spectrophotometric determination of brornate, iodate and...

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.

[http://ww\v.geocities.coni/RainForest/5161/w ater I htm]

http://ww/v.geocities.coni/RainForest/5161/w

Chapter VI Spectrophotometric phenoxazines

Jl^stract

A se^^sltcvi, sim^ple, selective eiiA^d ra-pid specttpphotrinêtrLc mêthod frr the

deteymLiA,atirt^ broiâte, icdate aiA,d perndate usina phet^cKaniiê (PN2L),

chtprrphenoxi^zlyie (CPZ^) aiA^d tnflcutotM.ethMLphetôKCiziiê (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 frrnêd iiA-dtcated maxikvium. absorbaiA.ce at SÔtn,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)

http://absorbaiA.ce

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


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


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


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


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,

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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


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


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


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