spectrophotometric determination of brornate, iodate and...
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C H A P T E R 6
H bond
Spectrophotometric determination of brornate, iodate and periodate using
Phenoxazines
water ccvgrs y-ifo of the earth's swrface fliA-d m.atees up 6 5 ^ pf cur bodies.
The water we use i-s taleeiA, f o^u Latees ai^d rLvers, av\.d frofM. u[/ider(?Ycuv^(i
{arouiAcivjater); d.i^d after we have uset^ it-- a\A.d cowtav\Aii/\.attci it-- m.ost of it
returt^s to these LocatLci/bs. (f it is iA,ot ttmttd before beli/vg plischarged L vto
waterwatjs, serious -poLLutlot Is the result. The maltA, s,Durce of polLutloiA- cni^ be
attributed to discharge of uiA,treated waste, dumpliA,g of t^vdustrlal efflueiA,t niA,d
ruiA,-off frow. flgrlcuLturflL fields. liA,dustrlaL gro'wth, urbaiA.lzatloiA, c\]A,d the
li/vcreasliA,CA use of sMiA-thetlc orc aiA lc substaiA,ces have serious ai^d adverse 1/M.pacts
01 water bodies. A whole vartetM of cheinA.lcaLs fvcvw liA-dustry, such as m,etaLs aiA-d
solvei/vts, aiA,d evei^ chei^lcals which are fcyn^td fro\M. the breafedovy^^ of ^^aturaL
wastes (am,m.cuv,La, for twstauvce) are poisei^cws.
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Chapter VI Spectrophotometric phenoxazines
Jl^stract
A se^^sltcvi, sim^ple, selective eiiA^d ra-pid specttpphotrin^etrLc m^ethod frr the
deteymLiA,atirt^ broi^ate, icdate aiA,d perndate usina phet^cKanii^e (PN2L),
chtprrphenoxi^zlyie (CPZ^) aiA^d tnflcutotM.ethMLphet^oKCizii^e (TMP) were
iutvestiaated as i/tew class r-f spectrcphrtcmetnc reaaei^ts LIA, presence rf cisapride as
electrrphilic cpupUyio reaaeyit. The reactipyi was carried out iiA. hudrrchlonc acid
mediuru.. The red crlrr frrn^ed iiA-dtcated maxikvium. absorbaiA.ce at S^Otn,m. for
PN^ 'cpsj and 510 for TMP method. The methods obeuied fleer's law. The color
dei'eloped was stable for -4 h at room temperature. The molar absot-ptivitu and
.sandelL's sensitivity aave different values with different reac>ents. interference
was not observed for the m.ost com.i'uon ion present in water. The m.ethods showed
aood reproducibilitui and can be satisfactorily applied for the determination of
bromate in oxonated water, bread and lodate in iodized edible salt and periodate in
water sam.ples.
K. EyWO'R.lys: Phei^cKazines.: birmat£; icdate: pe>'u"date: czcne water; icciLzec^ edi-bis salt
Microchem.ica .Acta (Comm-untcated)
Chapter VI Spectrophotometric Phenoxazines
VI.I. Introducation
Bromate is normally not present in natural waters; but it is a by-product of
bromide formed in water during ozonization. Ozonation has proved as the best
alternative to chlorination for water treatment [1]. Chlorination results in the
production of trihalomethanes that are hazardous to health [1,2]. Bromate
concentrations of 60-90 ng 1* have been reported in ozonated water [3,4]. The bread
making quality of freshly milled wheat flour tends to deteriorate after about two
months. However, the use of flour improvisers increases the shelf life of flour
considerably. Potassium bromate is relied upon as one of the most used flour
improvers [5]. Bromate has been classified in Group 2B by the International Agency
of Research Cancer (lARC) as a primary causative agent of cancer. Therefore, it is
necessary to confirm that there is no potassium bromate residue left in the bread.
Iodine is an essential component of thyroid hormones that play an important
role in the development of brain fimction and cell growth. Deficiency of iodine causes
serious delay in neurological development. On the other hand, an excess of iodine or
iodide can cause goiter and hypothyroidism as well as hyperthyroidism. Iodine
deficiency disorders can be prevented by iodine supplementation. Although various
methods for iodine supplementation are available, the most popular
methods include iodination of culinary salt and bread. Potassium iodate is
preferred over sodiimi iodate as the latter is susceptible for environmental
moisture and temperature. The concentration used in different countries ranges
from 10 to 80 i g ml' of elemental iodine [6]. Periodate is also a strong
oxidizing agent and can be used for disinfection [7].
Because of the potential negative and positive health effects of bromate,
iodate and periodate, maintaining the correct level of bromate, iodate and periodate in
drinking water and in foods meant for human consumption is extremely important.
Hence, there is an urgent need for simple, sensitive, rapid and reliable analytical
methods for the determination of bromate, iodate and periodate levels.
Several methods have been reported for the determination of bromate, iodate
and periodate which include chromatographic [8-13], electrochemical [14,15], and
optical methods [16-20]. Among the optical methods visible spectrophotometry is
99
Chapter VI Spectrophotometric Phenoxazines
the most appropriate analytical approach for the determination of bromate, iodate and
periodate, as it provides sensitive and reliable data of the analytes and offers practical
and economical advantages over other methods. Besides, visible spectrophotometric
detection is much more viable as a useful technique to develop on-line or at-line
systems.
Visible spectrophotometric methods reported for the determination of bromate
ions are limited and are mainly based on its oxidizing property. These methods
include: reduction of bromate with sodium nitrite [21], reaction with 2-(3,5-dibromo-
2-pyridylazo)-5-diethylaminophenol and thiocyanate in a strong acidic medium
[22,23], oxidation of l,2,4-trihydroxyanthraquinone-3-carboxylic acid in an acidic
medium, producing a change in color [24] and oxidation of phenothiazines to yield
radical cation colored product [25]. All these methods have limitation of one kind or
other. None of the above methods are suitable for determination at trace levels and in
most of the cases colours produced are unstable [20].
The visible spectrophotometric methods available for the determination of
iodate can be classified into two groups based on the type of reaction. One group of
spectrophotometric methods is based on the reaction with excess iodide to form
triiodide [26-28], while, another group of spectrophotometric methods for the
determination of iodate involves a prior step to oxidize iodate to periodate [29].
The work in this chapter is a systematic investigation based on phenoxazines
and cisapride as new analytical reagents. Phenozaxines are proposed as sensitive
spectrophotometric reagents in presence cisparide as coupling reagent for the
determination of bromate, iodate and periodate. Spectrophotometric determination of
bromate in ozonated water, iodate in iodized edible salt and periodate in
environmental water samples have been standardized. The results showed that these
reagents offer several advantages over most of the chromogenic reagents currently
being used and the procedures indicate positive features over existing methods
VI.2. Experimental
VI.2.1. Apparatus
Specord 50 UV-Vis spectrophotometer with 1.0 cm silica quartz matched cell
was used for measuring the absorbance.
100
Chapter VI Spectrophotometric Phenoxazines
VI.2.2. Reagents
Potassixim bromate, potassium iodate and potassium periodate (BDH,
India), Phenoxazines (Aldrich, India) and cisapride (USV Ltd., India). Standard
solutions (1000^g ml'*) of bromate, iodate and periodate were prepared by dissolving
known quantities of potassium bromate, potassium iodate and potassium periodate in
1 liter of distilled water. Solutions of the required strength were prepared by diluting
this stock solution with distilled water. A 0.025 % (w/v) of PNZ, CPZ and TMP were
prepared by dissolving 25 mg and diluting quantitatively to 100 ml with distilled
alcohol. This solution stored in amber bottle to protect from the sunlight. Solutions of
cisapride (0.05%, w/v) prepared in distilled water. Hydrochloric acid (2N) solution
was prepared by diluting quantitatively 176.99 ml of 35% HCl to 1 liter with distilled
water. Solutions of diverse ions were prepared by dissolving their respective salts.
All solutions were prepared from analytical grade chemicals unless specified
otherwise. All solutions used were prepared by using distilled water.
VI.2.3. General procedure
VJ.2.3.1. Bromate
To a series of 25 ml standard flask, 2 ml of 0.05%(M'/V) of cisapride, 2 ml of
0.025% (w/v) of PNZ/CPZ/ TMP, different aliquots of known concnetration of
bromate solution and 2ml of 2N HCL were added. Each flask was shaken well and
allowed to stand for 5 minutes at room temperature and then made up to the mark
with distilled water and the absorbance was read at 540 nm for PNZ/CPZ and 510 nm
for TMP against corresponding reagent blank.
VI.2.3.2. Iodate.
To a series of 25 ml standard flask, 2 ml of 0.05%(M'/V) of cisapride, 2 ml of
0.025% (w/v) of PNZ/CPZ/TMP, different aliquots of known concnetration of iodate
solution and 2ml of 2N HCL were added. Each flask was shaken well and allowed to
stand for 5 minutes at room temperature and then made up to the mark with distilled
water. The absorbance was read at 540 nm for PNZ/CPZ and 510 nm for TMP against
corresponding reagent blank.
101
Chapter VI Spectrophotometric Phenoxazines
VI.2.3.3. Periodate
To a series of 25 ml calibrated flasks 2 ml of 0.05%(w/v) of cisapride solution,
2 ml of PNZ/CPZ/ TMP (0.025%, w/v), 2 ml of 2M hydrochloric acid and different
aliquots of known concentration of periodate solution. Each flask was shaken well
and allowed to stand for 10 minutes in room temperature and then made up to the
mark with distilled water. The absorbance was read at 540 nm for PNZ/CPZ and 510
nm for TMP against corresponding reagent blank
VI.3. Results and discussion
Electrophilic coupling reaction has attracted considerable attention for
quantitave analysis of many environmental active compovmds. Phenoxazine is an
isolog of phenothiazine. It is a part of the chemical structure of actinomycin D, which
is known to exert intensive anticancer activity on malignant tumors in children [30]
and is reported to be more potent and less toxic chemosensitizer [31]. Phenoxazine
derivatives exist in neutral form, as monocations, as dications and even as trications
depending on the environment [32]. Their molecular structure and luminescent
properties have been studied to a great extent [33]. Besides, they have impressive
applications as biological stains [34], as laser dyes [35] and as redox indicators [36].
Phenoxazine derivatives are nervous system depressants particularly with sedative,
antiepileptic, tranquillizing activity [37] spasmalytic activity [38] antitubercular
activity [39] and anthelmentic activity [40]. hi recent years phenoxazine derivatives
are reported to be potential chromophoric compounds in host-guest artificial photonic
antenna systems [41].
Cisapride is a chemical containing aromatic primary amino group, which
depending on their structure exhibit varied medicinal properties [42]. Cisapride is a
gastrointestinal stimulant, effective in relieving gastrointestinal or esophagus
disorders and in the promotion of gastric emptying of a gastrointestinal motility.
Although, cisapride has been voluntarily withdrawn in the U.S. by Janssen
Pharmaceutica, it was available till July 14, 2000 and for a limited period, thereafter
for meeting specific criteria. The background to this development points to certain
adverse effects caused by cisapride. The regulatory authorities in India have not
officially armounced the discontinuation of cisapride fi-om the Indian market [43].
102
Chapter VI Spectrophotometric Phenoxazines
Cisapride is a substituted piperidinyl benzamide and a prokinetic agent is chemically
related to Metaclopramide.
VI.3.1. Spectral characteristics
The absorption spectrum of the red colored products with bromate, iodate and
periodate shows a wavelength of maximum absorption at 540 nm for PNZ/CPZ and
510 nm for TMP against corresponding reagent blank
VI.3.2. Optimization of analytical variables
Key parameters that influence the performance of the proposed methods were
studied in order to establish the optimum working configurations. All the data given
and % R.S.D. in the optimization steps for both physical and chemical parameters are
the mean values from successive determinations. All the optimization steps were
carried out with a chosen concentration of bromate, iodate and periodate as we
mentioned in Table VI. 1. Each parameter was optimized by setting other parameters
constant.
VI.3.3. Order of addition
During the course of the investigation, it was observed that the sequence of
addition of reactants was also important as it influence the intensity and the stability
of the color of the product to great extent. The sequence (i) cisapride + acid +
substrate + PNZ/CPZ/TMP and (ii) PNZ/CPZ/TMP + acid + substrate + cisapride
gave less intense and unstable color. While, (iii) cispride + PNZ/CPZ/TMP +
substrate + acid gave more intense and stable red color. So, sequence (iii) was
selected for further studies. For periodae, the change in order of addition had no
profound effect on stabilising the color.
VI.3.4. Effect of reagents and acid concentration
The effect of PNZ/CPZ/TMP reagents was studied in the range of 0.10 - 5.00
ml of (0.025%, w/v) solution of each to achieve the maximum color intensity, volume
of 0.50 - 3.00 ml of the solution gave good result. Hence, 2 ml of (0.025 %, w/v)
PNZ/CPZ/TMP solutions in 25 ml standard flask was selected for further studies,
103
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Chapter VI Spectrophotometric Phenoxazines
under optimized conditions. The same procedure was adopted to know the
concentration of cispride and acid required for getting constant and maximum color
intensity. Cisparide (0.025 %, w/v) gave maximum color in the range of
1.00- 5.00 ml. Therefore, 2 ml of cisapride (0.05 %, w/v) was selected for fiirther
studies.The maximum intensity of the red color was achieved in hydrochloric acid
medium.
Preliminary investigations showed that hydrochloric acid was better than
sulphuric, phosphoric or acetic acid. Maximum intensity of the red color was
achieved in the range of 1.0-6.0 ml of 2N HCl. Therefore, 2 ml of 2N HCl in 25 ml
standard flask was used for getting the best results.
VI.3.5. Effect of temperature and stability
Experiments were conducted to optimize the time for the determination of
bromate, iodate and periodate. An increase in the temperature decreases the intensity
of the red color. Hence, development of the red color was carried out at room
temperature. It was observed that the color developed in 5 min and was stable at this
temperature up to 4h.
VI.3.4. Interference
Interference of foreign species were investigated by analyzing standard
solution of bromate, iodate and periodate to which increasing amounts of interfering
species salts of anions and cations were added. The tolerable limit of a foreign species
was taken as a relative error not greater than ±3%. It was found that 100 ppm of
anions like, barium acetate, barium nitrate, magnesium sulphate, zinc sulphate, anions
like sodium fluoride, sodium nitrate, sodium sulfite and lead nitrate did not interfere
with the proposed method
VI.3.5. Applications
VI.3.5.1. Bromate in water samples
In order to assess the validity of these methods for the determination of
bromate in bread and in water samples from different sources were collected and
analyzed after adding known amount of bromate. The results presented in Table VI.2
and VI.3 show an error of acceptable range of ± 3%.
105
Table VI.2.
Sample
Tap water
Borewell
Lake water
Ozonated
water*
Bromate in water samples
Broj'
added
(fig ml ' )
200
250
300
200
250
300
200
250
300
200
250
300
Proposed method
Broj'
recoverd
(fig ml ' )
198
249
301
201
248
299
199
251
300
205
253
300
Recoverd %
±RSD'
99.00±0.11
98.90±1.00
100.21±0.9
101.00±1.2
99.05±1.0
99.95±0.95
98.00±1.99
100.00±0.63
100.22±0.25
103.25±0.23
102.00±1.02
100.00±0.21
*
Reported method
Recovered %
±RSD'
99.24±1.46
98.92±1.32
102.60±0.54
101.10±1.15
98.96±1.06
99.52±1.61
99.55±1.61
100.60±0.85
100.08±1.48
100.28±1.66
101.02 ±1.23
102.63±1.11
/- value"
0.98
1.32
2.38
0.61
0.70
1.87
1.87
2.64
0.92
1.21
0.37
2.55
F-value'
1.53
0.50
2.90
1.56
2.05
2.33
2.33
3.28
2.59
5.03
1.03
1.29
'Average of five determination ± relative standard deviation: "Tabulated t-value at 95% confidence level is 2.78: Tabulated F-value at 95% confidence level is 6.39: * samples were free from ozone at the time of determination
Table VI.3. Bromate in foodstuffs
Sample
Bread
Bread
Flour
Flour
Proposed
Broj' added
(fig ml-') 200
250
200
250
200
250
200
250
method
Broj-recovered (US ml ' )
199
251
201
248
198
249
201
251
Recovered % ± RSD*
99.8±1.21
100.7±0.93
101.5±0.92
98.42±1.18
97.12±1.51
97.96±0.78
102.58±1.0
101.26±1.0
Reported method
Recovered % ± RSD*
100.9±0.65
101.6±1.68
100.9±0.65
99.1±1.33
99.62±1.04
98.36±1.28
100.76±1.04
100.36±0.78
/-value''
1.21
0.98
1.21
0.86
2.45
0.59
2.71
2.68
F-value*
2.0
1.19
2.0
1.27
2.84
2.69
1.08
1.57
'Average of five determination ± relative standard deviation "Tabulated t-value at 95% confidence level is 2.77 Tabulated F-value at 95% confidence level is 6.39
106
Chapter VI Spectrophotometric Phenoxazines
VI. 3.5.2. lodate in iodized edible salts
The applicability of the proposed method was tested in three brands of iodate
added edible salts, which were purchased from the local market. It is clear from
Table VI.4 that the iodate concentrations determined in commercial samples of salts
are in close agreement with the values claimed by the manufacturer.
Table VI.4. lodate in salt samples
Brand No
1
2
3
Concentration of iodate ()ig ml'') Expected Value"
33
15
30
Proposed method 32.3
14.8
30.5
Error %
-0.7
-0.2
0.5
'as indicated on the cover of the packet.
VI3.5.3. Periodate in water samples
In order to access the validity of the method for the determination of
periodate, different water samples were collected and analyzed by employing
conventional standard addition method (Table VI.5). In tap water the iodate
percentage recovered was erratic. This is imderstandable as the tap water is
chlorinated. While, the bore-well water gave lesser values. The cause of low values in
the lake water (~-3.5%) may be attributed to various levels of organic and biological
pollutants.
107
Chapter VI Spectrophotometric Phenoxazines
Table VI.5. Periodate in water samples
Sample
Tap water
Borewell
Lake water
Ozonated
water *
KIO4 added
(Hg ml"')
200
250
300
200
250
300
200
250
300
200
250
300
Proposed method
KIO4 recoverd
(fig ml"')
201
250
299
201
248
299
198
249
301
201
253
303
Recoverd %
±RSD*
103.02±0.23
102.00±1.02
100.00±0.21
100.25±0.9
99.04±0.11
98.90±1.00
99.05± 1.0
99.92±0.95
101.00±1.2
100.24±0.9
101.05±1.2
100.22±0.9
Reported method
Recovered
% ± RSD'
99.6±1.23
100.2±1.18
99.92±1.53
100.20±1.12
100.10±1.52
98.05±1.62
99.1 Oil.72
97.12±1.51
100.90±0.65
99.85±1.21
101.60±1.68
100.70±0.93
t- value"
1.68
1.54
1.65
1.23
1.54
1.25
1.10
1.53
1.21
2.52
0.98
2.43
F-value'
3.62
2.56
1.60
0.50
2.82
0.61
1.57
1.64
2.0
1.73
1.19
2.74
'Average of five determination ± relative standard deviation "Tabulated t-va!ue at 95% confidence level is 2.78 'Tabulated F-value at 95% confidence level is 6.39 * samples were fi^e fixjm ozone at the time of determination
VI.4. Conclusion.
Phenoxazines involving electrophilic coupling reaction with cisapride for the
spectrophotometric determination of bromate, iodate and periodate are proposed for
routine analysis. The proposed methods have characteristic features of simplicity,
sensitivity and selectivity. For routine analysis, we recoirmiend the use of PNZ, CPN,
TMP and cisapride as reagent for the determination of bromate, iodate and periodate
in water and food samples.
108
Chapter VI Spectrophotometric Phenoxazines
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109
Chapter VI Spectrophotometric Phenoxazines
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