INTRODUCTION:
Barium, a naturally occurring alkaline earth metal has diverse industrial applications. Barium compounds are used in the plastics, rubber, electronics and textile industries, in ceramic glazes and enamels, in drilling muds, paint, bricks, rubber, in fireworks, in medical applications, in the form of alloys like barium-nickel alloy for spark-plug electrodes, etc [1, 2]. During industrial processes, certain barium compounds that dissolve easily in water get released and are observed in effluent thus creating an imbalance in the environment. Barium compounds that dissolve in water are harmful to human health. Short term exposure of barium causes vomiting, abdominal cramps, diarrhea, difficulties in breathing, increased or decreased blood pressure, numbness around the face, and muscle weakness. Excess barium intake causes high blood pressure, changes in heart rhythm or paralysis and possibly death [3].
Nevertheless 10 ppm of barium in drinking water has no significant effect on cardiovascular risk factor [4]. Researchers have used various analytical tools for the detection of barium ions such as Atomic Absorption Spectrometry (AAS) [5, 6], Flame photometry [7], Inductively Coupled Plasma - Atomic Emission Spectroscopy (ICP-AES) [8], X-ray Fluorescence spectrometry [9], Isotope dilution method [10,11]. However, these methods are very expensive for most analytical laboratories, tedious, time consuming and also require multi step sample preparation procedures. Hence, the present manuscript is focused on the development of a novel method for the determination of barium ions based on the use of ion selective electrode which offers a very simple, fast, inexpensive, non-destructive alternative with a wide dynamic range [12-15].
Potentiometric detection based on the use of ion selective electrode offers considerable advantages like portability, fast response time, broad working range, low detection limit, low cost, high selectivity and sensitivity, applicability to colored as well as turbid solutions [16-18]. By using DB24C8 as an ionophore which forms a very stable complex with barium [19-21], a graphite coated ion selective electrode was fabricated which exhibited a detection limit of 6.1 × 10-7 M, response time of <10s and good selectivity with respect to other cations [22]. This electrode was used for the determination of barium ions in water by calibration curve and standard addition method. The results obtained by this method were compared with ICP-AES method.
MATERIALS:
Analytical grade barium nitrate, sodium tetraphenyl borate (NaTPB), dibutyl phthalate (DBP), dibutyl maleate (DBM) was obtained from LobaChemie. High purity dibenzo24crown8 (DB24C8), o-nitrophenyl octylether (o-NPOE) were obtained from Chemical Centre, Multiwalled carbon nanotube (MWNT) was obtained from Sigma-Aldrich while tetrahydrofuran (THF) and polyvinyl chloride (PVC) were obtained from SD fine Chemicals and Chemical International respectively.
Methodology:
Fabrication of electrode:
Graphite electrode was coated with a membrane having composition 33% PVC, 52% 2-NPOE, 7.5% NaTPB, 2% MWNT and 5.5% ionophore DB24C8 in THF solvent, dried under an IR lamp for 24 hours and then conditioned in a 1×10-3 M Ba2+ solution for 48 hours.
Electromotive Force Measurements:
The potential measurements were made by setting up the following cell:
-SCE ││Ba2+ solution │membrane, graphite+
A digital dual channel Potentiometer Model (EQ-603) was used for the potential measurements.
Sample preparation:
Two tap water (Sample No. 1 and 2) and two lake water samples (Sample No. 3 and 4) were spiked with known amounts of barium nitrate (Table 1) and then given for ICP-AES analysis at SAIF, IIT- Bombay.
Quantitative analysis:
10cm3 of the sample was diluted to 100cm3 in a standard flask and the potential measured using the fabricated electrode against SCE (E1). The potential values obtained were used to determine the concentration of barium ions in water samples by the calibration curve and standard addition method. In the calibration curve method, standard solutions of Ba2+ having concentration 20, 40, 60, 80 and 100 ppm were prepared and their potentials measured against SCE. For the standard addition method, two standard solutions of Ba2+ having concentrations 10 and 100ppm were prepared and their potentials measured against SCE. Then the potential of 25cm3 of sample was measured after addition of 5cm3 of 100ppm Ba2+ standard solution (E2). The concentration of samples were calculated by using the following formula
C = 
Where Cs = concentration of standard, Vs = volume of standard added, Vu = volume of sample taken, ΔE = change in potential on addition of standard and m = slope.
Table 1: Preparation of water samples.
|
Sample No. |
Amount spiked (g/dm3) |
Concentration (ppm) |
|
1 |
0.540 g |
284.0 |
|
2 |
1.045 g |
549.2 |
|
3 |
0.540 g |
284.0 |
|
4 |
1.045 g |
549.2 |
RESULTS AND DISCUSSIONS:
Calibration curve method:
The calibration curve of Ecell vs. log C for the standard solutions of Ba2+ is shown below (Figure 1). From the equation of line, concentration of barium ions present in water samples was determined. The results are given in Table 2.
Figure 1: Calibration curve of Ecell vs. log for Ba2+ standard solutions.
Table 2: Concentration of Ba2+ obtained by calibration curve method
|
Sample No. |
E1 (mV) |
Concentration (ppm) |
|
1 |
351.3 |
286.42 |
|
2 |
360.0 |
559.86 |
|
3 |
351.3 |
286.42 |
|
4 |
360.0 |
559.86 |
Standard addition method:
The curve of Ecell vs. log C for 10 and 100 ppm Ba2+ standard solution exhibited a slope of 31.3 (Figure 2). The results obtained by measuring the potential of sample before and after addition of standard and using equation (1) are given in Table 3.
Figure 2: Calibration curve of Ecell vs. log C for Ba2+ standard solutions.
Table 3: Concentration of Ba2+ obtained by standard addition method
|
Sample No. |
E1(mV) |
E2 (mV) |
Δ E (mV) |
Concentration (ppm) |
|
1 |
351.3 |
356.0 |
4.7 |
286.21 |
|
2 |
360.0 |
361.7 |
1.7 |
552.96 |
|
3 |
351.3 |
356.0 |
4.7 |
286.21 |
|
4 |
360.0 |
361.7 |
1.7 |
552.96 |
The results obtained by using the fabricated ion selective electrode were found to be in good agreement with the ICP-AES method.
Table 4: Comparison of results obtained by using the fabricated ion selective electrode and ICP-AES method.
|
Sample No. |
Concentration of Ba2+ (ppm) |
||
|
ICP -AES |
Calibration curve method |
Standard addition method |
|
|
1 |
285.74 |
286.42 |
286.21 |
|
2 |
549.044 |
559.86 |
552.96 |
|
3 |
292.047 |
286.42 |
286.21 |
|
4 |
553.174 |
559.86 |
552.96 |
CONCLUSIONS:
The developed graphite coated electrode was successful in determining the concentration of Ba2+ in water samples. The fabricated electrode offered a very simple, economic and rapid method for the determination of Ba2+ in water at ppm levels.
ACKNOWLEDGEMENTS:
The authors are thankful to the Principal and Management of B N Bandodkar College of Science, Thane for their support and also to SAIF IIT Bombay for carrying out ICP-AES analysis.
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Received on 01.05.2017 Modified on 10.06.2017
Accepted on 15.07.2017 © AJRC All right reserved
Asian J. Research Chem. 2017; 10(4):517-519.
DOI:10.5958/0974-4150.2017.00084.0