ABSTRACT
A dual infrared frequency comb spectrometer with heterodyne detection has been used to perform time-resolved electrochemical attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). The measurement of the potential dependent desorption of a monolayer of a pyridine derivative (4-dimethylaminopyridine, DMAP) with time resolution as high as 4 µs was achieved without the use of step-scan interferometry. An analysis of the detection limit of the method as a function of both time resolution and measurement coadditions is provided and compared to step-scan experiments of an equivalent system. Dual frequency comb spectroscopy is shown to be highly amenable to time-resolved ATR-SEIRAS. Microsecond resolved spectra can be obtained with high spectral resolution and fractional monolayer detection limits in a total experimental duration that is 2 orders of magnitude less than the equivalent step-scan experiment.
ABSTRACT
An evaluation of several experimental aspects that can optimize electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) performance using a commercially available, specular reflection accessory is provided. A comparison of different silicon single-bounce internal reflection elements (IREs) is made with emphasis on different face-angled crystal (FAC) options. Selection of optimal angle of incidence for maximizing signal and minimizing noise is shown to require consideration of the optical throughput of the accessory, reflection losses at the crystal surfaces, and polarization effects. The benefits of wire-grid polarizers and antireflective (AR) coatings on the IREs is discussed. High signal-to-noise ratios can be achieved by omitting polarizers, using an AR-coated FAC with a larger face angle, and working at angles of incidence close to the maximum throughput angle of the accessory.
ABSTRACT
Food safety is a strategic topic entailing not only national public health aspects but also competitiveness in international trade. An important component of any food safety program is the control and monitoring of residues posed by certain substances involved in food production. In turn, a National Residue Control Plan (NRCP) relies on an appropriate laboratory network, not only to generate analytical results, but also more broadly to verify and co-validate the controls built along the food production chain. Therefore laboratories operating under a NRCP should work in close cooperation with inspection bodies, fostering the critical alignment of the whole system with the principles of risk analysis. Beyond producing technically valid results, these laboratories should arguably be able to assist in the prediction and establishment of targets for official control. In pursuit of analytical excellence, the Brazilian government has developed a strategic plan for Official Agricultural Laboratories. Inserted in a national agenda for agricultural risk analysis, the plan has succeeded in raising laboratory budget by approximately 200%, it has started a rigorous program for personnel capacity-building, it has initiated strategic cooperation with international reference centres, and finally, it has completely renewed instrumental resources and rapidly triggered a program aimed at full laboratory compliance with ISO/IEC 17025 requirements.