The Properties Of The Ion-selective Electrode
THE PROPERTIES OF THE ION-SELECTIVE ELECTRODE
WITH A PSEUDO-LIQUID POTENTIAL CREATING PHASE
IN KETOPROEN DETERMINATION
B. Marczewska, J. Lenik
Department of Analytical Chemistry and Instrumental Analysis, Faculty of Chemistry, Maria Curie-Sklodowska University,
Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland
The aim of the research was to create an electrode with a pseudo-liquid membrane phase with ketoprofen function on the basis of PVC as well as to establish its analytical parameters. The active substance of the liquid membrane phase was the ion pair type complex: methyltrioctylammonium 3-benzoil- α-methylphenylacetate (KET – MTOA) dissolved in a plasticizer. The electrode was used to the determination of ketoprofen in pharmaceutical preparation "Ketonal" (Lek Pharmaceutical and Chemical Company d.d.Slovenia) in condition of ampoule to injection
The electrode’s construction and the pseudo-liquid membrane phase preparation
The electrode’s liquid membrane phase contains two layers: the inner layer, containing the plasticizer PVC in which the electrode Ag/AgCl is placed and the outer layer, contacting with the examined solutions and containing the active substance (KET – MTOA) apart from the inner layer components. In order to prepare the outer layer, 0.05g (KET – MTOA – complex was dissolved in a mixed plasticizer (0.075g TBP+0.225g DBF), with 0.15g emulsion PVC added. The mixture was dissolved in THF and placed in drops on the inner layer, leaving THF to evaporate at room temperature. The sensors were conditioned for 1 hour before the measurements in the 10-3 M concentration ketoprofen solution.
The electrode’s analytical parameters
The electrode’s basic analytical parameters were established (Table 1.). The calibration curves were determined in the main ion and interfering ions solution at pH 8.5. The measurements of EMV of the system ketoprofen electrode – reference electrode Orion 90-02 were carried out at room
temperature using Multifunction Computer Meter CX – 721 (Elmetron, Poland). During measurements the solution were stirred with a mechanical stirrer. The potentiometric selectivity coefficient of ketoprofen electrode was determined with the Separate Solution Method (SSM) and the Matched Potential Method (MPM) proposed by Christian and Gadzekpo [1] (Table 2.).
Table 1. Analytical parameters of the polymer ketoprofen electrode.
Intercept (mV)
-0.1
Slope (mV/(lg CKet )-1
Standard deviation (mV)
-58.31.5
1.85
Linear range (M)
(mg/ml)
1×10-1 – 1×10-4
25.43 – 0.02543
pH range
5.5 – 8.5
Response time (s)
30
Detection limit (M)
5.75·10-5
Table 2. The comparison of the selectivity coefficients
Ion
SSM
MPM
Oxalate
1.15·10-3
1.47·10-2
Acetate
5.84·10-3
1.19·10-3
Citrate
6.99·10-4
2.30·10-2
Nitrate
5.93·10-1
6.85·10-1
Chloride
2.03·10-2
5.24·10-3
Sulfate
9.55·10-4
1.01·10-3
Ketoprofen determination
The analytical usefulness of the examined electrode was tested by determining of ketoprofen in pharmaceutical preparation "Ketonal" with the method of calibration curve and standard addition into the sample. The statistical parameters (Recovery 99 %, RSD 6.2 %) indicate the typical accuracy of the analytical methods employing ion – selective electrodes.
The examined electrode can be applied to ketoprofen determination in the concetration range of 25.43 – 25.430 μg/ml in water solution at pH5.5 – 8.5.
References
1. V.P.Y. Gadzekpo, G.D.Christian, Determination of selectivity coefficients of ion-selective electrodes by a Matched Potential Method, Anal. Chim. Acta 164 (1984) 279 – 282.
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