Colorimetry

Colorimetry : 

Colorimetry

Wheel of Colour : 

Wheel of Colour

Basic Principles of Colorimetry : 

Basic Principles of Colorimetry Visible light has a range of wavelength of 380 – 780nm. Coloured filters (Monochromator) are used to remove all but a narrow band (specific wavelength) of visible radiation. It is then passed (transmitted) through the sample contained within a little glass box (cuvette), and the absorbance or colour change measured.

Diagram of Colorimeter : 

Diagram of Colorimeter This filters out all wavelengths of light apart from the one needed Natural Light

Basic Principles of Colorimetry (2) : 

Basic Principles of Colorimetry (2) The colorimeter is calibrated by a reference sample (usually distilled water), so that the percentage of radiation absorbed is measured. The light leaving the actual sample is always less than the light with actually entered the compound.

Advance Colorimetry : 

Advance Colorimetry A colorimeter measures the intensity of light shining through a coloured solution compared to the intensity of light passing into the solution. A detector measures the transmittance (T) (% of light passing through) of the solution. This is mathematically converted to absorbance (A = -log10T). The absorbance is directly proportional to the concentration (Beer-Lambert law). Further information on Beer Lambert Law available:- http://en.wikipedia.org/wiki/Beer_Lambert_law http://www.thermo.com/com/cda/resources/resources_detail/1,2166,13310,00.html

Preparing Sample for Analysis - Solids : 

Preparing Sample for Analysis - Solids Weigh 2 portions of the solid accurately, to an accuracy of ±0.1 mg, directly into two 125 cm3 conical flasks. You may need to pipette 4cm3 of 3 mol dm-3 Sulphuric Acid (H2SO4). Then make up to the calibration mark with distilled water. Mix well by inverting and shaking the stoppered flask.

Preparing Sample for Analysis – Solids (2) : 

Preparing Sample for Analysis – Solids (2) Pipet 10 cm3 of this solution into a 50 cm3 volumetric flask Then in this exact order add 1 cm3 of 10% hydroxylamine hydrochloride solution, 10 mL of 0.1% bipyridyl solution and 4 cm3 of 10% sodium acetate solution. Be sure to mix well after the addition of each reagent, by gently shaking or swirling, but not inverting, the flask.

Preparing Sample for Analysis – Solids (3) : 

Preparing Sample for Analysis – Solids (3) After all reagents have been added fill the flask to the mark with distilled water and mix well by inverting and shaking. This solution will be called the Second Unknown Dilution (SUD). Determine the absorbance of the this solution using the previous blank solution as the reference and the wavelength of maximum absorbance determined earlier. Measure the absorbance at least three times. Empty the cuvette and refill it with another portion of solution and again determine the absorbance.

Calibrating Colorimeter : 

Calibrating Colorimeter A calibration curve is obtained by placing samples of known concentrations in the colorimeter and measuring the absorption and/or transmittance. The calibration curve can then be used to find the concentration of the test sample.

Calibration Curve : 

Calibration Curve

Uses of Colorimetry (1) : 

Uses of Colorimetry (1) Haemoglobin Content of Blood Sugar/Glucose in Blood Cholesterol Lead in Urine/Faeces Air Monitoring Tests - Chromium – Lead Anti-Icing Additive in Aviation Fuels

Uses of Colorimetry (2) : 

Uses of Colorimetry (2) Chlorophyll in samples

What you are expected to know : 

What you are expected to know The scientific principles of colorimetry Describe two applications in which colorimetry will be used, one using simple colour change and the other using light absorption Be able to prepare a sample for colorimetric analysis Follow a standard procedure to calibrate and use a colorimeter to determine the concentration of a solution Produce a comprehensive risk assessment for the procedure Process and interpret results to determine the concentration of a solution