REV. CHIM. (Bucharest) ♦ 64 ♦ No. 2 ♦ 2013 http://www.revistadechimie.ro 205 Ion Selective Electrodes for Microalgal Biotechnology MIHAELA CALUGAREANU 1,2 , GÉZA NAGY 3 , ANA MARIA JOSCEANU 1 *, LÍVIA NAGY 4 1 Politehnica University of Bucharest, 313 Splaiul Independentei, 060042, Bucharest, Romania 2 National Research and Development Institute for Chemistry and Petrochemistry –ICECHIM, 202 Splaiul Independentei, 060021, Bucharest, Romania 3 University of Pécs, Departament of General and Physical Chemistry,Ifjúság u. 6, 7624 Pécs, Hungary 4 University of Pécs János Szentágothai Research Center , Ifjúság u. 34, 7624 Pécs, Hungary This paper presents the results obtained in monitoring potassium, calcium, and magnesium ions content in Chorella homosphaera 424 culture media using in-house manufactured potassium, calcium and magnesium ion selective electrodes. The sensors were prepared with poly(vinyl chloride) plasticized with o-nitrophenyl octyl ether. Valinomycin(I), N,N,N’,N’- tetra[cyclohexyl]diglycolic acid diamine, and bis-N,N-dicyclohexyl- malonamide were chosen as ionophores. The membranes worked well in the 10 -4 - 10 -1 mol/L concentration range, displaying Nernstian slopes of 57.0±1.0, 27.0±1.0, and 27.0±0.5 mV per decade of K + , Ca 2+ , and Mg 2+ ions activity. The electrodes responses showed pH dependence at pH < 4.0 and at pH > 11.0. The selectivity coefficients, measured by the mixed solutions method, ranged from 1.0 . 10 -1 to 3.2 . 10 -9 . The newly prepared sensors gave good results in monitoring potassium, calcium, and magnesium levels in Chlorella homosphaera 424 culture media, as cross-checked by AAS. Keywords: ion selective electrode, selectivity coefficients, algal culture media Microalgal culturing techniques represent a fast growing branch of biotechnology. It is successfully used in producing fine chemicals [1,2], as well as growing algae as source of renewable fuels [3,4]. The media ionic composition is a crucial factor in microalgal culturing techniques, influencing the yield. Therefore continuous in situ measurement of concentration and control of different ionic species is highly beneficial. Usage of ion selective electrodes as transducers for the analysis is an obvious choice, as they display good selectivity and deliver specific and sensitive results in short time. They can be manufactured rapidly, at a very low cost, and can be used without complex pre-treatments and can be applied for in situ analysis in many types of aquatic environments. There are several reports on monitoring K + , Mg 2+ , and Ca 2+ ions concentrations with the aid of ion selective electrodes, applications ranging from clinical analyses to environmental projects [6-9]. Gupta et al. [8] developed magnesium ion selective electrodes using benzo-15crown-5 as ionophore. Best performance was exhibited by the membrane containing crown: PVC: NaTPB: DOP in the 10 : 150 : 3 : 150 ratio. The device worked well in the 10 -5 - 10 -1 mol/L concentration range, being used for determination of magnesium by potentiometric titration with EDTA in aqueous and non- aqueous media. No significant changes of slope or working range concentration were noticed when solutions contained up to 20% (v/v) non-aqueous fraction. ETH 5282 [(N’,N”,N”’-iminodi-6,l-hexanediyl)-tris(N-heptyl-N-methyl- malonamide)] was tested as magnesium selective carrier [10] in undiluted blood serum samples. The membrane contained ETH 5282 / PVC/ o-nitrophenyloctyl ether (1/33/ 65 by weight), and potassium tetrakis(p-chlorophenyl) borate (KTpClPB) in a molar ratio of 1.5 relative to the ionophore. However, the ionophore used suffered from calcium interference at 1% concentration. ªendil et al [11] proposed a potassium ion selective electrode based on benzo-15-crown-5 as neutral carrier, which worked well * email: ajosceanu@gmail.com; Tel.: 0214023908 in the 10 -4 - 10 -2 mol/L range, with a slope of 56.0 ± 3.0 mV/ decade of potassium ion concentration. This electrode gave good results in determining K + in orange juice, vitamin, and edible salt. Bedlechowicz et al. [7] studied the plasticizer effect on the response and selectivity of a calcium selective device containing [( )-(R,R)-N,N’ -bis- [11-(ethoxycarbonyl) undecyl]-N,N’ -4,5-tetramethyl-3,6- dioxaoctanediamide] (ETH 1001). (2-ethylhexyl)sebacate (DOS) and o-nitrophenyl octyl ether (o-NPOE) were used as plasticizers. o-NPOE extended the linear domain of the calibration curve and lowered the detection limit when compared to the DOS-containing device. The optimal activity of free Ca 2+ and Na + ions in the internal reference solution varied from 10 -4 to 10 -1 mol/L for DOS, and 10 -6 to 10 -1 mol/L for o-NPOE respectively. Other two calcium ion selective electrodes based on ETH 1001 and N,N,N’ ,N’ -tetracyclohexyl- 3-oxapentanediamide (ETH 129) were reported [12] and compared using a similar procedure. The detection limit decreased to 10 -8.8 mol/L when an internal filling solution buffered for the primary ion was employed. ETH 129 worked well for monitoring low Ca 2+ ions concentration in the presence of a significant K + , Na + , and Mg 2+ background. However, adaptation of ion selective electrodes for biotechnological applications is rather challenging, because of the significant concentrations of interfering chemical species. Also the aquatic environment needed for Chlorella homosphaera 424 growth as biofuel material undergoes pH variations during cultivation [5]. We present here the preparation of three ion selective electrodes based on poly(vinyl chloride) plasticized with o-NPOE for in situ determination of potassium, calcium, and magnesium ions in Chlorella homosphaera 424 growth media. Valinomycin ( I ), N,N,N’,N’- tetra[cyclohexyl] diglycolic acid diamine, and bis-N,N-dicyclohexyl- malonamide were used as carriers for the selective monitoring of potassium, calcium, and magnesium ions both in synthetic solutions and algal culture media.