4. Determination of nickel in its samples

In this chapter, two types of samples containing nickel were used. They were representative for food samples and stainless steel samples. Five steel samples (A–D) and one food (E) sample were chosen. On the one hand, 0.1 g of each stainless steel sample was dissolved into aqua-Regia, heated at 105�C, and diluted to 250 ml using bi-distilled water. This solution was measured directly. On the other hand, 0.5 g chocolate sample (E) was dissolved in 100 ml after digestion with HNO3, HClO4, and H2O2. In this case, 1 ml was diluted to 50 ml, and the result solution was subjected to potential measurements using the proposed Ni-selective electrode. The obtained Ni values into the stainless steel samples (A–D) were between 1.467 and 7.354 ppm. The chocolate sample E showed Ni content 14.707 ppm. All the obtained values agreed with the values given by AAS analysis of the same samples [19]. The obtained values of


Table 4. Determination of nickel in its samples using the proposed Ni-ISE.

The relation between ionic radius [18] of interferent cations and the values of selectivity coefficient for both electrode types is shown in Figures 8 and 9. It was found that there was an increase in the selectivity coefficient values with increasing the ionic radius of the tested cations. This was true for both electrode types I and II. The increment values in case of type I were less than those in case of type II. This was attributed to that the increase in ionic volume

z+) for Ni-ISE

Figure 8. Correlation between ionic radius (pm) of the tested cations and selectivity coefficient (KPot Ni2+, j

Table 3. Selectivity coefficient values for nickel electrodes based on β-CDX incorporating (DEP) [I], and (NPOE) [II] as

was suitable for the β-CDX cavity.

with membrane type I for 0.0001 M solutions.

Interferent KPot Ni2+, j

298 Cyclodextrin - A Versatile Ingredient

plasticizers.

z+

Ir3+ 7.67 <sup>10</sup><sup>5</sup> 1.4 <sup>10</sup><sup>2</sup> Fe3+ 4.38 <sup>10</sup><sup>5</sup> 1.3 <sup>10</sup><sup>2</sup> Zn2+ 1.1 <sup>10</sup><sup>3</sup> 6.1 <sup>10</sup><sup>2</sup> Co2+ 1.8 <sup>10</sup><sup>3</sup> 3.5 <sup>10</sup><sup>2</sup> Cu2+ 2.1 <sup>10</sup><sup>3</sup> 3.0 <sup>10</sup><sup>1</sup> Ba2+ 2.2 <sup>10</sup><sup>3</sup> 3.0 <sup>10</sup><sup>1</sup> Mg2+ 1.6 <sup>10</sup><sup>3</sup> 1.5 <sup>10</sup><sup>1</sup> Ca2+ 2.2 <sup>10</sup><sup>3</sup> 2.0 <sup>10</sup><sup>1</sup> Cd2+ 2.2 <sup>10</sup><sup>3</sup> 1.6 <sup>10</sup><sup>1</sup> Hg2+ 1.7 <sup>10</sup><sup>3</sup> 2.0 <sup>10</sup><sup>1</sup> Mn2+ 1.5 <sup>10</sup><sup>3</sup> 1.7 <sup>10</sup><sup>1</sup> Pb2+ 2.9 <sup>10</sup><sup>3</sup> 1.2 <sup>10</sup><sup>1</sup>

I-DEP II-NPOE

Ni in chocolate agreed with previously recorded values [20]. Table 4 shows the obtained results for analysis by using both the proposed electrode and an AAS method for the same samples.

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