Problems of Instrumental Analytical Chemistry

A Hands-On Guide

JM Andrade-Garda, A Carlosena-Zubieta;MP Gómez-Carracedo;MA Maestro-Saavedra;MC Prieto-BlancoRM Soto-Ferreiro

• Publisher: WSPC (EUROPE)
• Year: 2017
• eBook ISBN: 9781786341822
• Topic: Physical Sciences
• Subtopic: Analytic Chemistry

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The complex field of analytical chemistry requires knowledge and application of the fundamental principles of numerical calculation. Problems of Instrumental Analytical Chemistry provides support and guidance to help students develop these numerical strategies to generate information from experimental results in an efficient and reliable way. Exercises are provided to give standard protocols to follow which address the most common calculations needed in the daily work of a laboratory. Also included are easy to follow diagrams to facilitate understanding and avoid common errors, making it perfect as a hands-on accompaniment to in-class learning.

Subjects covered follow a course in analytical chemistry from the initial basics of data analysis, to applications of mass, UV-Vis, infrared and atomic spectrometry, chromatography, and finally concludes with an overview of nuclear magnetic resonance. Intended as a self-training tool for undergraduates in chemistry, analytic chemistry and related subjects, this book is also useful as a reference for scientists looking to brush up on their knowledge of instrumental techniques in laboratories.

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Contents:

• Fundamental Calculations in Analytical Chemistry (Alatzne Carlosena-Zubieta and José Manuel Andrade-Garda)
• Basic Data Analysis (José Manuel Andrade-Garda and María Paz Gómez-Carracedo)
• Ultraviolet and Visible Spectroscopy (Rosa María Soto-Ferreiro)
• Infrared Spectrometry (José Manuel Andrade-Garda and María Paz Gómez-Carracedo)
• Atomic Spectrometry (Rosa María Soto-Ferreiro and Alatzne Carlosena-Zubieta)
• Chromatographic Techniques (María del Carmen Prieto-Blanco)
• Nuclear Magnetic Resonance and Mass Spectrometries (Miguel Angel Maestro-Saavedra)

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Readership: Undergraduates in chemistry, analytic chemistry and related subjects; scientists looking to brush up on their knowledge of instrumental techniques in laboratories.
-->Analytical Chemistry;Spectrometry;Chromatography;Data Analysis;UV-ViS Spectrometry;Magnetic Resonance;Infrared Spectrometry0

CHAPTER 1

FUNDAMENTAL CALCULATIONS IN ANALYTICAL CHEMISTRY

Alatzne Carlosena-Zubieta and José Manuel Andrade-Garda

OBJECTIVES AND SCOPE

This chapter summarizes the units and the expressions of concentrations employed more often in the calculations associated to the analytical techniques presented in this book. How to (inter) convert them is also discussed, with special emphasis on conversion factors and mathematical relations between expressions/definitions. In our experience, this is a point where students present difficulties frequently throughout their B.S. degree. Another main objective here is to present a systematic approach for the student to deliver a final result taking into account every working step of the operational treatment of the samples or standards (drying, dissolution, dilution, concentration, digestion, etc.). This is an issue that will be reinforced in many examples throughout the other chapters contained in this book.

1.INTRODUCTION

It is critical for students to be aware of the importance of using the measurement units properly, to express the concentrations correctly and to consider the adequate number of significant figures. Throughout their professional careers, they will unavoidably have to master every operation related to scientific notation, conversions among units and relationships between concentration forms. The adequate development of any analytical procedure depends on that, from its inception and planning to the preparation of the reagents, the choice of suitable laboratory material and the final result and its interpretation.

The calculations reflect the different stages of the analytical process and, so, the more complex the analytical procedures become, the more intertwined the required calculations will be. In general, calculations are not too complex although it is essential to understand what is going on chemically in each step of the analysis. This would allow students to establish the appropriate mathematical relationships between the various stages of the analytical process.

To achieve satisfactory learning outcomes, you should be able to understand and justify every operation or calculation rather than only performing them mechanically, so that you yourself should be able to detect any gross error in the final solution. There is no single ‘magic’ formula to solve all exercises. Students have to learn problem-solving strategies and start developing some chemical intuition (’the chemical criterion’). This means that they must develop critical thinking skills to succeed in their professional lives.

A fundamental starting point that falls outside the scope of this book is that the students should know how to formulate (and name) all the compounds involved in the exercises to correctly write and balance the chemical reactions. (S)He has to know how to perform the necessary basic stoichiometric calculations. Without this essential background, (s)he will not achieve satisfactory results in their degrees or, worse, they will fail as chemists. When the compounds mentioned into the numerical exercises are not of common use, their chemical structure will be shown. This will be particularly so in Chapter 6.

1.1.Relevant units and expressions of concentration

Initially, it is worth starting this chapter by presenting some basic recommendations. As a general rule, scientific notation must be used in order to avoid working with very large or very small numbers, being advisable to obtain a number between 1 and 10, and to express its magnitude through an exponent. Thus, large numbers have positive exponents and small numbers have negative exponents.

Another way for chemists to avoid using very large or very small numbers is by selecting the most suitable measuring unit or concentration expression for each number. Furthermore, the units of measurement have a major role in making the numbers meaningful. In effect, a number itself makes little sense. If you read in a laboratory manual: mix 1 of sodium carbonate and 2 of sodium hydrogen carbonate, what would you do? You should ask for the lost units!

1.1.1.Units

From the previous discussions, it turns out that the value of a quantity should be reported as the product of a number and a unit. The number multiplying the unit is the numerical value of the quantity expressed in that unit.

For scientific measurements, the most convenient metric system is the International System of Units (Système International d’Unitès) with the international abbreviation SI, which is used worldwide, although in the United States of America and most countries associated in the Commonwealth, the so-called English system is applied frequently. This uses traditional units such as inches, yards and pounds instead of the metric system such as centimeters, meters and kilograms (see Table 1 for some examples).

The SI defines a set of basic units, prefixes and derived units. All related information is exhaustively compiled and updated at the official website of the responsible organization, the Bureau International des Poids et Mesures, BIPM [1].

Following International Union for Pure and Applied Chemistry (IUPAC) recommendations [2], the symbol of the unit is placed after the numerical value, separated by a space (i.e., t = 25 mL instead of 25 mL); it is written in roman (upright) type (km instead km); it should remain unaltered in the plural (i.e., 10cm, not 10cms) and should not be followed by a full stop (but at the end of a sentence). The symbols should be printed in lowercase letters, except for those derived from a personal name. An exception is the symbol for the liter, which can be uppercase (L, more advisable) and lowercase (l), to avoid its confusion with a one.

Table 1. Some common units and equivalences between the SI and the English system.

	International system (SI)	English system
Mass	1 kilogram (kg)	2.205 pounds (lb)
	453.59 grams (g)	1 pounds (lb)
	28.35 grams (g)	1 ounce (oz)
Volume	1 liter (L)	1.057 quarts (qt)
	3.785 liters (L)	1 U.S. gallon (gal)
	100 milliliters (mL)	6.10 cubic inch (in^3)

It is also advisable not to mix information with unit symbols. For example, the form ‘the copper content is 5mg/kg’ should be used instead of ‘5mg Cu/kg’ or ‘5mg of copper/kg’. When mathematical operations are performed, it should be made clear to which unit symbol a numerical value belongs to. Thus, 12 cm × 3 cm is used and not 12 × 3 cm; 54 mg ± 1 mg or (54 ± 1) mg, but not 54 ± 1 mg [3].

Commas are not used to separate digits into groups of three but a plain space, counting from both the left and the right of the decimal symbol. For example, 5 425.123 12 instead of 5,425.12312 is preferred.

When scientific measurements or results...

Table of contents

• Cover
• Halftitle
• Series Editors
• Title
• Copyright
• Preface
• About the Authors
• Chapter 1. Fundamental Calculations in Analytical Chemistry
• Chapter 2. Basic Data Analysis
• Chapter 3. Ultraviolet and Visible Spectroscopy
• Chapter 4. Infrared Spectrometry
• Chapter 5. Atomic Spectrometry
• Chapter 6. Chromatographic Techniques
• Chapter 7. Nuclear Magnetic Resonance and Mass Spectrometries
• Index