We have developed a simple analog-to-digital converter (ADC) by using free software such as computer-aided design (CAD) software for an electronic circuit, a filter circuit simulator, an integrated-developing environment (IDE) for programming a controller, and that for a PC to acquire and display the data. The ADC can record a temporal signal produced by chromatography and flow-injection analysis. It has two voltage measurement ranges: +/- 2.048 V and +/- 1.024 V, respectively, with 14-bit resolution and a four samples s(-1) sampling rate. The voltage resolution is 0.25 mV and 0.125 mV per one ADC reading for +/- 2.048 V and +/- 1.024 V, respectively. Its dimensions were 100x70x30 mm, and mass was 110 g. We have evaluated its performance, including the linearity and the difference between the two devices. For +/- 1.024 V range, the calibration curve for one ADC and another was D = 7954V 5 and D = 7946V + 30, respectively, where D is an ADC reading, and V is an input voltage. For another range, it was D = 3972V - 3 and D = 3968V + 15, respectively. Their slopes and intercept agreed with each other, and had good linearity, R-2 > 0.9999. We have then successfully applied it to the sequential injection analysis (SIA) of chromium(VI) using diphenylcarbazide as a coloring reagent. The circuit diagram and programs developed in this paper are available on our website.
