322
M. Vincenti . A. Irico
ing ions can be accelerated and possibly fragmented by collisional activation with an
inert gas or solvent molecules, in a region of relatively high pressure (about 1 torr).
This fragmentation, intentionally induced in ESI spectra, is often useful for the
structural characterization of analytes. Without this "in-source" collision induced
dissociation (Cm), ESI spectra generally exhibit only the protonated or deprotonated
molecular ions of solution components, as well as cationized and polymeric adduct
ions.
Alternatively, fragmentation can be induced by cm in a tandem mass spectrometry (MS-MS) experiment. The experiment most frequently encountered in marine
toxin LC-ESI -MS-MS analysis consists of selecting the toxin molecular ion by the first
mass analyser, then forcing it into a collision cell where it experiences multiple collisions with an inert gas. These collisions deposit an excess of internal energy into the
impinging ions, which eventually fragment. The daughter ions are determined by the
second mass analyser, operating eitlIer under continuous scanning (MS-MS or daughter
ion spectra) or under mass-hopping among tlIe fragment ion oflarger abundance. The
latter operating mode, called selected reaction monitoring (SRM) represents the MSMS equivalent of selected ion monitoring (SIM) in single-stage MS.
As mentioned before, ESI operates witlI constant flow of an electrolyte solution. This
can either be a suitable matrix, in which a solution of the pure toxin sample is flowinjected (FIA), the liquid flow of a capillary electrophoresys (CE) device, or, most frequently, the eluate of a liquid chromatograph (LC). In the latter case, some restrictions
are imposed on the eluant composition by ESI, which does not tolerate some buffer
components and high concentrations of ionic species. In general, the LC separation
should be programmed keeping in mind such restrictions. The efficiency of ESI is
maximized at low LC solvent flow rates. When the flow rate is increased, the increased
sample throughput does not determine an increased ion signal, but this remains approximately constant. Consequently, the sensitivity remains constant in terms of concentration, but decreases in terms of mass consumption, and the instrument contamination from solvent impurities increases considerably, thus affecting the long-term
stability of tlIe instrument. Therefore, LC-ESI-MS is often performed with small-bore
or microbore columns. Alternatively, most parts of tlIe eluate are split and eitlIer sent
to an UV detector or thrown away.
17.2
Dinophysistoxins and Related Toxins
One of tlIe applications within the field of marine toxins, in which LC-ESI -MS has been
most extensively applied is the detection of diarrhetic shellfish poisoning toxins.
Diarrhetic shellfish poisoning (DSP) is a serious gastroenteritis, resulting from eating contaminated shellfish. Besides acute toxic effects, these toxins are also reported
to be potent carcinogens. DSP toxins accumulate in shellfish, such as mussels and clams,
but are produced by toxic strains of certain dinoflagellates (phytoplankton). Upon
ingestion of these dinoflagellates shellfish becomes toxic. After the first identification
in Japan, the cases of DSP have markedly increased in many parts of the world, especially in Japan and Europe, posing a serious problem to human healtlI (Ragelis 1984;
Yasumoto et al. 1989; Yasumoto 1990; Hall and Strichartz 1990; Falconer 1993; Smayda
and Shimizu 1993).
M. Vincenti . A. Irico
ing ions can be accelerated and possibly fragmented by collisional activation with an
inert gas or solvent molecules, in a region of relatively high pressure (about 1 torr).
This fragmentation, intentionally induced in ESI spectra, is often useful for the
structural characterization of analytes. Without this "in-source" collision induced
dissociation (Cm), ESI spectra generally exhibit only the protonated or deprotonated
molecular ions of solution components, as well as cationized and polymeric adduct
ions.
Alternatively, fragmentation can be induced by cm in a tandem mass spectrometry (MS-MS) experiment. The experiment most frequently encountered in marine
toxin LC-ESI -MS-MS analysis consists of selecting the toxin molecular ion by the first
mass analyser, then forcing it into a collision cell where it experiences multiple collisions with an inert gas. These collisions deposit an excess of internal energy into the
impinging ions, which eventually fragment. The daughter ions are determined by the
second mass analyser, operating eitlIer under continuous scanning (MS-MS or daughter
ion spectra) or under mass-hopping among tlIe fragment ion oflarger abundance. The
latter operating mode, called selected reaction monitoring (SRM) represents the MSMS equivalent of selected ion monitoring (SIM) in single-stage MS.
As mentioned before, ESI operates witlI constant flow of an electrolyte solution. This
can either be a suitable matrix, in which a solution of the pure toxin sample is flowinjected (FIA), the liquid flow of a capillary electrophoresys (CE) device, or, most frequently, the eluate of a liquid chromatograph (LC). In the latter case, some restrictions
are imposed on the eluant composition by ESI, which does not tolerate some buffer
components and high concentrations of ionic species. In general, the LC separation
should be programmed keeping in mind such restrictions. The efficiency of ESI is
maximized at low LC solvent flow rates. When the flow rate is increased, the increased
sample throughput does not determine an increased ion signal, but this remains approximately constant. Consequently, the sensitivity remains constant in terms of concentration, but decreases in terms of mass consumption, and the instrument contamination from solvent impurities increases considerably, thus affecting the long-term
stability of tlIe instrument. Therefore, LC-ESI-MS is often performed with small-bore
or microbore columns. Alternatively, most parts of tlIe eluate are split and eitlIer sent
to an UV detector or thrown away.
17.2
Dinophysistoxins and Related Toxins
One of tlIe applications within the field of marine toxins, in which LC-ESI -MS has been
most extensively applied is the detection of diarrhetic shellfish poisoning toxins.
Diarrhetic shellfish poisoning (DSP) is a serious gastroenteritis, resulting from eating contaminated shellfish. Besides acute toxic effects, these toxins are also reported
to be potent carcinogens. DSP toxins accumulate in shellfish, such as mussels and clams,
but are produced by toxic strains of certain dinoflagellates (phytoplankton). Upon
ingestion of these dinoflagellates shellfish becomes toxic. After the first identification
in Japan, the cases of DSP have markedly increased in many parts of the world, especially in Japan and Europe, posing a serious problem to human healtlI (Ragelis 1984;
Yasumoto et al. 1989; Yasumoto 1990; Hall and Strichartz 1990; Falconer 1993; Smayda
and Shimizu 1993).