Chapter 1

Introduction

t ,

r

*•

1

The term ‘traces' appears to have its origin in the limitations of the early analytical

methods like gravimetry and titrimetry, where the smallest quantitatively determinable

concentration was 0.02, or 0.01 percent. Thus, concentrations at 0.01% level or lesser

were regarded as traces (1-5). Sometimes even concentrations up to 1000 ppm (0.1%)

were referred as traces (6). The environment around us, water, air and soil contains many

elements in trace quantities. These elements play a very important role in the life cycle of

humans and other living beings.

Trace elements have classified by Underwood (1) in three groups viz. (a) dietary

essential, (b) possible essential, and (c) non-essential. Some of these non-essential

elements which are environmental contaminants enter into the body and produce

undesirable effects. These are, therefore, referred as toxic elements e.g. Pb, Cd, Hg etc.

Studies regarding trace element requirements of plant and animal have been performed in

large numbers by withdrawing or adding some of the elements from the diet in an

otherwise controlled environment. The effects on growth, survival and the level of trace

elements in tissues have been studied for such elements (7).

The trace elements Cd, Hg, Pb, Zn, Ni, Mn, As, Sb, Bi etc. have been receiving

increasing attention in the recent past as toxic pollutants in aquatic ecosystems (8-12).

Environmental pollution which includes water, air and soil pollution, has emerged as a

major threat to the human beings, animals, merine life, plants and crops etc. With the

rapid industrialization (Chemical, pharmaceuticals, pesticides, textile industries etc.) ther

problem of disposal of waste has been increasing. There is always possibility in all the

effluents/waste water that several trace metals like Cd, Hg, Mn, Ni, Cu, Pb, Zn, As, Sb,

Bi etc. are present which also add to pollution of soil and plants (8-12).

A trace metal ion, that is essential for activity of a particular enzyme system, may

well become toxic if the concentration of the trace metal ion exceeds a certain limit (7);

whereas lead and mercury poisoning are well-known occupational hazards (13).

Obviously, more efficient and economical methods for removal of pollutants from*

industrial effluents are being devised.

2

The common characteristic of all the trace elements is that they occur and#

function in very low concentrations in ppm or ppb levels, and that their functional forms

and characteristic concentrations are maintained within narrow limits. With very low or

very high input of trace elements, the biological system is disturbed and may manifest in

a disease condition. A protective mechanism may, however, develop which may delay or

minimize the effects of trace elements deficiency or excess (1,7).

t

MODE OF ACTION OF TRACE ELEMENTS

The trace elements act primarily as catalysts in enzyme systems in the calls,

generally, in the form of metalloenzymes having the metal firmly associated with the

protein, the metal being irreplaceable by other metal. However, substitution of Zn by Co

and Cd has been reported (104, 105)

ATMOSPHERE

AMETAL EMISSION

Wash outFall out%•

0%

%0%

0% %

#%

0 %%

0 %

0

t0

Run of MixingFlowLAKESRIVERS

TERRESTRIALSYSTEMS

ESTUARIES OCEANSIrrigation

SEDIMENTS SEDIMENTS

0

Fig. 1 Routes of transport of trace elements in the environment (16)

0

3

Metals have always been an intrinsic component of the earth’s crust. With the

continuing trend towards an increase of human activities involving heavy metals, various

organisms in the ecosystem, including man, may become exposed to concentration of

toxic heavy metal presenting a potential threat for survival. While the nutritional

essentiality of several trace metals like Cu, Zn, Mn, Cr, As, Sb, Bi has been well

established, heavy metals like Pb, Hg, Se. Mo have mainly been studied for their toxic

effects. Interactions between the toxic heavy metals and essential metals are important as

they illustrate the way in which that depends on essential elements. The occurrence of

these impairments under controlled experimental conditions, suggests that similar

abnormalities might occur in free living humans and animals, under circumstances of

increased exposure to toxic elements.

Biological effect of heavy metals

The impact on human health of the biogeochemical cycling of a metal is

determined by its physical, chemical and biological properties (17). In eliciting biological

responses the following physical properties of a metal appear to be of special

significance.

Natural occurrence and availability

Volatility of the metal and its salt.

Adsorption and desorption by tissuesr

Transport and diffusion through membranes

Solubility in lipids

Particle size in the atmosphere

The following chemical properties of metals are of clinical importance

Speciation

Ease of formation, transport and stability of alkyls when such derivatives are

formed (e.g, mercury, lead).

Redox properties

Stability and solubilization of sulphide sedimentation

Ionic association and dissociation in aqueous media and ion exchange properties

(I)

(ii) / ,

(iii)

(iv)

(v)

(vi)

(i)

(ii)

(iii)

(iv)

(v)

4

(vi) Chemical complexing properties

(vii) Stability and persistence in the environment

The following biological characteristics of metals are largely derived from their#

above physico-chemical properties.

Toxicity to man

(ii) Rate of accumulation in the food chain-bioaccumulation and

biomagnifications.

(iii) Retention time in living organisms

(iv) Biological transformation e.g. methylation

(i)

From the view point of health, metals can be divided into the following four

major groups:-

Metals essential to life processes e.g. copper, zinc, chromium, manganese,

iron and cobalt

Metals probably not essential to living systems e.g. barium, aluminium, lithium

and zirconium

Metals toxic to some life processes e.g. tin and arsenic

Metals highly toxic to the system e.g. mercury, lead and cadmium.

(i)

(ii)

(iii)

(iv)

Characterisation of effects

The environmental contamination from lead to date is not known to have caused

any teratogenic effects. However, the treatment of chick embryos with lead salt has been%

shown to produce a toxic effect on the morphogenesis of the lead primordium

hydrocephalus and anterior meningoceles (18-20). The addition of 25 ppm of lead to

the drinking water of breeding can cause early deaths of the offspring (21). Lead levels

in the foetal blood and amniotic fluid were found to be 55% of that of the maternal blood

in a goat infused for 2 h with lead chloride (22).

5

The inclusion of tetraethyl lead as gasoline additive in the 1920’s was a landmark

event, as this decision resulted in a steep increase in lead emitted into the environment

(23). The modem studies on the effects of developmental exposure to lead have been

extensively reviewed (24-25). IQ was the outcome variable used in meta analyses of

modem lead studies (26-27) although this method of analysis has been criticized as0

invalid in part because non identical end points are combined (28).

Occupational exposure to lead still poses a threat to the health of workers,

resulting in peripheral neuropathy function (29,30). Environmental sources of lead are

producing intellectual impairment in children at levels that had come to be regarded as

normal (31). Occupational exposure limits have become more stringent over recent

In New Zealand, the Occupational Safety and Health Service of the

Department of Labour now recommends that workers with a sustained PbB of 54 ppm

above should be suspended (32). Recent epidemiological studies suggest that children

with PbB levels as low as 10 pg/dl are impaired, relative to children with lower PbB

levels (33). Lead levels in blood and milk from urban Indian cattle and buffalo ranged

between 0.03 and 0.68 ppm for milk and in blood it ranged between 0.10 and 0.99 ppm

(34,35). Inorganic lead can act as a cumulative poison (36) and may be absorbed through

the skin via sweat gland (37). Speciation of lead in environmental and biological samples

has been reviewed (38). The toxicity of the alkyl lead diminished in the sequence (39),

years.

,

+2 ,RiPb > R3Pb+ > R2Pb [R = C2H5>CH3],

0

but the ionic species are more persistent in the environment (40). Efforts to control lead

exposure require accurate information on PbB levels in specific populations. In the

United States PbB levels have shown a substantial decline in the entire population

probably due to the elimination of leaded gasoline in 1986 (41). The daily lead balance

for the Calcutta city resident is shown in Fig. 2.

6r

%

AIR PARTICULATE

10 ppm PbT

EXCRETED200 ppm PbWATER

(SOLUBLE &COMPLEXED)

MAN15PPMPb25 ppm Pb storedin the bones

FOOD(COMPLEXED) 200 ppm Pb

Fig. 2 Daily lead balance for a city resident (42)

Various analytical methods are available for the determination of trace metals

viz. spectrography, polarography, spectrometry, chromatography, and colorimetry (72-

77). Although these methods have a limited use and are expensive, colorimetry is still in

practice. Organic reagents viz., dithizone, P-diketones, diethyl ammonium diethyl-

dithiocarbamate are the most common reagents used for extraction of heavy metals (78,/

*

84). Some of these reagents are sensitive but no systematic study has been made and

several diverse ions are interfering in their determination.

With the horizon of complexation abilities and salient properties of calix(6)arenes

increasing, there is increase in the number of reports, monographs and patents. Most of

the recent applications are associated with their properties as molecular receptors (85).

For many years, analytical chemistry has been based on chemical methods of analysis,

i.e., methods using chemical reactions. This largely still true in present-day analysis. In

many cases, such reactions involve participating reagents (special compounds providing

an analytically useful effect). An important characteristic of such a reagent is its

selectivity, i.e., the capability of preferably reacting with one or a limited number of the

7

test mixture components. Much effort has been made to determine the factors that control

the selectivity of reagents (primarily, reagents for metals) and especially to create really

selective reagents. Considerable advances have been achieved nevertheless, a general

theory ot reagent selectivity has as yet hardly been developed, and the number of

available highly selective compounds is not great.

In large part, the selectivity in the interaction between macrocycles and metal ions has a

bearing on the cycles and cavities occurring in the molecules of such reagents, although

(as in other cases) the character of donor atoms, their electron densities, the

“compatibility'' of donor atoms with metal ions (e.g., according to the principle of hard

and soft acids and bases), and other factors play a great role. The relative sizes of the

macrocycle cavity and the metal ion, the conformation of the macrocycle, and the

possibilities of its change are all thought to be important factors affecting the selectivity

(other things being equal). The preferable interaction of the 18-membered crowns bearing

six oxygen (e.g., dibenzo-18-crown-6) with potassium is a classical example supporting

this concept.

The areas of applying macrocycles in chemical analysis are diverse. Extraction of metals

with the aim of separating their mixtures and subsequently determining specific elements

is of great importance. Extraction has long been used as a convenient method in the study

of complexation between macrocycles and metals, as a relatively simple tool to estimate

the selectivity of such an interaction. Not only analysts but almost all researchers

studying macrocycles use extraction in this way to some extent, occasionally even

organic chemists. In view of this fact, our discussion of extraction with macrocycles will

not be restricted only to analytical aspects. As already mentioned, extraction is not just a

way to selectively separate metals prior to determining or detecting them.

Studies of extraction with mactrocycles have yielded a considerable body of data, which

needs to be organized in order to provide a basis for further investigations and

many interesting and useful analytical applications ofapplications. Even today, there are

macrocycles, all of which are of considerable importance from the viewpoint of the

8

subject of this book. Macrocycles of various types find use as extractants; oxygen-

containing compounds are employed most extensively.

I

Using macrocycles as components of various sorbets also serves the purpose of isolating

elements to determine their concentrations. Preconcentration of microelements can be

performed in the batch mode, but separation of mixtures is more effective when

conducted dynamically, particularly by means of chromatographic techniques. There are

various methods tor preparing sorbets based on macrocycles, such as impregnation of

porous materials, immobilization of the surface of silica gel or polymeric matrices (either

by adsorption and grafting) and polymerization of macrocycles as such, which produces

heterochain sorbets. As in extraction, macrocycles of various kinds are in use in sorption

and chromatographic methods, in particular, oxygen containing crown ethers.

For an analytical chemist, macrocyclic compounds constitute one of the classes of

organic analytical regents and should be considered from the same stand point as other

reagents designed for analytical purposes. Indeed, the puiposes may be quite diverse. The

requirements for a reagent to be used in a photometric determination of a metal ion differ

in many respects from the requirements for a compound to be used in precipitation or

extraction. This is so in many respects but not in every one. Because the interaction

depends on complex formation between a reagent and a metal ion, the approaches

employed in describing such an interaction should be general, i.e., irrespective of the

expected analytical effect. r

Template reactions are invariably performed in the presence of metal ions, which activate

and orient one of the components of the macrocyclization reaction by means of

complexation. The template effect is employed in the synthesis of crown ethers, and one

noticeably improve the yield of the desired compound by an appropriate choice of the

metal cation. This effect is widely applied in the synthesis of macrocyclic Schiff bases,

which produces only polymeric products in the absence of metal ions.

can

9

Macrocyclic compounds synthesized by the template method always exhibit the ability to

form complexes, which stems from the method of their preparation. The method of

template reactions sutlers from many drawbacks; we list only the principal one below:

a. The route ot condensation is ambiguous. When a template reaching can produce#

several compounds with same cyclic size and identical sets of donor atoms,

mixture ot all possible isomers is formed [43].

b. A template synthesis usually yields complex of the macrocycle with the metal%

ion. Isolation of the pure ligand from this complex is often not attainable.

c. Minute changes in the structure of reacting components often make macrocycle

formation impossible. The structure of the products of template reactions is

difficult to predict. At present, there are scarcely any reliable guidelines for

choosing a metal ion suitable for a specific template reaction.

HNH

O OY Y / „

\_/1.96

(X.Y = O.S)

On no account does the foregoing survey presume to be exhaustive in describing the

macrocycles reported. However, we hope it demonstrates the abundance and great variety

of available macrocyclic compounds. The important class of phosphacrowns fell beyond

the scope of this chapter. For the same reason, the broad area of silacyclens has also been

left untouched, as have some other groups of macrocycles. We emphasize once agin that

10

the materials considered in this chapter has just been illustrative of this rapidly growing

field.

Extraction of Alkali and Alkaline-Earth Metals with Crown Ehters

We shall now discuss the general regularities of extraction with crown ethers, taking the

most thoroughly studied metals - the alkali and alkaline-earth metals - as examples. The

extensive literature on the extraction of these elements with crown ethers is reviewed in a

number of papers [44-61].

Metal Recovery and Stability of the Complexes

The efficiency of recovery of alkali and alkaline-earth metals with crown ethers, which

can be characterized by the extraction constant K<.x, is controlled by the stability of the

MLA complex in an aqueous solution (paq), by the partition constants of the macrocycle

(KD, L) and the complex (KD. MLA), as well as by the ion-association formation constant

for the aqueous phase (Kas,MLA) [53].

Key K D,L Paq K-as, MLA KD, MLA (I)/ ,

Constant, as might be expected from Eq. (1). \Vhen the character of the metal has little

effect on KD, MLA and the dissociation constants of the complexes in the organic phase are

close to each other [62], the following relationship true for a particular crown ether (KD, L*

= Const):

Log Kcx = log Paq + COnSt (H)

An example in which the character of the metal has a weak effect is the DB18C6-metal-

Pic combination. In the water-benzene system, the log KD, MLA values of potassium,#

rubidium, cesium, and the thallium (I) complexes are all within the 5.2-5.9 range [63].

11

In some cases, a strict linear relationship between Kcx and paq is possible. The following

relationships have been reported [64] for the extraction of alkali metal nitrates with

chloroform solutions of DC18C6 [63] and DB18C6 [65], respectively:

= 0.182 paq-2.0 (III)

Kex = 0.0273 Paq- 0.01 (IV)

For some systems, the correlation between the stability constants of the complexes in the

aqueous phase and the extraction constants is poorer than the correction between the

aqueous-phase stability constants and the constants of the equilibrium MA

MALorg [67]. In fact, the correlation with the stability constants of the complexes in the

organic phase is expressed by p

rigorously direct proportion between KeX and p is observable only for singe-charged

cations [99]; It is less pronounced for crown ethers with a very large cycle, such as

DB24C8 [53].

+ Loraorg

= Kcx/Kcx, ML[53]. Among the various crown ethers, aorg

In the majority of other cases, no such linear relationship can be observed because, along

with complexation, other factors affect the extraction efficiency. These factors include

ion-pair interaction between the anion and the cation, resolvation of the free and

macrocycle-bonded metal ions, as well as differences in partition of complexes in two-

phase systems. As a result, the selectivity of extraction with crown ethers is often higher

than the selectivity of complexation with these compounds in homogeneous systems, i.e.,

the difference in the log KeX values may be greater than the difference in log p. Moreover,

in some cases, an inversion of selectivity is observed, a fact particularly interesting for

analytical chemistry. Inverse selectivity of DB18C6 to the Naf/Rb' and Ag7Rbf pairs

has been revealed by the extraction of these elements in the presence of azo dyes [100].

DC18C6 exhibited inverse selectivity for Ba2+, Sr2+, which was attributed to entrophic

factors [62].

12

Transition Metals and the Elements of the IIIA-VIA Groups

Crown ethers have traditionally been thought of as extractants for alkali and alkaline-

earth metals, as well as for lanthanides and actinides. However, they can effectively

extract some other elements, primarily silver, mercury (II), lead (II), and thallium (I). The

extraction ot other conditions (e.g., with chelating reagents added as counter ions).

Like alkali metals, silver (I) and thallium (I) are markedly extractable with ail of the

crown ethers, including the reagents without substituents [67-73], DC18C6 [74-78J,

DB18C6 [75,79-85], and nontraditional macrocycles [68, 86, 87]. Picrate [80, 88, 63, 73,

74, 86], dipicrylaminate [85], di(2-ethylhexyl) phosphare [76-77], alkylbenzenesulfonates

[75] and dyes [80, 81, 82, 69, 89] are appropriate counter ions for the extraction. TOPO

enhances the extractability of the Ag(DB18C6) Pic ion pair, because it participates in the

formation of the Ag(DB18C6) (TOPO)2 Pic adduct [85]. Dicanol imporves the recovery

of thallium (I) picrate with DC18C6 [78]. Liu et al. [90] and Gokel et al. [68] have

investigated the effect of the length of the hydrocarbon bridges between the oxygen

atoms in crown ether molecules on the recovery of silver and thallium (I).

DC18C6 [91] and other crowns quantitatively extract lead from 1-2 M solutions of HNO3

[92], and 18C6, DC18C6, and DB18C6 this metal from 0.1-5 M solutions of HCIO4 [93].

Recovery from the solutions of counterions. However; extraction is feasible with

DC18C6 and 18C6 form iodide media [94]. Lead can be extracted from weakly acidic

solutions by using Tropaeolin [95], picrate [93, 96, 97], eosin [98], or organic acids [53,

99]. Under the conditions of lead extraction, the distribution ratios for Mn(II), Fe(III), Co,

Ni, and Bi range between 0.001 and 0.01; the copper distribution ratio is 0.05.

When extraction with touene solution DC18C is conducted at pH 2.5-3.0 in the presence*

of di-(2-ethylhexyl) phosphate, lead passes into the organic phase partially (i.e.,

fractionally) [76, 77]. Anions of trichloroacetic, caproic, and bromocaproic acids provide

13

quantitative recover)' of lead with 18C6 [98-112]. With polyethylene glycol, the

extraction constant is 4 orders ofmagnitude lower [98].

Benzocrowns are less effective in lead extraction. The extraction efficencey diminishes in

the sequence DC18C6»Db18C6> DC24C8 [69, 92, 95].

DC18C6 quantitatively extracts mercury from nitric acid solutions [101]; the extraction

makes it possible to separate [97]mercury from cadmium and zinc

Alkylbenzenesulfonates bearing the Cs — C15 alkyl radicals improve mercury recovery,

probably by serving as counterions [101, 103]. Appropriate reagents for extraction of

mercury' are 15C5, 18C6, DB18C6 along with its derivatives, and DC24C8 [93, 96, 106].

When mercury is extracted from chloride solutions with the latter reagent, mercury

distribution ratio increases with metal concentration and (HgCfeb L2 complexes can be

formed.

Various crowns can extract scandium in the presence of picrate; 18C6 provides

quantitative recovery into CH2CI2 at pH 3 - 5; this procedure separates scandium for

yttrium, lanthanides, zirconium, hafnium, niobium, and uranium. Scandium can be

subsequently extracted back into a 0.1 M solution ofnitric acid [107].

Bismuth(III) extraction is scantily known. Quantitative recovery is achievable with

18C6 and trichloroacetate [70].

Chloroform solutions of crown ethers extract cobalt in the form of CoOH+ C10"4 •L. 18-

Crown-6 provides the best recovery (D=4) when the metal is extracted from 3M NaC104

at pH 5.5. Crown ethers fall into the following order according to their ability to extract

cobalt: 18C6 > DC18C6 > DC24C8 > DB18C6 > 15C5 > 12C4 [108]. Under special

conditions, cobalt and nickel can be extracted more effectively. This is achievable by

using crown ether in combination with l-phenyl-3-methyl-4-benzo-5-pyrazolone (PMBP)

[ 109, 1 10] or thenoyltrifluoroacetone [111-116].

14

According to their ability to extract cobalt in the presence of PMBP, the extractant can be

arranged in ghe following sequences: acyclic polyoxyethylene surfactant Triton X-

100>18C6>DC18C6 [109]. Cationic cobalt (II, III) and nickel ammoniates are partially

extractable from ammonia solutions with macrocycles bearing ionizable groups such as

the carboxylamino or sulfur group. Cobalt is superior to nickel in extractability. The#

macrocycle size has little effect on extraction efficiency because there is no coordination

of the metal to the cycle donor atoms. Decylbenzo-16-crown-5-acetic acid also extracts

the ammoniacetates of metals. The extraction of cobalt is better than the extraction of

copper, nickel, and zinc; separation factors are in the 10- 14 range [116].

Extraction of other metals with crown ethers has yielded poor results. Distribution ratiosr

for copper and zinc extraction (with 12C4 or 15C5; picrate) fall in the range 10 - 10'“.

Adding TBP leads to the synergistic extraction of MLPic2 •TBP [112, 113]. When di-(2-

ethylhexyl) phosphoric extraction of Cadmium into toluene, adding DCI8C6 only

slightly increases the distribution ratio (from 0.1 to 0.2) [77]. In the form of thiocyanate,

cadmium can pass across a toluene membrane containing DC18C6 [114].

Whereas extracting alkali metals, 12C4, 18C6, DC18C6, and other crowns virtually do

not recover Fe(III), Ru(III), and Ce(III) in the presence of picrate; the recovery of

europium and yttrium does not exceed 6% DB18C6 does not extract Nb(V), Ru(III),/ .

Sb(III), and Zr(IV) at pH5 in the presence of picrate even when nitrobenzene is used as a

solvent [115-116]. There were attempts to extract a number of metals by crown ethers

with 15- to 21-membered cycles in the presence of didodecylnaphthalenesulfonic acid.

The acid per se recovers 50-99% of Co, Cu, Fe(II), Mn, Ni, and Zn from 0.1-1 M HNO3

solutions. Addition of a crown just diminishes the recovery of the metals. Only in the

case of manganese and zinc extraction with tert-butyl-CH15C5 in toluene, the log D

values increased by 0.3-1.0 units; no synergism was observed in the case of tert-butyl-

B15C5 [115, 116].

15

Aims and Scope

With the better understanding of the phenomenon of toxicity of trace elements and

continuous diminutions in the maximum allowable limits of (106) contaminants in the

effluents, the need for development of sensitive, selective, rapid, field adaptable and#

economical analytical methods for the detection and determination of elements at trace

levels has been growing.

Literature survey on crown ethers indicate that they are still finding new

applications as molecular receptors for highly selective ion complexation. Agrawal et.

al., having a major contributions in hydroxamic acid chemistry have brought forth new

molecules with supra molecular assests by fusing versatile hydroxamic acid with fleble

molecular baskets calix(6)arenas, crown ethers fullerenes etc. (117-126). Introducing a

chelating group into crown ethers will enhance the complexation properties of crown

ethers. With this a new crown ether with hydroxaic acid is synthesized and use the

extraction and trace determination of trace metals.

The Prsent Investigation

The thesis describes the preparation and properties of a new 15-Crown-5-

phenylbenzohydroxamic acid (CPBHA) are described. The preparations is (CPBHA, I)

made by reacting 15-Crown-5-phenylbenzohydroxamic acid with benzoyl chloride at lowr

temperature in diethyl ether solution containing aqueous suspensions of sodium

bicarbonate. The yield of once crystallized product is 80%.

The liquid-liquid extraction, speciation, sequential separation and trace

determinations of arsenic, antimony and bismuth with the synthesized 15-crown-5-

phenylbenzohydroxamic (CPBHA) is reported. Arsenic, antimony and bismuth are

extracted at pH 5.0, 2.5 and 2.5 M HCI, respectively in dichloromethane and recovered

them in presence of large number of cations and anions. The influences of CPBHA, pH

and molarity of HCI, diverse ions and temperature on the distribution constant have been

reported. Arsenics gives the light yellow coloured complex 400 nm with molar

16

absorptivity 2.5 x 104 L mol

nm having molar absorptivity 2.0 x 104 L mol

nm with molar absorptivity 1.8 x 104 L mol

-i cm'1, antimony gives light pink coloured complex A,™ 420

-l

___-i while bismuth is having Amax 430

cm’1. For the trace determination, the

extracts were directly inserted into plasma for ICP-AES measurements which enhances

the sensitivity 70 folds and obeys Beer’s Law for As(III) 3.0-32.0 ng ml*', for Sb(III) 8.5

- 88 ng ml 1 and for Bi(lll) 20.0-171.0 ng ml’1 . The trivalent and pentavalent

antimony and bismuth were simultaneous estimated. The method is applied for the

determination of As, Sb and Bi in alloys, industrial effluents, environmental and

biological samples.

A simple and sensitive extraction and spectrophotometric method for the

determination of cadmium is described. The binary complex formed between Cd-CPBHA

is extracted with dichloroemethane at pH 9.0, having the maximum absorbance at 380 nm

and molar absroptivity 4.0x10A Lmol

measurements is 0.28-3.0 ppm. The sensitivity of the method has been increased by the

cm

-i

arsenic,

-i -l. The optimal concentration range forcm

addition of 4-(2-pyridylazo) resorcinol after extracting cadmium with CPBHA at pH 9.5.

The Cd-CPBHA-PAR gives a reddish orange complex having the maximum absorbance

at 515nm and molar absorptivity 6.5 xlO4 Lmol-i -i. It obeys beer’s law in the range

of 0.17 to 2.50 ppm. The Sensitivity of the method has been increased by directly

inserting the Cd-CPBHA dichloromethane extract into the plasma for ICP-AES

measurements with 2 ng mL’1. Various experimental parameters have been studied forr

evaluating optimal condition for the extraction and spectrophotometric determination of

cadmium. The cadmium is determined in high purity grade alloys and environment

cm

samples.

A liquid - liquid extraction and spectrophotometric method is described for the

determination of trace amounts of zinc. Zinc is extracted at pH 8.0 with 15-Crown-5-

phenylbenzo acid and with stearylamine and determined spectrophotometerically after

the addition of l-(2-pyridylazo)-2-naphthol. Beer’s law is obeyed over the range 0.05-

1.92 pg mL'1 at 550 nm and 0.04-1.90 pg mL'1 at 550nm with molar absroptivities of 5 x

104 and 5.8 x 104 L moL'1 cm'1, respectively. For ICP-AES measurement the Zn-

CPBHA. Dichloromethane extract was directly introduced into the plasma to enhance the

17

-sensitivity several folds with the detection limit of 5 jig mL'.The effects of diverse ions

are discussed. The method was applied to the determination of zinc in high-purity alloy

and environment samples.

A selective and sensitive spectrophotometric and atomic absorption

spectrophotmetric method is developed for the determination of traces of mercury with

15-Crown-5-phenylbenzohydroxamic acid (CPBHA) in the environment. Mercury is

extracted into a dichloromethane solution of CPBHA at pH 8.5-10.0 and determined by

ICP-AES. The mercury CPBHA binary complex is yellow in colour having maximum

absorbance at 390 nm and molar absorptivity 4.3 x 103 L mol 1 cm'1, sandell sensitivity20.0466 pg/cnT. The ternary system using 1- (2-pyridylazo)-2-naphthol has molar

absroptivity 8.82 x 103 L mol-l__-i # • 9

at 550 nm, sandell sensitivity 0.0228 jig/cnT. Beer's

law is obeyed in the concentration range of 2.37-38.0 ppm and 0.80-19.5 jig mL 1 of

cm

mercury for binary and ternary system, respectively. The extraction of Hg-CPBHA

binary system is studied with a liquid cation exchanger, bis-(2-ethyl hexyl) phosphoric

acid (HDEHP) and found to have better selectivity than Hg-PCHA-PAN system. The

molar absorptivity of the Hg-CPBHA-HDEHP system is 8.82 x 10’ L mol

nm and Beer’s law is obeyed in the concentration range of 0.47-20 jig mL'1 of mercury.

-l cm at 390

The present method is applied to the determination of mercury in eye drops.

aurvedic drugs and environmental samples.

A rapid method for the extraction and spectrophotometric determination of lead in

the environment is described. The lead forms a yellow complex with 15-Crown-5-phenyl-

benzohydroxaic (CPBHA) acid at pH 9.5 which is extracted from chloroform. The molar

absorptivity was found 4.0 x 102 1 mol 1cm 'at 390nm. The phenylfluorone is used as a

synergestic. Pb-CPBHA complex is back extracted with 0.01 M acetic acid and after

rising to pH 9.5 lead is estimated by means of phenylfluorone which gives a yellow-red

coloured complex. The molar absorptivity is found to be 1.9 x 103 L mol

The effect of pH, electrolytes, reagent concentration and various ions is discussed. The

method is applied for the trace determination of lead in industrial effluents and natural

resources.

i-lcm' at 5 10 nm.

18

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