22.2. Mass spectrometry
A subsection of Chemistry, 9701, through 22. Analytical techniques
Listing 10 of 98 questions
Use Much of the preparation of evidence to solve crimes now relies on instrumental analysis. This question deals with some of the techniques used. Electrophoresis can be used to separate amino acids produced by hydrolysing proteins. The amino acids are placed in a buffered solution in an electric field. In a solution of given pH, what two factors affect the movement of a given amino acid? Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry are also used in the detection of certain molecules, particularly those containing hydrogen atoms. Explain how and why the NMR spectrum of propanal, CH3CH2CHO, would be different from that of propanone, CH3COCH3, which contains the same atoms. Explain how and why the mass spectrum of the two compounds in would be different. Examiner’s Use At one time, bromomethane, CH3Br, was widely used to control insect pests in agricultural crops and timber. It is now known to break down in the stratosphere and contribute to the destruction of the ozone layer. Samples can be screened for traces of bromomethane by subjecting them to mass spectrometry. Which peakwould show the presence of bromine in the compound? How could you tell by studying the M and M+2 peaks that the compound contained bromine rather than chlorine?
9701_s08_qp_4
THEORY
2008
Paper 4, Variant 0
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Chromatography is an important analytical technique in chemistry. There is a number of techniques under the general heading of chromatography. Paper and gas chromatography rely on partition to separate the components in a mixture, whereas thin-layer chromatography uses adsorption. Explain what is meant by partition and adsorption, in the context of chromatography. partition adsorption In paper or thin-layer chromatography, better separation may be achieved by running the chromatogram in one solvent, then turning the paper at right angles and running it in a second solvent. The chromatogram below was produced in this way. X solvent 2 sample applied here solvent 1 Ring the spot which was insoluble in solvent 1. Label as A and B the spots which were not resolved using solvent 1. The mass spectrum shown was obtained from a compound of formula CpHqX, where X represents a halogen atom. relative intensity 100 110 120 130 m / e R Deduce the identity of X, giving a reason. X is If the relative heights of the M and M+1 peaks are 9 and 0.3 respectively, calculate the value of p. Use this value and the m / e value of the molecular ion to calculate the value of q, and hence the molecular formula of the compound. Show your working. Suggest a formula for the ion responsible for the peak labelled R. In the fragmentation of alcohols which occurs in a mass spectrometer, small stable, neutral molecules are sometimes produced. Suggest the identity of two such molecules, each with an Mr less than 30.
9701_s11_qp_41
THEORY
2011
Paper 4, Variant 1
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DNA fi ngerprinting has become a very important technique for analysing samples from living or once-living organisms. After extraction and purifi cation, what is the fi rst step in analysing a sample of DNA? What can be done to increase the amount of DNA for analysis? During electrophoresis, it is observed that amino acids can move in different directions or not at all, whilst DNA fragments always move in the same direction. Explain these two observations. DNA fi ngerprinting can also be useful in archaeology. Which of the following would not be suitable for analysis by DNA fi ngerprinting? Put a cross in the appropriate box. a piece of leather from an Egyptian tomb a sample of skin from a mummifi ed body a fragment of ancient pottery a piece of wood from a Roman chariot X-ray crystallography can be used to help analyse the structure of macromolecules. What does this technique tell us about a particular macromolecule? Which element will show up most strongly in the X-ray crystallography of a biological polymer of general formula CvHwPxNyOz? Explain your answer. Explain what is meant by a partition coeffi cient. The partition coeffi cient of a particular pesticide between hexane and water is 6.0. A solution contains 0.0042 g of the pesticide dissolved in 25 cm3 of water. The solution is shaken with 25 cm3 of hexane. Calculate the mass of pesticide that will be dissolved in the hexane layer at equilibrium.
9701_s15_qp_41
THEORY
2015
Paper 4, Variant 1
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DNA fi ngerprinting has become a very important technique for analysing samples from living or once-living organisms. After extraction and purifi cation, what is the fi rst step in analysing a sample of DNA? What can be done to increase the amount of DNA for analysis? During electrophoresis, it is observed that amino acids can move in different directions or not at all, whilst DNA fragments always move in the same direction. Explain these two observations. DNA fi ngerprinting can also be useful in archaeology. Which of the following would not be suitable for analysis by DNA fi ngerprinting? Put a cross in the appropriate box. a piece of leather from an Egyptian tomb a sample of skin from a mummifi ed body a fragment of ancient pottery a piece of wood from a Roman chariot X-ray crystallography can be used to help analyse the structure of macromolecules. What does this technique tell us about a particular macromolecule? Which element will show up most strongly in the X-ray crystallography of a biological polymer of general formula CvHwPxNyOz? Explain your answer. Explain what is meant by a partition coeffi cient. The partition coeffi cient of a particular pesticide between hexane and water is 6.0. A solution contains 0.0042 g of the pesticide dissolved in 25 cm3 of water. The solution is shaken with 25 cm3 of hexane. Calculate the mass of pesticide that will be dissolved in the hexane layer at equilibrium.
9701_s15_qp_43
THEORY
2015
Paper 4, Variant 3
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Questions Discovered
98