Author Archive

Dimensions of NORM-JECT® syringes

We often get asked for dimensions of our NORM-JECT® syringes.  As a result, I decided to take the information tech service has been provided and put it in a convenient place for our customers.  Below is the information for Restek part #’s 22766 through 22778.  For those of you who need it, I hope you find this information useful.

NJf2

Fatty Acid Methyl Esters (FAMES) – converting % by weight to µg/mL

The first time I was asked by a customer about how to convert % by weight of one of our FAME reference standards to µg/mL, I needed to ask for some help.  Because we (tech service) occasionally get asked this question, I thought I would show the calculation in a post.

 

Let’s take Restek catalog number 35077 as an example.  The overall concentration of this Food Industry FAME Mix is 30mg/mL.   Individual compound concentrations range from 2 to 6% by weight.   So what are the individual compound concentrations in µg/mL?   I’m not going to list them all, but rather show you how to perform this calculation.

We list the first compound as C4:0 and at 4% by weight.  Since the total concentration of 35077 is 30mg/mL, to determine the concentration of C4:0 in µg/mL:

4/100 x 30mg/mL = 0.04 x 30mg/mL = 1.2mg/mL

To convert to µg/mL:  1.2mg/mL x 1000µg/mg = 1200µg/mL

 

          ampules

 

If you purchase a neat standard like 35066, then there will be one extra step to obtaining the final answer.   This catalog number contains approximately 100mg.  For the sake of simplicity, let’s say you remove exactly 100mg and dissolve this material into 10mL of methylene chloride.  This will produce a solution with a concentration of 10mg/mL.   Once again, I will use the first listed compound (C14:0 in this case) for an example calculation.

C14:0 is in the neat material at 6% by weight.  Since the total concentration of the solution you prepared is at 10mg/mL:

6/100 x 10mg/mL = 0.06 x 10mg/mL = 0.6mg/mL

To convert to µg/mL:  0.6mg/mL x 1000µg/mg = 600µg/mL

 

I hope you have found these examples helpful the next time you need to perform similar calculations.  Thanks for reading.

Contents inside your baseplate trap

We often get asked in tech service for a list of materials contained inside our baseplate traps from customers who are concerned about disposal regulations.  They have read our FAQ How do I dispose of used gas traps or filters?, but before contacting their waste disposal company, a list of the trap contents is requested.  Normally this information would be contained in a SDS, but the traps we sell are considered “Articles”, they do not require that one be sent with the product (for more information, please see Changes are coming to the MSDS; um, I mean the SDS).

So without further ado, below is what is contained in the following Restek catalog numbers.

Notes:  g = grams.  CAS = Chemical Abstract Service

 22028_ph_so_trp

# 22020  and # 21983 Replacement Triple Gas Filter (removes oxygen, moisture, and hydrocarbons). 

Includes Helium-Specific Triple Filter.

tripleC

 

# 22022  Replacement Fuel Gas Filter

22022C

 

# 22028  Ultra-High Capacity Moisture Filter

22028CA

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# 22029  Ultra-High Capacity Oxygen Filter

 22029C

 

# 22030  Ultra-High Capacity Hydrocarbon Filter

22030A

 

 

 

 

 

Troubleshooting GC Syringe Issues – Part 2

In an earlier post titled Troubleshooting GC Syringe Issues, I discussed several things to try if sticking plungers are the problem.  In this post, I’ll discuss what to do if the syringe is not pulling up the sample properly (or at all).

syringes

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So what can cause a syringe to have problems pulling up a sample?

 

The sample is too viscous.

If your sample is viscous, slow the plunger draw speed.  Many autosamplers have this functionality.

If this still doesn’t solve the issue, you may need to dilute your sample.

 

The syringe needle is plugged, or partially plugged.

Find out what is plugging your syringe needle.  Is it the sample or septa?

If it is particles in your sample, you may need to add a filtering step before injecting.  Sample Filtration

If you discover it is a piece of septum plugging your needle, try a different needle point style (Pt style #5 with side-hole are the least likely to plug).  Syringe Basics.

Pt Style 5

 

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The plunger is not making a good seal with the syringe barrel.

How worn is the syringe?

Eventually the plunger to barrel sealing performance of syringes degrades as it gets older and worn-out.  This is especially true when using Gas-Tight syringes which have PTFE-tipped plungers.

Most syringe manufacturers recommend that you do not use a plunger from one syringe in another (unless using Gas-Tight syringes where plungers are usually interchangeable).

 

There is a leak between the needle and barrel.

If using a removable needle syringe, make sure the PTFE seal between the needle and barrel is installed properly and not worn out.

If using a fixed needle syringe, verify that the cement holding the needle to the barrel hasn’t degraded.

 

The autosampler is not working properly.

Watch the autosampler as it tries to inject the sample.  Is the autosampler programmed properly?  Does it actually penetrate the sample vial deep enough to withdraw an aliquot?  Does the autosampler actually lift the plunger?

 

Hopefully one of these suggestions will help you out the next time your syringe is not pulling up a sample.  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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Need a replacement AC Adaptor/Charger for your Restek Leak Detector?

We all misplace items once in a while.  If you have misplaced your leak detector AC adaptor/charger, don’t worry, we sell replacements.  If you own leak detector catalog number 22655:

 22655

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The replacement AC adaptor/charger catalog number is 22653.

22653A

22653

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We also sell a car charger for this leak detector.  It is catalog number 22652.

22652.jpg (2)

22652

 

 

In addition, we sell the AC Adaptor/charger for the previous model leak detector 22839.

22839

22839

The replacement AC adaptor/charger catalog number for 22839 is 563816.

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Note:  Some of the older 22839 units may be getting close to needing their batteries replaced.  When your batteries will no longer charge, or will not hold a charge, you will need to return the unit to Restek for battery replacement.  Call Customer Service for a service repair by ordering catalog number 22839-R (orders cannot be placed for this service using the website).

 

Chemical Reference Standards; don’t just snap and pour

I still remember the first time I tried to prepare a chemical standard (back in the 80’s).  I failed miserably.  It was my first laboratory job and I was asked to snap open recently purchased ampules and dilute them to some concentration (which I don’t remember) for our 8270 analysis.  Back in those days there were no MegaMix® solutions, so I probably had eight or more ampules to dilute.  I double-checked my calculations, filled-out our laboratory notebook, measured the methylene chloride I was going to dilute the ampuled solutions into, and began snapping and pouring.  About halfway through the procedure I had a co-worker stop me and ask what I was doing.  Was this a trick question?  I was focused on the task and making good time, so I told him to back off (which he did).

                 refstd-mixes

Then the manager showed up to let me know why I was so rudely interrupted by my coworker.  He explained that just because the ampule listed 1mL on the label as the volume, chemical reference standard manufacturers actually put more than the listed volume into each ampule, so one needed to measure the volume removed and not assume the contents were exactly 1mL.  In summary, I learned that day that the proper process was to snap the ampule and precisely remove the volume of the solution needed for dilution.  The remaining contents should be immediately transferred into a screw-cap or crimp-cap vial and placed in storage according to the recommendations of the manufacturer.

So why did I write this post?  This week I spoke to two customers who were snapping and pouring.  I thought if they didn’t know the correct procedure, then maybe I should write a post to tell others who also may not know.

For additional information about our MegaMix® solutions and what separates our chemical reference standards from our competitors, please see the links below.  Thanks for reading.

8270 MegaMix®

8260B MegaMix®

World-Class Certified Reference Materials (CRMs) 10 CRITICAL STEPS

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.

Need some help choosing a hydrogen generator?

As customers continue to switch to gas generators as their main source for hydrogen, we often get asked for assistance to help them make the right choice.  As a result, I decided to write this post to help our customers in their selection.

 H2Generator

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In most cases, choosing the appropriate generator is as simple as answering two questions:

 

1.  What purity do you need?  In other words, are you going to use the hydrogen for GC carrier gas, fuel gas, or both?

If you are only going to use the hydrogen for fuel gas (or for some other purpose where the purity is not critical), we suggest a Parker Balston® PEM generator.

If you are going to use the hydrogen for carrier gas (where high-purity is critical), we suggest a Parker Balston® H2PEMPD generator.

 

2.  What flow rate and pressure is required?  After all, before you can select a generator, you need to have this information.

For most GC set-ups, seldom is maximum output (delivery) pressure critical unless the instrument(s):

A.  Are located several rooms away from the generator where pressure drop across the tubing may drastically decrease delivery pressure.

B.  Are using long packed columns which require high head pressure.

C.  Are using small internal diameter, or very long, capillary or micropacked columns which require high head pressure.

 

In most cases, flow rate will determine which generator you would choose.

A.  In order to calculate the maximum flow rate needed, you need to carefully look at each instrument to determine its total hydrogen flow rate used during peak consumption (which may include fuel gas, column carrier gas, and hydrogen exiting the split vent line).

B.  Once the flow rate is calculated for each instrument, add these up to determine the total flow rate needed for all instruments.

C.  Finally, multiply a buffer factor* of between 1.5 and 2.0 to this total flow rate.

* Example: if you calculated that the total hydrogen flow rate needed for all instruments is 300mL/min, you would want to choose a generator with an output of somewhere between 450mL/min and 600mL/min.  In this case, we would suggest one of our generators which have an output of 510mL/min (note: 1mL/min = 1cc/min).

 

To read more about these generators, you may want to review Gas Management Supplies for GC Labs and Hydrogen Generator FAQs.  If you still have questions, email us at support@restek.com  Thanks for reading.