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Measuring the approximate mass of an ion without using a standard can he accomplished via the following variant of the peak-matching technique described in Problem 2014 The peak matching technique

Measuring the approximate mass of an ion without using a standard can he accomplished via the following variant of the peak-matching technique described in Problem 20-14. The peak-matching technique is used to alternately cause the pion and the (P + I) + ions to reach the detector. It is assumed that the difference in mass between p+ and (P + I) - is due to a single 13C replacing a 12C atom.

(a) If the accelerating voltage for (P + 1)+ is labeled V2, and that for P- is V1 derive a relationship that relates the ratio V2/V1, to the mass of P+.

(b) If V2/V1 = 0.987753, calculate the mass of the P+ ion.

Problem 20-14

In a magnetic sector (single-focusing) mass spectrometer, it might be reasonable under some circumstances to monitor one m/z value, to then monitor a second m/z. and to repeat this pattern in a cyclic manner. Rapidly switching between two accelerating voltages while keeping all other conditions constant is called peak matching

(a) Derive a general expression that relates the ratio of the accelerating voltages to the ratio of the corresponding m/z values.

(b) Use this equation to calculate m/z of an unknown peak if m/z of the ion used as a standard, CF3+, is 69.00 and the ratio of V unknown /V standard is 0.965035.

(c) Based on your answer in part (b), and the assumption that the unknown is an organic compound that has a mass of 143, draw some conclusions about your answer in part (b), and about the compound.

Jun 23 2020 View more View Less

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