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EXTRACTION-SPECTROPHOTOMETRIC
DETERMINATION OF ANTIMONY
105
EXTRACTION - SPECTROPHOTOMETRIC DETERMINATION OF ANTIMONY
SUMMARY
A new extraction-spectrophotometric method for the
deter1fnation and speciation of antimony is proposed. It is
based on the extraction of antimony(V) with N-alkyl~aryl-N'-
phenylbenzamidines over 5.5-7.5 M HCl in toluene and
reaction of the extract with basic dyes viz. brilliant
green, malachite green, and crystal violet. The molar
absorptivity of the complex formed with 10 different N-
alkyl/-aryl-N'-phenylbenzamidines and the 3 basic dyes lie
in the range of (0.95 - 1.62)x 105 1
-1 mol -1 em at
absorption maximum, respectively. Amongst N-alkyl/-aryl-N'-
phenylbenzamidines and basic dyes used, the parent compoun~
N,N'-diphenylbenzamidine (DPBA) and brilliant green (BG)
have been chosen for the detailed studies. The detection
limit of the method is found to be 10 pg Sb -1
1 • The
-1 system followed Beer's law upto 0.7 pg Sb ml toluene with
slope, intercept, and correlation coefficient value of 0.97,
0 and+ 0.99, respectively. The method is almost free
from interferences of common metal ions except Tl(III). The
present method has been applied for the quantification of
inorganic antimony in water.
108
Antimony occurs in the earth's crust at low level. It
is also found in some ores, minerals and sands (1-3).
Antimony and its compounds are industrially significant
because of their unique contribution to the manufacture of
many commonly used products such as alloys, paints, and
textiles (3-5). Antimony has significant role in pharmacy.
Antimony pentasulfide and tarteremitic have medicinal appli-
cation and also important for preparation of therapeutic
agents (6).
Antimony is a toxic element (7-8) which exists in the
aquatic environment in two different oxidation states i.e.+3
and +5. Antimony(!!!) is more toxic and mobile than antim-
ony(V) (9). Direct contact of antimony with skin results in
dermatitis and skin eruptions (1,5). Antimony compounds are
slowly absorbed from the gastrointestinal tract and tend to
produce vomiting. The dusts of free metal was more toxic on
inhalation than any of the oxides and sulfides. Symptoms of
chronic poisoning consisted of headache, sleeplessness, ver-
tigo, loss of appetite, and muscular pains. The threshold
limit of exposure of antimony and its compounds is 0.5 mg Sb
-3 m of air (9).
A large number of methods have been proposed for the
spectrophotometric determination of antimony in complex mat-
erials. Of these iodide method (10-15) is widely used for
routine analysis, but its sensitivity is very low and it
also suffers from interferences of Hg(II), Pb(II), Bi(III),
107
Sn(II), Ni(II), Mo(VI), Cl-etc. Selectivity and sensitivity
of the classical iodide method has been enhanced by use of
rhodamine B (16), pyrocatechol violet +high molecular weight
amines (17), N,N'-diphenylbenzamidine (18) and N-hydroxy-N'
phenylbenzamidine (19}.
Various organic reagents viz. triphenyltetrazolium ch
loride (20), 7-diethylamino-3-(azo-p-N,N-diethylaniline}-5-
phenylazinium chloride (21}, 2-(5-bromo-2-pyridylazo}-5-(di
methylamino)phenol (22), 2-(5-bromo-2-pyridylazo)-5-diethyl
aminophenol (23-27), 1,3,3-trimethyl-2-formylindolineum per
chlorate-2-nitro-4-methoxyphenyl hydrazone (28), 1-(2-pyri
dylazo)-2-naphthol (29), diantipyrylmethane (30), phenosa
franine (31), trihydroxy-4'-sulphoazobenzene (32), molybd
oblue (33-34}, diethyldithiocarbamate (35), catechol violet
( 36) , [2,4,6-(2-hydroxy-4-sulfo-1-naphthylazo)]-s-triazine
trisodium salt (37~ and thiourea (38) have been reported for
the determination of antimony. Most of these methods invo-
lve poor sensitivity and interferences of some metal ions
e.g. Cr(III), Sn(IV)~ Fe(III), Bi(III), Pt(II}, Ga(III),
Cd (II), etc.
Several fluorones viz. 4,5-dibromophenylfluorone (39),
9(-p-di-methylaminophenyl)-2,3,7-trihydroxyfluorone-6 (40),
o-nitrophenylfluorone (41-42), vanillylfluorone (43), 2,6,7-
trihydroxy-9'-[4-(8-hydroxy-5 -quinolyazo)] - phenylfluorone
+ CTAB (44) have been proposed for spectrophotometric dete
rmination of antimony but most of them suffer by one or more
drawbacks i.e.critical acidity, less thermodynamic stability
108
of the complex,etc.
Many dyes viz. rhodamine B (16,45-51), brilliant green
(52-58), malachite green (59-62), methyl violet (63), meth
ylene blue (64-65), pyrocatechol violet (17,56), basic blue
K (67), crystal violet (68-70), bromopyrogallol red (71-72)
have been reported for
determination of antimony.
the extraction-spectrophotometric
They are sensitive but suffer by
requirement of a double extraction and poor reproducibility.
In the present investigation, N,N'-diphenylbenzamidine
(DPBA) and its 9 analogous and three basic dyes viz. bril
liant green, malachite green and crystal violet have been
tested for the extraction-spectrophotometric determination
of antimony(V) in order to select the most sensitive pair.
The basic amidine i.e. N,N'-diphenylbenzamidine (DPBA) and
brilliant green (BG) have been chosen for the detailed
determination. The present method remarkably increases the
sensitivity of the classical brilliant green method and also
improves the selectivity (52-58). Other drawbacks i.e. req
uirement of a double extraction, variation of colour ·with
respect to temperature, narrow acidity range, etc. have also
been overcome in the present method.
lO~J
EXPERIMENTAL
APPARATUS- As discussed in Chapter II.
CHEMICALS AND REAGENTS-
All chemicals and reagents used were of A.R.grade (E.
Merck/BDH).
STANDARD ANTIMONY(III) SOLUTION- The stock solution of
antimony was prepared by dissolving 0.100 g antimony metal
(99.9%) in 15 ml concentrated H2
so4
by heating over a hot
water bath and diluted the resulting solution to l litre
with l M HCl containing 0.1% (w/v) tartaric acid.
AMIDINE- N-Alkyl/-arylbenzamidines (73) were synthesized (as
described in chapter II) and their 0.15%, w/v solution in
toluene were employed.
DYES SOLUTION- 0.04% , w/v was employed.
CERRIC AMMONIUM SULPHATE- 6.4%, w/v (0.10 M) in l M H2so 4
was employed.
HYDROXYLAMMONIUM HYDROCHLORIDE- 1%, w/v (0.14 M) in water
was employed.
HYDROCHLORIC ACID- Concentrated hydrochloric acid (11.5 M)
was used.
SOLUTIONS OF DIVERSE IONS- Solutions were prepared as
described in chapter II.
In the case of lighter organic solvents, all solutions
employed were presaturated with the solvent.
110
PROCEDURE FOR EXTRACTION OF ANTIMONY-
An aliquot of standard solution containing upto ).0
pg antimony(III) was taken in a 125-ml separatory funnel.
In to this 5.5 ml hydrochloric acid (11.5 M) and 1 ml cerric
ammonium sulphate were added and diluted to 10 ml with
distilled water. The excess of cerric ammonium sulphate was
removed by reducing with hydroxylammonium hydrochloride with
dropwise addition till the solution became colourless. The
aqueous phase was shaken with 10 ml toluene solution of DPBA
for 2 min. The aqueous phase was discarded.
PROCEDURE FOR DETERMINATION OF ANTIMONY-
The extract obtained as above was reacted with 5 ml dye
solution and shaken for 2 min. The organic extract was dried
over anhydrous sodium sulphate (~ 2 g) in a 25-ml beaker.
The absorbance of the extract was measured at ~max against
the respective reagent blank.
111
RESULTS AND DISCUSSION
Basic dyes viz., brilliant green, malachite green, and
crystal violet have been reported for the extraction
spectrophotometric determination of Sb(V) from the strong
hydrochloric acid solution into benzene or toluene. The ex-
traction of [SbC16 ]-dye is critical. Therefore, in the
present investigation, N-alkyl/aryl-N'-phenylbenzamidine is
used for the prior extraction of Sb(V)-Cl- to enhance the
sensitivity of the classical dye method in a single extrac
tion.
OXIDATION OF ANTIMONY(III)-
Cerric ammonium sulphate, sodium nitrite and hydrogen
peroxide have been examined for the oxidation of antim-
ony(III) into antimony (V) (57). All of them were found
adequate for the oxidation but with the last two oxidants a
high blank absorbance was seen. Hence, cerric ammonium
sulphate was chosen for the further studies. At least 1 ml
of 0.01 M cerricammonium sulphate was found to be sufficient
for the maximum oxidation of antimony and upto 3 ml had no
adverse effect.
EXTRACTION OF ANTIMONY(V) -
Antimony(V) was extracted with N-alkyl}aryl-N'-phenylb
enzamidine into various water immiscible solvents viz.
benzene, toluene, carbon tetrachloride, chloroform, methyl
isobutyl ketone, ethyl acetate, 1-pentanol from strong
hydrochloric acid solution, Table 4.1. All the solvents
w (J
z <{
o.s
11 :~
A
~ 0.3 0 Ul co <{
Q.l
600
WAVELENGTH, nm
700
FIG.4.1 ABSORPTION SPECTRA OF Sb(V)-Cl -DPBA/-BG, Sb(V)-Cf/-DPBA
COMPLEX AND THE REAGENT BLANK IN TOLUENE.
L DPBA j ~ 5. Sx Hl 3 M, [ BG] ~ 8. 3x 10- 4 M, pH ~ 2. 0±.0 .2
(A)
(B)
(C)
-6 3.3x!O M (4.0 ~g/10 ml organic phase). -6 2.Sx10 M (3.0 ~g/10 ml organic phase). -6 l.SxlO M (2.0 ~g/10 ml organic phase).
(D) Reagent blank,
(E) Sb(V)-Cl- -DPBA Complex, [ Sb5+J ~ 2 .5x10-6 M.
113
TABLE-4.1 EFFECT OF SOLVENTS ON THE EXTRACTION OF THE METAL
AS Sb(V)-Cl--DP.BA COMPLEX, AND THE ABSORBANCE OF
Sb(V)-Cl -DPBA/-BG COMPLEX.
[Sb 5+] = 2.5Xl0- 6 M (3.0 f-19/ 10 ml aqueous phase)
[HCl] = 6.0 M
[DPBA] -3 = S.SxlO M
[BG) -4 = 8.3xl0 M
Solvent Percentage extraction of Sb as Sb(V)-Cl-
DPBA complex
%E
Benzene 99.5
Toluene 99.4
Carbon tetra- No extraction chloride
Chloroform 98.3
Ethyl acetate 97 .'4
Methyl isobutyl 94.5 ketone
1-Pentanol 97.0
Spectral characterstics of Sb(V)-Cl--DPBA/-BG
complex ----------------------->-mt• ~
l mol-l cm-l nm
640 1,62,000
640 1,54,000
Dye extractable
_ .. _
-"-
111
TABLE-4.2 EFFECT OF ACIDITY ON THE ABSORBANCE OF THE EXTRA-
CTED COMPLEX [Sb(V)-Cl -DPBA] IN TOLUENE.
[sb5+] : 2.5xlo- 6 M (3.0 pg/10 aqueous phase)
[DPBA) : 5 .5xl0- 3 M
Concentration of HCl M
4.0
5.0
5.5
6.0
7.0
7.5
8.0
8.5
Absorbance at 640 nm
0.250
0.340
0.380
0.375
0.380
0.385
0.360
0.330
115
except carbon tetrachloride quantitatively extract (94.5
99.5%) Sb(V) as ion-pair complex.
The extracted complex is colourless and shows practica-
lly negligible absorption over 500-700 nm, Figure 4.1.
Therefore, the effect of analytical variables on the
extraction of the analyte was studied in terms of absorbance
of Sb(V)-Cl--DPBA/-BG complex.
PERCENTAGE EXTRACTION - The percentage extraction was
determined by extracting 20.0 rg antimony(V) with N,N'-dip
henylbenzamidine (DPBA) at different acidity conditions. The
extract was collected in a 50-ml beaker by washing the sepa-
ratory funnel with 2x3 ml fresh toluene. It was evaporated
0 to almost dryness by keeping it over hot water bath ( 60 C).
The complex was reacted with bromopyrogallol red (BPR) as
described in the literature (71). The percentage extraction
(in a single extraction} was found to be 98.7± 0.2%, over
5.5-7.5 M HCl.
EFFECT OF ACIDITY- The effect of hydrochloric, and sulp-
huric acids have been tested towards the formation of the
complex. Sulphuric acid was not found to be adequate for the
acidification of the aqueous solution may be due to the
formation of unextractable sulphate- complex. With hydro-
chloric acid, the optimum acidity range is 5.5-7.5 M. All
experimental work was carried out at 6.0 M HCl, Table 4.2.
116
TABLE-4.3 EFFECT OF DPBA CONCENTRATION ON THE ABSORBANCE OF
Sb(V)-Cl -DPBA COMPLEX IN TOLUENE.
[sb5+J = 2.5xlo-6 M (3.0 ~g/10 ml aqueous phase)
[HClj = 6.0 M
------------------------------------------------------------Concentration of DPBA
0.05
0.07
0.10
0.20
0.40
0.70
1. 00
1.10
1. 20
Absorbance at 640 nm
0.270
0.330
0.385
0.380
0.380
0.375
0.380
0.290
0.180
117
TABLE-4.4 EFFECT OF VOLUME RATIO OF THE ORGANIC TO THE AQU-
EOUS PHASE ON THE ABSORBANCE OF THE COMPLEX.
[Sb5+] = 3.0 pg
[HCl) = 6.0 M
[DPBA] = S.Sxl0- 3 M
Volume ratio of the organic to the aqueous phase
2:1
1:1
2:3
1:2
2:5
l: 3
1:4
Absorbance at 640 nm
0.380
0.380
0.385
0.380
0.380
0.380
0.360
------------------------------------------------------------
118
EFFECT OF AMIDINE- The effect of concentration of N,N'-
diphenylbenzamidine(DPBA) on the absorbance of the extracted
complex in toluene was examined. It was found that at least
l.Oxlo-3M DPBA was necessary for the full colour development
of the complex and further addition upto 1.0 x 10-z M had no
adverse effect, Table 4.3. A 5.5xl0-J M DPBA in toluene was
used for the detailed studies.
EFFECT OF DILUTION- The effect of variation in the volume
of the aqueous phase towards the extraction of the complex
was studied. No change in the absorbance of the complex was
observed when the volume ratio of the organic to the aqueous
phase was varied from 2:1 to 1:3 , Table 4.4.
EFFECT OF TEMPERATURE, SHAKING TIME AND ELECTROLYTE-
The effect of temperature of the aqueous phase on the
extraction of the complex was investigated. The temperature
of 0
the aqueous phase from 10-40 C had no adverse effect on
the absorbance of the complex, Table 4.5. A shaking time of
1 min was needed for the full colour development of the
complex and further shaking upto 10 min had no adverse
effect on the absorbance of the extract. The effect of ele-
ctrolytes viz. KCl, NH4Cl, and K
2so
4 on the absorbance of
the complex was studied. No change in the absorbance of the
coloured system has been observed with the addition upto 1.5
M.
STOICHIOMETRY OF Sb(V)- DPBA COMPLEX-
In the concentrated hydrochloric acid solution Sb(V)
exists 1n the form of hexachloro antimonate,SbClG (57). The
11!)
TABLE-4.5 EFFECT OF TEMPERATURE ON THE ABSORBANCE OF THE
Sb(V)-C1--DPBA COMPLEX IN TOLUENE.
[sb 5+) = 2.5x1o- 6 M (3.0 pg/10 m1 aqueous phase)
(HC1] = 6.0 M
[DPBA] = 5.5x10-J M
------------------------------------------------------------Temperature Absorbance at
640 nm ------------------------------------------------------------
5 0.270
lO 0.310
15 0.385
20 0.380
25 0.385
30 0.370
35 0.380
40 0.320
45 0.280
0
Ol 0
0
-1
J2()
-5 -4
log [DPBA]
FIG. 4.2 CURVE-FI'ITING METHOD FOR THE DETERMINATION OF MOLAR RATIO
OF Sb(V) TO DPBA IN Sb(V)-Cr -DPBA/-BG COMPLEX IN TOLUENE.
121
TABLE-4.6 CURVE - FITTING METHOD FOR THE DETERMINATION OF
THE MOLAR RATIO OF Sb(V) TO DPBA IN Sb(V)-Cl-
DPBA/-BG COMPLEX IN TOLUENE.
(Sb5+) ~ 2.5xl0- 6 M (3.0 pg/10 ml aqueouus phase)
(HCl)
(BG)
Concentration of DPBA
-5 X 10 M
l. 30
l. 84
2.40
3.13
~ 6.0 M
8.3 X 10- 4 M
Log M
- 4.88
- 4.74
- 4.62
- 4.50
D = --~~.9 __ _ A -A max eq
0.32
0.47
0.57
0. 72
Log D
- 0.49
- 0.33
- 0.24
- 0.14
122
molar ratio of Sb(V) to DPBA complex in the extracted
complex was determined by curve-fitting method (74), by
plotting log distribution (log D) of the metal (D= A c(A -e max
Aeq) versus log molar concentration of DPBA {log M) taken. A
slope of 0.9 close to integer 1 was obtained, Table 4.6,
Figure 4.2. Thus the molar ratio of Sb{V) to DPBA in the
extracted complex is expected to be 1:1. The probable
extraction mechanism can be written as -
Where DPBA, and subscript o denote to N,N'-diphenylbenza-
midine, and the organic phase respectively.
COLOUR DEVELOPMENT OF THE EXTRACT WITH DYE-
The basic dyes {Dy) viz. brilliant green, malachite
green and crystal violet effectively substitute the associa-
ted amidine molecule, DPBA in the extracted complex in the
present investigation.
Where subscript o denotes to the organic phase.
CHOICE OF DYE - The basic dyes viz. brilliant green, mal-
achite green, crystal violet were tested towards the subst-
itution of the amidine in extract as in the procedure. The
value
to
of molar absorptivity of the complex varies
and lie in the range of {1.05-1.54) x 105
1
from dye
-1 -1 mol em
at
dye
)..max Table 4.7. Amongst them, brilliant green (BG) gave
the most sensitive colour reaction.
TABLE-4.7 SPECTRAL CHARATERSTICS OF THE COMPLEX WITH VARI-
OUS DYES IN TOLUENE.
[ HCl] = 6. 0 M
[DPBA) = 5.5xl0-l M
[DYE] = 0.04%, w/v
~~~--------------------------->: ____________________ € ______ _
nmmax 1 mol-l em -l
Brilliant green
Malachite green
Crystal violet
640
630
605
1,54,000
1,18,000
1,05,000
0.5.---------------------------------~
w u
0.3 z <t Ul IX 0 \/)
Ul <t
0.1
OL-------~--------~------~--------~ 580 640 700
WAVELENGTH, nm
FIG.4.3 ABSORPTION SPECTRA OF Sb(V)-Cl- -DPBA/-DYE COMPLEX AGAINST
RESPECTIVE REAGENT BLANKS IN TOLUENE
[HCl1 = 6.0 ;1, [DPBAj = S.Sx!03 "l,[DYE] = 0.04%, w/v
(Al Brilliant gree•1.
(B) ~!alachite green.
(C) Crystal violet .
0.5
A
w u z <! 0.3 en 0:: 0 (/)
en <!
0.1
OL-------~--------L-------~------~ 560 640
WAVELENGTH.nm
700
FIG.4.4 ABSORPTION SPECTRA OF Sb(V)-Cl--AMIDINEj-BG COMPLEX WITH
SOME AMIDINES AGAINST RESPECTIVE REAGENT BLANKS IN TOLUENE.
[AMIDINE] = 0.15%,;;/v, [BG) ~ 8.3xl0 4
M, pH~ 2.0±0.2
(A) Sb( V )- cC -N-( 2-Methy lpheny 1)-N:.phenyl benzamidine/ -BG
(B) Sb(V)-Cl- -N ,N:.Diphenylbenzamidine/-BG
(C) Sb(V)-Cl- -N-(3-Chlorophenyl)-N:.phenylbenzamidine/-BG
( D l Sb( V)-CC -N- ( 2, 5- Dichlorophenyl)-N= pheny lbenzamidine {-BG
128
ABSORPTION SPECTRA - The absorption spectra of Sb(V)-Cl--
DPBA/-dye, Sb(V)-Cl-amidine/-BG complexes against the resp-
ective reagent blank in toluene and the reagent blank
against the solvent are shown in Figure 4. 3, 4A • The pos
ition ofA varies from dye to dye and lie between 605-640 max
nm. The reagent blank shows some absorption at )- hence, max,
it was used as reference for all measurements. The position
of absorption maximum remains intact when concentration of
the metal is varied,Figure 4.2.
EFFECT OF SOLVENTS - The Sb(V)-Cl -DPBA extract obtained
into solvent: benzene, toluene, chloroform, ethyl acetate,
methyl isobutyl ketone, and 1-pentanol was separately reac-
ted with BG as described in the procedure. Among them,
aromatic hydrocarbons gave the most sensitive colour of the
extract with the least colour of the reagent blank unlikely
to other organic solvents, Table 4.1. In the view of lower
toxicity, toluene was used for further work.
EFFECT OF pH - The pH of the aqueous solution was adjusted
with dilute hydrochloric acid (0.1 M) and measured after
equilibration. Optimum pH range for maximum and constant
colour development of the complex is found to be between pH
1.0-3.0, Table 4.8. The detailed experimental work was car-
ried out at pH 2.0 + 0.2.
EFFECT OF BRILLIANT GREEN- The effect of concentration of
brilliant green (BG) for the full colour
complex has been examined. At least 3.0
development of the
-4 x 10 M was needed
127
TABLE-4.8 EFFECT OF pH ON THE ABSORBANCE OF Sb(V)-Cl--DPBA/
-BG COMPLEX.
[Sb5+] = 2.5xlo- 6 M (3.0 pg/10 ml organic phase)
[BG] = 8.3xl0- 4 M
pH of the aqueous solution containing BG
0.5
1.0
1.5
2. 0
2.5
3.0
3.5
4.0
Absorbance at 640 nm
0.320
0.380
0.385
0.380
0.380
0.380
0.350
0.320
TABLE-4.9
J28
EFFECT OF BRILLIANT GREEN (BG) CONCENTRATION ON
THE ABSORBANCE OF THE EXTRACT.
[sb5+] = 2.5x10- 6 M (3.0 pg/10 m1 organic phase)
pH = 2.0 + 0.2
concentration of BG Absorbance at
640 nm
0.1 0.300
0.2 0.340
0.3 0.385
1.0 0.380
2.0 0.380
3.0 0.380
4.0 0.370
4.2 0.350
4.5 0.280
5.0 0.210
for the maximum colour development of
change in the absorbance of the complex
was seen, Table 4.9.
1 2 ~)
the extract and no -3
upto 4.0 x 10 M BG
CHOICE OF AMIDINE - The extracts obtained from N,N'-
diphenylbenzamidine and its 9 analogous were reacted with
brilliant green. The value of molar absorptivity of the
complex is remarkably affected with respect to nature of
amidine used may be due to ease of substitution of BG to
the co-ordinated amidine. The most sensitive colour is seen
with +!(inductive effec~causing group e.g. -CH3 in N-
phenyl ring of amidine while reverse effect with -I effect
causing group e.g. cr-. In the present investigation, the
parent compound, N,N'-diphenylbenzamidine (DPBA) has been
chosen for the detailed studies, Table 4.10.
EFFECT OF DILUTION- The effect of variation in the volume
of the aqueous phase on the absorbance of the complex was
studied. No change in the volume ratio of organic to the
aqueous phase from 4:1 to 1 : 2 is observed, Table 4 .11.
STOICHIOMETRY OF THE COMPLEX-
The ratio of Sb(V) to BG in the extracted complex was
determined by plotting log (Aec(AmaxAeq> versus log molar
concentration of BG added, (74) Table 4.12, and Figure 4.5.
The result obtained showed the value of slope to be 1.9
close to integer 2. A number of oxidising reactions of
SbC16- salts of stable organic cations with aromatic amines,
ferrocene, phenoxide ions and I- ions have been
J30
TABLE-4.10 SPECTRAL DATA OF THE COMPLEX WITH DIFFERENT AMIDINES IN TOLUENE.
[HC1] = 6 .. 0 M
[ AMIDINE] = 0. 15
[ BG] = 8. 30
%, ( W/V)
-4 X 10 M
------------------------------------------------------------Amidine )- max f
Formula
Name
nm
N,N'-Diphenylbenzamidine c6 Hs 640
N-(2-Methylpheny1)-N'- 2-CH3-c6 H4 640 Pheny1benzamidine
N-(3-Methylphenyl)-N'- 3-CH 3 -c6H4 640 pheny1benzamidine
N-(4-Methy1pheny1)-N'- 4-CH 3-c 6H4 635 pheny1benzamidine
N-(2,5-Dimethy1pheny1)-N'- 2,5-(CH 3) 2-c 6H3 640 pheny1benzamidine
N-Octyl-N'-pheny1benza- CH3 - ( CH z) 7 635 midine
N-(2-Ch1oropheny1)-N'- 2-C1-C 6H 4 640 phenylbenzamidine
N-(3-Ch1oropheny1)-N'- 3-Cl-C f!! 4 635 phenylbenzamidine
N-(4-Chloropheny1)-N'- 4-Cl-C6H4 640 phenylbenzamidine
N-(2,5-Dich1orophenyl)-N'- 2, 5-(Cl lzC6H3 640 phenylbenzamidine.
-1 -1 1 mol em
1,54,000
1,62,000
1,48,000
1,46,000
1,32,000
1,18,000
1,22,000
1,26,000
1,30,000
95,400
------------------------------------------------------------
131
TABLE-4.11 EFFECT OF VOLUME RATIO OF THE ORGANIC TO THE
AQUEOUS PHASE ON THE ABSORBANCE OF THE COMPLEX.
pH =
3.0 pg
8.30xl0- 4 M
2.0 + 0.2
Volume ratio of the organic to the aqueous phase
4:1
2:1
1:1
2:3
1:2
2:5
1:3
Absorbance at 640 nm
0.380
0.380
0.375
0.380
0.385
0.320
0.275
-----------------------------------------------------------
132
].---------------------------~
0'" (!)
<l: c:r 'x QJ
<l: 0 0 E
<l:
CTI 0
-1~--------------~------------~ -6 -5 - 4
log [BG]
FIG.4.5 CURVE-FITTING METHOD FOR THE DETERMINATION OF MOLAR RATIO
OF Sb(V) TO BG IN Sb(V)-Cf -DPBA/-BG COMPLEX IN TOLUENE.
J 33
described{75).The salts containing the anion [SbX6 12- are
{NH4 ) 2 SbBr6 , Pb2SbC1
6, CoSbcl
6, etc. {76). The [SbX
6J 2- is a
resonance structure of the two canonical forms- [SbX6
J3- and
[SbC16 ] ~ In the same way [Sbcl6
JH.A. complex ma~y reduce to
a resonace structure In the present
investigation, this statement is supported by involvement of
2 moles of BG to per molKule of the extracted complex. The
probable reaction mechanism can be expressed as -
[SbC16J H.A 0 + HA
0 + e [SbCl
6J 2.HA
0
[ SbCl 6
) 2H. A0 + 2 BG: :::;=:::. [ SbCl 6J 2 BG o
Where A, BG+ and subscript o denote-to amidine i.e. N,N' -
diphenylbenzamidine, brilliant greent cation and the organic
phase, respectively.
BEER'S LAW, STATISTICAL DATA, MOLAR ABSORPTIVITY,SENSITIVITY
AND DETECTION LIMIT -
The calibration curve prepared as described in the
procedure passed through
-1
the origin and followed Beer's law
up to 0. 7 pg Sb ml of toluene with slope, intercept and
correlation coefficient value of 0.97, 0 1 and + 0.99,
respectively, Table 4.13, Figure 4.6. The validity of the
method was determined by taking 10
measurements at a level of 0.3 pg Sb
replicate independent
-1 ml toluene. The
relative standard deviation was found to be + 1.4%. The
confidence
absorptivity
-1 em at 95%
limit in terms of absorbance and molar
is 0.380 + 0.004 and (1.54 t O.Oiij x 10 51 mol-l
probability {77), Table 4.14. The Sandell's
sensitivity (10) [for absorbance = 0.001] of the present me-
13t1
TABLE-4.12 CURVE-FITTING METHOD FOR THE DETERMINATIO OF
MOLAR RATIO OF Sb(V) TO BG IN Sb(V)-Cl--DPBA/-BG
COMPLEX IN TOLUENE.
[Sb 5+] : 2.5x10- 6M (3.0 pg/10 ml aqueous phase)
[HCl] = 6.0 M
[DPBA] = 5.5 x 10- 3 M
Concentration of BG
X 10-SM
l. 04
1.49
l. 91
2.50
Log M
- 4.98
- 4.83
- 4.72
- 4.60
--~~9 __ _ A -A
max eq
0.22
0.45
0. 72
1.29
Log --~~9 ___ _
A -A max eq
- 0.66
- 0.35
- 0.14
0.11
------------------------------------------------------------
w u z <{
Ill Q:
0 U'l Ill <{
o.a
Q.6
0.4
0.2
, , ,. ---~
J3S
0 ~-L~---L-----L----~--~~~ 0.1 0.3 o.s Q.7 0.9
J.lg Sb(V) I mt TOLUENE
FIG.4.6 CALIBRATION-CURVE FOR THE DETERMINATION OF ANTIMONY(¥).
136
TABLE-4.13 CALIBRATION CURVE AND ITSSTRT!STICAL DATA FOR THE
DETERMINATION OF Sb(V).
[ HCl] "' 6. 0 M
[DPBA] "' 5.5 x 10- 3 M
[BG] = 8.3 X 10- 4 M
No.of Sb(V) absorbance Correlation Slope intercept obser- l.lg/rn1 at cOefficient vat ion organic 640 nrn
phase ( N) (Xi) ( Yi) (r) ( rn) (b) ------------------------------------------------------------
0.05 0.065
0.15 0.190
0.20 0.250
0.25 0.305
10 0.30 0.380 + 0.99 0. 97 0
0.45 0.570
0.50 0.630
0.60 0.760
0.70 0.880
TA
BL
E-4
.1
4
PR
EC
ISIO
N
OF
THE
MET
HO
D
[ Sb5 +
] -6
=
2
.5
x 1
0
M (
3.0
p
g/1
0
m1
aq
ueo
us
ph
ase
)
[DP
BA
] -3
=
5
.5
X
10
1<1
[BG
] -4
=
8
.3
X
10
M
pH
=
2.0
+
0
.2
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
No.
o
f A
bso
rb-
Mea
n S
tan
dard
o
bser-
an
ce at
ab
so
r-d
ev
iati
on
v
ati
on
6
40
nm
b
an
ce
( N)
(Xi)
(X
) (.:!
::. s)
0.3
85
0.3
75
0.3
85
10
0
.38
0
0.3
80
0
.00
52
0.3
85
0.3
75
0.3
80
0.3
80
0.3
75
0.3
70
Rela
tiv
e
-t·
sta
nd
ard
at
95%
d
ev
iati
on
C
.L.
lim
it
(.:!::.
%)
( t)
1.4
2
.26
2
co
nfi
den
ce li
mit
(C
.L.)
(x
~ ts
//N
)
----
----
----
----
----
----
----
----
-In
te
rms
of
ab
sorb
an
ce
(0.3
80
~0.
00
4)
In
term
s o
f m
ola
: ab
so
rpti
vit
y (E
:)
l m
ol -1
cr
a-l
( l. 5
4+
O.O
l6)x
l05
lo-A
c,
J ..
J
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
thad -2 was evaluated and found to be 0.0079 pg Sb em
138
The
detection limit [causing more absorbance than twice of the
standard deviation of 10 replicate measurements of the
analyte solution (78)) of the present method was found to be
-1 10 pg Sb l of the aqueous phase.
EFFECT OF DIVERSE IONS - Effect of various diverse ions in
the determination of 3 pg Sb/ 10 m1 of the aqueous solution
was examined separately. Of various tested ions, Tl(III)
caused serious interference in the determination of antimony
and removed by masking with EDTA. The tolerence limit of
various diverse ions are summarized in Table 4.15.
APPLICATION OF THE METHOD
The waste water samples of Bhilai Steel Plant (Bhilai,
India) were tested for the quantification of inorganic
antimony. Concentration of Sb(V) (without oxidation) and
total Sb (after oxidation with cerric ammonium sulphate)
were evaluated as recommended in the procedures. Sb(III)
content was obtained by substracting Sb(V) concentration to
the total Sb concentration. To compare the reliability of
the present method the total Sb content in water samples was
determined with rhodamine B by standard spike method, Table
4.16.
PROCEDURE FOR DETERMINATION OF ANTIMONY(V) -
10-20 ml of water sample was taken in a 50-ml beaker,
evaporated to ~3 ml, and transferred to 125-ml separatory
138
TABLE-4.15 EFFECT OF DIVERSE IONS ON THE DETERMINATION OF
ANTIMONY(V).
[ Sb5+) -6 (3.0 ~g/10 ml aqueous phase) = 2.5xl0 M
[HC1) = 6.0 M
[DPBA) = 5.5 X 10- 3 M
[BG) = 8.3 X 10- 4 M
------------------------------------------------------------* T1(III) TlC1 3 0.1
Nb( V) Tartar ate 0.5
Sn(IV) SnC1 4 0.5
Ag(I) AgN0 3 1
Hg (II) HgC1 2 1
Mo(VI) ( NH 4) 6Mo 70 2 4 . 4H 2o 1
Cu (II) CuSO 4. 5H 2o 1.5
Fe(III) FeCl 3• 6H 2o 1.5
Pb (II) Pb(N0 3) 2 2
Cd(II) CdS0 4. 8H 2o 2
Se(IV) Na z5e0 3 2
Zr (IV) Zr0Cl2 . 8H zO 2
W(VI) Naz wo4 . 2Hz o 2
Be (II) Beso4 . 4Hz0 4
Arsenate Na2 HAs04 . 7H2o 4
La (III) La ( N03 )3 . 6H2o 6
-----------------------------------------------------------Contd ....
140
TABLE-4.15 Contd ...
-----------------------------------------------------------Ti (IV) K2TiO(C 2o4 ) 2
2H:!O 6
V(V) NH4 vo3 6
Mn (II) MnC~. 4~0 10
Ni(II) NiSO 4• 7Hp 20
Co (II) CoSO 4• 7Hp 20
Al (III) Al(N03 )) . 9~ 0 20
Phosphate N~ P04 . 12f2 0 20
EDTA N";z ( EDTA) 20
Tartar ate NaKC4 H4 o6 • 41'2 0 20
Cr(III) Cr2 ( so4 )3
. A~ ( S04 )3
. 24f2 0 45
U(VI) UOz ( N0:3 )2 • 6f2 0 45
F- NaF 50
No; KN0:3 50
Oxalate N~ S 04. 2f2 0 50
+ causing error < 2%
* In the presence of EDTA (1 ml ,1% w/v)
141
funnel. Into this 6 ml concentrated HCl and 0.5 ml EDTA were
added and extracted with 10 ml toluene solution of DPBA for
2 min. The extract was transferred into another 125-ml
separatory funnel containing 5 ml brilliant green solution
and again equilibrated for 2 min. The extract was dried
over anhydrous sodium sulphate (~2 g) in a 25-ml volumetric
flask. The absorbance of the extract was measured at 640 nm
against the reagent blank. Sb(V) content present in the
given water sample was computed from the calibration curve
prepared.
PROCEDURE FOR DETERMINATION OF TOTAL ANTIMONY -
The water sample was evaporated and transferred to a
separatory funnel as above. It was oxidized by addition of
1 ml cerric ammonium sulphate and its excess was reduced by
adding hydroxyl ammonium hydrochloride. Sb(V) was extracted
and reacted with BG as above. The absorbance of the extract
was measured at ~ against the reagent blank. Total Sb max
present in the sample was evaluated from the calibration
curve prepared under similar condition.
142
TABLE-4.16 DETERMINATION OF ANTIMONY IN WATER SAMPLES.
------------------------------------------------------------Sample Rhodamine B Present method
method -------------------------------------
74.3
117.2
Total Sb
119 fl • (Rel.Std.Dev.)
+ %
75.2 ( l. 0)
118.0 ( l. 2)
Sb(V)
pg l-1
* ( Rel. Std. Dev. ) + %
64.1 ( 1.1)
55.8 ( l. 0)
Sb( III)
-1 pg 1
ll.l
62.2
s 1 & s 2 are waste water of Bhilai Steel Plant, (Bhilai,M.P.,
India) collected at two different zones.
* = Six measurements were made.
j4J
COMPARISON WITH OTHER SPECTROPHOTOMETRIC METHODS
Various spectrophotometric methods are reported for the
determination of antimony. The analytical characteristics
of some of the spectrophotometric methods are compared with
the present method, Table 4.17. The proposed method in
terms of selectivity and sensitivity is comparable to most
of the established methods.
TA
BL
E-4
.17
C
OM
PAR
ISO
N
WIT
H
OTH
ER
SPE
CT
RO
PHO
TO
ME
TR
IC
MET
HO
DS
FOR
D
ET
ER
MIN
AT
ION
O
F A
NT
IMO
NY
.
~~~~~~~-----------------~~~-----~~~~~~~---~-;;;----------~~--:~----;~~~;~----------------;~;~;~~~~--
Acid
ity
nm
1
mo
l em
Iod
ide
+
Am
idin
e
Tetr
ap
hen
yl
tetr
a
zo
liu
m ch
lori
de
2-(
5-b
rom
o-2
-p
yri
dy
lazo
)-5
-die
thy
lam
ino
ph
en
ol
Dia
nti
py
rylm
eth
an
e
+
Iod
ide
9-(
p-d
imeth
yla
min
o
ph
en
yl)
-2,3
,7-t
ri
hy
dro
xy
flu
oro
ne-6
2,6
,7-t
rih
yd
rox
y-9
-[4
-(8
-hy
dro
xy
-5-
qu
ino
lyla
zo
p
hen
yl]
fl
uro
ne
Bril
lian
t g
reen
1. o-
4.0
M
H
2so4
6.0
M
H
Cl
5.0
M
H
SO
2
4
0.2
-3
.0
M
HC
l
pH
1. 0
-1
.5
pH
5.0
-6
.0
3.5
N
H
Cl
Ch
loro
form
4
00
Dic
hlo
ro-
26
5
eth
an
e
+
Ch
loro
form
Ben
zen
e 6
10
Ch
loro
form
3
40
46
0
56
2
Ben
zen
e
64
0
6,8
00
45
,00
0
59
,00
0
52
,00
0
2,5
5,0
00
84
,60
0
Bi
cau
ses
seri
ou
s
18
in
terf
ere
nce
Fe,
Au
, T
l an
d
Ga
20
inte
rfere
d
Th
erm
od
yn
amic
S
tab
ilit
y
23
of
the
com
ple
x is
crit
ical
Pt,
P
d,
Os
an
d
Tl
inte
rfere
d
30
Cri
tical
pH,
low
4
0
rep
rod
ucib
ilit
y
Th
erm
od
yn
amic
sta
bil
ity
44
o
f th
e
com
ple
x is
crit
ical
KF
use
d
as
mask
ing
ag
en
t 5
2
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
co
ntd
..•
.•.
1->
A
...:.
TA
BL
E
4.1
7
Co
ntd
..... .
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
----
---
Heag
cn
t p
H/
So
lven
t ).
._m
ax
E-R
emar
k
Refe
ren
ce
Acid
ity
nm
1
mo:
f1 e
m -
1
Bril
lian
t g
reen
1
-2
M
To
luen
e
62
0
-F
e (I
I I)
in
terf
ere
d
56
HC
l seri
ou
sly
Cry
sta
l v
iole
t 2
.0-3
.0
To
luen
e
61
2-
74
,00
0
Th
erm
od
yn
amic
sta
bil
ity
68
M
HC
l 61
4 o
f th
e
com
ple
x is
crit
ical
Bro
mo
py
rog
all
ol
pH
6.6
-W
ate
r 5
60
3
5,0
00
ED
TA
is
use
d fo
r m
ask
ing
71
re
d
6.8
B
e,
Ca,
C
d,
Ce,
C
o,
Fe,
Mg,
N
i,
Pb
, S
r,
Tl,
w
, an
d
Zn
ion
s
N,N
'-d
iph
en
ylb
em
za-
5.5
-T
olu
en
e
64
0
1,5
4,0
00
H
igh
ly sele
cti
ve
and
PM
m
idin
e,
an
d b
ril
lian
t 7
.5
M
co
mp
ara
ble
sen
sit
ivit
y
gre
en
H
C1
---------------------------------------------------------------------------------------------------~
PM
=
Pre
sen
t M
eth
od
.
~
A c.,,
14G
CONCLUSION
The present method is proposed for the determination
and speciation of antimony. It is based on the extraction of
antimony(V) with N,N'-diphenylbenzamidine (DPBA) into
toluene, and subsequent reaction of the extract with
brilliant green (BG). The present method is free from most
of the experimental difficulties of the classical brilliant
green method. The method is successfully applied to water
samples at trace level.
147
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