Figure1
Particles released from traditional PLOTcolumns cancauseblockages.
2
Figure2
Inconsistent coating thicknesses result in restrictions that cause significant
variation in flow.
NewGenerationofPorousLayerOpenTubular (PLOT)Columns
• Stabilizedparticle layers improve robustness and reproducibilityof retention and flow.
• Fully compatiblewith valve switching andDeans switching systems.
• Highly efficient, reproducible analyses; ideal for permanent gases, solvents, andhydrocarbons.
• Newmanufacturingprocedure reduces particle generation and improves performance of porous
polymers,molecular sieves, andPLOT columns.
Porous layeropen tubular (PLOT) columns areverybeneficial for solvingapplicationproblems, especial-
ly for the analysis of volatile compounds. PLOT columns have aunique selectivity, allowing for the sepa-
ration of gaseous compounds at room temperature. Due to the adsorptionmechanism of the supports
used in PLOT columns, permanent gases and light hydrocarbons can be resolved at room temperature.
Columns can thenbe programmed tohigher temperatures to elutehigher boiling compounds.
TraditionalPLOTColumnsOfferPoorStability
The traditional PLOT column is built with a 5-50µm layer of particles adhered to the tubingwalls. Because
this layer of particles generally lacks stability, PLOT columnsmust be used very carefully, as particle release
is common and can cause unpredictable changes in retention time and flow behavior. PLOT columns gen-
erallymust beused in conjunctionwithparticle traps toprevent the contaminationof valves, injectors, and
GC detectors. Figure 1 shows an example of particle accumulation resulting in a blockage inside a Press-
Tight® liner. If particle traps arenot used, particleswill hit the detector resulting in electronicnoise, seen as
spikes on the baseline. In the case of valves, particles canbecome lodged in the valve and result in leaks.
NewStabilizedPLOTColumnsMinimizeParticleRelease
Restekhas developednewprocedures tomanufacture PLOT columnswith concentric stabilized adsorp-
tion layers. The new generation PLOT columns show a constant flow behavior (permeability) and have
significantly improved mechanical stability, resulting in easier operation, better chromatography, and
reduced particle release. Greater particle stabilitymeansmore reproducible retention times, virtually no
spiking, and longer column lifetimes. This innovative stabilization chemistry technology is currently
applied to Rt®-Alumina BOND, Rt®-Msieve 5A, Rt®-Q-BOND, Rt®-QS-BOND, Rt®-S-BOND, and
Rt®-U-BOND columns.
ConsistentFlowRestrictionFactor (F)GuaranteesReproducibleFlow
Thick layersof particlesaredifficult todeposit inahomogeneous layerand, in traditionallymanufactured
PLOT columns, this results in variable coating thicknesses. The positionswhere the layer is thicker act as
restrictions and affect flow (Figure 2).Depending on the number and intensity of these restrictions, tra-
ditional PLOT columns often show greater variation in flow restriction than wall coated open tubular
(WCOT) columns. Inpractice, conventional PLOT columnswith the same dimensions candiffer in flow
bya factorof 4-6,whenoperatedat the samenominal pressure.For applicationswhere flow is important,
such as withDeans switching, the nonreproducible flow behavior of most commercially available PLOT
columns is aproblem.
Ideal openpathcolumn
PLOTcolumnwith restriction
Particles forminga "plug".
