IRMS

Question 1

Continuous Flow IRMS (CF-IRMS)

Answer 1

IRMS is connected to a range of automated sample preparation devices (Bulk Stable Isotope Analysis, BSIA or Compound Specific Isotope Analysis, CSIA); Continuous flow allows for online sample preparation, use of small sample size, and interfacing with other techniques.; sample must be oxidized, reduced and separated; Special “traps” are used to remove unwanted species

Question 2

Introduction techniques of IRMS

Answer 2

Continuous Flow IRMS (CF-IRMS) and Dual Inlet IRMS (DI-IRMS)

Question 2

How does the IRMS spectrometer work?

Answer 2

-gaseous sample enter the ionisation chamber of the IRMS
-Helium is used as a carrier gas to carry the analyte gas into the ion source of the IRMS
-sample collides with a focused electron beam and produce positive ions
-The produced ions are accelerated out of the ionisation chamber to a flight tube surrounded by two poles of an electromagnet.
-Ions are separated according to their mass-to-charge ratio (m/z).
-Ions are collected by a collector array that consists of Faraday cups (FC).

Question 3

IRMS vs MS

Answer 3

IRMS instruments are different from conventional Mass spectrometers, in that they do not scan a mass range for characteristic fragment ions.

IRMS can only detect one chemical species at a time

Resolution is more important in MS while accuracy and sensitivity are more important in IRMS

Sample prep. in IRMS is more extensive than typical MS.

Question 4

Considerations about isotopic fractionation

Answer 4

-Hydrogen is extremely sensitive to fractionation effects
-Oxygen fractionation is largely due to the oxidation of the sample. The temperature is a deciding factor as to whether or not the sample is completely oxidised. - can occur within a sample vial
-Nitrogen fractionations in nature are mainly due to kinetic effects

Question 5

Advantage of IRMS

Answer 5

by profiling the isotopes in a compound using IRMS, we can identify the source of the compound and/or compare two samples of the same identity

Question 6

Isotope Ratios

Answer 6

each element has a dominant light isotopes and one or two heavy isotopes with a natural abundance of a few percent or less.

Question 7

How many elements don’t exist as a mixture of isotopes?

Answer 7

12

Question 8

IRMS

Answer 8

isotope ratio mass spectroscopy; provides information about the geographic, and chemical origins of substance from the relative isotopic abundances of the elements which comprise the material

Question 9

When are 2 compounds isotopically distingushable?

Answer 9

if they are derived from different sources or do not share the same orig

Question 10

Limitations of Current Analytical Techniques

Answer 10

although 2 substances are chemically indistinguishable, they may not be the same (e.g. come from different sources or be of different origins); results in a failure to positively link or exclude a suspect with a scene of a sample

Question 11

Isotopic fractionation

Answer 11

refers to any process that changed the relative abundances of stable isotopes of an element; results in the creation of specific isotope ratio values that are characteristic of the origin, purity, and manufacturing processes of the products.

Question 12

Two effects that lead to isotopic fractionation

Answer 12

kinetic isotope effect and thermodynamic isotope effect

Question 13

Kinetic isotope effect

Answer 13

produced by differences in reaction rates; when a compound undergoes a chemical reaction, a change in the isotope abundance occurs and lead to isotopes fractionation as there will be differences in the cleavage rates of the bonds (2 light or heavy isotopes have very different bond energies than 1 light and 1 heavy)

Question 14

Thermodynamic isotope effect

Answer 14

relates to the energy state of a system; free energy change that occurs when one atom in a compound is replaced by its isotope

Question 15

identifying the synthesis route of 3,4-methylenedioxymethampetamine

Answer 15

analyses the C13 h2 and N15 isotope analysis by IRIS.
if by Al/Hg then the N will have ratios

Question 16

id source of y-butyrolactone (GBL)

Answer 16

-butyrolactone (GBL) is used to produce GHB (γ-hydroxybutyric acid)
GBL is produced via the dehydrogenation of 1,4-butanediol (1,4-BD), dimethyl maleate or maleic anhydride.
1,4-butanediol is prepared from acetylene with formaldehyde
GBL can also be prepared via the oxidation of tetrahydrofurane.
The production of GBL involves purification by distillation.

Question 17

Bulk Stable Isotope Analysis

Answer 17

Uses automated elemental analyser for the conversion of the sample of interest into simple gases.
The sample is weighed into silver or tin capsules, then loaded into an auto sampler.
The sample is treated with an oxidizing agent at high temperature to form NOx, CO2, O2.
The Nox are then reduced to N2 and separated using GC.
H2O and CO2 are converted to H2 and CO gases. The gases are separated using GC.
The isotopic values obtained from the IRMS analysis represent the isotopic composition of all the components in the sample.

Question 18

Compound specific isotope analysis (CSIA)

Answer 18

The isotopic compositions of individual compounds within the sample are measured.
The sample is injected onto the GC to separate the different organic constituents.
The separated compounds are oxidised/reduced.
Like BSIA, simple gases are produced for analysis by the IRMS instrument.

Question 19

Dual Inlet

Answer 19

The samples are converted into simple gases for analysis off line
DI-IRMS is time consuming, requires large samples.
Contamination & isotopic fractionation may occur.
The sample gas is admitted into the IRMS via a gas reservoir called “the bellow”.
The reference gas is also admitted via a separate bellow reservoir.
Comparisons are made between the isotopic compositions of the gas sample of interest relative to that of a standard or reference gas.