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## Boronic acid as ionophores in potentiometric sensors for the determination of amino acids

### Martyna Niżnik

#### Abstract

Introduction: Amino acids are organic compounds with at least one amino- and one carboxyl group in their structure. They can bind with each other through an amide bond to form peptides and proteins, which are extremely significant for proper activity of human body. Quantitative and qualitative determination of amino acids is especially important in medicine and pharmacy, as there are many diseases associated with disorders of amino acid metabolism. There are many methods of determination of amino acids, but there a method that would also be inexpensive, rapid and does not require sample pre preparation (e.g. separation of analyte from the matrix) is not available. An alternative of current methods for the determination of amino acids, which allows to avoid these problems seems to be potentiometry, precisely ion-selective electrodes with the selective compounds as receptors in membrane. Boronic acids seem to be good receptors, which are very reactive compounds and have an affinity to several groups of analytes. So far, these compounds were applied as receptors for determination of such compounds as carbohydrates [1], catecholamines [2] or fluoride anions [3]. In the literature there are also reports of selective binding of amino acids by boronic acids [4]. Therefore, the 4-octyloxyphenylborate acid - KB5 was applied as a receptor in the membrane of ion-selective electrodes for the determination of several amino acids. Results and discussion: The research carried out in this paper involved: preparation of the membranes, constructing of the electrodes and measurements of the electromotive force of two electrodes (ion-selective electrode and reference electrode). The calibration curves (based on received results) was prepared for 4 amino acids - phenylalanine, glutamic acid, tyrosine and ornithine. Main working parameters of the electrodes were determined and the conditions of the measurements was optimized by changing the pH of the solution. The effects of KB5 boronic acid addition to the membrane and the type of lipophilic salt for the response of the electrodes were studied. Moreover, the composition of the membranes was modified. The influence of the polarity of plasticizer (DOS or o-NPOE) was determined. In the last stage of the work the selectivity coefficients (for 6 amino 75 acids: phenylalanine, proline, ornithine, alanine, tyrosine and glutamic acid) were calculated. Based on this, the selectivity of the constructed electrodes was defined. The results of this study have shown that the addition of boronic acid to the membranes did not change the response of the elctrodes and the detection limit. Moreover, the sensitivity of the constructed sensors was not changed. The slope of the calibration curves depended on the type of lipophilic salt. The selectivity of the electrodes was slightly affected by the presence of KB5 in the membrane. The selected plasticizer of the membrane influenced the value of the slope of the electrodes calibration curves. Conclusions: As demonstrated in this study, the presence of the 4-octyloxyphenylborate acid slightly affected the responses of the electrodes with membranes containing the ion-exchanger (KTFPB or TDMAC). Therefore boronic acids are not suitable as ionophores in membranes of ion-selective electrodes. The results confirmed that the boronic acids could binding of amino acids. Further research are required, consisting primarily of modifying the structure of ionophores (the use of the derivatives of the boronic acids) and the amount of additions of the lipophilic salt to membranes. In the next step the conditions of the measurements should be optimized.
Record ID
Diploma type
Master of Science
Author
Martyna Niżnik Martyna Niżnik,, Undefined Affiliation
Title in Polish
Kwasy boronowe jako jonofory w membranach sensorów potencjometrycznych czułych na aminokwasy
Supervisor
Wojciech Wróblewski (FC/CMB) Wojciech Wróblewski,, Chair of Medical Biotechnology (FC/CMB)Faculty of Chemistry (FC)
Certifying unit
Faculty of Chemistry (FC)
Affiliation unit
Department Of Microbioanalytics (FC/CMB)
Study subject / specialization
, Technologia Chemiczna
Language
(pl) Polish
Status
Finished
Defense Date
05-07-2012
Issue date (year)
2012
Keywords in Polish
-
Keywords in English
-
Abstract in Polish
urn:pw-repo:WUT515912b9a1234b85adf3c053675905cd