Fast voltammetric assay of water soluble phthalates in bottled and coolers water

PAPER www.rsc.org/methods | Analytical Methods

Fast voltammetric assay of water soluble phthalates in bottled and coolerswater

Munawar Saeed,*a Sirajuddin,a Abdul Niaz,b Afzal Shah,b Hassan Imran Afridia and Abdul Raufa

Received 4th March 2010, Accepted 10th April 2010

First published as an Advance Article on the web 17th May 2010

DOI: 10.1039/c0ay00156b

Detection of phthalic acid and phthalates esters is of growing interest due to their significant use and

potential toxicity. A fast, simple and highly sensitive Square Wave Voltammetric (SWV) method

developed for determination of total water soluble phthalates using a glassy carbon electrode (GCE) is

demonstrated using di-n-butyl phthalate (95%) (DBP) as a test example. The study showed that

100 mmol L�1 aqueous solution of DBP gives the best response with 0.05 mol L�1 tetrabutylammonium

bromide (TBAB), at stirring rate of 1400 rpm, deposition time, 20 s and pH 4.0 � 0.1. The optimum

frequency and scan rate was 100 Hz and 0.9 V s�1 respectively. Voltammetric response was linear over

3 ranges, 70–110 mmol L�1, 20–60 mmol L�1 and 2–10 mmol L�1 with regression coefficient of 0.9873,

0.9978 and 0.9935 respectively and limit of detection (LOD), 0.47 mmol L�1 for total water soluble

phthalates in aqueous medium. The method was successfully applied to the determination of total

phthalates in water samples taken from sources of water stored in PVC coolers and plastic bottles.

1. Introduction

Phthalates are a class of widely used industrial compounds,

known as dialkyl or alkyl aryl esters of 1,2-benzenedicarboxylic

acid. They are used in various products, however, the main area

for phthalate esters is their use as plasticizing agents in poly(vinyl

chloride) (PVC) products.1–4 Di-n-butyl phthalate (DBP) is used

as a plasticizer in elastomers such as polyvinyl, as a textile

lubricating agent, as a resin solvent, and in safety glass, printing

inks, paper coatings, adhesives, cosmetics, aerosols, as an anti-

foamer, as a skin emollient, and as a plasticizer in nail polish,

false fingernails and hair spray.4 There is concern towards some

phthalates, especially diethylhexyl phthalate (DEHP) and DBP

after the report of Earl Gray’s laboratory at US Environmental

Protection Agency according to which the male reproductive

development was acutely sensitive to these phthalates and

produced dramatic changes in male sexual properties when

exposure occurred in utero, at levels far below those of earlier

toxicological concern. The changes include increase in the rate of

hypospadias and indication of demasculinization.5

However, in terms of aquatic toxicity, the C6 or > C6 con-

taining phthalates have been termed as non-toxic due to their

limited solubility (< 1 mg L�1). Moreover, some in vivo and in

vitro analyses proved that DBP and butylbenzyl phthalate (BBP)

but not other phthalates were capable of interacting with estro-

genic receptors.6 Among the many potential sources for exposure

of living organisms especially humans to DBP and other water

soluble phthalates is the drinking water stored in bottles and

PVC coolers, due to their continuous aqueous solubility based

transfer, as compared to higher phthalates. Hence, an efficient

simple and sensitive method must be investigated for low level

aNational Centre of Excellence in Analytical Chemistry, University ofSindh, Jamshoro, 76080, Pakistan. E-mail: [email protected];Fax: +92 222 771560; Tel: +92 222 771379bUniversity of Science and Technology, Bannu, NWFP, Pakistan

844 | Anal. Methods, 2010, 2, 844–850

monitoring of water soluble phthalates. Several methods have

been proposed by various researchers to quantify phthalates in

different types of samples using different techniques. They

include, high performance liquid chromatography (HPLC)

related methods7–11 gas chromatography (GC) based,12–16 and

multidimensional liquid chromatography tandem mass spec-

trometry (LC/LC-MS/MS) method.17 The use of polarography is

rarely reported,18,19 for determining phthalates, because very

close values of half wave potentials produce problem in handling

of mixtures of phthalates19 and hence there have not been

significant recent advancements in this area. The problems with

the previously applied polarographic techniques for analysis of

total phthalates include, the use of an organic solvent assisted

medium and the use of a mercury electrode, both of which

present toxicity20 issues and hence are objectionable from envi-

ronmental point of view.

2 Experimental

2.1 Chemicals and instrumentation

A trace analyzer model 797, by Metrohm Version 1.1 was the

main instrument used for voltammetric analysis of total phtha-

lates present in various bottled and cooler waters. Three elec-

trodes, consisting of glassy carbon (3 mm) as working electrode,

platinum rod as counter electrode and calomel as reference

electrode equipped with voltammetric cell and N2 capillary were

used as voltammetric assembly.

All chemicals used were of analytical grade ultra pure quality.

Various phthalate esters such as dimethyl phthalate (DMP),

diethyl phthalate (DEP), dipropyl phthalate (DPP), dibutyl

phthalate (DBP), diethylhexyl phthalate (DEHP), dioctyl

phthalates (DOP), dicyclohexyl phthalate (DCHP), di-isononyl

phthalate (DINP) and electrolyte salts such as tetramethy-

lammonium bromide (TMAB), tetraethylammonium iodide

(TEAI) and tetrabutylammonium bromide (TBAB) were

This journal is ª The Royal Society of Chemistry 2010

purchased from Merck Germany. Lithium perchlorate (LiClO4)

and HCl were from BDH and NaOH was purchased from Acros

chemicals. Stock solutions such as 0.1 mol L�1 DBP and 1 mol

L�1 of electrolyte were prepared in HPLC grade methanol from

Fisher Scientific Company while the working standards were

made by dilution of stock solutions with de-ionized water. 1 mol

L�1 solution of each HCl and NaOH was prepared in de-ionized

water and used for pH adjustment.

2.2 Voltammetric procedure

All the measurements were performed at room temperature 25 �1 �C. Under optimized conditions, 10 ml aqueous solution con-

taining 1 � 10�4 mol L�1 DBP and 0.05 mol L�1 TBAB as sup-

porting electrolyte at pH 4.0 � 0.1 was taken in the

electrochemical cell. After applying all optimized parameters,

SW voltammograms were recorded in the range of �1.2 V –

�2.2 V, pulse amplitude, 0.1 V, frequency 100 Hz, scan rate

0.9 V s�1, stirring rate, 1400 rpm and deposition time, 20 s

without nitrogen purging. A blank solution was also scanned

under similar conditions. The peak potential for the DBP

working standard was around �1.85 V. Calibration plots were

obtained for a number of DBP standard solutions. The newly

developed method performed well for recovery tests on tap water

while the water samples from bottles and coolers were analyzed

after pretreatment and the concentration of water soluble

phthalates was calculated from a specific calibration plot.

2.3 Recovery tests

A voltammetric recovery test was performed by spiking tap water

samples with standard DMP, DEP, DPP and DBP in order to

check the % recovery under the combined matrix effect of various

ions such as, Na+, K+, Ca2+, Mg2+, Cl�, NO3�, CO3

2�, HCO3�,

etc. (present at their natural percentages) on the peak current of

phthalates following all optimized parameters.

2.4 Pretreatment and preparation of water samples for

voltammetric analysis

100 ml of water from a water storage bottle or water cooler was

evaporated until the volume was reduced to 5 ml. To this was

added 0.5 ml of 1 mol L�1 stock solution of TBAB pH adjusted to

4.0 � 0.1 and this was made up to 10 ml with de-ionized water.

The sample was then analyzed by SWV under the conditions

discovered during the method development process.

Fig. 1 SW Voltammograms of 1 � 10�4 mol L�1 M DBP in the presence

of 0.1 mol L�1 (a) LiClO4 (b) TMAB (c) TEAI and (d) TBAB. Amplitude

0.9 V, frequency 100 Hz, scan rate 0.9 V s�1, stirring rate, 2000 rpm,

deposition time, 0 s, equilibration time, 10 s, pH, 5.0 � 0.1.

3 Results and discussion

In our work we chose the GCE as a stable, easily renewable and

sensitive electrode for analysis of DBP as compared to other solid

electrodes such as; gold, silver and graphite electrodes. In the

initial sensitivity tests it was discovered that SWV produces

a better current signal response to DBP at a GCE than other

voltammetric modes. As a result, optimization studies were

carried out for the SWV method using a standard solution of

DBP. In all of the optimization studies the blank SWV peak

current was ignored, but corrections were applied in the case of

calibration plots and application for water samples

This journal is ª The Royal Society of Chemistry 2010

3.1 Optimization of experimental parameters

3.1.1 Choice of best electrolyte. The choice of electrolyte was

carried out in order to get voltammograms with enhanced peak

signal for DBP. Fig. 1 shows the variation of peak current

response for DBP in the presence of different electrolyte solu-

tions, each solution with the same concentration. The study

reveals that TBAB is the best supporting electrolyte with

maximum current signal and well defined voltammogram among

all of studied electrolytes. Two well defined reduction peaks are

obtained for phthalate in a non-buffered system using DPP

where usually the first signal has been selected for quantification

of phthalates.21 According to another report18 DBP gave two

polarographic signals at �1.52 V and �1.83 V in the presence of

0.2 M tetramethylammonium iodide. We also observed two peak

potentials of DBP at �1.68 V and �1.88 V in aqueous (5%

methanol) medium containing 0.1 mol L�1 TBAB at pH, 5.0.

Two peaks signals are true in case of other electrolytes as well.

The difference in values of peak signals in the present work is due

to difference in conditions like voltammetric mode, electrolyte,

electrode, etc. The first signal was selected for evaluation purpose

to enhance the value of current and to obtain well defined shape.

In Fig. 1, the enhanced response of DBP with TBAB may be

due to the formation of a greater number of alkyl ions which can

increase its adsorption properties on GCE surface and hence

results in maximum current. The maximum current in case of

TBAB also signifies greater interaction and hence maximum

reduction of DBP at cathode.22 The shift of peak potential to the

left for the cations follows the order; TBA+ > TEA+ > TMA+ and

further proves the greater adsorption by bigger cations. The size

of anions however, seems to play no role in such tendency. The

use of TBAB has been cited in aqueous medium for acrylamide

determination by differential pulse polarography (DPP)22 and

in 5% water/dimethyl formamide medium for evaluation of

4,40-bis[(4-phenylamino-6-methoxy-1,3,5-triazin-2-yl)amino]-

stilbene-2,20-disulfonic acid by DPP.23

3.1.2 Effect of TBAB concentration. The effect of TBAB

concentration in the range of 0.01–0.3 mol L�1 on the peak

current and peak potential of DBP was studied and shown in

Anal. Methods, 2010, 2, 844–850 | 845

Fig. 3 Effect of different solvents on SWV of 1 � 10�4 mol L�1 DBP

solution containing 0.05 mol L�1 TBAB (1) working aqueous solution

(actually 5% in methanol) (2) 10% methanol, (3) 10% ethanol, (4) 10%

propanol and (5) 10% acetonitrile per 10 ml of aqueous solution.

Fig. 2. The peak current decreased gradually with increasing

concentration of TBAB from 0.05 to 0.3 mol L�1 but the peak

potential shifted towards less negative values, except 0.01 mol

L�1 where broader peak and more negative potential was

obtained. This indicates that as the concentration of TBAB

increases, it is adsorbed on electrode surface and occupies more

sites than required for maximum response and thus results in

decrease of electron transfer. Another reason for decrease in

peak current may be the increase in methanol ratio with increase

of TBAB concentration (taken as 0.5 ml of methanolic TBAB

from its 1 mol L�1 stock solution in each successive step by going

from 0.05 to 0.3 mol L�1 as electrolyte in Fig. 2).

This study shows that 0.05 mol L�1 TBAB was the optimized

amount for maximum peak current and this concentration favors

the maximum interaction of electrolyte with DBP. The effect of

TBAB concentration has been reported for Brdieka and

presidium currents of bovine-serum albumin.24

3.1.3 Effect of organic solvents. Organic solvents increase the

viscosity of the buffer solution and change the dielectric constant

of the buffer. This brings changes in the double-layer phenom-

enon and decreases electro-osmotic mobility with decrease in

currents.25 Different solvents were investigated to determine their

effect on peak signal for DBP in the presence of TBAB and the

voltammograms are shown in Fig. 3.

It can be seen that the best signal response for DBP is observed

in water medium (5% in methanol) (because 0.5 ml methanol is

added from 1 mol L�1 methanolic TBAB per 10 ml of solution)

with less negative peak potential. The best peak current in

aqueous medium may be due to its strong dielectric constant and

more polar behavior as compared to other mixed solvents

mixtures. Another reason may be the decrease in zeta potential

after addition of organic solvent.25 In the case of water as solvent,

hydrogen bonding between bromide ions and hydrogen atoms of

water could lead to increased migration and hence results in

greater deposition of phthalates at GCE.

3.1.4 Stirring effect. The stirring or convection enhances the

speed of supporting electrolyte and phthalate ions towards the

Fig. 2 Effect of different concentration from (1) 0.01 mol L�1, (2)

0.05 mol L�1, (3) 0.1 mol L�1, (4) 0.15 mol L�1, (5) 0.2 mol L�1, (6)

0.25 mol L�1, (7) 0.3 mol L�1, of TBAB as supporting electrolyte with 1�10�4 mol L�1 DBP.

846 | Anal. Methods, 2010, 2, 844–850

glassy carbon electrode. Increasing the stirring rate from zero to

1400 rpm resulted in an increase of peak current response of the

analyte, due to maximum deposition on the surface of glassy

carbon electrode. The deposition remained constant from

1400 rpm to 2000 rpm which suggests that no further deposition

of ions occurs at the glassy carbon electrode, after onset of this

range. After this some decrease in peak current occurred with the

increase in stirring rate which may be due the overflow of solvent

from electrode and over the wall of cell container which can

influence the actual current of DBP at electrode surface.

So, 1400 rpm was selected as the optimum stirring speed for

maximum peak current in further study.

3.1.5 Effect of nitrogen gas purging. Nitrogen purging had

a very poor affect upon the peak current of DBP. In contrast an

enhanced peak current was observed in the presence of oxygen.

The non-significant role of N2 in voltammetric analysis has been

previously described in a study regarding the use of SWV

determination for the reduction of furazolidone.26 However, this

behavior can not be explained as no citation is available that can

clarify this point. As nitrogen purging was observed to be an

insignificant factor in an aqueous medium, hence this economizes

the process, reduces the analysis time and results in higher

sensitivity for reduction peak current of DBP .

3.1.6 Effect of deposition time. The deposition time plays

a key role as longer time increases the concentration of the

analyte on the surface of electrode and thus results in maximum

current response. The analytical signal becomes constant after

a time when there is no more space on the electrode surface for

further deposition of the species. SWV has been used for the

determination of nanomolar concentrations, as this wave form

results in fast and sensitive evaluation.27 Fig. 4 shows the effect of

various deposition times upon the peak height of the DBP

solution using previously optimized parameters.

It was observed that the peak signal of DBP increases with

increase in deposition time and reaches a saturation value with

maximum surface coverage. The peak was shifted with time

towards more negative potential value due to significant gap

between successive time intervals, the current was measurable

anyhow. As the peak shape was getting broader with increasing

This journal is ª The Royal Society of Chemistry 2010

Fig. 4 Effect of various deposition times (0–60 s) on the peak signal of

a 1 � 10�4 mol L�1 solution of DBP under previously optimized

parameters.

time of deposition, 20 s with a peak current of 219 mA was

selected as the optimum time for 1 � 10�4 mol L�1 solution of

DBP giving a good shape and narrower peak for further appli-

cations. The deposition at zero time and nonlinear behavior of

the plot proves that the process is adsorption controlled. The

effect of deposition time on peak current in SWV studies has

been reported elsewhere.27,28

3.1.7 Influence of pH. pH plays key role in decreasing or

increasing peak current values of a particular species because

some reactions are more favored at one pH, while hindered or

slowed down at others. So, various forces of attraction or

repulsion among components of a system can be influenced by

number of available protons and hence the electron transfer

kinetics. Extreme pH values are undesirable due to the possibility

of damage of electrode and possible hydrolysis of some useful

electroactive product into inactive metabolites. Fig. 5 gives the

change in peak height of DBP solution with change in pH from

of 3–9.

It is evident that the value of pH 4 results in the best peak

signal and hence this was selected as optimum pH for further

study. A pH value of 3.3 has been reported19 for maximum peak

Fig. 5 Effect of change in pH upon the peak current value of 1 � 10�4

mol L�1 DBP under all optimized conditions.

This journal is ª The Royal Society of Chemistry 2010

current value for 1 � 10�4 mol L�1 phthalic acid by DP polar-

ography in 0.1 mol L�1 KCl/HCl medium. They observed a linear

time–current dependence of phthalic acid at this pH value in

order to prove that the process was kinetically controlled.

According to a very old report29 the biggest fraction of total

phthalates was observed in the form of biphthalate ions at pH,

4.1. According to our opinion, the cationic part of TBAB

interacts with biphthalate ion to give them a positive charge and

these positive ions are then interacted/adsorbed at cathode for

reduction purpose as evident from zero deposition potential. As

equilibration time and 20 s deposition time is also applied after

final optimization study we believe that the process follows

a Chemical-Electrochemical (CE) route.

3.1.8 Linear calibration curves. Three linear calibration plots

were obtained for phthalates using DBP as a representative

example of total water soluble phthalates under all optimized

conditions as shown in Fig.6.

The linear ranges were true for 70–110 mmol L�1, 20–60 mmol

L�1 and 2–10 mmol L�1 DBP solution with regression coefficients

of 0.9873, 0.9978 and 0.9935 respectively. The highest range was

not defined well as the middle and lower ranges were. It means

that the method has excellent validity in the middle and lower

range and using this method for higher phthalate contents it is

advisable to dilute the sample to desired range. The limit of

detection (LOD) for total phthalates was 0.47 mmol L�1 as

calculated by the previously described method.22 This pre-

concentration method in case of samples containing low

concentrations of phthalates can bring the lower range and LOD

ten times below. The reproducibility of the developed method

was judged by 15 successive SWV measurements of 1 � 10�4 mol

L�1 DBP solution in 0.05 mol L�1 TBAB. The mean peak current

value at a peak potential around�1.85 V was found to be 221 mA

with RSD of 0.5%. This proves that the developed method has

excellent reproducibility. The use of a GCE in SWV mode with

LOD 0.47 mmol L�1 is quite comparable with the reported

method19 showing LOD of 0.5 mmol L�1 using DME. So the use

of GCE is very advantageous from an environmental point of

view, is easy to use in aqueous medium and requires only simple

treatment of sample. In addition the faster scan and N2 free

analysis make the method favourable for evaluation of total

water soluble phthalates.

3.1.9 Method for water soluble phthalates. Other phthalates

like DMP, DEP and DPP showed enhancement of peak current

in the similar way as true for DBP. This behavior is due to the

water soluble nature of these phthalates, however due to very

close peak potential values, it is impossible to separate these

phthalates by voltammetric method. Water insoluble (or spar-

ingly soluble) high molecular weight phthalates like, DEHP,

DCHP, DOP and DINP showed no increase in peak current of

DBP and hence proved as undeterminable by the current

method. The data are presented in Table 1.

The similarity of the values for peak current for DBP and the

other water soluble phthalates is due to the fact that after

dissolution of these phthalates into water [pH 4.0] they are

hydrolyzed to phthalic acid where all the phthalates have similar

type of reduction into bi-phthalate ions due to same number of

carboxylate ions. It has been already reported that the diffusion

Anal. Methods, 2010, 2, 844–850 | 847

Fig. 6 Calibration curves for aqueous solution of DBP as representative

of total water soluble phthalates in the range of 70–110 mmol L�1 (A), 20–

60 mmol L�1 (B) and 2–10 mmol L�1 (C).

Table 1 Peak current and peak potential of (c ¼ 1 � 10�5 mol L�1)different water soluble phthalate esters

Phthalateester

Peakcurrenta/mA

% of DBPpeak current

Decreasedresponse (%)

DMP 62.9 98.9 �1.1DEP 63.1 99.2 �0.8DPP 63.4 99.7 �0.3DBP 63.6 100.0 0.0DEHP N.R. — z�92DCHP do — z�95DOP do — z�96DINP do z�95

a Average of 3 values; N.R., negligible response; do, peak current andpeak potential of different water soluble phthalate esters each ata concentration of 10 mM.

Table 2 Application of method for assay of water soluble phthalates intape water (recovery test)

AnalyteAmountadded/mol L�1

Amountrecovered/mol L�1 % recovery

DMPa 1 � 10�5 1.012 � 10�5 101.2DEPa 1 � 10�5 1.004 � 10�5 100.4DPPa 1 � 10�5 0.980 � 10�5 98.0DBP 1 � 10�5 0.988 � 10�5 98.8

a peak current in each case was compared with that for DBP incalibration plot taken as 100%.

currents are directly proportional to the carboxylate content of

the molecule.21 So this study confirms that the newly developed

method is only suitable for water soluble phthalate determina-

tion in aqueous medium.

3.1.10 Application of developed method. In order to prove the

validity of the newly developed method, first of all a recovery test

was performed by applying the method to tap water samples.

According to the protocol, 10 mmol L�1 solution of each DMP,

848 | Anal. Methods, 2010, 2, 844–850

DEP, DPP and DBP and TBAB was prepared by addition of tap

water, under the optimized conditions and SW voltammograms

recorded as shown in Table 2.

The closer current value for each type of phthalate further

confirms the evidence of application of this method to total water

soluble phthalates as described. Tap water contains a number of

ions as mentioned earlier and all the values of recovered phtha-

lates are around 100% recovery. It means that the common ions

such as Na+, K+, Ca2+, Mg2+, Cl�, CO32�, HCO3

�, etc. present

even at elevated concentration produce no significant effect on

the determination of soluble phthalates in tap water.

The method was also applied to the determination of trace

levels of total water soluble phthalates in 10-fold pre-concen-

trated water samples taken from PVC coolers’ and bottled

mineral water which were stored for 10 days. In case of cooler,

the sample was collected in the form of clean filtered water

already stored in each cooler of specific manufacturer company

for desired time before testing. The samples of bottled water were

collected from local mineral water suppliers factories with

different brand names at the time of bottling and analyzed

10 days after the bottling date.

The reproducibility of the peak current shows that the method

is well suited for determination of total soluble phthalates at

trace levels in aqueous samples. Values obtained for this and

other samples were divided by a factor of 10 because each sample

was pre-concentrated from a 100 ml to final 10 ml (required

volume for voltammetric cell). The results are given in Table 3

and Table 4.

This journal is ª The Royal Society of Chemistry 2010

Table 3 Comparison of soluble phthalate contents in water from PVCcoolers of some manufactures by developed and previously reportedmethoda

Total water soluble phthalates/mmol L�1

Sample No. Cooler Brand

Actual concentration

Developed Method Reported Method

1 Eagle star 0.580 � 0.007 0.581 � 0.0082 Star 0.560 � 0.007 0.570 � 0.0073 Igloo 0.531 � 0.003 0.533 � 0.0064 Galaxy 0.512 � 0.004 0.521 � 0.0075 Arass 0.492 � 0.004 0.496 � 0.006

Average 0.5350 � 0.005 0.5402 � 0.007

a means standard deviation of triplicate sample in each case.

This pre-concentration technique for each water sample brings

the quantification limit as well as detection limit of this method

10 times further down of the calculated values. Therefore after

applying the concentration procedure, the detection limit of the

method becomes 0.047 mmol L�1 (instead of original 0.47 mmol

L�1) regarding the total soluble phthalates in aqueous samples.

Pre-concentration technique has been reported earlier19 where

800 ml of sample was reduced to a final 5 ml for quantification.

Employing pre-concentration technique, they were able to ach-

ieve a range of 0.3–30 mg L�1 for determination of total phtha-

lates in crude and treated waste-waters. The relative samples in

Table 3 were also tested by a reported method in order to see the

correlation and validity of the developed method. The data of

both methods were correlated by applying t-test and one-tailed

f-test calculated as 95% confidence limit at P value of 0.05

according to procedure cited elsewhere.30 According to the

observations, the null hypothesis was retained as the values

obtained in each case were non-significant. This proved the val-

idity and precision of the current method.

The data in Table 3, describes an overall average of 0.535 mmol

L�1 (0.149 ppm) for all samples studied as total water soluble

phthalates in coolers’ waters in terms of DBP. As stated18 the

phthalate esters are used as plasticizers in the manufacture of

poly(vinyl chloride) plastics, with three main constituents, such

as, DEHP, DBP and diheptyl phthalate (DHP). So the DBP

which is the most soluble among all the phthalates present and

contribute as smaller portion of total plasticizers used in PVC

Table 4 Comparison of soluble phthalate contents in bottled watersamples of various local companies by developed and previously reportedmethoda

Total water soluble phthalates/mmol L�1

Sample No. Water company

Actual concentration

Developed Method Reported Method

1 Hash 0.649 � 0.003 0.646 � 0.0042 MAZA 0.937 � 0.005 0.939 � 0.0053 VEY 0.591 � 0.003 0.594 � 0.0064 VITAL 0.780 � 0.003 0.780 � 0.0055 Sprinkle 0.682 � 0.003 0.684 � 0.005

Average 0.727 � 0.003 0.728 � 0.005

a means standard deviation of triplicate sample in each case.

This journal is ª The Royal Society of Chemistry 2010

coolers, is not a level of concern because the permissible exposure

limit (PEL) of DBP or other phthalate is 5 mg m�3 (or

0.44 ppm).31 In comparison, the other two (high molecular

weight) phthalates, DEHP and DHP play no role due to their

insolubility in water and hence insensitivity by the current

method. Due to higher cost of water filters, some poor people

store phthalate contaminated river or stream water in PVC

coolers for drinking purpose which can result in higher phthalate

contents and hence possible health complications.

The data in Table 4 reveals the overall average content of total

water soluble phthalates as of 0.728 mmol L�1 (0.203 ppm) in case

of bottled mineral water samples. The data in Table 4 was also

compared with the reported method19 by applying t-test and

f-test. The results in this case were true at 95% confidence limit

and showing good precision of the proposed method. These

values may be contributed by DBP and/or other water soluble

phthalates. According to a report,32 the acute and chronic

toxicity to microorganisms and other species living in water are

limited to lower molecular weight phthalate esters while higher

molecular weight phthalate esters are not acutely or chronically

toxic to aquatic organisms. Therefore, water soluble phthalates

are of special interest and their assay in drinking water is essential

for environmental monitoring.

4 Conclusion

This newly developed SWV method focuses on the use of GCE as

a green alternative to toxic DME previously used for determi-

nation of phthalates at trace levels at an optimum pH 4.00. The

method is quicker, sensitive and simpler and specific for assay of

total water soluble phthalates in drinking waters. The analysis of

soluble phthalates in the absence of N2 free medium provides

economy, better sensitivity and shorter analysis time. The

recovery test for tap water samples confirms its applicability for

use in an ion rich medium and proves its validity for assay of all

types of water samples regarding the quantification of water

soluble phthalates. The pre-concentration technique lowers the

limit of quantification as well as the LOD for the evaluation of

water soluble phthalates in water samples. The data obtained by

the developed method for drinking water stored in coolers and

plastic bottles show that water stored in this way does not pose

a threat to health from phthalate content, as the observed levels

are below the PEL.

Acknowledgements

We are thankful to the Director, National Center of Excellence in

Analytical Chemistry, University of Sindh, Jamshoro, for tech-

nical assistance and Higher Education Commission of Pakistan

Islamabad for financial support in this project.

References

1 G. Latini, A. Del Vecchio, M. Massaro, A. Verrotti and C. De Felice,Toxicology, 2006, 226, 90.

2 Z. Y. Xie, R. Ebinghaus, C. Temme, R. Lohmann, A. Caba andW. Ruck, Environ. Sci. Technol., 2007, 41, 4555.

3 T. Berman, D. Hochner-Celnikier, A. M. Calafat, L. L. Needham,Y. Amitai, U. Wormser and E. Richter, Environ. Int., 2009, 35, 353.

4 M. Ema, E. Miyawakia and K. Kawashima, Reprod. Toxicol., 2000,14, 13.

Anal. Methods, 2010, 2, 844–850 | 849

5 L. E. Gray, C. Wolf, C. Lambright, P. Mann, M. Price, R. L. Cooperand J. Ostby, Toxicol. Indus. Health, 1999, 15, 94.

6 A. B. Christopher and T. Paul, Aquatic Toxicity of Phthalate Esters,The Handbook of Environmental Chemistry, Vol. 3, (Part Q) 2003:pp. 263.

7 P. Cocco, N. Kazerouni and S. Hoar Zahm, Environ. HealthPerspect., 2000, 108, 1.

8 K. Mitani, S. Narimatsu, F. Izushi and H. Kataoka, J. Pharm.Biomed. Anal., 2003, 32, 469.

9 K. Kambia, T. Dine, B. Gressier, A. F. Germe, M. Luyckx, C. Brunet,L. Michaud and F. Gottrand, J. Chromatogr., B: Biomed. Sci. Appl.,2001, 755, 297.

10 H. M. Koch, H. Drexler and J. Angerer, Int. J. Hyg. Environ. Health,2004, 207, 15.

11 K. Kato, M. J. Silva, L. L. Needham and A. M. Calafat,J. Chromatogr., B: Anal. Technol. Biomed. Life Sci., 2005, 814, 355.

12 H. M. Chen, C. Wang, X. Wang, N. Hao and J. Liu, Int. J. Cosmet.Sci., 2005, 27, 205.

13 D. D. Orsi, L. Gagliardi, R. Porra, S. Berri, P. Chimenti, A. Granese,I. Carpani and D. Tonelli, Anal. Chim. Acta, 2006, 555, 238.

14 P. W. Albro, S. Jordan, J. T. Corbett and J. L. Schroeder, Anal.Chem., 1984, 56, 247.

15 W. Qian and S. K. Birgit, Polym. Test, 2005, 3, 290.16 A. O. Earls, I. P. Axford and J. H. Braybrook, J. Chromatogr., A,

2003, 983, 237.17 M. J. Silva, N. A. Malek, C. C . Hodge, J. A. Reidy, K. Kato,

D. B. Barr, L. L. Needham and J. W. Brock, J. Chromatogr., B:Anal. Technol. Biomed. Life Sci., 2003, 789, 393.

18 A. F. Williams and D. Kenyon, Talanta, 1959, 2, 79.

850 | Anal. Methods, 2010, 2, 844–850

19 K. Tanaka and M. Takeshita, Anal. Chim. Acta, 1985, 166, 153.20 J. Fischer, L. Vanourkova1, A. Danhel1, V. Vyskocil1, K. Cizek1,

J. Barek, K. Peckova, B. Yosypchuk and T. Navratil, Int.J. Electrochem. Sci., 2007, 2, 226.

21 G. C. Whitnack, J. Reinhart and E. St. C. Gantz, Anal. Chem., 1955,27, 359.

22 A. Niaz, Sirjuddin, S. Afzal, M. I. Bhanger, M. Saeed, M. K. Jamaliand M. B. Arain, Talanta, 2008, 74, 1608.

23 J. Barek and R. Hrncir, Collect. Czech. Chem. Commun., 1994, 59,1018.

24 I. M. Kolthoff and K. Yamashita, Proc. Natl. Acad. Sci. U. S. A.,1975, 72, 2863.

25 V. Virtanen, G. Bordin and A. R. Rodriguez, Chromatographia, 1998,48, 637.

26 H. Parham and B. A. Esfahani, J. Iran. Chem. Soc., 2008, 5, 453.27 N. A. El-Maali, J. C. Vibe, G. J. Patriarche, M. A. Ghandour and

G. D. Christian, Anal. Sci., 1990, 6, 245.28 D. Abd El-Hady, M. Ibrahim Abdel-Hamid, M. Mahmoud Seliem

and N. Abo E-Maali, Arch. Pharmacal Res., 2004, 27, 1161.29 N. H. Furman and C. E. Bricker, J. Am. Chem. Soc., 1942, 64,

660.30 J. C. Miller and J. N. Miller, Statistics for Analytical Chemistry, 2nd

edn, 1988, Publisher, John Wiley & Sons, New York, Chichester,Brisbane, Toranto.

31 Mallinckrodt Baker. Inc. Material Safety Data Sheet (MSDS) 2001,pp 1–5.

32 C. A. Staples, W. J. Adams, T. F. Parkerton, J. W. Gorsuch,G. R. Biddinger and K. H. Reinert, Environ. Toxicol. Chem., 1997,16, 875.

This journal is ª The Royal Society of Chemistry 2010