VALVES
129
APPLICATIONNOTE
DualModeSampleLoopLoading:
Partial-Fillingvs. Complete-Filling
Partial-Filling
Use thepartial-fillingmethod if youneed toconserve sample, or if you
want to vary sample volume frequently.
Inpartial-filling, the syringe sets the volume injectedonto thecolumn.
There isno samplewaste, and the volume injectedonto thecolumn is
equal to thatdispensed from the syringe. Reproducibility is1.0% relative
standarddeviation (RSD). The volumeof the sample loaded is limited to
half the sample loop volume. For example, themost youcan load intoa
200µL sample loop is100µL.
Complete-Filling
Use thecomplete-fillingmethod if youhaveplentyof sample, if youdo
not vary sample volume, or if youneedhigh reproducibility.
Incomplete-filling, the loop sets the volume loadedonto thecolumn.
Useexcess sample (two tofive loop volumes) to replaceall themobile
phase in the loop. SeeFigure2.Change the loop to vary the sample
volume. Reproducibility is typically0.1%RSD for loop sizes≥5µL.
Accuracy is limitedas loop volumesarenominal.
Q:
“Whichmethod should I useandwhichRheodyne
®
sample injection
valvesuse thismethod?”
A:
Thereare two typesof injection valvesavailable: dualmodeand
singlemode.Dualmode injection valvesallowbothpartial- and
complete-fillingwhereas singlemode injection valvesallowonly
complete-filling. Seemanual injection valves, page132.
If youarecollectingexperimental data, sample is scarce, and/or you
want tousedifferent samplevolumes, adualmode injectorwitha large
volume sample loop isappropriate.Onlydualmode injectionvalvesallow
thepartial-fillingmethod foreasilyvaryingyour volumes (up tohalf your
sample loopvolume) by setting the syringevolume.Onceyoubegin
routineanalysis, and/or youhaveanabundanceof sample, either adual
modeor singlemode injector isappropriate.Both typesof injectionvalves
allow thecomplete-fillingmethod inwhichyouoverfill the sample loop.
Complete-fillingmaximizes the reproducibilityof your results.
SelectionValves
Selection valvesenablediscreteconnections amongmultiple system
liquids (mobilephase, reagents, buffers) bymeansof acommonport
(inletoroutlet) connected toanumberofdifferent reciprocalports. In
Diagnosticor Sequencingapplications, the selectionvalvealternates
betweendifferent reagents or sample streams. Selection valves also
enable fractionation formultiple sampleanalyses.
Numerous configurations exist among selection valves (e.g.,
6-position 7-port, or 10-position 11-port), but these valves always
operate betweenmore than two positions. The ports are usually
spaced radially, or outward in somemanner around the center port
of the stator.
APPLICATIONNOTE
Sixcolumn selectionusing two selection valves.
Pump
Sample
Injector
1
6
5
4
3
2
1
7
2 3
4 5 6
1
6
5
4
3
2
Detector
Flowpath for the typical dual mode injector
INJECT
LOAD
Waste
Waste
1
3
4
5
6
2
Column
NeedlePort
Pump
Waste
1
3
4
5
6
2
NeedlePort
Waste
Pump
Column
Flowpathof Six-Position, Seven-Port Selector Valve
7
6
1
2
3
4
5
Valve Functions
