UNIVERSITI PUTRA MALAYSIA

DETERMINATION OF TIN IN LEAD-BASE, COPPER-BASE AND IRON-BASE ALLOYS BY SPECTROPHOTOMETRY AND GRAPHITE

FURNACE ATOMIC ABSORPTION SPECTROPHOTOMETRY

UMI SIBYAN JAIS

FSAS 1987 2

It is hereby certified that we have read this thesis entitled 'Determination on Tin in Lead-Base, Copper-Base and Iron-Base Metals Alloys by Spectrophotometry and Graphic Furnace Atomic Absorption Spectrophotomet ry' by Umi Si byan bt Jais, and in our opinion it is satisfactory in terms of scope, quality and presentation as par tial fulfi lment of the requirements for the degree of Master of Science .

AU��:' Ph . D . Assoc . Professor /Dean of Graduate Studies

Universiti Pertanian Malaysia (Chairman Board of Examiners )

P A�THUif DEREK CAMPBELL, Ph . D .

Professor /Chairman of the Department of Chemistry

University of Otago Dunedin, New Zealand

(External Examiner)

"""--].::!!.!!:�����--!.l£����Ph. D. Lecturer

Depar tment of Chemistry Universiti Pertanian Malaysia

(Internal Examiner )

l ___ �� -�-- -�-----­

ASMAH HAJI YAHYA, Ph.D. Lecturer

Department of Chemistry Universiti Pertanian Malaysia

(Supervisor)

This thesis was submitted to the Senate of Universiti Pertanian Malaysia and was accepted as partial fulfilment of the requirements for the degree of Master of Science.

Date: ,15 JUl 1987

DETERMINATION OF TIN IN LEAD-BASE, COPPER-BASE AND IRON-BASE ALLOYS BY SPECTROPHOTOMETRY AND GRAPHITE FURNACE

ATOMIC ABSORPTION SPECTROPHOTOMETRY

by

UMI SIBYAN JArS

A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in the

Faculty of Science and Environmental Studies , Universiti Pertanian Malay s ia

April 1987

ACKNOWLEDGEMENT

First and foremost , I would like to thank my supervisor ,

Dr . Asmah Hj Yahya for her kind guidance and the laboratory

staff for their help in the smooth running of the whole

project .

Secondly , my sincere thanks to SIRIM , particularly to the

staff of Scientific Testing Unit for their help and support in

providing me a number of chemicals and suggestions . Their

constructive comments are highly valued and appreciated .

My thanks also go to the School of Applied Science , MARA

Institute of Technology for their trust in allowing me to use

the Graphite Furnace Atomic Absorption spectrophotometer .

Last but not least , I would like to express my thousand

thanks to my beloved husband , Muhamad Rosli Sulaiman who had

been very understanding and had given me full support when

needed . His endless encouragement had given me inspiration and

strength to complete the whole course.

thank him for typing the thesis .

iii

I would also like to

TABLE OF CONTENTS

PAGE

ACKNOWLEDGE}ffiNTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i i i

TABLE OF CONTENTS iv

LIST OF TABLES viii

LIST OF FIGURES ix

ABSTRACT • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • xi

CHAPTER 1 INTRODUCTION

General Introduction 1

Objectives of Thesis 2

Summary of Present Work . • • • • • • • • • • • • • • . • • • • . • • • . . . • 3

CHAPTER 2 SPECTROPHOTOMETRIC METHOD USING CATECHOL VIOLET AND CETYLPYRIDINIUM BROMIDE

Introduction 9

Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2

Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Instrumentation • • . • . . • . . • • • • • • • • . . • • • • . • . • • • • • 20

1 . Principle of Operation • . • . • . . • . . • • . 20

Chemical and Reagents 20

Procedure 24

Results and Discussion • • • . • • • • • • • • • • • • • • • • . • • • • • • • • 34

Spectral Characteristics • • • • • • • • • • • • • • • • • • • • • • 34

Optimum Conditions for Colour Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

iv

PAGE

1. Basic Consideration • • • • • • • • • • • • • • • • 37

2. Oxidation State of Tin • • • • • • • • • • • • • 37

3. Effect of pH • • • • • • • • • • • • • • • . • • • • • • • 38

4. Effect of Temperature and Time . . . . . . . . . . . . . . . . . . . . . • . . . . • . . . . 41

5. Effect of Concentration of Reagents • • • • • • • • • • • • • • • • • • • • • • • • • • • 44

6. Effect of Keeping of Reagents . . . . . . . 46

Cali bra tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

1. Precision and Sensitivity . . . . . . . . . . 47

Composition of the Complex • . • • • • . • . . • . . • • • • • • • 49

Interference Studies • • • • • • • • • • • . • • • • • • • • • • • • • • 51

1. Masking of Interfering Ions • • • • • • • • 53

Analysis of Certified Reference Materials • • • • • 57

Conclusion

1. Method of Masking Only . . . . . . . . . . . . . 57

2 . Separation of Major Interferent by Simple Precipitation Followed by Masking • . • • . • • . • • • • • • • • 59

3. Separation of Tin by Solvent Extraction Followed by Masking 60

. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 64

CHAPTER 3 - GRAPHITE FURNACE ATOMIC ABSROPTION SPECTROPHOTOMETRY

Introduction . • • • • • • • • • • • • • • • • • • • . • • • • • • . • • . • . . • • • • • 67

Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . 69

v

PAGE

Instrumentation . • . • • • . • • . • . • . . . . • • • • • • • • • • . • . • 69

Principles of Operation • • • • • • • • • • • • • • • • • • • • • • • 70

Factors Affecting Precision in Graphite Furnace Analysis • • • • • • • • • • • • • • • • • • • • • 74

Reagents and Materials • • • • • • • • • • • • • • • • • • • • • • • • 78

Procedure

1 . Coating of Graphic Tubes/

79

Platform • • • • • • • • • • • • • • • • • • • • • • • • • • • 79

2 . Deterimination of Optimum Ashing and Atomisation Temperature • • • • • • • • • • • • • • • • • • • • . • • . 79

3 . Sample Preparation 80

4 . Measurement 8 1

5 . Calibration 8 1

6 . Precision and Reproducibility 82

7 . Life of Tube Furnace • • • • • • • • • • • • • • • 83

8 . Accuracy 83

Results and Discussion . . . . . . . . . . . . . . . . . . . . . • • . . • . . . 83

Basic Consideration . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Optimisation of Ashing and Atomi sation Tempera ture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • • . 84

Sensitivity and Precision 85

Life of Tube Furnace • • • • • • • • • • • • • • • • • • • • • • • • • • 90

Accuracy 92

Conclusion • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 96

vi

PAGE

CHAPTER 4 TITRIMETRIC AND GRAVIMETRIC METHODS

Introduction • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 98

Ti trimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Complexometric Titration Using EDTA • • • • • • • • • • • 99

1 • Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

2. Reagent s . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

3. Procedure . . . • . • • • • • . . . . . . . . • • . . . . . • 101

I odometric Tritration of Stannou s Tin • • • • • • • • • 102

1. Reagents . . . . ....................... 103

2. Procedure • • • • • • • • • • • • • • • • • • • • • • • • • • 103

Results and Discussion • . • • • • • • • • • • • • • • • • • • • • • • 104

Conclusion . . . . . .. . . . . . . . . . .. . . .. .. .. .. . . . . . .. .. . .. .. . . . 108

Gravimetry .... . . .. . . . ...... . ... . . . . ...... . . . . .. . . . . .. . . .... . .. . . . . 109

CHAPTER 5

Theory .. .. .. .. .. .. . . .. .. . .. .. .. . .. .. . . .. .. .. . .. .. . .. .. .. ...... .. . . .. .. .. .. .. 110

Reagents • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • III

Procedure . ..... . . . ..... ..... . . . . . . . ............... ..... . . . . 111

Results and Discussion • • • • • • • • • • • • • • • • • • • • • • • • 112

Conclusion • • • . • • • • • • • • • • • • • • • • • . . • • . • • . • • • • • • • 113

OVERALL CONCLUSION • • • • • • • • • • . • • . • . • • • • • • • • 115

REFERENCES • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 122

APPENDIX 1 - Compositions of Reference Standard Materials . .. ... .. .. .... .. .. .. .. .. .. . . . .. . .. .. .. .. .. . . .. .. .. .. .. .. .. 132

APPENDIX 2 - Optimum Conditions for Colour Development of Visible Spectrophotometric Method • • • • • • • 133

vii

LIST OF TABLES

TABLE

1 Colours of Different Wavelength Region • • • • • • • • •

2 Effect of pH on initial tin solution • • • • • • • • • • •

3 Effect of keep ing of catechol violet on absorbance

4 Precision and sensitivity . • • . • • • • • • • • • • • • • • • • • •

5 Effect of presence of foreign ion on absorbance

6 Effect ive masking agents • • • • • • • • • • • • • • • • • • • • • • •

7 Method of masking only

8 Method of separating major interferent followed by masking • . . • • • • • • • . • • • • • • . . . • . • • • • • •

9 Percentage recovery of solvent extraction • • • • • •

10 Solvent extraction method • • • • • • • • • • • • • • • • • • • • • •

11 Anal ysis of reference standard materials

12 Furnace conditions for impregnated tube/

PAGE

17

39

46

49

53

55

57

60

62

63

65

platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

13 Furnace condit ions for t in determinat ions 82

14 Effect of atomisation condit ions on sensit iv i ty 88

15 Precision of wall and platform atomisa-

16

17

18

19

tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Anal ysis of certif ied reference materials • • • • • • 95

Titrimetric method of determining tin 105

Gravimetric determination of tin as metastannic acid . . • • • • • • • • • • • • • • • • • • • • • • • . • • . • . 113

Compar ison between the different niques of determining tin in alloys

viii

tech-119

FIGURE

1

2

3

4

5

6

LIST OF FIGURES

Bonding and Antibonding Molecular Orbitals • • • • •

Kinds of Transitions . . • • . . • • . . • . • • • • . . . • • • • • . • .

Energy Levels Diagram • • • • • • • • • • • • • • • • • • • • • • • • • •

Absorption of Monochromatic Radiation • • • • • • • • • •

Optical Layout of Hitachi Double Beam Spectrophotometer Model 200-20 • • • • • • • • • • • • • • • • •

Spectra of Complexes of Tin • • • • • • • • • • • • • • • • • • • •

PAGE

12

14

16

17

21

36

7 Effect of pH on Absorbance of Sn-CV-CPB

8

Complex . . . • . . . • . . . . . . . . . . . . • • . • • . . . • . • . . . . • . . . . . 40

Effect of Temperature on Absorbance of Sn-CV-CPB Complex • . . . • • • . • • . . . . . • . . • • • . . • • • • • • • • 42

9 Effect of Catalyst on Absorbance of Sn-CV-CPB Complex . • . • . . • • • . • • • • . • . . . . • • . . • • • • . . • 43

10 Effects of Reagents on Absorbance of

11

12

13

14

15

16

Sn-CV-CPB Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Calibration Graph for Sn-CV-CPB Complex • • • • • • • •

Composition of Method Sn : CV

Composi tion Method Sn

of CPB

Complex by Mole-ratio

Complex by Mole-ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

Effect of Masking Agents on Absorbance of Sn-CV-CPB Complex • • • • • • • • • • • . • . . • • • • • • • • • • • • •

Atomic Absorption Spectrophotometer . Perkin Elmer model 2380 • • • • • • • • • • • • • • • • • • • • • • . •

Graphite Furnace Assembly . Perkin Elmer

48

50

52

56

71

HGA 300 • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • 72

ix

FIGURE

1 7

1 8

Model 2380 Optical Schematic AA Mode • • • • • • • • • •

Optimisation Temperature

of Ashing and Atomisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19 Calibration Curves of Tin Solutions Using Various Kinds of Tubes by Wall and

PAGE

73

86

Platform Atomisation • • • • • • • • • • • • • • • • • • • • • • • • • • • 87

20 Degradat ion of Various Kinds of Tubes • • • • • • • • • • 91

x

An abstract of the thesis submitted to the Senate of Universiti Pertanian Malaysia as partial fulfilment of the requirements

for the degree of Master of Science

DETERMINATION OF TIN IN LEAD-BASE , COPPER-BASE AND IRON-BASE ALLOYS BY SPECTROPHOTOMETRY AND GRAPHITE

FURNACE ATOMIC ABSORPTION SPECTROPHOTOMETRY

by

UMI SIBYAN JAIS

April 1987

Supervisor Asmah Hj . Yahya , Ph . D .

Faculty Science and Environmental Studies

This method development study of tin determination in

alloys is divided into three parts, namely visible spectro-

photometry , flameless atomic absorption spectrophotometry

( FAAS ) and classical method s . Visible spectrophotometry was

chosen as the main technique because atomic absorption spectro-

photometry by the f lame mode (another popular method for tin)

was known to give a lot of problems . However, FAAS using

graphite furnace was also studied in this project since this

appraoch was claimed to give better sensitivity .

The spectrophotometric method of determining tin in alloys

using catechol violet and cetylpyridinium bromide is discussed

in detail. Oxalic acid and lactic acid were found to speed up

xi

the colour development process from approximately 2 hours to

about 30 minutes . Calibration graph is rectilinier up to 1.6

ppm Sn at wavelength of maximum absorption (662 nm) . The

selectivity of the method was tested on lead tin-base white

metals , brass , steel and foundary iron from Bureau o f Analysed

Samples (UK). Several approaches were tried involving masking

and separation . Satisfactory results were obtained with method

of separating major interferent by precipitation followed by

masking .

Graphite furnace AAS method discussed the analysis o f tin

using Zr and W coated graphite tubes which were claimed to have

improved the sensitivity of analysing Sn by this technique .

The performance of these tubes was compared with the normal

graphite and, pyrollitically coated tubes . Both matrix modifier

and masking agents were tried . Ammonium hydroxide was used as

matrix modifier while lactic , ascorbic and tartaric acids which

worked quite well with spectrophotometric technique were tried

as masking agents . Atomisation from L'vov platform was also

attempted with marked improvement in sensitivity.

however, remains poor, R.S.D. at 5 - 6 percent .

Precision ,

Classical wet methods commonly applied to analysis of

alloys namely titrimetry and gravimetry we r e also carried out

as comparative techniques . For titrimetry , complexometric

titration using EDTA and iodometric titration methods were

xii

adopted while for gravimetry tin was precipitated as meta-

stannic acid and determined as tin oxide ( SnO ) .

2

Comparison with regard to accuracy, precision, sensitivity

and simplicity of the various techniques was discussed . Among

these , for the samples analysed in this project, spectrophoto-

metric technique was found to be the most precise and accurate .

xiii

Abstrak tesis yang dikemukakan kepada Senat Universiti Pertanain Malaysia sebagai memenuhi sebahagian daripada syarat

keperluan ijazah Master Sains

PENENTUAN TIMAH DALAM ALOI-ALOI PLUMBUM , KUPRUM DAN FERUM DENGAN KAEDAH SPEKTROMETRI TAMPAK DAN

SPEKTROMETRI SERAPAN ATOM TANPA NYALAAN

oleh

UMI SIBYAN JAIS

Apr il 1987

Penyelia Asmah Hj . Yahya , Ph . D.

Fakulti Sains dan Pengajian Alam Sekitar

Kaj ian penentuan timah dalam aloi ini terbahagi kepada

tiga bahagian . Ujikaj i yang terpenting sekali ialah untuk

mendapatkan kaedah yang paling sesuai dengan teknik

spektrofotometri tampak . Teknik ini dipilih kerana penentuan

timah dengan teknik spektrofotometri sera pan atom (AAS ) dengan

men ggunakan nyalaan termaklum ban yak memberi masaalah . Walau

bagaimana pun AAS dengan menggunakan relau grafit telah juga

dikaji kerana keputusan yang lebih memua skan dapat diperoleh i

dengan kaedah ini. Kaedah-kaedah yang lazim digunakan juga

dilakukan untuk tujuan perbandingan .

Kaedah spektrofatometri tampak dalam menentukan kandungan

timah dalam alai dengan menggunakan 'catechol violet' dan

'cetylpyr idinium bromide' telah dibincangkan dengan mendalam .

xiv

Asid oksalik dan asid laktik didapati dapat mempercepatkan

proses pembentukan kompleks Sn-CV-CPB dan dari itu pertukaran

warna dari dua jam ke anggaran tiga puluh minit .

Graf penentuan bagi kompleks timah ini adalah lurus hingga

ke kepekatan timah setinggi 1.6 ppm pada panjang gelombang

keserapan maksima 662 nm . Kepilihan kaedah ini bagaimana pun

amat rendah bila diu j i dengan aloi/logam piawai dari 'Bureau of

Analysed Samples ( U . K . ) . Beberapa langkah memperbaiki kaedah

telah dibuat seperti pengasingan dan penopengan . Di antara

langkah-Iangkah ini , keputusan yang menggalakkan telah didapati

dengan gabungan kaedah pengasingan melalui pemendakan dan

penopengan .

Teknik spektrometri serapan atom dengan relau grafit pula

membincangkan tentang penentuan timah dengan menggunakan

salutan zi rkonium dan tungsten ke atas tiub grafit yang

dikatakan boleh meninggikan kepekaan timah . Kecekapan tiub-

tiu b bersalut ini telah dibandingkan dengan kecekapan tiub-tiub

grafit . normal dan tiub-tiub pirol itik . Kesan pengubahsuai

matriks dan agen penopengan juga telah dikaji. Ammonium

hidroksida telah digunakan sebagai pengubahsuai matriks,

manakala asid laktik , asid askorbik dan asid tartarik telah

didapati berkesan sebagai agen penopeng . Pengatoman dari

pelantar L'vov juga telah dikaji dan didapati kepekaan timah

bertambah dua kal i ganda . Walau bagaimanapun kej ituan masih

lagi tidak memuaskan (5-6 peratus ) .

xv

Kaedah titrimetri dan gravimetri telah juga dikaji bagi

tujuan perbandingan. Untuk titrimetri dua kaedah yang biasa

telah digunakan iaitu pentitratan kompleksometri dengan

menggunakan EDTA dan pentitratan iodometri yang menggunakan

larutan piawai iodin untuk mengoksida timah(II) ke timah(IV).

Bagi gravimetri pula, timah telah dimendakkan sebagai asid

metastannik dan, setelah dibakar dalam relau pada suhu 1000°C,

ditentukan sebagai stanum oksida (Sn02).

Perbandingan yang berdasarkan kepada kejituan, kepekaan,

ketepatan dan keringkasan tiap-tiap teknik yang telah diujikaji

telah dibincangkan. Di antara teknik-teknik tersebut, bagi

sampel-sampel yang dianalisis dalam projek ini, teknik

spektrofotometri telah didapati paling baik dari segi ketepatan

dan kejituan.

xvi

CHAPTER 1

INTRODUCTION

GENERAL INTRODUCTION

Tin in alloys has been determined most commonly by either

gravimetry ( Vogel , 1978; Gilbert , 1962; Wilson , 1 962;

Kolthoff , 1 961) or titrimetry ( Vogel , 1 978; Gilbert , 1 962;

Wilson , 1962; Kolthof f , 1961; Dixon , 1962; Furuya , 1963; ASTM ,

1972) . Gravimetric methods for tin are normally subjected to

errors caused by adsorpt ion , co-precipitation or occlusion of

other elements present and may requi re elaborate separation or

purification of the f inal oxide ( Vogel , 1978; Gilbert , 1962;

Kolthof f , 196 1 ) . The t itrimetric determination based on

oxidat ion to the quadrivalent state by means of a standard

iodate solut ion is definitely superior but very tedious and

complete reduction of tin to the bivalent state and subsequent

prevent ion of oxidation to tin ( IV) (Vogel , 1978; Nobuhiko , 1 983

and Kinnunen , 1957) really demand for spec ial care o f

apparatus. The other widely applied titrimetric method

involves complexing the tin with ethylene diamine tetraacet ic

acid (EDTA) (Raoot , 1 984, Kinnunen , 1 957; Dixon , 1 962) the

excess of which is titrated against standard lead nitrate ,

Pb( NO ) solution using xylenol orange as the indicator . The 3 2

tin is then released from its tin EDTA complex by sodium

1

2

fluoride at pH 5-6 and the liberated EDTA titrated against lead

nitrate solution. The method , however , works well only with

solders and with samples of high t in content ( more than 50

percent w/w) . Atomic absorption spectrophotometry is fast

gaining popularity as an alternative method to determine tin at

low levels because of its rapidity . But tin was proven to be

very insensitive towards the flame mode ( Thomerson , 1971 ;

Burke , 1 972 ; Headridge , 1 972 ; Thornton , 1974) such that either

extract ion (Headridge , 1972 ; Thornton , 1974), distillation

(ASTM , 1972 ) or an additional device (Fleming , 1 976 ; Jia , 1985 ;

Liu, 1985 ) had to be used . Atomisation from graphite furnace

although seemed promising for a direct analysis since most of

the matrix could be burnt off during the ashing step, is not

without problems . The problems are mainly associated with the

t endency of tin to form volatile compounds and to interact with

the graphite surface (Thamba , 1 979; Tominaga , 1979 ; Fritzsche ,

1979 ; Regan , 1976 ; Vickrey; 198 1, Luo , 1985 ; Volyn , 1984 ).

Tin can also be determined by visible spectrophotometric

method that is by forming a coloured tin compl ex and determined

by taking absorbance in the visible region . To date the most

promising complexing agent for tin is phenyl fluorone ( Sandell,

1959 ; Bennet , 1959) but this reagent often gives rise to

colloidal solutions when applied to tin determination in alloys

(Ross , 1 961 ) . In addi tion the tin-phenylfluorone complex is

not water soluble such that the determination is often done in

alcoholic medium instead . Catechol violet , another complexing

3

agent for tin on the other hand forms water-soluble complex

with tin and therefore is much easier to handle . The method

using catechol violet , however , suf fers from its lack of

sensit ivity due to the fact the reagent blank absorbs very

strongly at the wavelength of maximum absorbance of the

complex . Currently a lot of efforts have been put in to

improve the method and this include the use of sensitizing

agents like gum arabic , sodium lauryl sulphate and cetyl

trimethyl ammomium bromide .

OBJECTIVES OF THE THESIS

The study is mainly concentrated on improving the current

methods of determining tin in alloys with emphasis being placed

on analytical factors like sensitivity , accuracy , precision ,

speed and simplicity and to compare with regard to these

factors against established classical methods namely titrimetry

and gravimetry . Two main techniques were used for this purpose

i . e . visible spectrophotometry and graphite furnace atomic

absorption spectrophotometry . These techniq ues were chosen due

to their wide usage in chemical analysi s .

SUMMARY OF PRESENT WORK

The work was divided into three sections namely

spectrophotometry , graphite furnace atomic absorption

spectrophotometry and classical analysis , i . e . titrimetry and

gravimetry .

4

Spectrophotometric Method

Tin was determined as Sn-CV complex .

The effects of two different surfactants namely cetyl

pyridinium bromide CCPB) and alkyl phenyl polyethylene glycol

(TRITON) on the absorption maximum of the complex were studied .

The method using CPB as the dispersant is a modification

of other published methods and was tested on some certified

reference materials with varying tin content from the Bureau

of Analysed Samples Limited (BAS) .

Several methods of eliminating the ef fects o f interfering

ions were also tried and the results compared . These include :

1 ) Masking Alloys

of Interfering Ions Commonly Found in

Masking agents used are specific except when only small

amounts of interfering ions were present (less than 1 percent)

where lactic acid was found adequate . Tartaric acid was found

effective in masking. large amounts of lead and antimony,

ascorbic acid for i r on and thiourea or maleic a cid for copper

and nickel .

2) Combination of The Two Method s t hat i s Separation Followed by Masking

a) separation by simple prec i p i tation of the major

interferent followed by masking .

5

Lead in the Pb-base white metal is

separated as PbSO , 4

copper as eu-thiourea ,

iron in steel and foundary iron as Fe (OH) •

3

b) separation of tin from other matrix elements by

solvent extraction using :

i) toluene .

Tin in the sample was extracted into

toluene as tin( IV) iodide from a strongly

acidic solution ( sulphuric acid 8M) containing

O . lM potassium iodide . The tin extracted was

then back-ext racted into aqueous media using

sodium hydroxide solution ( SO percent v/v) and

then acidified by quickly running the aqueous

layer with constant stirring into a highly

acidic solution of hydrochloric acid ( 5M) t o

give a final p H of approximately 1 . 5 before

proceeding with colour development . This

method , however , gave very poor results and

poor recovery factor probably due to serio u s

hydrolysis of tin occuring when the pH was

changed first from acidic to alkaline and later

back to acidic .

ii) trioctyl phosphine cyclohexane

oxide (Tapa) in

In this case tin was extracted from acidic

solution of hydrochloric and sulphuric acid

6

mixture as tin ( IV ) chloride. The cyclohexane

extract containing the tin was evaporated to

solvent and the residue get rid of the

redissolved in hydrochloric acid ( 10 percen t

v/v) . Compared t o the method of extraction

using toluene, this method is of course

superior, evaporation of the organic solvent

proved to be much simpler than back extraction .

However , the accuracy of the results obtained

were only comparable to the method of masking

only (Method A). Method B ii) : separation by

simple precipitation followed by masking still

gave the best and most accurat e results .

Atomic Absorption Spectrophotometric Method

Several approaches of wall and platform atomisations were

tried using different kinds of tube furnaces namely ordinary

graphite as well as pyrollitic, tungsten (W) and zirconium ( Zr)

coated tubes . Comparison with regard to accuracy , precision ,

sensitivity and tube performance were carried out with the

certified reference materials . Poor precision and accuracy

were recorded with uncoated graphite tube but with coated and

pyrollitic tube the performances were comparable , however ,

longest life of tube was recorded with using pyrollitic tube ,

more than 100 injections against about 50-60 injections with

tungsten and zirconium coated tubes under the conditions used

in this work .

7

Better sensitivity was obtained with Standard Temperature

Platform Furnace ( STPF) method but precision was only slightly

improved . Analysis of tin using platform atomisation , thus

could turn out to be very costly considering the short life and

the cost of the platform which presumably is about that of the

tube at the conditions of this work .

Gravimetry and Titrimetry

These classical methods were carried out for comparison

purposes .

accuracy ,

methods .

Emphasis

speed

Only the

was placed on analytical

and simplicity against the

widely applied methods for

aspects like

investigated

analysis of

alloys were carried out , i . e .

1 . Titrimetry

Complexometric titration of Sn( IV) with EDTA using xylenol

orange as indicator and iodometric titration of Sn C I I ) using

starch as indicator.

tin

Complexometric

content like

titration only worked with samples of high

tin base metal and solders . It is not

suitable for alloy s that contain too much copper like brass and

iron like steels and foundary iron . Iodometric method also

worked well with samples of high tin content and samples that

do not contain appreciable amounts of lead and antimony which

gives rise to serious interference problems .