Archive for the ‘Packed Columns’ Category

Verify your GC packed/micropacked column carrier gas flow to obtain reproducible results

Working in technical service has taught me many things, but one of the most important has been “don’t assume anything”. This is especially relevant when it comes to verifying the carrier gas flow through GC columns.  To obtain reproducible results from column to column, this verification should always be done after installing a different packed/micropacked column into your GC oven.

 

 Packed Column

Setting and verifying the carrier gas flow for packed/micropacked columns is commonly done using an electronic flow meter.  This should absolutely be done with every column installation because each packed/micropacked column has a unique pressure drop. Remember that these columns contain packings which are not of a uniform particle size, but rather contain particles which fall within a specified range.  In addition, particle size distribution within this specified range can vary.  To read more about this topic, please see Understanding packed column mesh size ranges

As far as I know, there is no instrument software that can automatically set the desired flow rate. Even for those GC’s which have inlets controlled by a mass flow controller, it is still is a good idea to measure/verify the flow rate exiting the column.

To set and/or verify the desired carrier gas flow rate when using a packed or micropacked column, you will need a flow meter, electronic or bubble.  Below are a few steps which you may want to follow.

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  1. Cool all heated zones and then turn off all GC gases.  Allow the current packed/micropacked column (if one is installed) to depressurize so that its removal from the GC (more specifically, the inlet) doesn’t cause a pressure surge which can expel packing from the column.
  2. Install the new column into the injection port.  Do not connect to the detector at this time.   Do not turn on any heated zones.   Slowly increase the head-pressure just until carrier gas starts exiting from the column (holding a thin strip of tissue paper at the column outlet and observing when it moves is a good indicator).
  3. Attach an electronic flow meter (or soap-bubble flow meter) to the outlet of the column and once again begin slowly increasing the inlet’s head-pressure.   When the desired column flow rate has been obtained, continue to monitor the exiting carrier gas flow rate for five minutes to make sure it is stable.

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Very long packed columns, packings with irregular shaped particles, very small mesh sizes, and/or very small internal diameter micropacked columns, require high head pressures to obtain proper carrier gas flow.  As a result, many of these columns are commonly used with valve (switching) systems because obtaining reproducible results using a syringe injection can be difficult (sample loss through a punctured injection port septum is common).

By verifying the column’s carrier gas flow rate when you install a different packed/micropacked column, you should obtain reproducible results every time. Thanks for reading.

Understanding packed column mesh size ranges

If you have ever ordered a packed column, you are aware that mesh size of the solid support (packing) is one of the specifications you will need to know.  But have you ever wondered what mesh size actually means?

To find the answer, let’s look at the products and process.  The necessary products are ASTM Certified Standard Brass (or Stainless Steel) Test Sieves*, like shown below, and of course, the material to be screened.

* Depending upon the specific procedure, Compliance, Inspection or Calibration test sieves may be needed.

 

                 F8112-01~wl

Photo from Fisher Scientific website

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In order to obtain particles within specific a mesh size range, two screens are used in addition to a cover and a pan.  The pan is placed on the bottom, then the top and bottom screens are placed on the pan.  The top screen will have larger openings than the bottom screen.

Let’s assume in this example that the top screen is 80 mesh, which means that for every linear inch of screen, there are 80 little square openings.  Let’s also assume the bottom screen is 100 mesh, meaning that there are 100 little square openings for each linear inch of screen.  As you can guess, the openings in the 100 mesh screen are smaller than in the 80 mesh screen.  If interested in reviewing additional sieve screen specifications, click here.

The bulk material is loaded on the top screen, the cover is placed on top, and the sieves are shaken (manually or mechanically) side-to-side while gently tapped.  The particles which are small enough pass through the 80 mesh screen fall onto the 100 mesh screen, and if the particles are small enough, they also pass through the 100 mesh screen and are caught in the pan (these particles are referred to as “fines”).  The particles which are caught on the 100 mesh screen are the desired size, and are referred to as 80/100 mesh size particles.

You will notice that many test sieves are often designated using the term microns (µm) instead of mesh.  The relationship between these two terms can be found in this link.

So now that you know about particle mesh size, how does choosing a different range affect your analysis?  Generally speaking, using smaller particles (100/120 mesh) rather than larger particles (80/100 mesh) of the same packing in the same dimension column will provide more separation power (theoretical plates), but carrier gas head pressure will need be higher (to maintain constant flow rates) and longer analysis times are common (especially for isothermal analysis).

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Optimizing the performance of your D3606 column set

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My previous post “Simple tips to help your D3606 column set last longer” provided several recommendations for maximizing the lifetime of this column set.  In this post, I will provide suggestions to help you reproduce the results of the QA test chromatogram which was included with your column set.

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1.  Thoroughly review the included instruction sheet for this column set.

2.  Verify the temperature of your GC oven is 135°C by using an accurate thermometer or digital thermocouple thermometer.  Do not simply rely on the instrument temperature display.

3.  Verify the carrier gas flow rate (of helium or nitrogen) is 20mL/min by using a high quality digital flow meter.  Head pressure will be approximately 65psi.

4.  Carefully follow the instructions listed in ASTM D3606 for setting the correct back-flush time for your particular instrument (approximately 2.4 minutes).

5.  Make sure columns are correctly installed (oriented) to your inlet and valve (see our instruction sheet for details).

6.  Using a high quality electronic leak detector, thoroughly check each connection to verify it is leak-free.

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gc_pc1224

Click here to Enlarge

 

I hope you have found this information helpful.  If you have any questions, please email us at support@restek.com.

Simple tips to help your D3606 column set last longer

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Years ago, Restek developed a packed column set for ASTM D3606 “Standard Test Method for Determination of Benzene and Toluene in Finished Motor and Aviation Gasoline by Gas Chromatography”.  More specifically, this two column set (catalog number 83606-___) replaces the three column set listed in ASTM D3606-10, “Appendix X1. Resolving Benzene from Ethanol, Section X1.2 Modification A”.

Over the years, many customers have successfully used the columns to separate ethanol, benzene, 2-butanol, and toluene.  They are much more robust than the TCEP columns previously used.  However, in order to obtain the longest lifetimes for this column set, several simple precautions should not be overlooked.

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1.  Ultra-high purity carrier gas (helium or nitrogen) is essential.  Not only should the highest quality gas be purchased from your supplier, but high quality indicating gas traps should be located as close to your GC as possible.  Our baseplate traps are ideal for this application.  It is imperative that you keep moisture and oxygen from entering these columns..

2.  Properly set the back-flush time.  I can’t stress enough the importance of keeping C9 and heavier components off of column #2 (the 16ft column)..

3.  Never exceed the maximum temperature of 165°C for column #2.  Damage to this column will be irreversible.

83606-800L

By following the three simple steps above, you will obtain the full lifetime of this column set.  If you are experiencing any difficulties using these columns, please review Optimizing the performance of your D3606 column set.

Thanks for reading.

Molecular Sieve 5A & 13X packed columns – Installation / Conditioning / Helpful Hints

Molecular Sieve 5A & 13X Columns (packed)

Molecular Sieve 5A & 13X (micropacked)

Things to Consider Before Ordering a Packed Column

pkdcol_ph_co_pkd.

Following the steps below will ensure that your Molecular Sieve packed column is ready to use just several hours after installation.  You should only use dry high-purity Nitrogen as the carrier gas to condition (and/or dry) your column.  If using a different carrier gas than nitrogen, temporarily switch out gas supplies when conditioning or drying columns.  For additional information, see “Molecular Sieve Packed Columns and Fixed (Permanent) Gas Analysis“.

1.  Cool all heated zones and then turn off all GC gases.  Please allow the current packed column (if one is installed) to depressurize so that its removal from the GC (more specifically, the inlet) doesn’t cause a pressure surge which can expel packing from the column (see Helpful Hints C below for additional information).

2.  Install the new column into the injection port.  Do not connect to the detector at this time.   Do not turn on any heated zones.   Slowly increase the head-pressure just until carrier gas flow starts exiting from the column.

3.  Attach an electronic flow meter (or soap-bubble flow meter) to the outlet of the column and once again begin slowly increasing the head-pressure.   When the desired column flow rate has been obtained*, continue to monitor the exiting carrier gas flow rate for five minutes to make sure it is stable.

4.  Remove the flow meter and purge the column for an additional 10 minutes.  Set the GC oven temperature to 110°C and program the oven to ramp at 5°C/min to 300°C.  Heat the GC injection port (if applicable) to the desired temperature, but do not expose the column to higher temperatures than the maximum temperature of the column (350°C).  Begin the GC oven program ramp.  When 300°C is reached, hold it at this temperature for 3 hours.

5.  Cool the GC oven (Do not turn off the carrier gas unless you need to switch out the nitrogen for another carrier gas; if you do, see Steps #1-3 above).  Install the column into the detector and heat the detector to the desired temperature, but do not expose the column to higher temperatures than the maximum temperature of the column (350°C).

6.  Your column should be ready to use.

22654_co_gca_small.

Helpful hints:

A.  If you notice any degradation with the chromatography, you may need to “dry” the column.  To do so, use dry, hydrocarbon-free nitrogen as the carrier gas.  After purging the column for 10 minutes using the flow rates listed below, increase the GC oven temperature to 300°C and hold for 3 hours.  This should remove all traces of water vapor (and carbon dioxide).   (Additional note:   With a dry 5A or 13X column, methane (CH4) elutes before carbon monoxide (CO).  If CO elutes with methane, or before methane, your column needs to be dried).

If drying the column doesn’t improve chromatography, you may need to “regenerate/reactivate” the column (a tailing carbon monoxide peak is a common indicator of surface activity; another may be a decrease in response for the oxygen peak**).  To do so, use dry, hydrocarbon-free compressed air as the carrier gas.  After purging the column for 10 minutes using the flow rates listed below, increase the GC oven temperature to 300C and hold for 3 hours.  This should reactivate the surface of the zeolite molecular sieve packing.

** If you experience a decrease in response for the oxygen peak, but the carbon monoxide peak does not tail, the problem may be with the pre-column (stripper column), especially if this pre-column is a porous polymer.

B.  Always use high quality gas traps on your carrier gas line.  As mentioned earlier, molecular sieve packings like to absorb everything.

C.  Never perform any GC maintenance (such as replacing the septum or liner) or remove a packed/micropacked column from a GC, without having the carrier gas turned off and allowing the column/instrument to depressurize.  Otherwise the packed column’s bed may collapse or particles may be expelled.

D.  If the column is not going to be used for several days, all the instrument’s heated zones should be cooled and the carrier gas turned off.  The column should be removed and the ends should be capped to keep air/moisture out of the column.  If the column is going to be used the following day, do not cool instrument’s heated zones, leave the carrier gas on, and set the GC oven temperature to 150°C.

E.  When using a high sensitivity detector like a HID, DID, FID, etc. a micropacked column (0.53mmID through 1.0mmID) should work well.  However, when using a low sensitivity detector like a TCD, consider using a 2.0mmID (1/8”OD) packed column (for capacity).

F.  Molecular Sieve columns are extremely retentive.  For gas analysis, compounds larger than C2+ (ethane), or compounds with a boiling point greater than 50°C, should not be injected onto these columns.  If you suspect your samples may contain “heavies”, consider using a system which incorporates a pre-column and valve switching.

G.  If you need help installing a column, please review the FAQ link below.  If you still need help, send an email to support@restek.com

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http://www.restek.com/Pages/faq_pkd

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* Common conditioning carrier gas flow rates for packed/micropacked columns:

0.53mmID (0.74mmOD) = 5mL/min

0.75mmID (0.95mmOD) = 7.5mL/min

1.0mmID (1/16”OD) = 10mL/min

2.0mmID (1/8” OD) = 20mL/min.

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PLEASE READ

Safety Note:  If using hydrogen as the carrier gas, please safely vent the hydrogen during the conditioning process.  Do not vent the gas into a confined space, like the GC oven.  Several of the links in this post contain useful safety information when using hydrogen.  GC Carrier Gases – Alternatives to Helium

 

Molecular Sieve Packed Columns and Fixed (Permanent) Gas Analysis

For some reason, I find molecular sieve packed columns interesting.  Maybe it’s because they have a niche as the go-to columns for fixed (permanent) gas analysis.  Maybe it’s because they are old school technology that a new generation of analysts are always asking questions about.  Maybe it’s because using them successfully is a function of skill, art, and some luck.

As I researched molecular sieve packed columns over the years, I realized that for something that has been around more than 50 years, there wasn’t a whole lot of published information about them (at least not that I could find).  Application chromatograms were few and far between, and troubleshooting information seemed even rarer.  As a result, I decided to write this post on molecular sieve packed columns to help our customers.  This information came from books, the internet, coworkers, or was provided by our customers.   If you have any additional or contradictory information, I would love to hear from you.

I have written two other posts on molecular sieve packed columns.  One was titled “ShinCarbon columns – Installation / Conditioning / Helpful Hints”, and the other “Molecular Sieve 5A & 13X packed columns – Installation / Conditioning / Helpful Hints”.   So what’s the difference between these columns?  Let’s start with Molecular Sieve 5A and 13X packed columns.

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Click on Chromatogram to Enlarge

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Molecular Sieve 5A and 13X

Molecular Sieve 5A and 13X are referred to as zeolite molecular sieves.  These crystalline materials are synthetically produced and have very uniform internal cavities.  I am not going to discuss structural/composition details of Molecular Sieve type A materials verses Molecular Sieve type X materials, but rather focus on helping new analysts understand these packing and their applications a little better.

So what is the difference between 5A and 13X?  Well, as I already mentioned, material structure is one difference.  Pore size is another; a 5A has an effective pore size of 5 angstroms and a 13X has an effective pore size of 10 angstroms.  In order for a compound to be able to pass through these pores, it must be smaller.  For the compounds I plan to discuss (He, H2, Ar, O2, N2, CH4, and CO), each is able to pass through these pores.

So which compounds won’t pass through these pores?  Well, I’m going to answer a different question and list several common gaseous compounds which should not be introduced onto these columns.  These compounds include CO2, H2O, SO2, H2S, Cl2, HCl (and other corrosive vapors), compounds larger than C2 (ethane) and/or compounds with boiling points greater than approximately 50C (please note: there are several high temperature hydrocarbon applications, but I will not discuss them here). Larger gaseous compounds may actually make it through the column, but many will have no retention because they cannot fit into the pores (like SF6 when using 5A).  Other larger compounds may simply not make it through the column.

So what are some of the advantages of using these columns for gas analysis?  The primary advantage is baseline separation between O2 and N2 with a relatively short column and at room temperature.  Another is the separation of CO from air and CH4 (a difficult separation for any non-molecular sieve packed column).

So what are the disadvantages of these columns?  The primary disadvantage is that these packings will trap CO2 and H2O, which is why these columns are typically used with a pre-column (stripper column) and valve switching.  However, if CO2 and H2O do get trapped in these columns, the effects are reversible (see “Molecular Sieve 5A & 13X packed columns – Installation / Conditioning / Helpful Hints”).

Although zeolite molecular sieve packings are commonly used for argon/oxygen separation, a disadvantage of using a packed column is that a very long length (approximately 24ft from what I have read) is needed to separate oxygen from argon at room temperature.  For (O2/Ar) separation, we usually recommend one of our Molecular Sieve 5A PLOT columns (click on chromatogram below to enlarge).

gc_pc1182

gc_pc1182

gc_pc1182Finally, one needs to be cautious when using any carrier gas other than nitrogen to dry/condition these columns.  Because these materials contain surface metals that cannot be easily removed, it is believed that other carrier gases like hydrogen, argon and helium (at high temperatures) can remove the oxidation layer on the metal’s surface, which can lead to activity (especially for CO).

 

ShinCarbon ST

ShinCarbon ST is a synthetically manufactured carbon molecular sieve material with a very high surface area of approximately 1500m2/gm and a pore size of 10-12 angstroms.  Its surface is very inert, and very non-polar.  It is typically used for separation of fixed gases and light hydrocarbons, but also can be used for the analysis of SO2 (usually elutes after ethane) and N2O (usually elutes after CO2 but before acetylene).

So how does a carbon molecular sieve column (ShinCarbon) compare to a zeolite molecular sieve (5A & 13X) column?  Let’s start by looking where it doesn’t quite match-up with a 5A or 13X.  First, it can be difficult to get baseline separation between O2 and N2 using a carbon molecular sieve column (customers report that a 10ft x 1/8” OD column is needed).  In addition, it is even more difficult to separate O2/Ar (I have read that cryogenic cooling is a necessity).  And just like the 5A & 13X, a ShinCarbon isn’t meant for corrosive gases or H2S.

gc_pc00666

Click on Chromatogram to Enlarge

So why would you use a ShinCarbon?  First, unlike zeolite molecular sieves, CO2, SO2 and H2O will not get trapped in the pores (note: it will be difficult to quantitate H2O because the peak will tail).  Plus, you can easily chromatograph larger compounds (up through and including pentane; hexanes will elute but tail).   If H2O does condense inside the column, 30 minutes at 250⁰C will dry a ShinCarbon (unlike the 5A & 13X which needs 300⁰C for 3 hours), and using a carrier gas other than nitrogen does not seem to add surface activity.

I hope that you have found this information useful.  As I mentioned, if you have any additional information, or you had an experience which is contradictory to something here, please let me know.  Thanks for reading.

Gas Flows in Packed and Micro Packed Columns

2011-jaap-pasfoto4We received a question from a customer who did not obtain the correct flow through his micro packed column.  It is often not clear what flow is used in packed columns.  General the optimization  of flow setting using packed columns, does not have a priority as packed columns are –per definition-  low efficiency systems and a few plates less or more by optimization does not make a big difference.  For this reason, we see a lot of users also use nitrogen as carrier gas.

 

What are the typical flow ranges that we use with such columns?

formula flow

Formula 1. Flow in ideal system

In an ideal system, the flow in a tube is quadratic with the internal radius, see formula 1. Here F is the column flow in mL/min, R is column radius in cm, U is the linear gas velocity in cm/s. It means that when the column radius is reduced by a factor 2, the flow will roughly reduce by a factor 4 keeping the linear velocity constant. In capillary tubes, acc to Poiseuille, compressibility becomes a major issue and flow is dependent on the radius to the fourth power, which was used in a special application for vacuum GC. http://www.restek.com/pdfs/PL13-Vacuum-0-53mm-Restriction_in_liner.pdf

figure 1-tabel packed2

Table 1 Generall flow guideline for different diameter packed columns using SilcoSmooth tubing

 

 

Flow indications for SilcoSmooth packed columns are listed in Table 1.

It is clear that especially for the micro-packed columns, the flows are relative small.  That also means that for avoiding peak broadening in some detection systems, one may need to use some make up gas or use a detector designed for capillary columns. Especially for using TCD this can be important.

 

For higher mesh sizes one can use similar flow rates, but the restriction increases rapidly and this results in much higher pressures. Also compressibility will become more important.

Things to Consider Before Ordering a Packed Column

Let’s say you are starting your next GC project and realize that it is a packed column method.  However, you normally use capillary columns, and are not familiar with what you need to know before you order a new packed column. Believe me when I say “you are not alone.” Hopefully this post will help simplify the transition from a capillary column method to a packed column method.

The first thing you should do is to review our Packed Column FAQ’s, which can be found at this link. Packed & Micropacked Columns FAQ   These FAQs explain how to obtain a quote and/or how to order a packed column. There is also useful information on how to install and condition your packed column.

Let’s assume your method specifies which packed column is recommended. If so, our FAQ #1 How do I order a packed GC column? should be the first place to look to determine if we already have a catalog number available. If you find the column you need, but not for the instrument you will be using, take a look at the suffix list below and see if your instrument make/model is listed. If it is, just add the three-digit suffix to the five-digit packed column catalog number. If not, we will need you to provide Customer Service with the packed column dimensions. Or, you can simply photocopy (onto an 8.5” x 11” piece of paper) a packed column you already own and send its silhouette to Customer Service.

-810 Agilent 5880, 5890, 5987, 6890, 7890
-811 Agilent 6850
-820 Bruker/Varian 3700,Vista Series, FID
-821 Bruker/Varian 3800
-830 PerkinElmer 900-3920, Sigma 1,2,3
-840 PerkinElmer Auto System 8300, 8400, 8700, Clarus 500 (C500)
-841 PerkinElmer Auto Sys XL
-845 ABB 3100, AAI (4″ coil)
-850 Shimadzu 14A, 2014
-851 Shimadzu 8A
-852 Shimadzu 9A
-853 Shimadzu 17A, 2010
-854 Shimadzu Mini 2
-860 Thermo Scientific – TRACE 2000
-865 Carlo Erba
-870 Tremetrics/Tracor
-874 HNU 310 & 311 (4.5″ coil)
-875 Analytical Controls Configuration
-880 Carle 40030
-881 Hitachi 263
-885 Pye Unicam 4500
-890 Gow Mac 590
-891 Gow Mac 550
-892 Gow Mac 750
-893 Gow Mac 816 (3″ coil, 3″ spread on the arms, and a total height of 5″)
-894 Gow Mac 580
-895 SRI 8610C
-895R SRI 8610C Dual GC Right Side
-895L SRI 8610C Dual GC Left Side
-896 SRI 9300

If we don’t list a column which matches what is specified in the method, or your instrument is not listed above (especially true for In-Line and Process GCs), you will need to complete our Custom Packed Column Form. Once submitted, Customer Service will generate a quote for the requested column. Please verify everything is correct before ordering, because custom products are non-returnable and non-refundable.

Once you have determined which packed column you will order, make sure you have the necessary fittings, ferrules and/or adaptors to install it into your particular GC. For most packed column GCs, a ferrule and nut may be all that is needed. Or, you may need certain adaptors. Because of the wide variety of GCs manufactured, there is no way for us to know what you may need, so some preliminary planning on your part will prevent you from receiving a packed column that you cannot immediately install and use. Several of the most common calls we (tech service) receive are:

1.  The customer has a capillary column injection port. (Note: Consider using a “pigtail” as shown in the photo below).

2.  The customer has a Shimadzu GC with metric fittings (Note: Restek does not carry metric fittings or adaptors).

3.  The customer has an older GOW-Mac that uses 1/8 inch packed columns which have ¼” “ballooned” ends  (Note: Restek does not carry this tubing).

4.  Small oven GCs or GCs which contain multiple columns. (Note: To make sure your column will fit into your oven, please specify the necessary dimensions on the Custom Packed Column Form)

 

pigtail_closeup

How do I install a packed column into a capillary GC injection port?

In summary, purchasing a packed column and necessary fittings (for installation) can be a time consuming, and sometimes frustrating task for those who normally use capillary columns, but spending a little extra time prior to any purchases can save you days, or even weeks, and frustration. Restek Customer Service is here to help you with your questions prior to purchase, and Technical Service after your purchase. Thanks for reading.

Chromosorb® packings – looking ahead

As many of you know, there have been shortages of many Chromosorb® materials for several years now. Not only are some diatomaceous earth packings in short supply, but so are many of the porous polymers. For several packings, we have exhausted our supplies, as have other manufacturers. Although we continue to look for new sources of these materials, this past year has shown us that this is a challenging task. As a result, we continue to only offer packed and micropacked columns for the packings we still have available; we are not selling any Chromosorb® packings in bulk.

Earlier this year I wrote a few posts on Chromosorb® packings. With a new year almost upon us, I decided to remove the older posts, and replace them with this single, updated one. Looking forward, I am trying to remain optimistic that new chromatographic grades of scarce packings will be found, but the pessimist in me will make sure I’m prepared to offer alternative packings/columns to customers when a particular Chromosorb® packing is not available.

When looking for a Chromosorb® packed or micropacked column, the first thing you should do is to check our website for a “stock” product (see links below). I put the word “stocked” in quotes because most packed columns we have listed on the website are made-to-order for your specific gas chromatograph, and are not actually on the shelf in our warehouse. Typical lead time to manufacture a packed column is approximately 7-10 business days.

Chromosorb® Diatomaceous Earth Supports

Porous Polymer Columns (packed)

20% TCEP on 80/100 Chromosorb® PAW

 

If you do not see the specific column you are looking for, you will need to complete this online form Custom Packed/Micropacked Column Request Form and Customer Service will provide you the following information:

1. If we can/cannot manufacture the column.

2. The price.

3. Expected shipping date.

 

Sometimes we may not be able to provide you the Chromosorb® column you are looking for. In this situation, you will either need to look for another supplier, or consider an alternative column. If there is some flexibility in your method, we may have a solution for you. Because most Chromosorb® diatomaceous earth solid supports are coated with a liquid phase, you may be able to switch to a capillary column which contains a similar liquid phase. For example, a 10% OV-1 on Chromosorb® WHP packed column can usually be replaced with a MXT-1 capillary column (of course a similar fused-silica column could be used instead of the metal version – just make sure it will fit into your GC oven). Both phases are non-polar 100% dimethyl polysiloxane.

For the average six foot, 1/8 inch OD (2mmID) packed column, usually a 15m x 0.53mmID x 1.0µmdf MXT column has enough theoretical plates to do the same analysis. Please note, though, that the MXT column capacity will be less than a 1/8” packed column, so you may need to decrease your sample volume (on-column concentration) to prevent overloading the capillary column. However, because of the sharper peak shape provided by a capillary column, sensitivity may actually increase (signal/noise).

Other common phase substitutions are MXT-50 for OV-17 and MXT-WAX for Carbowax 20M. Below is a link to our complete line of MXT columns.

Metal (MXT) Capillary

Substituting a Chromosorb® porous polymer packing with either HayeSep® or Porapak® porous polymer can be tricky, since equivalent substitutions (like those found between HayeSep® and Porapak®) are not as obvious. In my opinion, the best way to see if there is a Chromosorb® substitute is to provide us the specifics of your analysis, and we can try and determine if one of the HayeSep® or Porapak® porous polymers can be substituted.

 

For some guidance on converting your GC from packed to micropacked or capillary column, please review our Frequently Asked Questions: Packed & Micropacked Columns . To read more about Chromosorb packings, I’ve included several links below (these files are rather large, somewhere around 6MB each).

CHROMOSORB® Diatomite Supports

CHROMOSORB® Polymer Supports

As always, if you have any questions, please contact technical service, whether it involves substituting a capillary column for a packed column, or converting your packed column instrument to accept capillary columns, we are just one phone call or e-mail away. Thanks for reading.

ShinCarbon columns – Installation / Conditioning / Helpful Hints

 

ShinCarbon ST Columns (packed & micropacked)

Application Note

 Things to Consider Before Ordering a Packed Column

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For those of you who may be interested in using a ShinCarbon for the first time, I’ll walk you through the process of getting your new column ready for analysis. Even though we take great care to minimize the time you will need to condition your column after you receive it, please remember, this packing, like all molecular sieves, likes to absorb everything it is exposed to, so any column will need some conditioning after you receive it.  For additional information, see “Molecular Sieve Packed Columns and Fixed (Permanent) Gas Analysis“.

 

Following the steps below will ensure that your column is ready to use just several hours after installation.

1. Cool all heated zones and then turn-off all GC gases. Please allow the current packed column (if one is installed) to depressurize so that its removal from the GC (more specifically, the inlet) doesn’t cause a pressure surge which can cause expel packing from the column (see Helpful Hints C below for additional information).

2. Install the new ShinCarbon into the injection port. Do not connect to the detector at this time. Do not turn on any heated zones. Slowly increase the head-pressure just until carrier gas flow starts exiting from the column.

3. Attach an electronic flow meter (or soap-bubble flow meter) to the outlet of the column and once again begin to slowly increase the head-pressure. When the desired column flow rate has been obtained*, continue to monitor the exiting carrier gas flow rate for five minutes to make sure it is stable.

4. Remove the flow meter and purge the column for an additional 10 minutes to remove all traces of air. Set the GC oven temperature to 40⁰C and program the oven to ramp at 5°C/min to 275°C. Heat the GC injection port (if applicable) to the desired temperature, but do not expose the column to higher temperatures than the maximum temperature of the packing (300°C). Begin the GC oven program ramp. When 275°C is reached, hold it at this temperature for 3 hours.

5. Cool the GC oven (do not turn off the carrier gas). Install the column into the detector and heat the detector to the desired temperature, but do not expose the column to higher temperatures than the maximum temperature of the packing (300°C). .

6. Your column should be ready to use.

Restek ProFLOW 6000 Electronic Flowmeter

 

Helpful hints:

A. If you notice any degradation with the chromatography, you may need to “dry” the column. To do so, increase the GC oven to 250⁰C and hold for 30 minutes. This should remove all traces of water vapor.

B. Always use high quality gas traps on your carrier gas line. As mentioned earlier, molecular sieve packings like to absorb everything.

C. Never perform any GC maintenance (such as replacing the septum or liner) or remove a packed/micropacked column from a GC, without having the carrier gas turned-off and allowing the column/instrument to depressurize. Otherwise the packed column’s bed may collapse or particles may be expelled.

D. If the column is not going to be used for several days, all the instrument’s heated zones should be cooled and the carrier gas turned off.  The column should be removed and the ends should be capped to keep air/moisture out of the column.  If the column is going to be used the following day, do not cool instrument’s heated zones, leave the carrier gas on, and set the GC oven temperature to 150°C.

E. When using a high sensitivity detector like a HID, DID, FID, etc… a micropacked column (0.53mmID through 1.0mmID) should work well. However, when using a low sensitivity detector like a TCD, consider using a 2.0mmID (1/8”OD) packed column (for capacity).

F. Carbon molecular sieve columns are extremely retentive. Generally speaking, compounds larger than C6+ (hexanes), or compounds with a boiling point greater than 80°C, should not be injected onto these columns. If you suspect your samples may contain “heavies”, consider using a system which incorporates a pre-column and valve switching. Ideally, only compounds which are gases at room temperature should be injected onto these columns.

G. If you need help installing a column, please review the FAQ link below. If you still need help, send an email to support@restek.com.

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Frequently Asked Questions: Packed & Micropacked Columns

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* Common carrier gas flow rates for conditioning packed/micropacked columns:

0.53mmID (0.74mmOD) = 5mL/min
0.75mmID (0.95mmOD) = 7.5mL/min
1.0mmID (1/16”OD) = 10mL/min
2.0mmID (1/8” OD) = 20mL/min.

 

PLEASE READ

Safety Note:  If using hydrogen as the carrier gas, please safely vent the hydrogen during the conditioning process.  Do Not vent the gas into a confined space, like the GC oven.  Several of the links in this post contain useful safety information when using hydrogen.  GC Carrier Gases – Alternatives to Helium