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 .