A Low-Cost Precision Colorimeter M. Jalfar Quaid-i-Azam University, Islamabad, Pakistan Qazi Zahid University Grants Commission. Islamabad, Pakistan Modern technology has introduced numerous efficient, versatile, and long-lived components capable of furnishing electroanalytical information with a high degree of reliability and accuracy. The use of these components in the design and fabrication of rather inexnensive instruments has been known over the past two decades ( I ) . Several publications are available em~hasizineureencv .. . for ~romotina ' lab teaching through the k e uf such equipn>ent't2-6,. In kcevine. with the fact that colorimetricestima~ioniplay an impoitait role in quantitative analysis as well as in studies leadinc to mechanistic explorations in colored solution media of iaried nature, an attempt has been made in the present work to bring out a simple, but reliable, colorimeter fabricated from low-cost, locally available compoenents. Construction Aspects The schematic of the colorimeter and the relevant circuit details are eiven in Fieure 1. The basic nrincinle of the colorimeter ys the absorption of radiation of a characteristic wavelength, selectable through appropriate filters within the 400-750-nm range, by a colored solution of variable concentration. The absorption of radiation is detected and estimated with the help of a photoelectric selenium cell energized with the emergent radiation from the quartz absorption cell. The intensity of radiation is manually controlled in 11steps through a multiswitch, thus allowing ahsorption measurements of a wide range of analyte concentrations. T h e display in t h e present version utilizes a microampmeter, fed by the photoelectric output as a function of variable beam intensity a t a given wavelength. The filters for use with the colorimeter are adapted from a whole lot of flame photometric filters no longer in use. The radiation source is an ordinary filament bulb energized by 12-V ac
E"! ? 3 W
Lens Flter Cell ff;gcm ~ l d r dHOI~R
Shutter Pbtocell
Figure 1. The biocklclrcuit diagram of the colorimeter
Llsl and Specillcationsof Parts
Pan
Specificatlonlmske
Transformer
General-purpose,stepdown. 220 V ac. 50 HL input. 12 V BC. 1 A output. locally made. Attenuator Paper wound enamelled wire coil. 15 0 per step. locally made. Multiple switch lzatep, Philips, rotary type. Microampmeter 0-50 @A FSD. coil resistance 1500 0. accuracy i f % , Leitgeb AG Co.. Taiwan. Photo~ell Selenium type. 250 mV dc output. Elektromedycma. Poland. Lamp Filament type. 12 V. 3 W. locally made. Lens Convex. 9 cm 1. Cannon. Black metallic strip. 1.5 X 4.5 cm, rotation 0-90-180°. Shutter localiy made. Absorption cell Quartz ceil. 1 X 4.5 cm, BOSC~. Cell housing Perspex, locally made. supply obtained from 220-V acmains line using an appropriate step-down transformer. The instrument affords a direct read-out of the ahsorhance and transmittance values. The orieinal printed scale of the microampmeter is replaced by an"absorbance1transmittance scale. The zero rest noint of the meter pointer is inscribed on the scale as O%, Ghile the full-scale deflection, corresponding to the transmittance of pure water, adjustable with the shutter, is taken as 100% T. The scale is then linearly divided from 0 to 100%. The absorption, A, values are then scaled through the use of the relationship: A = 2 log T(%). The table provides the list and specifications of
u Awere Meter
Figure 2. K2Cr207absorption in aqueous phase at various cancentratlonf. Volume 65 Number 12 December 1988
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parts used in the fahrication of the colorimeter. T h e performance of the colorimeter may he judged from the absorbance vs. concentration relationshiw shown in Fieure 2. The instrument has been extensively used invanalytical situations of varied nature. Followine- is t h e outline of experiments done on the instrument: ( 1 ) Determination of ammonia using an alkaline solution of tetraio-
domercurate(I1): the latter reacts with ammonia to produce a deeo brown solution. 1 2 , 1)etermination oi iron with orthophenanthnhe. (.(, Dewrminatiun or nickel as dimethyl glwxime complex in alkaline medium. (4) Kinetic study of the reaction between iodine and persulfate (5) Evaluation of acid-base ionization constants for indicators. ( 6 ) Simultaneous estimation of manganese and chromium when converted into ~ermanaanate and dichromate through oxida. tion. (7) Kinetic study of the reaction between bromine and metbanoic acid.
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Journal of Chemical Education
T h e procedural details on these experiments may he found in any text on analytical chemistry. T h e overall accuracv of the instrument lies within fO.O1 and *O.5 of absorption and transmittance scale values. T h e cost of the finished product i i ahcrut 1JS $50. Acknowledgment . We are grateful to University Grants Commission. Islamabad. Pakistan, for the financial helw that rewltrd in the fahrication of the colorimeter unde; the low-cost project scheme. Llterature Clted 1. WsddingLon.0. JInfemaf. Nelusl. Chem. Edue 1982.17.6. 2. WaddingLon, 0. J., Ed. A Sourrebook of Chemieoi Experiments: UNESCOflUPAC: 1976: Vol. 1. 3. Bayyuk. S. I.;Freemontlo, M.; Watt0n.E. C. A Sourcebook ofChemico1 Exp~rimenD; UNESCO: 1976; Vol.2. 4. Padilla, J.; Baseunar, A. Monvoi d%priimsntos Quirnicos; UNESCO: 1978: Val. 3. 5. Clou, 0.: Msurin, M. Monuold'Erpwiences de Chimis; UNESCO: 1980; Vol.5. 6. Waddingtan. D. J. "Chemical Education in Developing Countries": COSTED Report, 1979; p 59.
