chromatography + concentrations

Question 1

how can the concentration of a solution be measured quantitatively?

Answer 1

• use colourimetry: to measure absorbance / %transmission, interpolate a calibration curve from solutions of known concentration
• use biosensors: a bioreceptor detects the presence of a chemical, a transducer converts the response into a detectable electrical signal

Question 2

outline the principles and process of paper / thin layer chromatography

Answer 2

1. use capillary tube to spot solution onto pencil ‘start’ line (origin) 1cm above bottom of paper
2. place chromatography paper in solvent - origin should be above solvent level
3. allow solvent to run until it almost touches other end of the paper, molecules in the mixture will move different distances based on relative solubility in solvent / attraction to paper

Question 3

what are Rf values? how can they be calculated?

Answer 3

• ratios that allow comparison of how far molecules have moved in chromatograms
• Rf value = distance between origin and centre of pigment spot / distance between origin and solvent front