oa South African Journal of Chemistry - A Stable Glutamate Biosensor Based on MnO Bulk-modified Screen-printed Carbon Electrode and Nafion(R) Film-immobilized Glutamate Oxidase



An amperometric glutamate biosensor was developed using screen-printed carbon electrodes bulk-modified with MnO&lt;sub&gt;2&lt;/sub&gt; (5%, m:m) onto which glutamate oxidase was immobilized via Nafion&lt;sup&gt;(R)&lt;/sup&gt; film entrapment. The analytical performance of the biosensor was assessed in a flow injection mode and peak heights of the current response were used to evaluate results. Best responses were recorded at an applied potential of 440 mV (&lt;I&gt;vs&lt;/I&gt; Ag/AgCl) a flow rate of 0.2 mL min<sup>-1</sup>, and a pH of 7.75 of the carrier (0.1 mol L&lt;sup&gt;-1&lt;/sup&gt; phosphate buffer). The calibration curve exhibited linearity in the concentration range 10-160 mg L<sup>-1</sup>, with a detection limit (as 3<SPAN lang=AF style="FONT-FAMILY: Symbol; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-char-type: symbol; mso-symbol-font-family: Symbol"><SPAN style="mso-char-type: symbol; mso-symbol-font: Symbol"&gt;s&lt;/SPAN&gt;&lt;/SPAN&gt; value) of 1.7mg L<sup>-1</sup>, and a relative standard deviation 3.3% (c=20 mg L<sup>-1</sup>, <I>n</I>=10). This biosensor was used for the determination of monosodium glutamate in food seasonings, and the values obtained were similar to those obtained with spectrophotometry. The biosensor exhibited extraordinary stability when left on the FI system at a flow rate of 0.1 mL min&lt;sup&gt;-1&lt;/sup&gt; at room temperature retaining 50% of the original response towards glutamate even after 65 days. Stored in the working buffer for more than 60 days, the same biosensor showed extended linear range, 20-710 mg L<sup>-1</sup>. This 'aged' (stored) biosensor was used to determine monosodium glutamate in food seasonings and gave similar result to those obtained with a freshly prepared biosensor.


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