Optional unit for the GCMS-NX Series
SMCI stands for Solvent Mediated Chemical Ionization, a soft ionization method for GCMS. The headspace reagent gas from the sample bottle is introduced into the GCMS ionization unit to be ionized, which then causes chemical ionization (CI) of the target molecule via protonation*. Previous CI methods have required the use of flammable reagent gas cylinders, but SMCI can be carried out with a general organic solvent such as methanol or acetonitrile, together with nitrogen or argon gas. This results in greater safety and lower running costs.
- A safe and simple ionization method
Cylinders of flammable gas such as methane or isobutane are not used in this method, so it is easy and safe to install the equipment.
- Can handle a large number of compounds
Compared to the CI substitution method, the SMCI method with methanol is less dependent on the compound, but can produce the same results. Because the SMCI method results in less fragmentation, it is very effective for verifying molecular weights for qualitative analysis.
- Provides unique structural information to identify compounds
SMCI can provide structural information in addition to molecular weights. For example, using acetonitrile as the reagent gas with a TQ, it is possible to identify the position of double bonds in unsaturated fatty acids.
- Low running costs
The reagent gas is less expensive than for other CI methods, so running costs can be reduced by over 80%.
Principles of SMCI
There are many cases where the ionization energy for EI is too high to verify molecular weights, but a soft ionization method such as SMCI is effective. For example, SMCI can be used to verify the molecular weights of bis(2-ethylhexyl)phthalate, whereas EI cannot. SMCI can obtain the same results as previously-existing CI methods, but is less dependent on the compound.
The functionality of unsaturated fatty acids varies greatly depending on branching and the position of double bonds. Using SMCI with acetonitrile as the reagent gas, particular reaction ions selectively attach to the double bonds. If a product ion scan is then carried out, fragmentation will occur at these attachment sites, so the positions of double bonds in the original fatty acid can be identified.
■Compatible GCMS models
GCMS-TQ8050 NX, GCMS-TQ8040 NX, GCMS-QP2020 NX
HPLC grade methanol or acetonitrile Nitrogen or argon gas (99.99+% purity)