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Electronic Cigarettes Part IX: Vapor Analysis – What does all this mean?

Sorry for the two month blog delay, but by now you know we were utilizing multi-bed thermal desorption (TD) tubes to collect and analyze electronic cigarette vapor (see our last blog here). You also know that we found some interesting volatile organic compounds (VOCs) like formaldehyde, acetaldehyde, acrolein, xylenes, as well as siloxanes in electronic cigarette vapor. It is important to stress that the hazardous air pollutants (HAPS) formaldehyde, acetaldehyde, and acrolein were found in the vapor of four commercially available 1st generation e-cigarettes; however, these compounds were not present in the solutions. It is also important to note that these compounds were not found in the background air. Lastly, I must emphasize that our peers like Goniewicz et al. and Kosmider et al. have made the same observations for e-cig vapor. So we are just one of a few of the messengers (remember that when you are looking to shoot the messenger).

Up until now we have only talked about the presence of carcinogenic and toxic VOCs being identified in electronic cigarette vapor. However, we have not put any of this into a context, which may help make all these blogs more relevant to human health. To expound upon this further, it is important for me to acknowledge that I am more than likely breathing high pptv to low ppbv levels of formaldehyde, benzene, and other toxic VOCs as I type this blog. Therefore it is unjust to merely point out that we identified toxic VOCs in e-cig vapor.

So without further ado… remember that the HAP acrolein was not found in electronic cigarette solutions. In addition, acrolein was not found in the background air. However, acrolein was found in the vapor from all four of the e-cigarettes evaluated in our work. The acrolein concentrations ranged from 1.5 to 6.7 ppmv per 40 mL puff (0.003 to 0.015 µg/mL), which is comparable to the 0.004 µg/mL Goniewicz et al. reported. To put these concentrations into perspective, these levels exceeded the National Institute of Occupational Safety and Health (NIOSH) short-term exposure limit (STEL) of 350 ppbv. It is important to note that although we were not calibrated at the time for formaldehyde and acetaldehyde, the vapor concentrations for these two compounds appeared to be approximately the same as the acrolein concentrations observed. Again, the observation is consistent with what Goniewicz et al. reported.

It then becomes clear to me why end users experience what is often referred to as “throat hit.” These three carbonyls are well known mucous membrane (including eyes, nose, and respiratory tract) irritants, and inhaling ppmv levels (as those observed in the current study and our peers’ studies as well) of these three carbonyls would surely illicit said sensation. And we have not even begun to talk about the other identified and numerous unidentified VOCs we observed.

But as the title begs… WHAT DOES ALL THIS MEAN? Well obviously this means we cannot tell you electronic cigarettes contain no toxic chemicals. In fact, some e-cig manufacturers are already putting out disclaimers about their products.

 

M.L. Goniewicz, J. Knysak, M. Gawron, L. Kosmider, A. Sobczak, J. Kurek, A. Prokopowicz, M. Jablonska-Czapla, C. Rosik-Dulewska, C. Havel, P. Jacob III, N. Benowitz, Levels of selected carcinogens and toxicants in vapour from electronic cigarettes, Tob Control 23 (2014) 133.

Kosmider, A. Sobczak, M. Fik, J. Knysak, M. Zaciera, J. Kurek, M.L., Goniewicz,Carbonyl compounds in electronic cigarette vapors: effects of nicotine solvent and battery output voltage,Nicotine Tob Res 16 (2014) 1319.

 

Maximum temperatures of packed columns – Sulfur Gases

For my fifth and final post in this series, I would like to focus on packed columns for light sulfur gases.  Compounds include (but not limited to) hydrogen sulfide, sulfur hexafluoride, carbonyl sulfide, sulfur dioxide, methyl mercaptan, ethyl mercaptan, etc.

Because some analysts prefer PTFE tubing and/or PTFE frits for their columns, the maximum temperature may be limited to this hardware (which is 200°C).

If the columns below are in SilcoSmooth® tubing, their maximum temperatures are shown below.

Max Temp

Column and/or Packing

(°C)

Rt-XLSulfur

290

1.5% XE-60 / 1% H3PO4 on CarboBlack B

250

Chromosorb® T

250

 

To read my previous posts from this series, please see the links below.  I hope you have found them useful.

Maximum temperatures of packed columns – Porous Polymers

Maximum temperatures of packed columns – Liquid Phases

Maximum temperatures of packed columns – Hydrocarbon Analysis

Maximum temperatures of packed columns – Molecular Sieves

Maximum temperatures of packed columns – Molecular Sieves

For my forth post in this series, I would like to focus on molecular sieve packed columns.   At Restek, our three most common molecular sieve packings are the ShinCarbon, 5A, and 13X.  The ShinCarbon is a carbon molecular sieve, while the 5A and 13X are zeolite molecular sieves.  To read more about these packings/columns, please review Molecular Sieve Packed Columns and Fixed (Permanent) Gas Analysis.

 

Max Temp

Column and/or Packing

(°C)

ShinCarbon

280 / 300*

Molecular Sieve 5A

300 / 350*

Molecular Sieve 13X

350

 

* May be briefly programmed to this temperature.

Maximum temperatures of packed columns – Hydrocarbon Analysis

For my third post in this series, I would like to focus on specialty packed columns for hydrocarbon analysis.  In some cases, the packings in these columns are proprietary, so detailed information cannot be provided.  In other cases, application information may be limited.  However, we can provide maximum temperature limits (see table below).

For other columns used for hydrocarbon analysis, you should be able to find the maximum packing temperature based upon the maximum temperature of the liquid phase(s) and/or the porous polymer(s) in one of the links below.

Maximum temperatures of packed columns – Liquid Phases

Maximum temperatures of packed columns – Porous Polymers

If there is a packed column for hydrocarbon analysis (which is sold by Restek) and not included in this table or in either link above, email us at support@restek.com .  Thank you.

 

Max Temp

Column and/or Packing

(°C)

D3606 Column Set

165

0.19% picric acid on CarboBlack C

120

23% Rt-1700 on Chromosorb PAW

110

n-Octane on Res-Sil C

150

OPN on Res-Sil C

150

2abc Refinery Gas Column Set

110

Alumina F-1

300

Rtx-1 SimDist 2887

350

My GC capillary column was not sealed when I received it!

Traditionally, GC capillary column manufacturers have used several different methods to seal their products while in transit and storage. These sealing options include septa, silicone plugs, flame sealing, and press-fit caps.

 image1

I’m not going to discuss the advantages and disadvantages of these various approaches in this post. However, what I would like to address is a question that comes up periodically here in our technical service group:

What happens if you receive a brand new GC capillary column and one (or both) of the seals are no longer in place?

Is the column compromised? Will it still work? These are good questions to ask and consider.

Most of us have been told that exposing a capillary column to air (oxygen) can damage the phase. We are also aware that moisture or particles might enter an uncapped or unsealed column. What should you do if your column arrives without a proper seal?

Keep in mind that sealing a column is only intended to help protect column ends from damage and to keep particles from physically entering the column. These sealing mechanisms will not keep light or diffusive gases (such as hydrogen or helium) inside the column for very long.

Don’t panic. Although sealing the ends of columns is considered to be a good industry practice, occasionally, septa or silicone plugs will come loose, flame seals will break off, and column caps will disconnect. Yes, the column is now “exposed” and there is the possibility of “stuff” entering the column. However, the column is usually at relatively low (ambient) temperatures when this occurs, so the phase should be fine and it’s highly unlikely that the column has suffered any damage.

So, what should you do?

Install the column, leak-check the installation, and completely purge the column for a minimum of 20 minutes with clean, high quality carrier gas to help remove residual oxygen and moisture that may have entered the column during storage and transport.

This is a critical step. GC capillary columns MUST be thoroughly purged before being heated in the GC oven! Otherwise, stationary phase damage will occur.

Condition the column per the manufacturer’s recommendations. This will stabilize the baseline and minimize bleed. The following links provide detailed information on how to condition your columns:

How to Condition a New Capillary GC Column

PLOT column instruction sheet

Micropacked (0.53mmID) column instruction sheet

How do I condition a new packed or micropacked column?

In summary, it’s very unlikely that a missing end seal (or two) will result in damage to your column.

Thank you for reading!

The Most Useful Pesticide Standard Ever…monitoring GC inlet “dirtiness”

I have spent most of my time over the past several years testing pesticides and there is one standard that I simply can’t live without…QuEChERS Performance Standards Kit.

It is based on a really interesting article* on analyte protectants with a few compounds added.

The standard has 40 compounds housed in three vials for long term stability. The smart folks in our Reference Standards department made each vial 300 ppm in acetonitrile/ acetic acid (99.9:0.1). This makes it simple to blend equal volumes of the three vials to get a mix at 100 ppm.

  • It has compounds from different pesticide classes
  • Covers a range of polarities and volatilities (so good for GC and LC)
  • Has “good” or easy pesticides and problem pesticides
  • Read more at the product page

The mix is a great method development tool and we use it to evaluate both sample preparation and instrument performance.  Certain compounds make excellent probes for certain aspects of instrumental performance and I will show you one here. I monitor deltamethrin to determine the “dirtiness” of my inlet.
From our experience, we know that deltamethrin forms an isomer as nonvolatile material builds up in the GC inlet especially in the liner. It can also happen with high inlet temperatures too.

I am always monitoring the formation of this deltamethrin isomer to keep an eye on my liner performance and can quickly replace my liner when the breakdown is bad enough. In order to monitor the breakdown isomer, I have to make sure to add it to my mass spec method. I have been using GC-MS/MS lately and I simply use the same MS/MS transitions that I use for deltamethrin. The breakdown isomer will elute just before deltamethrin on “5” type columns.

In this example, I am running on an Rxi-5ms column using efficiency optimized flow and optimal heating rate.

You can see that tracking the deltamethrin isomer formation and the decrease in deltamethrin signal is a good indication of inlet performance. As more orange samples are injected, more nonvolatile material deposits on the liner causing a decrease in deltamethrin signal. After some predetermined point…maybe loss of 20% of the signal…I replace the inlet liner.

Stay tuned for more ways I use The Most Useful Pesticide Standard Ever

 

deltameth1

 

 

 *Combination of Analyte Protectants To Overcome Matrix Effects in Routine GC Analysis of Pesticides in Food Matrixes,  Katerina Mastovska, Steven J. Lehotay, and Michelangelo Anastassiades, Anal. Chem. 2005, 77, 8129-8137.

Maximum temperatures of packed columns – Liquid Phases

For my second post in this series, I would like to focus on liquid phases.  As you know, for packed columns, a liquid phase needs a solid support.  Combined, these are what makes the “packing”.  In most cases, it is the liquid phase which limits the packed column’s maximum temperature, and not the solid support.

Therefore, like my last post (Maximum temperatures of packed columns – Porous Polymers), I will make the following assumption:  The column’s maximum temperature is due to the liquid phase, and not the solid support, the column’s tubing, end plugs, fittings/adaptors and/or ferrules used for installation. If you have a packed column which includes non-metal tubing or end-plugs other than glass wool or metal, email us at support@restek.com.

In addition, if the solid support is not a Chromosorb® diatomaceous earth, Silcoport®, CarboBlack®, or Res-Sil®, email us at support@restek.com

The table (below) contains the minimum and maximum temperatures of many of our liquid phases.  The link below has the same information in a format that is easier to read.

Packed Column Instruction Sheet   See page 2.

To summarize, the maximum temperature of a liquid phase on a solid support packed column is almost always determined by the liquid phase.  Keep watching for future posts on this topic.

 

Liquid Phases

Maximum temperatures of packed columns – Porous Polymers

We often get asked about the maximum temperature limit of our packed columns, so I decided to write a post series which will provide this information for the majority of the packed columns which we sell.  I thought I would start with the least complicated packed columns, those whose packings are typically not coated with a liquid phase.  These packings include porous polymers.

For this post, I will only be focusing on HayeSep®, Porapak®, and Tenax® packings.  I decided not to include Chromosorb® porous polymers because they are either in short supply, or currently unavailable.

I am going to make the following assumption:  The column’s maximum temperature is limited to the packing, and not the column’s tubing, end plugs, fittings/adaptors and/or ferrules used for installation. If you have a packed column which includes non-metal tubing or end-plugs other than glass wool or metal, email us at support@restek.com .

Please note:  The catalog (part) numbers shown below are just for the packing, and not any packed column.

Keep watching for future posts on maximum temperatures of packed columns.  Thank you.

 

HayeSep1

 

Porapak 1

Tenax

 

Packed Column information for the beginner

We seem to be getting more calls from first time users of packed columns, so I decided to write this post for these beginners to help them understand the terminology commonly used when describing these products.

 

What is a packed column?

Unlike GC capillary columns, which are referred to as WCOT (Wall Coated Open Tubular), or PLOT (Porous Layered Open Tubular), packed columns are what their name implies, they are packed full of fine particles and not “Open” (like a drinking straw). Because they are packed, they have a much higher pressure drop across the column. This is why they tend to be much shorter in length than a capillary column.

  • Packed columns consist of:
    • Tubing
    • Packing
    • End Plugs
  • All packed columns contain particles, as mentioned earlier. Particles may be uncoated or coated (with a liquid phase). When the particles are uncoated, they are usually referred to simply as the “packing”.
  • When coated, these particles are referred to as a “solid support”. In other words, the particle is the support for the liquid phase.

 

So why would someone use a packed column instead of a capillary column?

  • Many older methods, which are still used today, were written using packed columns.
  • In many cases, does a better job at separating light gases than capillary columns.
  • Less expensive.
  • Much more compound capacity. Usually preferred when using a TCD as the detector.
  • Many unique selectivity phases/packings not available in capillary dimensions.
  • Advantage – Packed:
    • Price
    • Capacity
    • Light gas analysis
    • Unique selectivity phases/packings available
  • Advantage – Capillary:
    • Many more theoretical plates (separation power) than a packed column.
    • Can be used with mass spectrometers because of narrower ID’s.
    • Most modern GC’s designed for use with capillary columns.
    • Columns used in most current methods.
  • Don’t forget:
    • Make sure you have the necessary fittings for installation.
    • Some sort of flow meter is a necessity.
    • Never, ever cut (trim) a packed column like you would do with a capillary column.  This would most likely cause the bed to collapse.

 

I hope you have found this useful.  For additional information on packed columns, please review our FAQ’s and blog posts.  Thank you.

 

It’s All in the Split Vent Trap

Recently I came across a situation where I wanted to make a series of constant flow GC-FID runs, during which, the inlet pressure would increase from 2 to 6 PSI over the temperature program. I also wanted to use split injection with a split ratio of at least 20:1, in this case that translated to a split vent flow of about 150 mL/min.

I realized that I would be pushing the lower limit of reliable inlet pressure control but those parameters should be within the range of a (relatively) modern EPC controlled HP 6890 GC.  Of course, as I installed the column and got to work it was clear that something wasn’t right.

The inlet pressure would rise above the set point and stay there completely stable, like there was some sort of constant offset preventing the GC from becoming ready. I noticed that as I increased the split flow the real-time inlet pressure would rise further and further above the set point.
Pi bad trap

 

I started going through the standard troubleshooting motions, pressure decay test, leak checking, everything was good! At one point I flipped the inlet into splitless mode and the pressure equilibrated right to the set point. Now we are getting somewhere.

Looking at a flow diagram for the inlet and EPC system I became convinced that there must be some kind of flow restriction between the pressure sensor and the proportional valve on the split vent. This mystery restriction had to be the cause of the  build up of inlet pressure.

 

split inlet

 

 

I set about replacing the 1/8” copper split vent line, replaced the split vent trap, cleaned the inlet fitting with methanol, and installed a Low Pressure Drop Precision Split Inlet Liner. None of this worked and I was quickly running out of options.

What I didn’t know at the time was that there are two different styles of split vent trap commonly used on the 6890. The classic “pencil trap” (top in figure) was standard on instruments made before 1997 and the newer “cartridge type” (bottom in figure) that is now used on the 7890 series. My instrument was equipped with a pencil trap.

 

comparison

 

Ah-ha, this must be the key! The two different styles of trap actually provide different amounts of flow restriction and I had never realized this until I attempted to run the instrument at low inlet pressure, where the slight difference becomes apparent.  Sure enough when I swapped my brand new pencil trap for the cartridge type everything worked fine and my inlet pressure went right to the set point.

 

Pi good trap

 

In fact, using the cartridge type trap and the Low Pressure Drop Precision Split Inlet Liner I was able to get split vent flows of up to 500 mL/min at 5 PSI inlet pressure. If you ever run into a problem like this at low inlet pressures make sure to take a look at your split vent trap!