**4. Plasticizer and detection limit**

Plasticizers affect the detection limit of the different type of electrodes. **Bedlechowicz et al**, **2002** *Journal of Electroanalytical Chemistry,* studied the effect of the plasticizer on the extended linear calibration curve and on the selectivity of a calcium selective electrode with ETH 1001 ionophore as a function of calcium activity in the internal solution. (2-Ethylhexyl)sebacate (DOS) and *o*-nitrophenyloctyl ether (*o*-NPOE) were used as plasticizers. The poly(vinylchloride) membrane also contained potassium tetrakis(4-chlorophenyl)borate. The linear part of the calibration curve of the electrode with *o*-NPOE is longer and the detection limit is lower compared to values for the electrode containing DOS as the plasticizer. The optimal activity of free Ca2+ and Na+ in the internal reference solution was 10−4 and 10−1 for the membrane with DOS and 10−6 and 10−1 for the membrane with *o*-NPOE, respectively. The repeatability of the response for electrodes with the lowest detection limit is similar in the case of both plasticizers. The selectivity coefficients were determined for electrodes having activities of calcium ion in the internal solution in the range from 10−2 to 10−10. The properties of the electrodes can be correlated with the transport properties of their membranes.

The same conclusion was recorded by **Gupta et al 2000**, *Talanta*, for Cd electrode. They studied the potential response of cadmium(II) ion selective electrode based on cyanocopolymer matrices and 8-hydroxyquinoline as ionophore has been evaluated by varying the amount of ionophore, plasticizer and the molecular weight of the cyanocopolymer. The sensitivity, working range, response time, and metal ions interference have shown a significant dependence on the concentration of ionophore, plasticizer and molecular weight of cyanocopolymers. The electrodes prepared with 2.38×10−2 mol kg−1 of ionophore, 1.23×10−2 mol dm−3 of plasticizer and 2.0 g of cyanocopolymer (molecular wt., 59 365) have shown a Nernstian slope of 29.00±0.001 mV per decade activities of Cd2+ ions with a response time of 12±0.007 s. Electrodes have shown an appreciable selectivity for Cd2+ ions in the presence of alkali and alkaline earth metal ions and could be used in a pH range of 2.5–6.5. The cyano groups of the copolymers contributed significantly to enhance the selectivity of the electrode. The electrode has shown an appreciable average life of 6 months without any significant drift in the electrode potential and found to be free from leaching of membrane ingredients. Electrode response is explained considering phase boundary model based on thermodynamic considerations.

Plasticizers and Their Role in Membrane Selective Electrodes 123

higher phr ratios for all plasticizers. Tangent stiffnesses were generally 1.7 times secant stiffnesses. They concluded that for all plasticizers, ductility increased to a constant value of 15 mm at a phr ratio of two. The molecular structures of the plasticizers influenced the mechanical properties. For a given phr ratio, plasticizers having lower hydrodynamic volumes increased the strengths, stiffnesses, and toughnesses of the membranes. Compared to prior dielectric testing, the strength, toughness, and stiffness increased as the ionic resistivity increased. In electrodes and biosensors phr ratios should be reduced to a

Many vinyl products contain additional chemicals to change the chemical consistency of the product. Some of these additional chemicals called additives can leach out of vinyl products. Plasticizers that must be added to make PVC flexible have been additives of particular concern. The leaching out of plasticizers during measurements and their volatility (during

preparing membranes) are the main causes of the toxicity by the plasticizers.

Chanda, Manas; Roy, Salil K. (2006). *Plastics technology handbook*. CRC Press. pp. 1–6.

Zamani, H. A., Hamed-Mosavian, M. T., Hamidfar, E., Ganjali, M. R., Norouzi, P., *Materials* 

Espadas-Torre C., Bakker E., Barker S., and Meyerhoff M., *Anal.Chem.* 1996, 98, 1623-1631.

Odashima K., Yagi K., Tohda K., and Umezawa Y., *Anal. Chem.*, 1993, 55, 1074-1083

Zareh M., Ismail I., and Abd El-Aziz M., *Electroanalysis* 2010, 22, 1369-1375.

Spichiger U.E., Simon W., *Analyt. Chim. Acta*, 1994, 289, 1-13. Gupta V., Jain A., Agarwal S., Maheshwari G., *Talanta* 2007, 71**,** 1964-1968. Sil A., Ijeri V., Srivastava A., *Sensors and Actuators B: Chemical* 2005, 106, 648-653.

K. Tohda, S. Yoshiyagawab, Y. Umezawaa, *J. Mol. Str.*, 1997, 408/409, 155. Buck R., and Lindner E., *Pure and Applied Chem* 1994, 12, 2527-2538.

Péreza M., Maŕnb L. P., Quintanab J., Yazdani-Pedramc M., *Sensors and Actuators B:* 

Watanabe K., Okada K., Oda *H.,* Furuno K., Gomita Y., Katsu T., *Analytica Chimica Acta* 1995*,*

Ekmekci, G., Uzun, D., Somer, G., Kalayc, Ş., *Journal of Membrane Science* 2007, 288, 36-40. Eugster R., Rosatin T., Rusterholz B., Aebersold B., Pedrazza U., Ruegg D., Schmid A.,

Buck R.P. and Lindner E., Pure & App. Chem. 1994, 66, 2527–2536. J. Janata, *Principles of Chemical Sensors*, 1989, Plenum Press, New York,

*Science and Engineering: C* 2008, 28, 1551-1555. Zareh M., Malonwska E., Kasiura K., *Analyt.Chim. Acta* 2001, 447, 55.

Quagraine E. and Gadzekpo V., *Analyst*, 1992, 117,1899-1903.

Khayatian G., Rezatabar H., Salimi A., *Anal. Sci*. 2005, 21, 297-302

Mashhadizadeh, M. H., Shoaei, I. S., Monadi, N., *Talanta* 2004,

minimum of one.

**8. References** 

**7. Plasticizers and health** 

Zareh M., *Sensor Letters*, 2010, 8, 1-8.

http://www.tciamerica.com/catalog/S0025.html.

*Chemical,* 2003, 89, 262–268.

316, 371-375.

Zareh M., *Anal.Sci.* 25, 1131(2009).
