Figure3
Traditional PLOTcolumns show significant flowvariability,
indicating inconsistent columncoating thicknesses.
800-356-1688or 814-353-1300
3
Figure4
Restek’snew stabilizedPLOTcolumnsoffer consistent flow
resistance, givingmore reproducible results column-to-column.
Inorder to evaluate flow restriction reproducibility, Restek is introducing a new factor: the flow restriction factor (F). This factor is
basedon the retention time of anunretainedmarker compound, asmeasuredonboth coated anduncoated tubing using the same
backpressure setting (Equation 1). For quality control purposes, methane is used as themarker when evaluating porous polymer
columns andhelium is used for testingRt®-Msieve 5A columns.
Flow restriction factor determination canbeusedboth to assess thedegreeof column restriction and to evaluate the reproducibility
of the column coating process. Percent flow restriction can alsobe calculated (Equation 2). Figure 3 shows typical results for PLOT
columnsmanufacturedusing a conventional process.Becauseof thedifference in flow restriction, individual columns have verydif-
ferent flow characteristics. In contrast, Figure 4 shows results for columns made using the new PLOT column process (Rt®-QS-
BOND, bonded porous polymer). Clearly, the newmanufacturing process results in greater consistency in both column coating
thickness and flow restriction;which, in turn, results inmore stable retention times andbetter performance inDeans switching and
related flow switching techniques.
Equation1
Flow restriction factor (F) isused to
demonstratecoatingconsistency.
In summary,Restek’snewPLOT columnmanufacturingprocess produces exceptionally robust PLOT columns, featuring concentric
stabilized coating layers.Thesenew columnshavemore consistent flow resistance andare recommended for applications sensitive to
variation in retention timeor flow.These columns are a significant advance inPLOT column technology and are ideal formore effi-
cient, reproducible analyses of permanent gases, solvents, andhydrocarbons.
Equation2
Percent flow restrictionof coated
column.
% restriction= (1 - F) x100
t
R1
of unretained component
(uncoated tubing)
t
R2
of unretained component
(coated column)
F=
NumberofColumns
NumberofColumns
t
R
= retention time
Note, F valueswill always be<1 as the coated column
always hasmore restriction than the uncoated column.
Restek
Porous Layer
Agilent/J&W
Supelco
Alltech
Varian/Chrompack
Quadrex
Rt-Alumina BOND /Na
2
SO
4
Aluminum oxide
GS-Alumina,
Alumina-PLOT
AT-Alumina
CP-Al
2
O
3
/NA
2
SO
4
——
HP PLOT S, HP PLOTM
Rt-Alumina BOND / KCl
Aluminum oxide
GC-Alumina KCl
——
——
CP-Al
2
O
3
/KCl
——
Rt-Msieve5A
Molecular sieve 5A
GS-Molsieve,
Molsieve 5A PLOT
AT-Molesieve
CP-Molesieve 5A
PLT-5A
HP PLOT/Molesieve
Rt-Q-BOND
DVB porous polymer
——
Supel-Q-PLOT
AT-Q
CP-PoraPlot Q,
——
PoraBondQ
Rt-QS-BOND
Intermediate polarity
GS-Q
——
——
——
——
porous polymer
Rt-S-BOND
DVB vinylpyridine
——
——
—— CP-PoraPlot S
——
polymer
Rt-U-BOND
DVB ethyleneglycol-
HP-UPLOT
——
—— CP-PoraPlot U,
——
dimethylacrylate polymer
PoraBondU
PLOTColumnPhaseCross-Reference:SimilarSelectivity
F
F
