Exploring Chemical Analysis
Exploring Chemical Analysis
5th Edition
ISBN: 9781429275033
Author: Daniel C. Harris
Publisher: Macmillan Higher Education
Question
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Chapter 23, Problem 23.22P

(a)

Interpretation Introduction

Interpretation:

For each concentration limit of detection and the limit of quantitation has to be calculated.

Concept Introduction:

The detection limit is the smallest quantity of analyte that is significantly different from the blank.

Limit of detection or minimum detectable limit is calculated as follows:

    Limitofdetection=(3)(Relativestandarddeviation)

Quantitation limit is the smallest amount that can be measured with reasonable accuracy.

Quantitation limit is calculated as follows:

    Limitofquantitation=(10)(Relativestandarddeviation)

Relation between limit of detection and quantitaion limit is as follows:

    Limitofquantitation=(103)(Limit of detection)

(a)

Expert Solution
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Explanation of Solution

The relative standard deviation of 14.4% of 0.2μgL1 is calculated as follows:

    (0.2μgL1)(14.4100)=0.0288μgL1

Limit of detection of first concentration value of bromated ion is calculated as follows:

    (3)(Relativestandarddeviation)=(3)(0.0288μgL1)=0.0864μgL1

The relative standard deviation of 6.8% of 0.5μgL1 is calculated as follows:

    (0.5μgL1)(6.8100)=0.034μgL1

Limit of detection of first concentration value of bromated ion is calculated as follows:

    (3)(Relativestandarddeviation)=(3)(0.034μgL1)=0.102μgL1

The relative standard deviation of 3.2% of 1.0μgL1 is calculated as follows:

    (1.0μgL1)(3.2100)=0.032μgL1

Limit of detection of first concentration value of bromated ion is calculated as follows:

    (3)(Relativestandarddeviation)=(3)(0.032μgL1)=0.096μgL1

The relative standard deviation of 1.9% of 2.0μgL1 is calculated as follows:

    (2.0μgL1)(1.9100)=0.038μgL1

Limit of detection of first concentration value of bromated ion is calculated as follows:

    (3)(Relativestandarddeviation)=(3)(0.038μgL1)=0.114μgL1

Hence mean of these four detection limit of concentration is calculated as follows:

    0.0864μgL1+0.102μgL1+0.096μgL1+0.114μgL14=0.0996μgL1

Mean quantitation limit of concentration is calculated as follows:

    (103)(Detectionlimit)=(103)(0.0996μgL1)=0.332μgL1

(b)

Interpretation Introduction

Interpretation:

Absorbance of Br3 in the 6.00mm pathlength detection cell of the chromatograph has to be calculared

Concept Introduction:

The detection limit is the smallest quantity of analyte that is significantly different from the blank.

Limit of detection or minimum detectable limit is calculated as follows:

    Limitofdetection=(3)(Relativestandarddeviation)

The relation between the absorbance and concentration of the analyte is calculated from the Lambert Beer’s law as follows:

    A=(ε)(c)(l)

Here, A is the absorbance.

ε is the molar absorption coefficient.

c is the concentration of analyte.

l is the optical path length.

(b)

Expert Solution
Check Mark

Explanation of Solution

The relative standard deviation of 14.4% of 0.2μgL1 is calculated as follows:

    (0.2μgL1)(14.4100)=0.0288μgL1

Limit of detection of first concentration value of bromated ion is calculated as follows:

    (3)(Relativestandarddeviation)=(3)(0.0288μgL1)=0.0864μgL1

The relative standard deviation of 6.8% of 0.5μgL1 is calculated as follows:

    (0.5μgL1)(6.8100)=0.034μgL1

Limit of detection of first concentration value of bromated ion is calculated as follows:

    (3)(Relativestandarddeviation)=(3)(0.034μgL1)=0.102μgL1

The relative standard deviation of 3.2% of 1.0μgL1 is calculated as follows:

    (1.0μgL1)(3.2100)=0.032μgL1

Limit of detection of first concentration value of bromated ion is calculated as follows:

    (3)(Relativestandarddeviation)=(3)(0.032μgL1)=0.096μgL1

The relative standard deviation of 1.9% of 2.0μgL1 is calculated as follows:

    (2.0μgL1)(1.9100)=0.038μgL1

Limit of detection of first concentration value of bromated ion is calculated as follows:

    (3)(Relativestandarddeviation)=(3)(0.038μgL1)=0.114μgL1

Hence mean of these four detection limit of concentration is calculated as follows:

    0.0864μgL1+0.102μgL1+0.096μgL1+0.114μgL14=0.0996μgL1

The reaction between BrO3 and Br is as follows:

    BrO3+8Br+6H+3Br3+3H2O

Hence, molar concentration of Br3 is 3 times greater than the molar concentration of BrO3.

Hence molar concentration of Br3 at mean detection limit is calculated as follows:

    Molar concentrationof Br3atmeandetectionlimit=(3)(detection limitofBrO3inμgL1)(MolarmassofBrO3)=(3)(0.0996μgL1)(127.90gmol1)=2.3362×109M

Absorbance of Br3 at mean detection limit is calculated as follows:

    Absorbace=(Molarabsorptivity)(Molarconcentation)(Pathlengthincm)=(2.3362×109M)(40900M1cm1)(0.6cm)=0.00005733

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