A multichannel photometer based on an array of light emitting diodes for use in multivariate calibration

The development of a multichannel photometer based on an array of eight light emitting diodes (LED) as light sources is described. Optical fibre bundles were employed to guide the light radiation of the LED to the measuring cell and from the cell to the photodiode detector. The instrument was controlled by a microcomputer and was designed to perform absorbance measurements in a single wavelength continuously as well as in all wavelengths (470, 500, 562, 590, 612, 636 and 654 nm) sequentially, allowing its application in multivariate analysis methods. The photometer presented a drift lower than 2 (mu)V h^-1, allowing absorbance measurements with a precision better than 0.003 units. The instrument was applied for the simultaneous determination of Zn(II) and Cu(II) in pharmaceutical and metallic alloy samples, whose pH adjustment followed by the addition of xylenol orange complexing agent were accomplished by employing a monosegmented flow system. Solutions containing both metal ions in the concentration range from 1.0 to 4.0 mg L^-1 were employed to constructed the calibration model based on multiple linear regression (MLR), providing root mean square errors of prediction of 0.06 and 0.12 mg L^-1 for Zn(II) and Cu(II), respectively. The results obtained by employing the photometer were compared with those obtained by flame atomic absorption spectrometry, showing no significant differences at the 95 % confidence level.