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ChemistryPrinciples of Instrumental Analysis(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.Start your trial now! First week only $4.99!*arrow_forward*

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7th Edition

Douglas A. Skoog + 2 others

Publisher: Cengage Learning

ISBN: 9781305577213

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 V_{x} of an unknown solution which have a concentration C_{x} are measured into volumetric flasks with volume V_{t} and then a standard solution with concentration Csis added in variable volumes of V_{s}. 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.

k is a proportionality constant. According to above equation the instrumental signal versus V_{s} is a plot in the form of

Concentration of unknown then can be obtained by following equation.

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 S_{yy}, S_{xx} and S_{xy} should be determined.

The slope of the line,

The intercept,

Interpretation Introduction

**(e)**

**Interpretation:**

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

**Concept introduction:**

Standard deviation about regression,

N − number of points used.

The standard deviation of the slope,

The standard deviation of the intercept,

Interpretation Introduction

**(f)**

**Interpretation:**

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

**Concept introduction:**

C_{x} − concentration of the unknown solution

C_{s} − concentration of standard solution

V_{x} − 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:**

S_{v} − standard deviation in volume

S_{y} − standard deviation in signal

m −slope

N − number of points

S_{c} − standard deviation in concentration