(a) Interpretation: The chemistry of the analytical method should be explained. Concept introduction: Quenching is the process of nonradiative energy transfer from an excited species to another molecule. This requires a contact between the excited species and a quenching agent. The rate of quenching is higher when the quencher concentration is high, because of higher number of collisions during the lifetime of the excited state.

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Principles of Instrumental Analysis

7th Edition
Douglas A. Skoog + 2 others
Publisher: Cengage Learning
ISBN: 9781305577213
BuyFind

Principles of Instrumental Analysis

7th Edition
Douglas A. Skoog + 2 others
Publisher: Cengage Learning
ISBN: 9781305577213

Solutions

Chapter 15, Problem 15.16QAP
Interpretation Introduction

(a)

Interpretation:

The chemistry of the analytical method should be explained.

Concept introduction:

Quenching is the process of nonradiative energy transfer from an excited species to another molecule. This requires a contact between the excited species and a quenching agent. The rate of quenching is higher when the quencher concentration is high, because of higher number of collisions during the lifetime of the excited state.

Interpretation Introduction

(b)

Interpretation:

A plot of data should be constructed.

Concept introduction:

Standard addition method is used to analyze complex samples which matrix effect is significant. One common approach is standard addition technique is spiking of sample. In this method, one or more increments of a standard solution is added to the several aliquots of sample containing same volume. Each solution is then diluted to a fixed volume and experiment is proceeded.

Interpretation Introduction

(c)

Interpretation:

A relationship for multiple standard additions should be derived. An equation for the unknown concentration should be obtained in terms of the slope and the intercept of the standard addition plot.

Concept introduction:

Several aliquots with volume Vx of an unknown solution which have a concentration Cx are measured into volumetric flasks with volume Vt and then a standard solution with concentration Csis added in variable volumes of Vs. Then other reagents that aid for the detection are added and each volumetric flask is topped up to the maximum volume. Then instrumental measurements are made on each solution. If the instrumental response is proportional to the concentration of analyte, following equation can be derived.

S=kVscsVt+kVxcxVt  (1)

k is a proportionality constant. According to above equation the instrumental signal versus Vs is a plot in the form of S=mVs+b, where,

m=kcsVt

b=kVxcxVt

Concentration of unknown then can be obtained by following equation.

cx=bcsmVx   (2)

Interpretation Introduction

(d)

Interpretation:

The equation for the line representing the decrease in fluorescence relative to volume of standard should be determined.

Concept introduction:

In the least squares method, in order to find the slope and the intercept the three quantities Syy, Sxx and Sxy should be determined.

Syy=(yiy¯)2Sxx=(xix¯)2Sxy=(xix¯)(yiy¯)

The slope of the line, m=SxySxx

The intercept, b=y¯mx¯

y¯ - mean of y values

x¯ - mean of x values

Interpretation Introduction

(e)

Interpretation:

The standard deviation of the slope and the intercept should be determined.

Concept introduction:

Standard deviation about regression, sr=Syym2SxxN2

N − number of points used.

The standard deviation of the slope, sm=sr2Sxx

The standard deviation of the intercept, sb=srxi2Nxi2(xi)2

Interpretation Introduction

(f)

Interpretation:

The concentration of F- in the sample in parts per billion should be determine.

Concept introduction:

cx=bcsmVx

Cx − concentration of the unknown solution

Cs − concentration of standard solution

Vx − volume of unknown solution

m − slope of the instrumental signal versus volume of standard added curve

b − intercept of the instrumental signal versus volume of standard added curve

Interpretation Introduction

(g)

Interpretation:

The standard deviation of the result in (f) should be determined

Concept introduction:

sv=sym1N+(0y¯)2m2Sxx

Sv − standard deviation in volume

Sy − standard deviation in signal

m −slope

N − number of points

sc=sv(csVx)

Sc − standard deviation in concentration

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