Separation, Preconcentration and Spectrophotometry in Inorganic Analysis (eBook)

Maria Balcerzak, Z. Marczenko (Autoren)

E. Kloczko (Herausgeber)

eBook Download: PDF

2000 | 1. Auflage
528 Seiten
Elsevier Science (Verlag)
978-0-08-054108-2 (ISBN)

Infos

Spectrophotometry enables one to determine, with good precision and sensitivity, almost all the elements present in small and trace quantities of any material. The method is particularly useful in the determination of non-metals and allows the determination elements in a large range of concentrations (from single % to low ppm levels) in various materials.

In Separation, Preconcentration and Spectrophotometry in Inorganic Analysis, much attention has been paid to separation and preconcentration methods, since they play an essential role in increasing the selectivity and sensitivity of spectrophotometric methods. Separation and preconcentration methods have also been utilised in other determination techniques.

Spectrophotometric methods which are widely used for the determination of the elements in a large variety of inorganic materials are presented in the book whilst separation and preconcentration procedures combined with spectrophotometry are also described.

This book contains recent advances in spectrophotometry, detailed discussion of the instrumentation, and the techniques and reagents used for spectrophotometric determination of elements in a wide range of materials as well as a detailed discussion of separation and preconcentration procedures that precede the spectrophotometric detection.

Inhalt

Front Cover 1
Separation, Preconcentration and Spectrophotometry in Inorganic Analysis 4
Copyright Page 5
Contents 6
Preface 8
Abbreviations 9
Part I: General 10
Chapter 1. Separation and preconcentration of elements 10
Chapter 2. Principles of spectrophotometry 31
Chapter 3. Spectrophotometric methods 44
Chapter 4. Spectrophotometric reagents 58
Part II: Determination of Elements 80
Chapter 5. Alkali metals 82
Chapter 6. Aluminium 88
Chapter 7. Antimony 97
Chapter 8. Arsenic 104
Chapter 9. Beryllium 112
Chapter 10. Bismuth 118
Chapter 11. Boron 126
Chapter 12. Bromine 134
Chapter 13. Cadmium 138
Chapter 14. Calcium 145
Chapter 15. Carbon 152
Chapter 16. Chlorine 157
Chapter 17. Chromium 164
Chapter 18. Cobalt 172
Chapter 19. Copper 182
Chapter 20. Fluorine 194
Chapter 21. Gallium 203
Chapter 22. Germanium 209
Chapter 23. Gold 215
Chapter 24. Indium 221
Chapter 25. Iodine 227
Chapter 26. Iron 231
Chapter 27. Lead 243
Chapter 28. Magnesium 252
Chapter 29. Manganese 258
Chapter 30. Mercury 267
Chapter 31. Molybdenum and tungsten 275
Chapter 32. Nickel 289
Chapter 33. Niobium and tantalum 298
Chapter 34. Nitrogen 309
Chapter 35. Oxygen 320
Chapter 36. Palladium 323
Chapter 37. Phosphorus 331
Chapter 38. Platinum 339
Chapter 39. Rare-earth elements 346
Chapter 40. Rhenium 355
Chapter 41. Rhodium and iridium 362
Chapter 42. Ruthenium and osmium 370
Chapter 43. Scandium 380
Chapter 44. Selenium 384
Chapter 45. Silicon 390
Chapter 46. Silver 397
Chapter 47. Strontium and barium 404
Chapter 48. Sulphur 408
Chapter 49. Tellurium 417
Chapter 50. Thallium 423
Chapter 51. Thorium 429
Chapter 52. Tin 436
Chapter 53. Titanium 443
Chapter 54. Uranium 451
Chapter 55. Vanadium 461
Chapter 56. Zinc 471
Chapter 57. Zirconium and hafnium 479
Appendix 488
Index 519

Textauszug

Chapter 1

Separation and preconcentration of elements

Zygmunt Marczenko; Maria Balcerzak    Department of Analytical Chemistry, Warsaw University of Technology, Naokowskiego 3, 00-664 Warsaw, Poland

The spectrophotometric determination of elements is usually preceded by their separation from major components (matrix) and from interfering elements, the effects of which cannot be eliminated by other methods such as masking or change of pH of the medium. In the trace analysis of high-purity materials, separation from the matrix involves simultaneous concentration of the trace components. General methods of preconcentrating and separating elements have been outlined in several monographs and reviews [1–4].

The present Section provides a discussion of the following separation and preconcentration methods: solvent extraction, precipitation and co-precipitation with collectors, volatilization, and methods based on the use of ion-exchangers and other sorbents. These methods are used not only with spectrophotometry, but also in conjunction with other methods of determination.

1.1 Solvent extraction

1.1.1 Introduction

The extraction process and extractive methods for separation and preconcentration of elements are described in several monographs and reviews [5,6].

Solvent extraction separation is based on differences in the solubilities of elements and their compounds between two immiscible liquid phases. Usually, the initial phase is an aqueous solution and the second phase is an organic solvent, immiscible with water. Some properties of the more common organic solvents are listed in Table 1.1. The ion to be extracted into the non-aqueous phase should first be transformed into an uncharged species.

Table 1.1

Physical properties of some organic solvents

Acetate, n-amyl

0.87

149

4.8

0.2

n-butyl

0.88

126

5.0

0.5

ethyl

0.90

77

6.0

8.6

Acetone

0.89

57

20.7

misc.

Alcohol, n-amyl

0.81

138

13.8

2.2

n-butyl

0.81

118

17.1

7.9

ethyl

0.79

78

24.3

misc.

methyl

0.80

65

32.6

misc.

Benzene

0.89

80

2.3

0.2

Carbon tetrachloride

1.59

77

2.2

0.1

Chloroform

1.50

61

4.8

1.0

Cyclohexane

0.78

81

2.0

0.01

o-Dichlorobenzene

1.30

180

9.9

0.01

1,2-Dichloroethane

1.26

83

10.4

0.9

Dioxan

1.03

101

2.2

misc.

Ethers, di(2-chloroethyl)

1.22

178

23.0

1.0

Diethyl

0.72

35

4.3

7.4

di-isopropyl (DIPE)

0.73

68

3.9

0.7

Hexane

0.66

69

1.9

0.02

Methyl isobutyl ketone (MIBK)

Methylene chloride (dichloromethane)

0.80

116

13.1

2.0

Mesityl oxide

1.34

40

9.1

2.0

Nitrobenzene

0.85

129

15.6

3.2

1-Octanol

1.21

211

34.8

0.2

Tetrachloroethylene

0.83

194

10.3

0.05

Toluene

1.63

121

2.3

0.02

Trichloroethyiene

0.87

111

2.4

0.05

1.46

87

3.4

0.1

misc. – completely miscible

Stripping (“re-extraction”, “back-extraction”, or “scrubbing”) involves bringing the element from the organic extract back into the aqueous phase.

The extraction efficiency, i.e., the degree of transfer of the species from the aqueous to the organic phase, is defined in terms of the distribution- (or extraction-) coefficient, (D). The quantity D is the ratio of total concentration (i.e., the concentration of all the existing forms) of the element in the organic phase (Σc0) to the total concentration in the aqueous phase (Σcw) in the aqueous phase, at equilibrium

=∑co∑cw

The extraction efficiency (%E) is also expressed as the extraction percent

E=100DD+vw/vo

where D is the distribution coefficient, and vw and vo are the volumes of the aqueous and the organic phases, respectively.

When the distribution coefficient of a given element in a specified system is large (e.g., 1,000, i.e., log D = 3), a single extraction will suffice. In most extraction systems the partition coefficients change as the concentration of the substance extracted changes; in most cases they decrease with decreasing concentration [7].

Shaking the phases in a separating funnel during the extraction or re-extraction must be continued until equilibrium is attained. The time required for the system to reach equilibrium varies from seconds to several minutes, depending on the kinetics of the process [8–10], When the shaking time recommended is more than two minutes, it is advisable to use a mechanical shaker.

Extraction is equally useful in the preconcentration and separation of small amounts of elements, and in the separation of macrocomponents from traces. Extraction methods generally require less time than precipitation methods. The former give also “purer” separation of elements owing to the small area of phase contact. Co-extraction occurring in some cases [11] has not been widely used in extraction separations.

1.1.2 Extraction systems

Extraction systems may be divided into two classes: (1) uncharged covalent species (simple molecules and chelates), and (2) ion associates (ion pairs).

Simple molecules (e.g., I2, HgCl2, AsCl2, BiI3, GeCl4, OSO4) are extracted with nonpolar solvents such as benzene, CHCl3, CCl4. The extraction of this type of compound is comparatively selective and is widely applied in separation of some elements [5,12,13].

Inner chelates (uncharged chelates) are formed when metal ions react with bifunctional ligands, such as dithizone (formula 1.1), 8-hydroxyquinoline [14] (formula 1.2), dithiocarbamates (formulae 1.3 and 1.4), ethyl xanthates [15,16], cupferron (formula 1.5), BPHA (N-benzoyl-n-phenylhydroxylamine) [17,18], acetylacetone (formula 1.6) and thenoyltrifluoroacetone (HTTA) (formula 1.7) [19,20].

  (1.1)

  (1.2)

  (1.3)

  (1.4)

  (1.5)

  (1.6)

  (1.7)

Inner chelates are extracted with non-polar solvents (mostly with CHCl3 and CCl4). Synergism [21,22] is important in the extraction of some chelates.

Some inner chelates were extracted into chloroform solutions of diantipyrylmethane (DAM) (formula 1.8) [23]. The effects of salting-out agent, solvent, and temperature on the

  (1.8)

extraction have been discussed [20]. Selectivity can be increased by using the exchange technique, in which a less-stable metal chelate is the source of the chelating agent [24].

The extraction of chelates is usually applied to preconcentration and separation of small amounts of metals. Owing to their low solubility in organic solvents, most chelates can not be used for the extraction of macrocomponents. Cupferronates and acetylacetonates are exceptions.

Chelates of metal ions with alkyl- and arylphosphoric and thiophosphoric acids can be extracted into chloroform and other solvents [25,26], Such systems enable one to separate, by means of extraction procedures, many metals from strongly acid solutions. Examples of such reagents are di-(2-ethylhexyl)phosphoric acid (HDEHP) and di-n-butyldithiophosphoric acid (formulae 1.9 and 1.10). HDEHP is a viscous liquid (density...

Produkt-Details

• Erscheint lt. Verlag: 18.10.2000
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie ► Analytische Chemie
• Themenwelt: Naturwissenschaften ► Chemie ► Anorganische Chemie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik
• ISBN-10: 0-08-054108-9 / 0080541089
• ISBN-13: 978-0-08-054108-2 / 9780080541082