Archive for the ‘Miscellaneous’ Category

How Dirty Are You? Part 4…Manual Syringe Rinsing…The Answer

So how many times do you need to rinse a syringe?

Well, I can tell you the answer for the experiment we did. Let me first refresh your memory on specifically what we did.

Sequence of manual syringe rinsing:

1. 20 µL draw of a 500 ppm hydrocarbon standard and expel it
2. 20 µL draw of acetonitrile – eject into sample vial – test via GC-FID
3. Repeat step 2 many times

Each “rinse” was tested via GC-FID.

How many 20 µL acetonitrile rinses were needed to show no signal (FID)?

The answer is 4.


I want to thank everyone that commented when I posed the question. Most people were right on track with about 4 rinses. It is also funny that people tended to do “extra” rinsing regardless of what they thought was required. I still do this with about 6 to 10 rinses depending on the situation.

I wanted to share some helpful hints from people who commented:

  • - Use more than one rinse solvent especially in situations were analytes have a wide range of polarity
  • - Use more than one rinse vial
  • - Use the same solvent for rinsing as is used for the sample and standard solutions

Here is a chromatogram of a 50 ppm hydrocarbon standard followed by chromatograms of consecutive rinses. The 50 ppm chromatogram can be used as an intensity reference because the y-axis is the same for all chromatograms.



How Dirty Are You? Part 4…Manual Syringe Rinsing…The Question


I don’t even want to guess how many times you would need to rinse this syringe before removing all traces of reanimation “reagent”

This How Dirty Are You? blog should really be credited with inspiring the entire project. I was discussing the number of times I rinse my syringes with a colleague, Michelle Misselwitz, a few years ago. We were working in the same hood and I noticed that she rinsed her syringe a lot…I do too. I was even reminded of my rather obsessive rinsing at Thanksgiving this year. I was washing a few dirty dishes by hand and my mother mentioned that I was rinsing them a lot…and that my grandmother would have been upset because I was wasting so much water…but “What about the soap residue?” I said.

Over the years, I have been told different things about the number of times a syringe should be rinsed to prevent carryover/contamination…and I have been asked the same question many times. I was told early in my lab career that 7 was the magic number…so just to be sure, I got in the habit of using 10 rinses.

What We Did

There are a lot of variables to consider…sample matrix, compound concentration, sample solvent, rinse solvent(s), rinse volume etc. But to keep things simple, we used a hydrocarbon standard at a high level and rinsed with the same solvent as the sample solution, acetonitrile. We also defined the volume of a “rinse” as 20 µL. We started the experiment with a 20 µL draw of a 500 ppm hydrocarbon standard. The hydrocarbon standard was expelled and then consecutive rinses were performed. Each rinse was tested by GC-FID.

Sequence of manual syringe rinsing:

1. 20 µL draw of a 500 ppm hydrocarbon standard and expel it
2. 20 µL draw of acetonitrile – eject into sample vial – test via GC-FID
3. Repeat step 2 many times


Post or Email me with your answers and look for the data in my next blog.

1. How many 20 µL acetonitrile rinses were needed to show no signal (FID)?

 (Hint: The answer is between 1 and 15…I didn’t say it was a good hint.)



 (photo credit:

Lab Hack: Quickly Reducing GC Inlet Pressure on an Agilent GC Prior to Changing the Septum and/or Inlet Liner

Have you ever been changing your Agilent GC inlet liner (you do change that routinely, right?), particularly a single taper with wool type, and pulled it out to see the wool at the top of the liner (Figure 1) when it should be at the bottom of the liner (Figure 2), the proper placement where injected sample can hit it and be transferred to the GC column?  How does this occur?  Sudden depressurization of the GC inlet can cause the wool to pop to the top of the liner.  It probably doesn’t matter if this happens when you’re changing the liner, since you’re going to throw the old liner away, but it can also happen when you’re changing the GC inlet septum if you haven’t properly depressurized the inlet, and then unknowingly you’re left with the liner wool at the top of the inlet, where it’s not effective for its purposes of keeping the sample from hitting the bottom seal (where compounds like DDT can degrade), heat transfer, and preventing nonvolatile “dirt” from collecting on the head of the more expensive GC column.

In the following sets of figures, I’ll show you how I depressurize my Agilent 6890 GC inlet to prevent the inlet liner wool from jumping up.  As always, it is much better to completely cool all heated zones before inlet maintenance procedures.

Go to the Agilent GC Keyboard, and press “Col 1” (Figure 3), depending on the Column and Inlet in use.  You’ll see the Display showing similarly to Figure 4.  If necessary, use the “Up” or “Down” symbol key on the Keyboard to move the Display arrow to “Pressure” (it is on “Flow” in the Figure 4 example).   When the Display arrow is on “Pressure”, use “0.1 Enter” (or even “0 Enter”) from the Keyboard (Figure 5), which should cause the Pressure to drop down relatively quickly, but not so quickly that it causes the inlet liner wool to move (the pressure does not drop all the way to zero, typically, Figure 6).  [Note:  On newer Agilent GCs you may hear the “rattlesnake” as the pressure drops.]  Use the “Up” symbol key to move the Display back to “Pressure” and then press “Off” on the Keyboard (Figure 7).  Again, the “Pressure” may not completely zero out, but the GC inlet is now ready for a septum and/or liner change.  Why don’t we just use “Off” immediately instead of “0.1”.  When you use “Off” the pressure bleeds off very, very slowly through the GC column and if you open the inlet too soon the liner wool can move in the liner.

Don’t forget to restore pressure/flow before you heat the GC inlet and column up, and it’s always good to leak check after inlet maintenance.

Fig 1x

Fig 2x

Fig 3

Fig 4


Fig 5xx

Fig 6

Fig 7

Fig 8

Need help finding the correct ferrule to install your GC column? Part 1: Agilent GC ferrules

You’re ready to install a column into your GC and realize you do not have ferrules to do the job. But which ferrule do you choose?  The parameters to consider when choosing the correct ferrule are instrument make and model, nut size and type, ferrule material, and column ID size. A visit to our ferrules home page will provide a general overview of variety of ferrules offered by Restek.  By navigating the page, you can narrow the selection by choosing these parameters. This is the first in a series of posts that will hopefully make this selection process easier. We begin with Agilent systems because they have more choices available.

Capillary Column Ferrules

For this section, I will assume the GC is already configured to install capillary columns with 1/16 inch fittings. Restek offers two options on nuts and ferrules for Agilent capillary column installation. There are compact ferrules and standard ferrules, each with their own style of nut. The compact ferrule and nut are considered the Agilent-style. The broad taper on the compact ferrules was designed to match the taper on the bottom of the inlet seal. Standard ferrule and nut can also be used effectively on an Agilent system.

Here are the visual differences between the standard and compact ferrules:

Standard                                                                         Compact

standferrule                                                             Compferrules          

Capillary Ferrules                                   Compact Ferrules (Fit ≤ 0.28mm ID Fused Silica Columns)

                                                                Compact Ferrules (Fit 0.32mm ID Fused Silica Columns)

                                                                Compact Ferrules (Fit 0.45/0.53mm ID Fused Silica Columns)


Here are the catalog numbers of the corresponding applicable nuts:

FTnut                    capnut                 hotswapFT2nut


Finger-Tight Capillary Column Nuts Capillary Column Nuts Hot Swap Capillary Column Nuts Looped Finger-Tight Capillary Nuts
Brass Stainless Steel
Standard Ferrules 21041 21879 20883 22347 21312
Compact Ferrules 21040 21878 21884 22348 21311


This is a cross-cut look at the insides of the standard capillary nut and shows the length of the ferrule and the depth of the nut hole. This helps to show how necessary it is to match the ferrule with the proper nut; otherwise there will not be an adequate seal. If you are unsure which of these nuts you have on hand to install your columns, take note the Agilent style nut has a notch on the hex-nut portion, the standard does not.


comp                                     stand


“Compact”  Agilent-style Ferrule and nut                       Standard  ferrules and nut


Once you’ve matched the nut type to the correct ferrule type, now we need to match the capillary column ID to the ferrule ID. The table on sizes below gives an overview of how to match fused silica and MXT capillaries.


The next step in determining the correct ferrule is the material. The chart below explains the differences between the material choices. For installation into the inlet and most detectors, either graphite or the softer 60/40 vespel graphite should work fine. For GC/MS, it is recommended to use the standard, long ferrule vespel/graphite installed with an MSD source nut.  This material is a good fit for MS because it will not fragment or allow oxygen to permeate into the system under vacuum applications.

Agilent has suggested that 100% vespel ferrules be only used for isothermal analysis.

MSD Source Nut



A note on the Agilent TCD, it has an 1/8 inch compression fitting port. In order to use our Agilent style or standard design nuts and ferrules you would need to have the Agilent supplied adaptor fitting. Restek does not have that fitting. Alternatively, Agilent does supply a two piece ferrule to install capillary column with a 1/8 inch compression nut. Restek does not sell the two piece ferrule and we do not recommend using a one piece graphite reducing ferrule.


Packed Column Ferrules

Typical Agilent packed column inlets are sized to accommodate ¼ inch OD packed columns; verify the fitting size of your inlet and detector. Agilent systems generally use standard compression style nuts and ferrules. If you doing on column injections, installing a 3/16 or 1/8 inch OD column will require inlet adaptors to center the column inside the ¼ inch injection port. If your instrument is equipped with an adaptor with a glass insert, on column injection will not be necessary, therefore a nut and ferrule would be all that is required to connect the column. Again you will need to verify the size nut and ferrule required. If you are installing a packed column into a capillary column inlet and detector we suggest a pig-tail configuration.

Notes on Agilent detectors- verify the size of the fitting required to connect the column. Agilent TCD’s for example are 1/8 inch compression fittings. If you want to install a 3/16 packed column, make sure your detector is adapted to accommodate ¼ inch packed column so you can use a reducing ferrule and ¼ inch nut.

Packed Column Inlet Adaptor


In summary, the key points to remember are:

  • Match the ferrule with the proper nut
  • Know the ID of your column to match with the correct ferrule size.
  • Know system requirements for the ferrule material.
  • For packed columns: Verify the fitting sizes of you inlets and detectors.


Look for future posts on nuts & ferrules for other instrument manufacturers. Thanks for reading.

I would like to thank my Colleague, Erin Herrold for her assistance and insight with this blog post.

How Dirty Are You? Part 3…Gloves…The Answers

Read The Question first…

Let’s review…we soaked small pieces of different gloves in acetonitrile for 30 minutes. The samples were tested using GC-TOFMS. For relative intensity, a dashed line at the peak height of a 2 ppm PAH standard is drawn on the chromatograms.

Which gloves produced the worst background? GREEN GLOVES


Bright green, yellow latex and royal blue gloves had similar background levels even though the chromatograms look different. Baby blue gloves and green gloves had higher background. Green gloves had the highest intensity background peaks. Let’s look at the data…

brightgreen cgram


yellow glove

















































































I have to admit that I was a bit surprised at the answer to the next question. Several people emailed me answers and UV stabilizers was the most popular choice. However, we saw several antioxidant compounds in the glove samples. A couple of compounds are shown below. Check out the signal from antioxidant “Nocrack NS 6″ in the baby blue gloves!

Antioxidants are added to rubber to prevent oxidative damage that degrade the physical and mechanical properties of rubber materials.

q2 gloves


glove antiox 1 glove antiox 2




Philae: Goodnight but Not Goodbye. Unlocking the Origins of Life: Comet 67P/Churyumov-Gerasimenko

Rosetta's Philae on the surface of 67P/C-G. Photo Courtesy of ESA (European Space Agency).

Rosetta’s Philae on the surface of 67P/C-G. Photo Courtesy of the European Space Agency.

On September 28th, 1969 a bright fireball exploded, shaking houses as it lit up the daytime sky outside of Murchison, Australia. Over the next forty-five years scientists have studied the Murchison Meteorite and found 14,000 compounds to include 92 different amino acids. Of the amino acids discovered, only 19 are found on earth. This rock, and evidence from other encounters with space objects, reveals that life-forming amino acids may have originated deep in space even before the formation of the sun.  In addition amino acids have been found on Saturn’s moon Titan, comets and newly forming stars (Large Molecule Heimat, Sagittarius B2).

Comets are of specific interest because they are the oldest objects in the Solar System, preserving four-billion-year-old organic molecules. Comet 67P/Churyumov-Gerasimenko is a short period comet (Jupiter Family) with an orbital period of 6.5 years. These objects are believed to originate from the Kuiper belt, a region of icy rocks just outside of Neptune’s orbit. A collision with another object can cause these rocks to fall into orbit around the sun.

Philae’s COSAC (Cometary Sampling and Composition) experiment was able to analyze samples taken from below the surface of the comet before the batteries died from lack of sunlight. ESA (European Space Agency) reported the lander bounced and is located under a cliff where it only receives 90 minutes of sunlight every 12 hours. When Philae receives enough sunlight it will again power up and send a signal to Rosetta. The last transmission was received on Friday, November 15th but ground control confirmed that COSAC sent back analytical data.

Striking images of Philae's harrowing journey to 67P/C-G. Courtesy of European Space Agency.

Striking images of Philae’s harrowing journey to 67P/C-G. Courtesy of European Space Agency.

Restek in Space:

Comet Impacts May Have Jump-Started Life on Earth

Amino Acid Detected in Space

New Organic Molecule in Space


Comet 67P/Churyumov-Gerasimenko: Data from Rosina.

Mosaic of 4 images combined. Gas and dust from comet can clearly be seen from the center. Courtesy: European Space Agency (ESA).

Mosaic of 4 images, gas and dust from comet can clearly be seen from the center. Courtesy: European Space Agency (ESA).

While anxiously waiting for data from the COSAC (Cometary Sampling and Composition Experiment) aboard the Philae lander, we turn to some of the information that has already been sent by the Rosetta’s Rosina (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument.  While sampling the comet’s coma they have found carbon dioxide in nearly the same proportions as water. Rosina has the ability to measure the ratio of hydrogen to deuterium in water.  Deuterium is believed to have been created in the Big Bang 13.8 billion years ago.  Since deuterium accounts for approximately 0.0156% of all hydrogen found on earth, this data may shed light on the origin of our water.

So far the following compounds have been detected by Rosina:

Water, Carbon monoxide, Carbon dioxide, Ammonia, Methane, Methanol, Formaldehyde, Hydrogen sulfide, Hydrogen cyanide, Sulphur dioxide, Carbon disulfide and ethanol.


The ‘Perfume’ of 67P/C-G

Restek in Space


GC capillary columns for the European Pharmacopoeia methods

Have you ever viewed a European Pharmacopoeia method and tried to figure out which Restek GC capillary column you should use? To make the selection a little easier for our customers, I decided to match the nomenclature listed in the European Pharmacopoeia “Reagents” chapter to the appropriate Restek columns.  I hope you find the table below helpful.  If you have any questions, simply send them to or contact your local distributor.  Thank you.



EU Capillary 5

How Dirty Are You? Part 3…Gloves…The Question


This third installment of How Dirty Are You? is all about gloves. Outside of solvent compatibility, there is a lot of room for personal preference regarding the type of lab gloves people can use.

I found 5 different gloves in our lab. The bright green gloves and yellow gloves are the two types most often used by my lab mates. I use the bright green gloves. I work with QuEChERS extracts all the time so I was most interested in background resulting from gloves contacting acetonitrile. I have already investigated the bright green gloves when I was tracking down some peaks in my process blank for a QuEChERS experiment. I was seeing some repeating peaks which were identified as alkanes via GC-TOFMS. Through some further investigation, I was able to confirm that these alkane peaks were from my favorite bright green gloves. That got me thinking about contamination peaks from other gloves…

What We Did


We tested the background generated by the 5 glove types found in our lab by soaking a small piece of glove in 1 mL of acetonitrile for 30 minutes. The samples were tested via GC-TOFMS after the 30 minutes. For relative intensity, a dashed line at the peak height of a 2 ppm PAH standard is drawn on the chromatograms. But you will not see the results until my next blog!



Post or email me your answers.

Email me with your answers and look for the data in my next blog.

1. Which gloves (see below) gave the worst background?


Bright Green Gloves

Baby Blue Gloves

Yellow latex Gloves

Green Gloves

Royal Blue Gloves

2. What common additive was found in multiple gloves tested?




UV Stabilizers


Think twice before purchasing a 3/16” OD packed column

So you may be asking yourself, why the cautionary statement? Well, it’s very simple, many of our customers who purchase 3/16” OD (outside diameter) packed columns have a difficult time installing them into their GC oven.  Why?  Sometimes finding the appropriate fitting/ferrule is difficult.

Let’s say you have a packed column instrument. If your injection port was designed for 1/4” OD columns, then installation is usually not an issue.  Most customers can use a 1/4” x 3/16” OD reducing ferrule, like Restek 20258. To center the column properly (which is recommended if you plan to inject your sample into the packed column) and if you have an Agilent GC with a packed column injection port, you can use our kit 21650, which resembles what is shown in the photo below.  The silver thing that looks like a GC injection port liner is called a “centering sleeve”, and as you may guess, its purpose is to center the packed column in the injection port.



Now let’s look at a few scenarios where installing a 3/16” OD packed column is not so simple. Many modern GC’s have injection ports designed for 1/8” packed columns.  So how does one install the larger 3/16” OD packed column into this smaller injection port?  You will need a short piece of 1/8” OD tubing and a 3/16” to 1/8” reducing compression (straight) union like Swagelok SS-300-6-2. Unfortunately, we do not sell this fitting.  However, we do sell a 1/4” x 1/8” reducing union, Restek 23170.  Simply replace the 1/4” metal ferrule set with ferrule 20258.

What if you have a GC designed for only capillary columns? Normally we would recommend a “pigtail” set-up, like described in this FAQ.  How do I install a packed column into a capillary GC injection port?  However, you would need a 3/16” x 1/16” reducing (straight) union, like Swagelok SS-300-6-1. Unfortunately, we do not sell this fitting either.  However, we do sell a 1/4” x 1/16” reducing union, Restek 23169.  Simply replace the 1/4” metal ferrule set with ferrule 20258.

In summary, before purchasing a 3/16” OD packed column, make sure you have the proper fittings/ferrules available for installation. I briefly mentioned this in my post titled Things to Consider Before Ordering a Packed Column.  To save yourself frustration, do a little homework first to determine if a 3/16” OD column is really your best choice, and if not, consider an alternative OD based upon your particular instrument.