No.

Sample

Fe³⁺, ppm

RTD^a, %

Spectrophotometric method

Proposed ISE method

1

Sample (1)

0.050

0.049

2.1

2

Sample (2)

0.060

0.065

1.9

3

Sample (3)

0.022

0.019

1.7

4

Sample (4)

0.022

0.020

1.67

5

Sample (5)

0.081

0.078

1.8

6

Sample (6)

0.0058

0.0057

2.2

7

Sample (7)

0.058

0.052

2.13

8

Sample (8)

0.120

0.120

0.95

9

Sample (9)

0.360

0.370

1.1

10

Sample (10)

0.027

0.025

1.5