Isotope dilution analysis

The isotope dilution analysis (IVA, engl. Isotope dilution ) is a technique for trace and ultra-trace analysis with stable isotopes . Until the early 1990s it was mainly used for geological questions, but later it was used as a routine application in analytical laboratories, particularly in the field of dioxin analysis .

method

Most elements have a natural isotope distribution that is approximately the same for natural occurrences of the elements all over the world. When analyzing a sample using IVA, an isotope standard with a non-natural but known isotope distribution is added. This changes the isotope distribution for the compound sought in the sample. After determining the ratio of the isotopes using a mass-selective detector , the concentration of the (native) compound in the sample can be calculated from the added amount of the isotope standard used as an internal standard. The concentration of the desired (native) compound can be calculated using the following formula:

${\displaystyle C_{probe}={\frac {C_{Standard}*m_{Standard}*M_{Probe}}{m_{Probe}*M_{Standard}}}\cdot {\frac {A_{Standard}-R_{M}*B_{Standard}}{R_{M}*B_{Probe}-A_{Probe}}}}$

requirements

• The element to be determined must have isotopes that are long enough
• a mass-selective detector must be used
• the added given standard must match the sample in chemical equilibrium are

Advantages of this technique

• After adding the standard, a loss of substance during sample preparation does not falsify the analysis result
• a single point calibration is often possible
• the consumption of materials is extremely low
• IVA is an absolute method
• it is highly precise

disadvantage

• not every element has stable (long-lived) isotopes
• Mass-selective detectors are usually expensive
• isotope-labeled standard compounds are also expensive or complex to synthesize
• reaching chemical equilibrium is not possible with every sample matrix

Typical isotopes used

• deuterium
• ¹³ C
• ³⁷ Cl

literature

• Mike Sargent, Rita Harte, Chris Harrington: Guidelines for Achieving High Accuracy in Isotope Dilution Mass Spectrometry (IDMS) . Royal Society of Chemistry, 2002, ISBN 978-0-85404-418-4 , p. 58.
• J. Ignacio Garcia-Alonso, Pablo Rodriguez-Gonzalez: Isotope Dilution Mass Spectrometry . Royal Society of Chemistry, 2013, ISBN 978-1-84973-333-5 , p. 453.