Measuring Sulfur Isotopes; Introduction; Procedure - Thermo Scientific EA IsoLink IRMS System Operating Manual

6
Using EA IsoLink IRMS System for CNSOH

Measuring Sulfur Isotopes

Measuring Sulfur Isotopes
This section provides the instructions for measuring sulfur isotopes.

Introduction

In comparison to isotope ratio measurements of nitrogen (
inorganic matter, the analysis of sulfur (
Analyzing biological sulfur makes experimental difficulties caused by the low abundance of sulfur in
organisms (for example 0.2 wt% [mg/mg] in plants), as well as by the fact that sulfur is present as a
mixture of organic and inorganic compounds.
Difficulties in using the Elemental Analyzer arise due to a large amount of carbon in the same samples,
which quickly exceeds the capacity of combustion reactors. This causes incomplete combustion.
Thermo Fisher Scientific has developed a technique for precise, accurate and fast sulfur measurement,
which puts it on a par with carbon and nitrogen in terms of ease of use and sample size.
Due to the high natural abundance of the heavier isotope
become necessary for all Delta IRMS before Delta
It is recommended to use a smaller resistor (1 * 10

Procedure

Sulfur measurements are performed using a specially equipped Elemental Analyzer. Combustion and
reduction are carried out in a single reactor filled with tungsten oxide (WO
reducing agent.
The technique used for sulfur determination is based on the quantitative Dynamic Flash Combustion
method. The samples - sometimes together with vanadium pentoxide (V
capsules and placed into the autosampler. Then they are continuously purged with helium to remove
any traces of water and nitrogen. When a sample is dropped into the reactor, the helium stream is
temporarily enriched with pure oxygen.
The sample and its container melt as the tin promotes a violent reaction flash combustion). Under
these favorable conditions, even thermally resistant substances are completely oxidized.
In the reactor, for example barium sulfate (BaSO
The following reactions can then take place. See Bailey, S.A. and Smith, J.W., 1972):
Bailey, S.A. and Smith, J.W. (1972): An improved method for the preparation of sulfur
Note
dioxide from barium sulfate BaSO
Although the process does not require oxygen (O
oxygen (O
(O ) pressure is low or a bad catalyst is selected or the reactor has too much ash, combustion will
2
proceed slowly.
108 EA IsoLink IRMS System for CNSOH Operating Manual
) is injected and vanadium pentoxide (V
2
15
34
S) has always been more challenging.
34
plus
XP (since 2002).
10
Ω) on the cup for mass 66 (usually 3 * 10
) is thermally decomposed within a tin capsule.
4
→
BaSO 4 BaO + SO 2
→
BaSO 4 BaO + SO 3
1
→
SO 3 SO 2 + -- - O 2
2
) for isotope ratio studies. Anal. Chem. 44, 1542-1543.
4
), better combustion has been experienced when
2
O ) is added to the sample. If either the oxygen
2 5
13
N) and carbon ( C) in organic and
S, less amplification is required and may
) and copper (Cu) as
3
O ) - are wrapped in tin
2 5
1
+ -- - O 2
2
10
Ω).
Thermo Scientific