Restek PLOT Column Family

Are You Having Problems with Your PLOT Columns and Particle Release?

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Traditional PLOT columns offer poor stability. The traditional PLOT column is built with a 5-50 μm layer of particles adhered to the tubing walls. Because this layer of particles generally lacks stability, PLOT columns must be used very carefully as particle release is common and can cause unpredictable changes in retention time and flow behaviour. Traditional PLOT columns also must generally be used in conjunction with particle traps to prevent the contamination of valves, injectors, and GC detectors. Detectors contaminated with particles typically generate electronic noise, which shows up chromatographically as a spike in the baseline.
In extreme cases, detector flow can be obstructed by particle buildup. Particles can also affect valves by becoming lodged in the valve
and causing leaks or restricting flow.

Figure 1: An example of blockage caused by particle accumulation inside a Press-Tight connector.

Have Your Heard About the Next Generation of Porous Layer Open Tubular (PLOT) Columns?

Restek PLOT Columns Offer Improved Stability to Minimize Particle Release!

Restek has developed technology and procedures to manufacture PLOT columns with concentric stabilized adsorption layers. These next 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 stability means more reproducible retention times, virtually no spiking, and longer column lifetimes. This innovative Restek stabilization chemistry is currently applied to all fused silica and metal PLOT columns featured here.

*A particle trap is still recommended to protect valves and detectors.

Consistent Flow Restriction Factor (F) Guarantees Reproducible Flow

Thick layers of particles are difficult to deposit in a homogeneous layer, and in traditionally manufactured PLOT columns, this results in variable coating thicknesses. The positions where the layer is thicker act as restrictions and affect flow (Figure 2). Depending on the number and intensity of these restrictions, traditional PLOT columns often show greater variation in flow restriction than wall coated open tubular (WCOT) columns. In practice, conventional PLOT columns with the same dimensions can differ in flow by a factor of 4 to 6 when operated at the same nominal pressure. For applications where flow is important, such as with Deans switching, the non reproducible flow behavior of most commercially available PLOT columns is a problem.

Figure 2: Inconsistent coating thicknesses result in restrictions that cause significant variation in flow.

In order to measure flow restriction reproducibility, Restek introduced a new factor: the flow restriction factor (F). This factor is based on the retention time of an unretained marker compound as measured on both coated and uncoated tubing using the same back pressure setting (Equation 1). For quality control purposes, methane is used as the marker when evaluating porous polymer columns, and helium is used for testing molecular sieve 5A columns.

Flow restriction factor determination can be used to assess both the degree of column restriction and the reproducibility of the column coating process. Figure 3 shows typical results for PLOT columns manufactured using a conventional process. Because of the difference in flow restriction, individual columns have very different flow characteristics. In contrast, Figure 4 shows results for columns made using our Rt-QS-BOND (bonded porous polymer) PLOT column process. Clearly, Restek's manufacturing process results in greater consistency in both column coating thickness and flow restriction, which results in more stable retention times and better performance in Deans and related flow switching techniques. Flow restriction factors are specified on the certificate of analysis (CofA) included with every Restek PLOT column, and the values are listed on the report.

Figure 3: Traditional PLOT columns show significant flow variability, indicating inconsistent coating thicknesses.

Equation 1: Flow restriction factor (F) is used to demonstrate coating consistency.

Note: F values will always be <1 as the coated column always has more restriction than the uncoated column.

Figure 4: PLOT columns from Restek offer consistent flow restriction, giving more reproducible results column to column.

Restek’s PLOT columns are exceptionally robust, featuring concentric stabilized coating layers. They allow for more consistent gas flows and are recommended for applications sensitive to variation in retention time or flow. These PLOT columns are a significant advance in technology and are ideal for efficient, reproducible analyses of permanent gases, solvents, and hydrocarbons.

PLOT Column Phase Cross-Reference: Similar Selectivity

Restek Rt and MXT Columns	Porous Layer	Supelco	Alltech	Agilent (J&W, Varian, Chrompack)	Quadrex
Alumina BOND/Na₂SO₄	Aluminum oxide	Alumina-Sulfate	AT-Alumina	GS-Alumina, CP-Al₂O₃/NA₂SO₄	—
Alumina BOND/KCl*	Aluminum oxide	Alumina-Chloride	—	GS-Alumina KCl, HP PLOT Al₂O₃, CP-Al₂O₃/KCl	—
Alumina BOND/CFC*	Aluminum oxide	unique product
Alumina BOND/MAPD	Aluminum oxide	—	—	Select Al₂O₃ MAPD	—
Msieve 5A	Molecular sieve 5A	Molsieve 5A	AT-Molesieve	HP PLOT Molesieve, CP-Molesieve 5A	PLT-5A
Q-BOND	100% Divinylbenzene	Supel-Q-PLOT	AT-Q	HP PLOT Q ,CP-PoraPlot Q, PoraBond Q	—
QS-BOND*	Intermediate polarity porous polymer	—	—	GS-Q	—
S-BOND*	DVB vinylpyridine polymer	—	—	CP-PoraPlot S	—
U-BOND*	DVB ethylene glycoldimethylacrylate polymer	—	—	HP PLOT U, CP-PoraPlot U, CP-PoraBond U	—

*Available only with fused silica tubing.

Rt-Alumina BOND Columns

Restek Rt-Alumina BOND columns are highly selective for C1-C5 hydrocarbons and separate all saturated and unsaturated hydrocarbon isomers above ambient temperatures. The reactivity of the aluminum oxide stationary phase is minimized, by deactivation with inorganic salts like KCl or Na₂SO₄, to improve column response for polar unsaturates, such as dienes, and the column’s sensitivity (or response) ensures linear and quantitative chromatographic analysis for these compounds. Strong bonding minimizes particle generation and release, which allows valve switching with minimal risk to the injection or detection systems.
And because they are stable up to at least 200°C, Rt-Alumina BOND columns can be regenerated to restore full efficiency and selectivity by conditioning at their maximum temperature if water is adsorbed. High capacity and loadability give you exceptionally symmetrical peaks, making these columns ideal for volatile hydrocarbon separations at percent levels, as well as impurity analyses at ppm concentrations. Restek Rt-Alumina BOND PLOT columns are manufactured on fused silica tubing; select phases are also available on metal MXT tubing.

To ensure reproducible retention times and predictable flow behavior column to column, each Rt-Alumina BOND column is extensively tested. A hydrocarbon test mix confirms proper phase retention and selectivity. To calculate k (retention or capacity factor), which is a measure of phase retention, 1,3-butadiene is used, while selectivity is measured using retention indices for propadiene and methyl acetylene. The resolution of trans-2-butene and 1-butene is also verified and, to measure efficiency, plates per meter are checked using 1,3-butadiene.

Rt-Alumina BOND/Na₂SO₄ Columns (fused silica PLOT)

(Na₂SO₄ deactivation)

Acetylene and propadiene elute after butanes.
Best separation for butene isomers (impurities in butene streams).
Methyl acetylene elutes after 1,3-butadiene.
Cyclopropane (impurity in propylene) elutes well before propylene.
Stable to 200°C.
Also available on metal MXT tubing

Rt-Alumina BOND/KCl Columns (fused silica PLOT)

(KCl deactivation)

Restek’s lowest polarity alumina column.
Low moisture sensitivity reduces the need for frequent regeneration.
Acetylene elutes before n-butane.
Methyl acetylene (impurity in 1,3-butadiene) elutes before 1,3-butadiene.
Stable to 200°C.

Rt-Alumina BOND/CFC Columns (fused silica PLOT)

Improved inertness for chlorofluorocarbon (CFC) compounds.
Highly selective alumina-based column, separates most CFCs.
High retention and capacity for CFCs.
Stable to 200°C.

The Alumina BOND/CFC adsorbent is ideal for retaining volatile halogenated compounds, especially CFCs (chlorinated fluorocarbons). It offers high selectivity, allowing a wide range of CFC isomers to be resolved at above ambient temperatures. The Rt-Alumina BOND/CFC column is thoroughly deactivated to reduce the reactivity of alumina. Even though there is still some residual reactivity for some mono- or disubstituted CFCs, the majority of these compounds can be accurately quantified from main stream processes or in impurity analyses.

Rt-Alumina BOND/MAPD Columns (fused silica PLOT)

Optimized deactivation produces maximum response when analyzing trace levels of acetylene, methyl acetylene, and propadiene.
Stable response factors make this column ideal for process-type applications where recalibration must be minimized.
High loadability reduces peak tailing and improves separations.
Extended temperature range up to 250 °C for fast elution of high molecular weight (HMW) hydrocarbons and accelerated column regeneration following exposure to water.
Stable to 250°C.
Also available on metal MXT tubing!

Restek’s R&D chemists have optimized the deactivation technology applied to their Rt-Alumina BOND/MAPD column for improved analysis of trace concentrations of polar hydrocarbons like acetylene, methyl acetylene, and propadiene in hydrocarbon streams containing higher levels of C1-C5 hydrocarbons. Their alumina PLOT deactivation produces an incredibly inert column that offers superior reproducibility and stable response factors to maximize the number of analyses before recalibration is required. Its high sample capacity reduces peak tailing, thereby improving the separation of target compounds. In addition, a 250°C maximum operating temperature lets you more quickly elute hydrocarbons up to dodecane and reduces regeneration time when the column is exposed to water from samples or carrier gases.

Molecular Sieve 5A PLOT Columns

Restek’s Molecular Sieve 5A PLOT columns are designed for efficient separation of argon/oxygen and other permanent gases, including carbon monoxide. Special coating and deactivation procedures ensure chromatographic efficiency and the integrity of the porous layer coating. Molecular sieves have very high retention, allowing separations of permanent gases at temperatures above ambient. Restek's deactivation technology also allows carbon monoxide to elute as a sharp peak. Additionally, their unique immobilization process guarantees that the uniform particles remain adhered to the tubing – even after continuous valve cycling.

Rt-Msieve 5A Columns (fused silica PLOT)

Improve accuracy with sharp, symmetrical peaks for argon, oxygen, and carbon monoxide.
Easily separate permanent gases at temperatures above ambient.
PLOT technology reduces particle release, improving flow reproducibility and reducing downtime for maintenance.
Stable to 300°C.
Also available on metal MXT tubing!

Porous Polymer Columns

Porous polymers are unique, highly retentive stationary phases with a wide application range that are able to elute both polar and nonpolar compounds. They are very hydrophobic, so water has no impact on retention times and even elutes as a good chromatographic peak. Restek's Q-BOND is their most nonpolar and widely used porous polymer column; functional groups can be added to increase polarity (i.e., QS-, S-, and U-BOND). The process used to manufacture porous polymer PLOT columns causes the particles to adhere strongly to the walls of the tubing, so there is virtually no particle generation. You get reproducible performance from column to column, including selectivity and flow.

Rt-Q-BOND Columns (fused silica PLOT)

100% divinylbenzene

Nonpolar PLOT column incorporating 100% divinylbenzene.
Excellent for analysis of C1 to C3 hydrocarbons as well as isomers and alkanes up to C10.
High retention for CO₂ simplifies gas analysis; CO₂ and methane separated from O₂/N₂/CO.
(Note: O₂/N₂/CO not separated at ambient temperature.)
Use for analysis of oxygenated compounds and solvents.
Maximum temperature of 300°C.
Also available on metal MXT tubing!

Rt-QS-BOND Columns (fused silica PLOT)

porous divinylbenzene homopolymer

Intermediate polarity porous polymer PLOT column incorporating low 4-vinylpyridine.
Separates ethane, ethylene, and acetylene to baseline.
Stable to 250°C.

Rt-S-BOND Columns (fused silica PLOT)

porous divinylbenzene homopolymer

Midpolarity porous polymer PLOT column, incorporating high 4-vinylpyridine.
Use for the analysis of nonpolar and polar compounds.
Stable to 250°C.

Rt-U-BOND Columns (fused silica PLOT)

divinylbenzene ethylene glycol/dimethylacrylate

Restek’s highest polarity porous polymer column.
Polar PLOT column, incorporating divinylbenzene ethylene glycol/dimethylacrylate.
Highly inert for the analysis of polar and nonpolar compounds.
Common applications include: H2S, COS, and mercaptans in hydrocarbon streams.
Stable to 190°C.

Metal MXT PLOT Columns

Advantages of metal MXT PLOT columns include:

Can be made in small coil diameters – perfect for tight spaces.
Rugged material withstands rough handling and shock.
Designed for robust performance in process GCs and field instruments.
Available in 3.5″-coil diameter or 7″-diameter, 11-pin cage.

Restek chemists have developed technology that allows many of their popular PLOT columns to be made on Siltek-treated stainless steel. These columns have
the same characteristics and performance as fused silica PLOT columns, but offer additional benefits for process GCs and field applications as they are virtually unbreakable and can be coiled into very small diameters.

MXT Low Dead Volume Connector Kits for Metal Columns

Connect a guard column/transfer line to an MXT stainless steel column.
Low thermal mass tracks rapid oven temperature programming.
Stainless-steel ferrules and nuts.
Available in “Y” and union configurations.
Siltek treatment ensures ultimate inertness.

Each kit contains the MXT union, two 1/32-inch ferrules and nuts.

For more information on the MXT Columns
For more information on the PLOT Columns

Still Have Questions?

You can give us a call or email us and we can find the right PLOT Column product number for your application. It's our pleasure to help you and it's free!

1-800-267-8103 or tech@chromspec.com