Do Now Hand in any PAG books that have not already been handed in These will be given back to you on Friday Have your revision Q booklet out so I can flick through and see how you’ve got on Planners out – I have moved the test to next Friday (4th November) due to needing to do the chromatography PAG next Wednesday

Colourimetry and Biosensors Learning objective To know about colourimetry Success Criteria Explain quantitative methods to determine concentrations of a chemical in solution To include colourimetry and biosensors

What is colourimetry? Colorimetric techniques are used to identify coloured solutions and measure their concentration It can be used to determine the concentration of certain substances in aqueous solutions Q: Where do you think this technique would come in useful in a practical that you have done?

How does colourimetry work? Colourimetry relies on coloured solutions absorbing light of a particular wavelength. Different concentrated solutions will have a different colour intensity Solutions that are more concentrated will have a greater colour intensity It looks at how much light is absorbed, compared to that of a ‘blank’ The sample is place in a sample tube called a cuvette and placed in a colourimeter

36% How does it work? Bulb Colorimeter Filter Cuvette with sample Display Cuvette with sample Photocell

How does colourimetry work? We can either measure transmission of light, or absorbance of light A reference sample is used so that the samples to be tested can be compared to the reference The filter is used so only a narrow band of visible light is absorbed or transmitted by the sample If a substance is colourless, colourimetry can still be used if the substances reacts with a dye

How does transmission / absorbance tell us concentration? Calibration curves are created by measuring the absorbance or transmission of a number of solutions of known concentration A graph is then drawn You then test an unknown sample. By taking it’s absorbance or transmission, the concentration of the sample can be found

Or it may be a straight line The curve may actually be a curve % Absorbance Concentration

Or it may be a straight line % Absorbance Concentration

% Absorbance Concentration Take samples % absorbance. Draw across to curve. % Absorbance Draw down and read off concentration Concentration

TASK: Exam questions from Sarah. And link this to sugar and Benedict’s reagent

Biosensors e.g. enzymes, antibodies Biosensors use biological components to determine the presence, or concentration, of specific molecules e.g. glucose STRETCH: Why would you want to be able to test for the presence of glucose? (HINT: Think medical application) Pregnancy tests are an example of a commonly used biosensor This tests for the presence of human chorionic gonadotrophin hormone (hCG) This hormone is produced by the fertilised egg, and is used as marker to indicate pregnancy It can be detected in the urine 10 days after fertilisation. Traditionally would use dip sticks to determine if someone had diabetes. Biosensors can now be used to measure the sugar content in blood, to see if they’re controlling their blood glucose concentration

How a pregnancy test works The biological component that acts as the detector is immobilised antibodies that are on a stick These antibodies are attached to a dye If the hormone is present in urine, it will pass up the stick, and bind to the complementary antibodies This makes the dye become visible There are two lines present on a pregnancy test The first shows pregnancy The second acts as a control, to show that the test is working If you have two coloured lines = positive result

TASK: Pregnancy Test PPQ

Homework Revision for test that will now be next Friday (3rd November) Review GCSE work on Enzymes, as we will be starting this topic on Friday