An experiment using time-based detection in flow injection analysis

Abstract

We present a laboratory experiment, suitable for im plementation in analytical chemistry courses at the under graduate level, that demonstrates the utility of time-based measurements with doublet peaks in flow injection analy sis. The measurements are taken with an instrument that incorporates a simple solid-state detector, which has as its source a light-emitting diode (LED) and as its detecting element a photodiode (PD). The system studied here is a simple acid-base titration. The experiment could be adapted to any number of chemical reactions that result in a product that absorbs light of the LED wavelength signif icantly.

Solid-state microprocessor-controlled detector for doublet peak measurements in flow-injection analysis

“…lA. A Rheodyne 6-port valve is mounted in the front side of the project box; small segments of flow tubing (0.9 mm i.d., Chemplast, Chemfluor ® Teflon ® spaghetti tubing) are used to connect the ports for injection loop, sample introduction, and waste output to unions mounted in the container wall. For purposes of testing the performance of the DPD, a simple, single-line manifold was cho sen, of the type used in our previous studies [7,8]; however, the DPD has additional ports for use in more complicated manifold configurations. The mixing component used is a 60-cm length of flow tubing, and is more tightly coiled than that used in the previous LED-based instrument, in order to better approximate a well-stirred tank [7].…”

“…For purposes of testing the performance of the DPD, a simple, single-line manifold was cho sen, of the type used in our previous studies [7,8]; however, the DPD has additional ports for use in more complicated manifold configurations. The mixing component used is a 60-cm length of flow tubing, and is more tightly coiled than that used in the previous LED-based instrument, in order to better approximate a well-stirred tank [7]. This component is connected to the detector module by a short segment of flow tubing.…”

“…The circuitry used to power the LEDs, per form current-to-voltage conversion of the signal from the PDs, and to offset the output voltage is modified slightly from that described previously [7]. It differs from the earlier circuit design in the voltage reference for the offset circuitry; com plete circuit diagrams may be obtained from the authors.…”

“…For the purposes of characteriz ing the performance of the DPD, the same sim ple acid-base reaction with indicator that was used in previous work is employed [7]. The car rier stream contained 1.0 X 10- …”

“…Previous work by our group involved the development of a sim ple instrument for doublet-peak measurements suitable for use in teaching laboratories [7]. This instrument had as its optical sources LEDs and as detectors PDs; the output from the PD was plotted on an integrator, and !J.t values were calculated based on the difference in recorded time of each peak [7]. In an effort to streamline the process, and to develop an instrument that is both more versatile and more easily portable than the first iteration, a microprocessor has been incorporated into the new instrument.…”