Talanta 77 (2009) 1155–1159 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta A portable, inexpensive and microcontrolled spectrophotometer based on white LED as light source and CD media as diffraction grid Germano Veras a,b , Edvan Cirino Silva a,∗ , Wellington Silva Lyra a , Sófacles Figueredo Carreiro Soares a , Thiago Brito Guerreiro a , Sérgio Ricardo Bezerra Santos c a Universidade Federal da Paraíba, Departamento de Química, 58.051-970, João Pessoa, PB, Brazil b Universidade Estadual da Paraíba, Departamento de Química, 58.109-753, Campina Grande, PB, Brazil c Centro Federal de Educac ¸ão Tecnológica da Paraíba, 58.015-430, João Pessoa, PB, Brazil article info Article history: Received 17 April 2008 Received in revised form 18 August 2008 Accepted 19 August 2008 Available online 27 August 2008 Keywords: White LED CD media Programmable interrupt controller (PIC) microcontroller Visible spectrophotometer Food colorants Iron (II) abstract A portable, microcontrolled and low-cost spectrophotometer (MLCS) is proposed. The instrument com- bines the use of a compact disc (CD) media as diffraction grid and white light-emitting diode (LED) as radiation source. Moreover, it employs a phototransistor with spectral sensitivity in visible region as phototransductor, as well as a programmable interrupt controller (PIC) microcontroller as control unit. The proposed instrument was successfully applied to determination of food colorants (tartrazine, sun- set yellow, brilliant blue and allura red) in five synthetics samples and Fe 2+ in six samples of restorative oral solutions. For comparison purpose, two commercial spectrophotometers (HP and Micronal) were employed. The application of the t-paired test at the 95% confidence level revealed that there are not sig- nificant differences between the concentration values estimated by the three instruments. Furthermore, a good precision in the analyte concentrations was obtained by using MLCS. The overall relative standard deviation (R.S.D.) of each analyte was smaller than 1.0%. Therefore, the proposed instrument offers an eco- nomically viable alternative for spectrophotometric chemical analysis in small routine, research and/or teaching laboratories, because its components are inexpensive and of easy acquisition. Published by Elsevier B.V. 1. Introduction Since the seventies of the last century, when researchers as Flaschka et al. [1] developed photometers based on light-emitting diode (LED), LEDs have been applied on spectrophotometric instru- mentation as radiation sources having relatively small effective bandwidth [2,3]. However, the increasing demand for chemical analyses makes necessary to develop LED-based instruments to work in a wide range of wavelengths what requires multiple radiation sources. The approach increases cost and complexity of the optical and electronic system. For example, optical fibers are usually employed to direct the radiation towards the detector and a more elaborated hardware is necessary to control the LED drift. Nowadays, it is easy to acquire white LEDs that substitutes the complex optical system obtained when monochromatic LEDs are used as sources of several wavelengths in the visible region. ∗ Corresponding author. E-mail address: edvan@quimica.ufpb.br (E.C. Silva). Therefore, it is possible to develop simple spectrophotometers using a single white LED with an adequate disperser of the white light. For this purpose, the literature reports two works only that employ white LED as radiation source [4,5]. Shimazaki et al. [4] were pioneers in the development of a white LED- based spectrophotometer which was used in determination of Fe 2+ in river water by the o-phenantroline method. Li et al. [5] described a portable multi-function instrument using different spectrophotometric techniques. As application, the spectropho- tometric determination of Cr 6+ and Al 3+ was carried out using diphenylcarbazide and pyrocatechol violet as chelant and chro- mogenic reagents, respectively. Commercial spectrophotometric instrumentation commonly employs absorption or interference optical filters, prisms or diffrac- tion grids as radiation dispersers. In most of these instruments, the dispersive device is a diffraction grid, an optical component con- taining series of grooves traced on a glass plate or polished metal. In this context, a compact disc (CD) media could be used as diffraction grid due to its grooves. Despite the use of CD media as radiation dis- perser [6], no application in spectrophotometric instrumentation has been found. 0039-9140/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.talanta.2008.08.014