preprocessed by toluene-water partitioning in order to remove
unwanted polar constituents such as sugars. Following development
of an appropriate reversed-phase HPLC separation system,
extract constituents eluted as individual HPLC peaks were trapped
on solid-phase extraction cartridges using a Prospekt-2 SPE device
(Spark Holland), which handles two trays with 96 cartridges each
and thus enables trapping of a large number of individual HPLC
peaks in automation. The SPE cartridges were subsequently dried,
and the analytes were eluted into the CapNMR probe for NMR
analysis.
Since total volume of the CapNMR probe is 5 íL, with an
additional volume needed to fill up feed lines, analyte elution
profiles from the SPE cartridges are crucial for success of the
experiment. Moreover, solvent volumes used for cartridge elution
and analyte transfer must be calibrated for optimal sample
centering in the probe. Since thapsigargin (1, Table 1) was
expected to be a major constituent of the extract of T. garganica
fruits,41,43 determination of SPE elution parameters was performed
with a purified sample of this compound. Using the same
procedure as for the HPLC-SPE trapping of extract constituents
(see below), 10 1 mm i.d. Hysphere GP SPE cartridges were
loaded with 1 by injecting 48 íg into the HPLC column. The dried
cartridge containing 48 íg of 1 (assuming that no loss occurred
during HPLC separation and SPE trapping) was placed in a hand
clamp, connected to the probe, and eluted with the dead volume
of the cartridge plus a total of 40 íL of methanol-d4 in 1-íL
intervals. 1H NMR spectra were recorded for each volume
increment. The obtained signal-to-noise ratios plotted as a function
of the solvent volume are shown in Figure 2. It can be seen that
the maximum concentration of the desorbed compound reaches
the active probe region after injecting 12 íL of the solvent
(following the 10 íL of the solvent used to fill up the dead volume
of the cartridge and connecting capillaries). The total elution
volume of 1 from the SPE cartridge was roughly 10 íL. Figure 2
also shows the corresponding profile after direct injection of an
preprocessed by toluene-water partitioning in order to remove
unwanted polar constituents such as sugars. Following development
of an appropriate reversed-phase HPLC separation system,
extract constituents eluted as individual HPLC peaks were trapped
on solid-phase extraction cartridges using a Prospekt-2 SPE device
(Spark Holland), which handles two trays with 96 cartridges each
and thus enables trapping of a large number of individual HPLC
peaks in automation. The SPE cartridges were subsequently dried,
and the analytes were eluted into the CapNMR probe for NMR
analysis.
Since total volume of the CapNMR probe is 5 íL, with an
additional volume needed to fill up feed lines, analyte elution
profiles from the SPE cartridges are crucial for success of the
experiment. Moreover, solvent volumes used for cartridge elution
and analyte transfer must be calibrated for optimal sample
centering in the probe. Since thapsigargin (1, Table 1) was
expected to be a major constituent of the extract of T. garganica
fruits,41,43 determination of SPE elution parameters was performed
with a purified sample of this compound. Using the same
procedure as for the HPLC-SPE trapping of extract constituents
(see below), 10 1 mm i.d. Hysphere GP SPE cartridges were
loaded with 1 by injecting 48 íg into the HPLC column. The dried
cartridge containing 48 íg of 1 (assuming that no loss occurred
during HPLC separation and SPE trapping) was placed in a hand
clamp, connected to the probe, and eluted with the dead volume
of the cartridge plus a total of 40 íL of methanol-d4 in 1-íL
intervals. 1H NMR spectra were recorded for each volume
increment. The obtained signal-to-noise ratios plotted as a function
of the solvent volume are shown in Figure 2. It can be seen that
the maximum concentration of the desorbed compound reaches
the active probe region after injecting 12 íL of the solvent
(following the 10 íL of the solvent used to fill up the dead volume
of the cartridge and connecting capillaries). The total elution
volume of 1 from the SPE cartridge was roughly 10 íL. Figure 2
also shows the corresponding profile after direct injection of an
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