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By Chris Rattray and Jack Cochran
Optimizing an Agilent-Style Splitless Inlet
for Concurrent Solvent Recondensation–Large Volume
Splitless Injection (CSR-LVSI)
Large volume injection (LVI) can be quite advantageous when analyz-
ing trace-level compounds because the increased amount of analyte
introduced onto the column significantly improves detectability. This
approach can work well for clean matrices like drinking water; how-
ever, a special injection port, such as a programmable temperature
vaporization (PTV) inlet, is generally required. Since PTV involves the
expense of a specialized inlet and is limited to applications with large
differences between the boiling points of the solvent and target ana-
lytes, Restek’s chemists have been developing applications using con-
current solvent recondensation–large volume splitless injection (CSR-
LVSI) in a completely unmodified Agilent-style inlet as an alternative.
Building on the work of chemists at Thermo Scientific [1,2], Restek’s
applications laboratory has successfully demonstrated that CSR-LVSI
can be used without any modification to an Agilent-style splitless
injection port for a variety of analyses, including polycyclic aro-
matic hydrocarbons (PAHs), total petroleum hydrocarbons (TPH), EPA
Method 8270 semivolatiles [3], and brominated flame retardants [4], as
well as many organochlorine, organonitrogen, and organophospho-
rus pesticides. You can configure your instrument for these and other
CSR-LVSI analyses using the basic setup illustrated in Figure 1.
Setting up for CSR-LVSI Success
CSR-LVSI is very similar to a standard splitless injection that incor-
porates solvent focusing; the primary difference being that a large
uncoated (but deactivated) precolumn is used to provide enough
surface area for the large solvent volume to evenly wet and maintain
a mechanically stable film. (Table I gives some starting points for
precolumn dimensions based on injection volume.) This recondensa-
tion step requires that the GC oven be set at or below the pressure-
adjusted boiling point for the solvent during the duration of the
solvent transfer. Unlike a splitless injection, you cannot begin the oven
temperature program immediately after completing solvent transfer;
evaporative cooling prevents the segment of column holding the ana-
lytes of interest from heating with the GC oven, so all the transferred
solvent must be evaporated first. This yields a very narrow analyte
band at the head of the analytical column, which results in the sharp,
symmetrical peaks needed for accurate trace-level analysis.
Example Application: Lower Detection Limits for
Volatile DrinkingWater Contaminants
When using a PTV inlet, the solvent-venting, analyte-concentrating
step requires a relatively large difference in boiling points between
solvent and solute (>100 °C) in order to prevent analyte loss to the split
vent. This rules out using LVI with a PTV-type injection port for volatile
analytes. CSR-LVSI does not share this disadvantage. In fact, it is the
only way to further lower detection limits for non-purgeable organic
compounds like 1,4-dioxane and tetrahydrofuran. Recent work in our
laboratory achieved low ppt levels for these drinking water contami-
nants, as well as several nitrosamines, which are an emerging class of
contaminants [5,6]. While CSR-LVSI allows accurate quantification at
very low levels, there is a trade-off in that increasing the injection vol-
ume increases the analysis time (by approximately 1 minute for every
10 µL injected) because the solvent must evaporate completely before
starting the oven temperature program. Figure 2 shows the time offset
seen in the same analysis using 10 µL and 50 µL injections. Note that
when calculating the splitless hold time for the CSR-LVSI injection, we
used the same value recommended by the EZGC® flow calculator for
both injections.
While the CSR-LVSI approach results in a moderate increase in analysis
time, it allows lower detection limits for important drinking water
contaminants. Using the setup described here, the CSR-LVSI technique
can be applied when greater sensitivity is needed for compounds in
clean matrices without the expense of a PTV inlet.
Read the full application at
CSR-LVSI gives you the sensitivity of large
volume injection without the expense of
a specialized PTV injection port.