Automated electrochemical free radical scavenger screening in dietary samples.

An automated electrochemical microtiter plate assay for the quantification of free radical scavengers (antioxidants) in food samples is described. Dietary antioxidant capacity measurements were achieved using the radical compound 2,2-diphenyl-1-picrylhydrazyl (DPPH·) as an amperometric redox indicator, with a pencil lead working electrode, in conjunction with a Pt counter-electrode and Ag/AgCl reference electrode, moving sequentially through the 24 vials of a standard 6 × 4 microtiter plate. Programmed analyses were performed successfully with synthetic antioxidants of known concentrations and with tea infusions, fruit juices, and vegetable extracts. The novel methodology is simple and convenient as, unlike common DPPH· antioxidant electroanalysis, it avoids the time-consuming cleaning of electrochemical cells between measurements. Microtiter plate-based robotic electrochemical antioxidant assaying is thus a good option for handling large sample collections and may be applicable in the production of food and herbal remedies.

A novel automated electrochemical ascorbic acid assay in the 24-well microtiter plate format.

Automatic ascorbic acid (AA) voltammetry was established in 24-well microtiter plates. The assay used a movable assembly of a pencil rod working, an Ag/AgCl reference and a Pt counter electrode with differential pulse voltammetry (DPV) for concentration-dependent current generation. A computer was in command of electrode (z) and microtiter plate (x, y) positioning and timed potentiostat operation. Synchronization of these actions supported sequential approach of all wells and subsequent execution of electrode treatment procedures or AA voltammetry at defined intervals in a measuring cycle. DPV in well solutions offered a linear current/concentration range between 0.1 and 8.0 mM, a sensitivity of about 1 µA mM(-1) AA, and a detection limit of 50 µM. When used with a calibration curve or standard addition, automated voltammetry of samples with added known amounts of AA demonstrated good recovery rates. Also, the assay achieved the accurate determination of the AA content of vitamin C tablets, a fruit juice and an herbal tea extract. Robotic AA voltammetry has the advantage of conveniently handling multiple samples in a single measuring run without the continuous attention of laboratory personnel. It is a good option when the goal is cost-effective AA screening of sample libraries and has potential for applications in health care and the food processing, cosmetic and pharmaceutical industries.