chapter-5 section (i): review on spectrophotometric...
TRANSCRIPT
107
CHAPTER-5
Section (i): Review on Spectrophotometric determination of lead
Lead exists in +2 and +4 forms. It is a dense, relatively soft, malleable metal
with low tensile strength. It is a poor conductor of heat and electricity. Although lead
has a lustrous silver–blue appearance when freshly cut, it darkens upon exposure to
moist air because of the rapid formation of an oxide film which protects the metal
from further oxidation (or) corrosion.
The single most important commercial use of lead is in the manufacture of
lead–acid storage batteries, antifriction metals, solders and type metal. Lead is used
for covering cables and as a lining for laboratory sinks, tanks and the “chambers” in
the lead chamber process for the manufacture of sulphuric acid. It is extensively used
in plumbing. Lead is also employed as protective shielding against X–rays and
radiation from nuclear reactors.
Although lead and most of its compounds are only slightly soluble in water,
the use of lead pipe to carry drinking water is dangerous since lead is a cumulative
poison that is not excreted from the body.
Lead is a highly toxic metal whose neurotoxin has had sickening and deadly
affect on humans. Unlike other chemicals lead does not vapourise (or) break down
over time. As a result, coming into contact with particles of this metal, whether
through inhalation (or) ingestion can result in “Lead poisoning”. Lead takes a
devastating fall on the developing brain, but a person at any age can be fatally
affected.
Lead interferes with a variety of body processes and is toxic to many organs
and tissues including the heart, bones, intestines, kidneys, reproductive and nervous
system. It interferes with the development of the nervous system causing potentially
108
permanant learning and behaviour disorders. Symptoms include abdominal pain,
confusion, headache, anemia, irritability and in severe, causes seizures, coma and
death.
Routes of exposure to lead include contaminated air, water, soil, food and
consumer products. The main tool for diagnosis is a measurement of the blood level
(or) a urine text. There are two units for reporting blood lead level, either micrograms
per deciliter (µg/dl) (or) microgram per 100gms(µg/100g) of whole blood.
The centers for Disease Control (CDC) has set the standard elevated blood
level for adults to be 25 (µg/dl) of blood. The desirable limit of lead in drinking water
is 0.05 ppm. Provisional tolerable weekly intake of 25 µg per kg body weight for all
age groups was established.
109
Table – 6.(i).1
Table – 6.(i).1
110
Section (ii): Spectrophotometric determination of Pb(II) using salicylaldehyde
111
acetoylhydrazone(SAAH)
Yellow coloured solution was formed instantaneously when salicylaldehyde
acetoylhydrazone (SAAH) was added to Pb(II) taken in ammonia–ammonium
chloride buffer solution. This colour reaction was investigated in detail and
developed a spectrophotometric method for the determination of Pb(II) in aqueous
medium.
a. Absorption spectra of SAAH and its Pb(II) Complex
The absorption spectra of the solution containing Pb(II) – SAAH complex
against reagent blank and that of SAAH solution against water blank were recorded at
pH 8.25 by employing the procedure described in 2 iv.a in 250 – 600 nm wavelength
range. The typical spectra are presented in Fig. 5.ii.a. The figure indicates that the
Pb(II) complex shows broad peak with maximum absorbance at 375 nm where the
reagent blank has less absorbance. Hence, the wavelength 375 nm was chosen for
further studies.
b. Effect of pH on the absorbance of Pb(II) complex
The effect of pH on the colour intensity of the Pb(II) – SAAH complex was
studied and the optimum pH was established by adopting the procedure given in
2.iv.b and the results are presented in Fig. 5.ii.b. The graph indicates that the complex
shows maximum and constant absorbance in the pH range 8.0 – 8.5. Hence, pH 8.25
is chosen for subsequent studies.
112
Fig: 5.ii.a. Absorbance Spectrum of
a. Pb (II) – SAAH complex Vs SAAH Solution
b. SAAH Vs Water blank
[Pb (II)] = 2.0 × 10-5
M
[SAAH ] = 4.0 × 10-4
M
pH = 8.25
DMF = 10% (V/V)
340 360 380 400 420 440 460 480 500
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
a
b
Ab
so
rba
nce
Wavelength (nm)
113
6.0 6.5 7.0 7.5 8.0 8.5 9.0
0.1
0.2
0.3
0.4
0.5
0.6
Ab
so
rba
nce
pH
Fig: 5.ii.b. Effect of pH on the absorbance of Pb(II) – SAAH complex
[Pb (II)] = 4.0 × 10-5
M
[SAAH ] = 4.0 × 10-4
M
Wavelength(λ) = 375 nm
DMF = 10% (V/V)
114
c. Effect of reagent concentration on the absorbance of the complex
The amount of reagent necessary for full colour development was established
by the following the procedure in 2.iv.c. The results are presented in Table 5.ii.1.
Table 5.ii.1
Effect of SAAH concentration on the absorbance of Pb(II) complex
[Pb(II)] = 4 × 10–5
M
pH = 8.25
λ = 375nm
Pb(II) : SAAH Absorbance
1 : 05 0.234
1 : 10 0.261
1 : 20 0.269
1 : 40 0.288
1 : 60 0.293
1 : 80 0.301
The data in Table 5.ii.1 indicate that a 10–fold molar excess of reagent is
sufficient for full colour development. Therefore, further studies were carried out
using 10–fold molar excess of reagent to Pb(II).
d. Effect of time on the absorbance of Pb(II) complex
The absorbance of Pb(II) – SAAH complex was measured at different time
intervals to ascertain the time stability of the complex as described in 2.iv.d. The
absorbance of the Pb(II) complex was measured at 375 nm. The concentration of
[SAAH] and [Pb(II)] were 4 × 10–4
M and 4 × 10–5
M respectively. The colour
development is instantaneous and remains constant for 2 hours.
115
e. Effect of the order of addition of constituents
The order of addition of constituents (buffer, lead(II) ion and reagent SAAH)
has no adverse effect on the absorbance of the Pb(II) – SAAH complex.
f. Applicability of Beer’s law
To examine the applicability of Beer’s law for the present system, the
procedure given in 2.iv.f was adopted. A linear plot between absorbance and amount
of Pb(II) is shown in Fig. 5.ii.c. The straight line obeys the equation A375 = 0.0548C
+ 0.0057. Further, the calibration of graph suggests that the system obeys Beer’s law
in the range of 1.0 – 9.90 µg/ml of Pb(II). The molar absorptivity and Sandell’s
sensitivity are 0.92 × 104 lit mol
-lcm
-1 and 0.225 µg cm
–2 Pb(II) respectively. The
specific absorptivity of the system is found to be 0.044 ml g-1
cm-1
. The standard
deviation for ten determinations of 6.21 µg/ml of Pb(II) is 0.0037. The relative
standard deviation of the method is 1.72%.
g. Tolerance limits of foreign ions
The effect of foreign ion was studied with a view to examine the applicability
of the method in presence of foreign ions. Interference of various ions was studied
with 6.21 µg/ml of lead by adopting the procedure given in 2.iv.g. The tolerance limit
value was taken as the amount of foreign ion required to cause ± 2% error in the
absorbance of Pb(II) – SAAH complex. The tolerance limit values for foreign ions
are presented in Table 5.ii.2.
116
Fig. 5.ii.c : Calibration plot for Pb(II) determination
pH = 8.25
[SAAH] = 4 × 10–4
M
Wavelength(λ) = 375 nm
DMF = 10% (V/V)
0 2 4 6 8 10
0.0
0.1
0.2
0.3
0.4
0.5
0.6 A375
= 0.0548C + 0.0057A
bso
rba
nce
Amount of metal ion (µg/ml)
117
Table 5.ii.2
Tolerance limit of foreign ions in the determination of 6.21 µg/ml of lead
Ion added Tolerance limit
µg/ml Ion added
Tolerance limit
µg/ml
Hypo 632
Hg(II) 40
Tartrate 415
Ag(I) 22
Sulphate 384
Mo(II) 2
Thiocyanate 350
Cu(II) 1.3
Bromide 320
Co(II) 1.2
Thiourea 304
Mn(II) 1.1
Phosphate 304
Fe(III) 0.9
Iodide 254
Zn(II) 0.8
a
Nitrate 248
Ni(II) 0.5
Chloride 142
Al(III) 0.22
Fluoride 76
Oxalate 2
EDTA 0.75
aMasked with 300 µg/ ml of thiocyanate.
h. Applications
Lead was estimated in various environmental water samples by employing the
procedure given in Chapter 2.iv.h. Data are given in Table 5.ii.3. The results of
present method are comparable with data obtained using dithizone method.
118
Table 5.ii.3
Determination of lead in some environmental water samples
S. No Sample Amount of lead* found (µg/ml)
SAAH Dithizone
1. Tap watera 0.120 0.127
2. Pond waterb 2.02 2.07
3. Tank waterc 0.130 0.132
4. Drain waterd 2.04 2.07
5. River watere 0.530 0.540
* Average of five determinations
a = Akuthotapalli tap water
b=Madanapalle pond water
c = Madanapalle tank water
d = Madanapalle drain water
e = Pennahobilam river water (Anantapur)
i. Composition and stability constant of Pb(II) – SAAH complex
Job’s continuous variation and molar ratio methods are employed to determine
the composition of the complex. The stability constant of the complex was calculated
using the data obtained in the Job’s plot.
a. Job’s continuous variation method
The procedure given in 2.iv.i.a was used in this method. A graph is prepared
between the molefraction of reagent and absorbance. Job’s plot (Fig. 5.ii.d) indicates
that 1 mole of reagent react with one mole of the metal ion. Therefore, the
composition of the complex in solution is 1 : 1 (M : L). The data obtained in the Job’s
119
curve are used in the calculation of stability constant of the complex. The stability
constant of 1 : 1 complex was calculated using the following equation
C
) - (1 β
21 : 1α
α=
Where
α = degree of dissociation constant (0.068)
C = Concentration of ligand corresponding to intersection point (9.0 × 10-5
M).
By the values of α = 0.068 and C = 9.0 × 10–5
obtained in the Job’s method
curve, the stability constant of the complex is calculated and the stability constant of
the complex is found to be 2.28 × 104.
120
Fig. 5.ii.d : Job’s Curve
Pb(II) = SAAH = 4 × 10–4
M (Stock solution)
Wavelength (λ) = 375 nm
pH = 8.25
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.28
0.30
0.32
0.34
0.36
0.38
Ab
so
rba
nce
Mole fraction of the reagent
121
Fig. 5.ii.e : Molar ratio plot
Pb(II) = 4 × 10–4
M (Stock solution)
Wavelength(λ) = 375nm
pH = 8.25
b. Molar ratio method
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Ab
so
rba
nce
Mole of reagent per mole of metal ion
122
The molar ratio plot (Fig. 5.ii.e) gives the composition of the complex as 1 : 1
[Pb : SAAH]. Thus, molar ratio method supports the composition of the complex
obtained in Job’s method.
Based on the composition of the complex following structure is tentatively
assigned for the complex( Fig. 5.ii.f.)
Fig 5.ii.f Structure of Pb(II) - SAAH complex
Summary
Salicylaldehyde acetoylhydrazone (SAAH) forms a pale yellow coloured
species with Pb(II) in basic medium. The important physico-chemical and analytical
characteristics of the Pb(II) – SAAH system are summarized in Table 5.ii.4.
123
Table 5.ii.4
Physico – chemical and analytical characteristics of Pb(II) – SAAH complex
S. No. Characteristics Results
1 λmax (nm) 375
2 pH range (optimum) 8.0 – 8.5
3 Mole of reagent required per mole of
metal ion for full colour development 10 fold
4 Time stability of the complex (in hrs) 2
5 Beer's law validity range (µg/ml) 1.0 – 9.90
6 Molar absorptivity (lit mol-1
cm-1
) 0.92 × 104
7 Specific absorptivity (ml g-1
cm-1
) 0.044
8 Sandell’s sensitivity µg of Pb(II) cm-2
0.225
9 Composition of the complex as
obtained in Job's and molar ratio
methods (M : L)
1 : 1
10 Stability constant of the complex 2.28 × 104
11 Mean absorbance 0.217 ± 0.0002
12 Standard deviation in the
determination of 6.21 µg/ml of Pb(II)
for ten determinations
0.0037
13 Relative Standard deviation (RSD) % 1.72
14 Y–intercept 0.0057
15 Angular coefficient 0.0548
16 Detection limit (µg/ml) 0.0517
17 Determination limit (µg/ml) 0.155
Section (iii): Spectrophotometric determination of Pb(II) using Salicylaldehyde
isonicotinoylhydrazone(SAINH)
124
Orange–yellow coloured solution was formed instantaneously when
salicylaldehyde isonicotinoylhydrazone (SAINH) was added to Pb(II) taken in
ammonia–ammonium chloride buffer solution. This colour reaction was investigated
in detail and developed a spectrophotometric method for the determination of Pb(II)
in aqueous medium.
a. Absorption spectra of SAINH and its Pb(II) Complex
The absorption spectra of the solution containing Pb(II) – SAINH complex
against reagent blank and that of SAINH solution against water blank were recorded
at pH 8.25 by employing the procedure described in 2 iv.a in 250 – 600 nm
wavelength range. The typical spectra are presented in Fig. 5.iii.a. The spectra
indicates that the Pb(II) complex shows maximum absorption at 390 nm where the
reagent blank has less absorbance. Hence, the wavelength 390 nm was chosen for
further studies.
b. Effect of pH on the absorbance of Pb(II) complex
The effect of pH on the colour intensity of the Pb(II) – SAINH complex was
studied and the optimum pH was established by adopting the procedure given in
2.iv.b and the results are presented in Fig. 5.iii.b. The graph indicates that the
complex shows maximum and constant absorbance in the pH range 8.0 – 8.5. Hence,
pH 8.25 is chosen for subsequent studies.
125
340 360 380 400 420 440 460 480 500
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
a
b
Absorb
ance
Wavelength (nm)
Fig: 5.iii.a. Absorbance Spectra of
a. Pb (II) – SAINH complex Vs SAINH Solution
b. SAINH Vs Water blank
[Pb (II)] = 2.0 × 10-5
M
[SAINH ] = 4.0 × 10-4
M
pH = 8.25
DMF = 10(V/V)
126
6.0 6.5 7.0 7.5 8.0 8.5 9.0
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.28
Ab
so
rba
nce
pH
Fig: 5.iii.b. Effect of pH on the absorbance of Pb(II) – SAINH complex
[Pb (II)] = 4.0 × 10-5
M
[SAINH ] = 4.0 × 10-4
M
Wavelength(λ) = 390 nm
DMF = 10(V/V)
127
c. Effect of reagent concentration on the absorbance of the complex
The amount of reagent necessary for full colour development was established
by the following the procedure in 2.iv.c. The results are presented in Table 5.iii.1.
Table 5.iii.1
Effect of SAINH concentration of the absorbance of Pb(II) complex
[Pb(II)] = 4 × 10–5
M
pH = 8.25
Wavelength (λ) = 390 nm
Pb(II) : SAINH Absorbance
1 : 05 0.220
1 : 10 0.222
1 : 20 0.228
1 : 40 0.230
1 : 60 0.240
1 : 80 0.250
The data in Table 5.iii.1 indicate that a 5–fold molar excess of reagent is
sufficient for full colour development. Therefore, further studies were carried out
using 5–fold molar excess of reagent to Pb(II).
d. Effect of time on the absorbance of Pb(II) complex
The absorbance of Pb(II) – SAINH complex was measured at different time
intervals to ascertain the time stability of the complex as described in 2.iv.d. The
absorbance of the Pb(II) complex was measured at 390 nm. The concentration of
[SAINH] and [Pb(II)] were 4 × 10–4
M and 4 × 10–5
M respectively. The colour
development is instantaneous and remains constant for 3 hours.
128
e. Effect of the order of addition of constituents
The order of addition of constituents (buffer, lead(II) ion and reagent SAINH)
has no adverse effect on the absorbance of the Pb(II) – SAINH complex.
f. Applicability of Beer’s law
To examine the applicability of Beer’s law for the present system, the
procedure given in 2.iv.f was adopted. A linear plot between absorbance and amount
of Pb(II) is shown in Fig. 5.iii.c. The straight line obeys the equation A390 = 0.2514C
– 0.0002. Further, the calibration of graph suggests that the system obeys Beer’s law
in the range of 0.2 – 2.0 µg/ml of Pb(II). The molar absorptivity and Sandell’s
sensitivity are 1.20 × 104 lit mol
-lcm
-1 and 0.173 µg cm
–2 Pb(II) respectively. The
specific absorptivity of the system is found to be 0.056 ml g-1
cm-1
. The standard
deviation for ten determinations of 1.0 µg/ml of Pb(II) is 0.0050. The relative
standard deviation and mean absorbance are 2.28% and 0.219 ± 0.0005 respectively.
g. Tolerance limits of foreign ions
The effect of foreign ion was studied with a view to examine the applicability
of the method in presence of foreign ions. Interference of various ions was studied
with 8.28 µg/ml of lead by adopting the procedure given in 2.iv.g. The tolerance limit
value was taken as the amount of foreign ion required to cause ± 2% error in the
absorbance of Pb(II) – SAINH complex. The tolerance limit values for foreign ions
are presented in Table 5.iii.2.
129
Fig. 5.iii.c : Calibration plot for Pb(II) determination
pH = 8.25
[SAINH] = 4 × 10–4
M
Wavelength(λ) = 390 nm
DMF = 10%(V/V)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
0.0
0.1
0.2
0.3
0.4
0.5A
390 = 0.2514C - 0.0002
Ab
so
rba
nce
Amount of Pb(II) (µg/ml)
130
Table 5.iii.2
Tolerance limit of foreign ions in the determination of 1.0 µg/ml of Lead
Ion added Tolerance limit
µg/ml Ion added
Tolerance limit
µg/ml
Citrate 653
Ag(I) 130
Tartrate 592
Hg(II) 32
Sulphate 384
Cu(II) 1.8
Bromide 319
Mo(II) 1.5
Thiourea 304
Co(II) 1.2
Oxalate 281
Mn(II) 1.0
Iodide 253
Fe(III) 0.7
Nitrate 248
Al(III) 0.53
Chloride 141
Zn(II) 0.5
a
Fluoride 76
Ni(II) 0.4
Phosphate 15
Cd(II) 0.4
EDTA 3.7
a Masked with 300 µg/ ml of thiocyanate.
h. Applications
Lead was estimated in various environmental water samples by employing the
procedure given in chapter 2.iv.h. The results are presented in Table 5.iii.3. The
results of the present method are comparable with data obtained using dithizone
method.
131
Table 5.iii.3
Determination of lead in environmental water samples
S. No Sample Amount of lead* found (µg/ml)
SAINH method Dithizone method
1. Tap watera 0.110 0.115
2. Pond waterb 1.850 1.860
3. Tank waterc 0.109 0.100
4. Drain waterd 2.146 2.192
5. River watere 0.425 0.415
* Average of five determinations
a = Akuthotapalli tap water
b= Madanapalle pond water
c = Madanapalle tank water
d = Madanapalle drain water
e = Pennahobilam river water (Anantapur)
i. Composition and stability constant of Pb(II) – SAINH complex
Job’s continuous variation and molar ratio methods are employed to determine
the composition of the complex. The stability constant of the complex was calculated
using the data obtained in the Job’s plot.
a. Job’s method
The procedure given in 2.iv.i.a was used in this method. A graph is prepared
between the mole fraction of reagent and absorbance. Job’s plot (Fig. 5.iii.d) indicates
that 1 mole of reagent react with one mole of the metal ion. Therefore, the
composition of the complex in solution is 1 : 1 (M : L). The data obtained in the Job’s
132
curve are used in the calculation of stability constant of the complex. The stability
constant of 1 : 1 complex was calculated using the following equation
C
) - (1 β
21 : 1α
α=
Where
α = degree of dissociation constant (0.005)
C = Concentration of ligand corresponding to intersection point (10.2 × 10-5
).
By using the values of α = 0.055 and C = 10.2 × 10–5
obtained in the Job’s
method, the stability constant of the complex is calculated and the stability constant of
the complex is found to be 3.15 × 104.
133
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Ab
so
rba
nce
Molefraction of ligand
Fig. 5.iii.d : Job’s Curve
Pb(II)= SAINH = 5 × 10–4
M (Stock solution)
Wavelength (λ) = 390 nm
pH = 8.25
134
Fig. 5.iii.e : Molar ratio plot
Pb(II) = 5 × 10–4
M (Stock solution)
Wavelength (λ) = 390 nm
pH = 8.25
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Ab
so
rba
nce
Mole of reagent per mole of metal ion
135
b. Molar ratio method
The molar ratio plot (Fig. 5.iii.e) gives the composition of the complex as 1 : 1
[Pb : SAINH]. Thus, molar ratio method supports the composition of the complex
obtained in Job’s method.
Based on the composition of the complex following structure is tentatively
assigned for the complex.
C
H
N
N C
O
Pb
OH2
N
O
Structure of Pb(II) – SAINH complex
Summary
Salicylaldehyde isonicotinoylhydrazone (SAINH) forms an orange–yellow
coloured species with Pb(II) in basic medium. The colour reaction between Pb(II) and
SAINH is almost instantaneous and the absorbance of the complex remains constant
for 3 hours. The order of addition of constituents [buffer, Pb(II) ion and SAINH] has
no adverse effect. The important physico-chemical and analytical characteristics of
the Pb(II) –SAINH system are summarized in Table 5.iii.4.
136
Table 5.iii.4
Physico – chemical and analytical characteristics of Pb(II) – SAINH complex
S. No. Characteristics Results
1 λmax (nm) 390
2 pH range (optimum) 8.0 – 8.5
3
Mole of reagent required per mole of metal ion
for full colour development
5 fold
4 Time stability of the complex (in hrs) 3
5 Beer's law validity range (µg/ml) 0.2 – 2.0
6 Molar absorptivity (lit mol-1
cm-1
) 1.20 × 104
7 Specific absorptivity (ml g-1
cm-1
) 0.060
8 Sandell’s sensitivity µg of Pb(II) cm-2
0.173
9
Composition of the complex as obtained in
Job's and molar ratio methods
1 : 1
10 Stability constant of the complex 3.15 × 104
11 Mean absorbance 0.219 ± 0.0002
12
Standard deviation in the determination of 1.0
µg/ml of Pb(II) for ten determinations
0.0050
13 Relative Standard deviation (RSD) % 2.28
14 Y–intercept –0.0002
15 Angular coefficient 0.0503
16 Detection limit (µg/ml) 0.068
17 Determination limit (µg/ml) 0.2040
137
Section (iv): A comparative account of Physico – chemical and analytical
characteristics of Pb(II) – SAAH and Pb(II) – SAINH complexes
The colour reactions between Pb(II) and the reagents are instantaneous.
SAAH form yellow coloured species and SAINH form orange–yellow coloured
species in basic medium (pH = 8.25). In SAAH method 10–fold molar excess of
reagent while in SAINH method 5–fold molar excess of reagent required for full
colour development.
Both reagents form 1 : 1 (M : L) complexes with Lead. Pb(II) – SAINH
complex is more stable when compared with Pb(II) – SAAH complex. Further, the
tolerance limit values of foreign ion are quite high in Pb(II) – SAINH. The higher
values of SAINH method suggest that the reagent is more selective for Pb(II). The
selectivity of the reagent may be due to its ability to form more stable complex (3.15
× 104) with Pb(II). Other physico–chemical and analytical properties of complexes
are compared and presented in Table 5.iv.1. SAINH method is more sensitive when
compared with SAAH method. The standard deviation of SAAH method is less than
SAINH method.
138
Table 5.iv.1
Comparative account on physico-chemical and analytical properties of Pb (II)
complexes with SAAH and SAINH
S. No. Characteristics Pb–SAAH Pb–SAINH
1 λmax (nm) 375 390
2 pH range (optimum) 8.0 – 8.5 8.0 – 8.5
3 Mole of reagent required per mole of
metal ion for full colour development 10 fold 5 fold
4 Time stability of the complex (in hrs) 2 3
5 Beer's law validity range (µg/ml) 1.0 – 10.0 0.2 – 2.0
6 Molar absorptivity (lit mol-1
cm-1
) 0.92 × 104 1.20 × 10
4
7 Specific absorptivity (ml g-1
cm-1
) 0.044 0.060
8 Sandell’s sensitivity my of Pb(II) cm-2
0.225 0.173
9 Composition of the complex as obtained
in Job's and molar ratio methods (M : L) 1 : 1 1 : 1
10
Stability constant of the complex 2.273 × 10
4 3.15 × 10
4
11 Mean absorbance 0.217 ± 0.0002 0.219 ± 0.0002
12 Standard deviation in the Pb(II) for ten
determinations 0.0037* 0.0050**
13 Relative Standard deviation (RSD) % 1.72 2.28
14 Y–intercept 0.0057 –0.0002
15 Angular coefficient 0.0548 0.0503
16 Detection limit (µg/ml) 0.0517 0.068
17 Determination limit (µg/ml) 0.155 0.2040
* In the determination of 6.21 ppm of lead(II)
** In the determination of 1.0 ppm of lead(II)
139
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140
Table- 5.(i).1
A List of spectrophotometric determination of lead(II) with reagents
Name of the Reagent λmax(nm) pH Beer’slaw
range(ppm)
Molar
absorptivity(ε)
(L mol-1
cm-1
)
M:L Ref.
Pyridine-2-Acetaldehyde salicyloylhydrazone 380 8.6-9.3 1.5-6.2 1.93 x 104 1:2 1
1,2-Diaminocyclohexane-N,N,N1,N1-Tatra
acetic acid(DACT) 246 10-11 1.65-8.28 - 1:1 2
4(2-pyridylazo) resorcinol (PAR) 518 - 1.0-15.0 - - 3
N-P-Chloro phenyl benzohydrox mic acid (N-
P-Cl-BHA) 388 9.0 - 4.5 x 10
2 - 4
Dithizone 750 2-3 0.2-14.0 1.4 x 104 - 5
2[Benzothiozolyl Azo]-4-Benzyl phenol
(BTABP) 393 9.0 - 2.1 x 10
4 1:2 6
Mercapto Sephadex (MS-50) 482 - - 2.4 x 105 - 7
2-(5-Bromo-2-Pyridylazo)-5-diethylamino
phenol-ammonium tetraphenyl borate 500 5.5 0.2-40 - - 8
Cyanidin 555 4.2 0.1-5.0 - - 9
Diphenyl thiocarbazone - - - - - 10
1-(2-pyridilazo) -2- naphthol (PAN) 555 9.0 1.3-4.5 2.02 x 104 - 11
4-(2-pyridylazo)-resorcinol (PAR) 518 - 1.0-10.0 - - 12
3, 5 – Dimethoxy -4- hydroxy – benzel dehyde
isoniotinoyl hydrazone (DMHBIH) 430 9.0 0.4-10.36 1.82 x 10
4 1:1 13
2-[( Benzo thiazolyl) azo]-4-benzyl phenol
(BTABP) 410 - 0.2-20.0 1.6 × 10
4 - 14
N1,N2-Diphenyl hydrazine-1,2-
dicarbothioamide - 6.7 0.01-0.90 2.0 × 10
5 - 15
109