Cpe Cr(Iii) Reagent 8-Hq

+ Mn(II) extraction efficiency is equal to the ratio of the determined concentration to the initial concentration. The experiment was conducted 3 times, the average Mn(II) extraction efficiency is presented in table 3.3.

Table 3.3. Effect of 8-HQ concentration on Mn(II) extraction efficiency

STT

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The dependence of the Mn(II) blind spot extraction efficiency on the concentration of the complexing agent 8-HQ is shown in Figure 3.5.

100

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C 8-HQ .10 4 (mol/L)

40

0

1

2

3

4

5

H (%)

From the obtained results, it can be seen that the Mn(II) extraction efficiency increases when the concentration of 8-HQ increases. When the concentration of 8-HQ is 4.0.10 -4 M, the CPE efficiency reaches a maximum of 96.7 ± 1.9%. Then the extraction efficiency decreases when the concentration of 8-HQ continues to increase. Therefore, we choose the concentration of 8-HQ 4.10 -4 M as the optimal value to conduct CPE Mn(II).

Figure 3.5. Effect of 8-HQ concentration on Mn(II) extraction efficiency

C Mn(II) = 0.2 mg/L; pH = 10; C TX-100 = 0.4%

3.1.2.2. Investigation of optimal 8-HQ concentration for blind spot extraction of Cr(III)

Investigation to find the optimal concentration of 8 - HQ for blind spot extraction of Cr(III) in phosphate buffer medium with pH = 8 and fixing other conditions such as: Triton X-100 concentration, NaCl concentration, extraction temperature, extraction time, centrifugation time. Procedure

The experimental procedure is as follows:

+ Pipet 1.0 mL of 20.0 µg/L Cr(III) standard solution into a 10 mL glass centrifuge tube. Add 1.0 mL of pH = 8 borate buffer solution to create an environment for the complexation reaction between Cr(III) and 8-HQ.

+ Add V mL of 2.10 -3 M 8-hydroxyquinoline solution.

+ Add 1.0 mL of 2% Triton X - 100 surfactant solution. Add another 1.0 mL of 5% NaCl solution.

+ Make up to 10 mL with double distilled water, boil in a water bath at 95 o C for 40 minutes.

The experiment was carried out three times, and the average Cr(III) extraction efficiency results are shown in Table 3.4.

Table 3.4. Effect of 8-HQ concentration on Cr(III) extraction efficiency

STT

The dependence of Cr(III) extraction efficiency on the concentration of complexing agent 8-HQ is shown in Figure 3.6. The Cr(III) extraction efficiency increases in the concentration range of 8-HQ 0.5.10 -4 ÷ 2.10 -4 M, then the extraction efficiency gradually decreases when the concentration of 8-HQ increases. The extraction ensures quantification when the concentration of 8-HQ > 1.10 -4 M. The extraction efficiency reaches the highest value of 97.9 ± 2.92 % when the concentration of complexing agent 8-HQ is 2.10 -4 M. Therefore, the concentration value of 8-HQ 2.10 -4 M is used to conduct further studies in

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1

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C 8-HQ .10 4 (M)

3 4 5

H (%)

Cr(III) blind spot extraction.

Figure 3.6. Effect of 8-HQ concentration on Cr(III) extraction efficiency

C Cr(III) = 2.0 μg/L; pH = 8; C TX-100 = 0.2%

3.1.3. Investigation of the influence of surfactants

For blind spot extraction, the selection of micelle-forming surfactants to dissolve the metal complexes is a decisive factor. In recent studies, two types of surfactants commonly used in blind spot extraction are Triton X-100 (TX-100) and Triton X-114 (TX-114). These two types of surfactants were investigated for blind spot extraction of Mn(II) and Cr(III).

3.1.3.1. Investigation of surfactants for Mn(II) extraction

The influence of surfactants TX-100 and TX-114 on the extraction efficiency of Mn(II) blind spot was investigated by fixing the surfactant concentration and factors such as pH, 8-HQ concentration, extraction temperature and time, NaCl concentration, and centrifugation time. The experimental procedure is as follows:

+ Pipet 1.0 mL of 2.0 mg/L Mn(II) standard solution into a 10 mL glass centrifuge tube. Add 2.0 mL of pH = 10 borate buffer solution and 1.0 mL of 4.10 -3 M 8-hydroxyquinoline solution.

+ Add V mL of 4.0 % Triton X-100 solution or V mL of 4.0 % Triton X-114 solution. Add 1.0 mL of 5.0 % NaCl solution and make up to 10 mL with double distilled water.

+ Soak the reaction mixture in a water bath at 95 o C for the time

50 minutes. Then, take it out and centrifuge it for 10 minutes at 3500 rpm, cool it by soaking it in ice water for 10 minutes to let the viscous mixture solidify.

Table 3.5. Effect of TX-100 and TX-114 concentrations on Mn(II) extraction efficiency

STT

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0

0.2

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0.6

C TX-100 (%)

0.8 1

H (%)

The effect of TX-100 and TX-114 concentrations on the extraction efficiency of Mn(II) with the complexing agent 8-HQ is shown in Figure 3.7.

Figure 3.7. Effect of TX-100 concentration on Mn(II) extraction efficiency

- 4

C Mn(II) = 0.2 mg/L; pH = 10;C 8-HQ = 4.10 M

The dependence of Mn(II) blind spot extraction efficiency on the concentration of Triton X-114 surfactant is shown in Figure 3.8.

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40

0

0.2

0.4

0.6

C TX-114 (%)

0.8 1

H (%)

Figure 3.8. Effect of TX-114 concentration on Mn(II) extraction efficiency

- 4

C Mn(II) = 0.2 mg/L; pH = 10; C 8-HQ = 4.10 M

In the case of using Triton X-100 surfactant, when increasing the concentration of Triton X-100, the Mn(II) extraction efficiency increased and reached the maximum value of 93.8 ± 3.25% when increasing the concentration of TX-100 by 0.6%. For Triton X-114 surfactant, the extraction efficiency increased when increasing the concentration of Triton X-114 in the range of 0.1% ÷ 0.4%, then the extraction efficiency decreased slightly when increasing the concentration of Triton X-114. The experimental results are completely consistent because when the surfactant content is small, the Mn complex will not be completely dissolved, but when the surfactant concentration is large, the volume of the viscous phase increases, leading to an increase in the viscosity of the sample, thereby reducing the analytical signal.

The extraction efficiency of Mn(II) with the complexing agent 8-HQ in the case of using surfactant Triton X-100 is higher than when using Triton X-114. This can be explained as follows: the chemical formula of Triton X-100 is C₈H₁₇C₆H₄(OCH₂CH₂) n OH with n = 9 ÷ 10, the chemical formula of Triton X-114 is C₈H₁₇C₆H₄(OCH₂CH₂) n OH with n = 7 ÷ 8. Thus, Triton X-100 and Triton X-114 are homologous to each other, because TX-100 has more - OCH₂CH₂ - groups than TX-114, so its ability to dissolve the complex is better. At the same concentration, TX-100 solution has a higher blind spot temperature than TX-114 solution. Therefore, Triton X-100 will form micelles and separate phases more slowly than Triton X-114. Therefore, Triton X-100 will extract MnQ 2 complex better than Triton X-114. Triton X-100 was chosen for further studies on Mn(II) blind spot extraction.

The Mn(II) blind spot extraction can be quantitatively obtained when the Triton concentration is in equilibrium.

X-100 was greater than 0.2%. The highest Mn(II) extraction efficiency reached 93.8 ± 3.25 % at Triton X-100 concentration of 0.6%. Therefore, the Triton X-100 concentration of 0.6% was selected as the optimal concentration for blind spot extraction of Mn(II).

3.1.3.2. Investigation of surfactants for Cr(III) extraction

The influence of type and concentration of surfactant on the blind point extraction of Cr(III) with complexing agent 8-HQ and pH = 8 phosphate buffer system was investigated according to the following procedure:

+ Pipet 1.0 mL of 20.0 µg/L Cr(III) standard solution into a 10 mL glass centrifuge tube. Add 2.0 mL of borate buffer solution pH = 8 and add 1.0 mL of 2.10 -3 M 8-hydroxyquinoline solution.

+ Add V mL of 2% Triton X-100 surfactant solution or V mL of 2% Triton X-114 solution.

+ Add 1.0 mL of 5.0% NaCl electrolyte solution to promote phase separation of TX-100. Make up to 10 mL with double distilled water, soak the reaction mixture in a water bath at 95 o C for 50 minutes.

+ Then, take it out and centrifuge it for 10 minutes at a centrifugation speed of 3500 rpm, cool it by soaking it in ice water for 10 minutes.

Table 3.6. Effect of TX-100 and TX-114 concentrations on Cr(III) extraction efficiency

CHDB Volume

2% (ml)