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Agilent’s Multimode (MMI) Inlet can be used as a PTV (programmable temperature vaporization) type inlet for large volume injections, with the advantage of using standard sized split/splitless liners. This technique requires careful optimization of a number of parameters, which starts by choosing a proper inlet liner. I recommend trying a Sky 2.0 mm Single Taper Liner with wool.
When performing large volume injections with solvent venting (LVI-SV), you are essentially trying to inject your sample at a low temperature, evaporate most of the solvent out, and then rapidly elevate the inlet temperature (after closing the vent) to transfer analytes to the column. In order to perform solvent venting, there should be a “platform” on which to catch and hold your sample, and serve as a “staging area” for the solvent venting to occur. Wool makes a great platform for this, as it has a large, relatively even surface area and can contain a great amount of heat energy with which to evaporate the solvent from. The wool will essentially catch your sample as it’s injected (preventing it from going straight out the vent) and simultaneously allow for evaporation of solvent, while retaining analytes of interest. Solvent venting allows for the introduction of large volumes of liquid, which can potentially lower detection limits, reduce solvent use by starting with lower sample volume, or require less prep time by not needing to concentrate the final extract as much.
As an example, I performed some injections of Restek’s QuEChERS performance mixes using an MMI inlet in solvent venting mode with a Sky 2.0 mm single taper liner with wool. The mixes were diluted in acetonitrile, which can be a tricky solvent due to its polarity and high expansion coefficient. With solvent venting, however, you can eliminate most of the solvent prior to transferring your analytes to the column, allowing for better focusing and no issues with overloading the liner with solvent.
Choose an inlet starting temperature that is below the boiling point of the solvent. I chose 80⁰ C, which though very close to the boiling point of acetonitrile (~82⁰C), worked fine due to the inlet actually being significantly cooler at the bottom, where the wool resides. Once you choose a starting temperature, injection speed and venting time must be optimized around the elimination rate of your solvent. I recommend using a solvent elimination calculator, such as the one included in Agilent’s software, to get a basic idea of where to start. From here you can adjust parameters until you get desired results. A venting time that is too long can lead to loss of analytes, whereas a short venting time will lead to excess solvent in your column, causing focusing issues and/or a large tailing solvent peak.
Vent pressure is a variable that will affect the amount of solvent that gets vented vs. loaded onto your column. Higher vent pressures will lead to more solvent loading onto the column. Vent flow affects elimination rate; with higher flows leading to quicker venting. For inlet ramp rate, you generally want to choose a relatively high rate to help reduce time for negative interactions between the analytes and active sites in the inlet, once heating begins.
I kept the oven starting temperature well below the boiling point of acetonitrile to ensure good focusing at the head of the column.
As a final warning, while wool makes an efficient and consistent platform for solvent venting and retaining analytes during this process, there is always the risk of activity towards certain sensitive analytes. From the QuEChERS mixes, I had issues with dicofol breaking down into DCBP, which may have been due to interactions with the wool. I also saw decreasing responses of dichlofluanid, captan, and folpet (three related pesticides) with consecutive injections. I did find this latter issue to be the case in liners without wool, as well though, and believe that the acetonitrile may have been negatively impacting these base sensitive pesticides and their interaction with the deactivation. I’d be interested to know if anyone else has run into this and found ways around it. Fortifying with acetic or formic acid may make a difference, though I did not get a chance to try this.
I’d love to hear about your experiences with solvent venting and what works/doesn’t work for you.
Jacob de Boer Gives Opening Lecture at the 7th International Symposium on Flame Retardants (BFR 2015)
Jacob de Boer from the VU University, Institute for Environmental Studies, Amsterdam, The Netherlands, gave the first plenary lecture at BFR 2105 in Beijing, “Recent Trends in the Use and Environmental Occurrence OF Flame Retardants: More – Less Persistent – More Toxic?” As expected, his thought-provoking talk covered a wide range of brominated flame retardants (e.g. PBDEs, HBCD, TBBPA) and their environmental impacts, but he also spent time on phosphorus-based flame retardants (PFRs), which are sometimes touted as safer alternatives to BFRs, even if they are halogenated PFRs. And, he emphasized that chlorinated paraffins, which are not only used as flame retardants but more often as cutting fluids, are showing up in alarmingly high concentrations in environmental samples. The challenges for quantitatively analyzing this class of compounds include lack of good reference materials (mainly middle-carbon chlorine-substituted congeners) and sample complexity (there are 1000s of congeners based on opportunity for hydrocarbon type and chlorine position).
The challenge for separating complex samples is exactly why I’m glad to work for Restek, one of the only chromatography companies to focus on unique GC and LC stationary phases. We have to remember that mass spectrometry cannot do all of the work, especially when isobaric congeners are involved. Chromatography lives!
On a personal note, one of the reasons I got into gas chromatography, and particularly multidimensional gas chromatography like GCxGC, was based on reading Jacob de Boer’s elegant works decades ago on heart-cut GC of PCB congeners. I hope Jacob’s current work continues to inspire other scientists.
Many of you may know that Restek recently developed and released a standard to support the determination of certain polycyclic aromatic hydrocarbons (PAHs) in food because they may be genotoxic and carcinogenic to humans. You can find details on the EFSA Scientific Opinion that lists the so-called 15+1 PAHs here. Hopefully you also know that we have an excellent Rxi-PAH GC column that separates these 16 PAHs from other potential interfering PAHs, which is not trivial in the land of isobaric congeners.
Shown below are some separations I was able to achieve using the Rxi-PAH with GC-FID, after translating a method that my colleague Chris Rattray gave me that he developed for GC-MS. I’m using the 40m x 0.18mm x 0.07µm format, which is the column we built for speed while still rugged enough to be used for food analysis. Importantly, I also show the potential interferences in two of the chromatograms below, and I even threw in a bonus zoomed-in chromatogram for the NIST 2260a standard to demonstrate the dibenz anthracenes separations on the Rxi-PAH. Those too can be subject to bias on other GC columns.
If you’ve selected another Rxi-PAH column format, or are using GC-MS, or are using hydrogen carrier gas (or all of the above!), give the Method Translator a try and you’ll separate the EU 15+1 PAHs, from each other and interferences, too.
You’re ready to install a column into your GC and realize you do not have the correct ferrules. 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. A visit to our ferrules home page will provide a general overview of various ferrules offered by Restek. By navigating the page, you can narrow the selection by choosing these parameters. This post will cover Thermo Scientific GC options and tips.
Thermo Scientific TRACE GC Ultra and Focus GC split/splitless injection ports and detectors use adaptors (pictured below) to install capillary columns. Restek sells both Thermo Scientific style and compression style adaptors.
Thermo Scientific style fittings use M4 style ferrules and specific capillary column fixing nuts. These are compatible with the following Thermo Scientific injectors; Spilt/Splitless, PTV, and Purged Packed.
Restek Compression style alternative adaptors for Split/Splitless injection ports use standard compression ferrules and nuts.
Please see part 1 of this series for tables of ferrule size versus column ID and ferrule material choices.
Thermo Scientific TRACE 1300/1310 GCs use ferrules that are slightly shorter than standard ferrules. If you use standard size ferrules, you would need to pre-crush them before inserting them into the inlet. Currently Restek does not have the correct size ferrules for these GCs.
Before you begin, make sure you have the correct size packed column adaptor installed in the GC. Restek does not sell these adaptors, you would need to obtain them from Thermo Scientific. Once that has been established, all that is reqiuired to install a packed column is the correct size compression nut and standard ferrule.
Stay tuned for my final post in this series on Shimadzu ferrules.
- Is the problem with standards or only with samples? If the low response is only with extracted samples, the problem is elsewhere in your method. Please see the blog post Now you see it, now you don’t-Troubleshooting method recovery problems.
- When was the standard ampule opened? If not fresh, open a new one. As mentioned in the blog post Extending the expiration date on a reference standard, the expiration date no longer applies once the container is opened.
- What were the storage conditions for the standard? As discussed in the blog post Handling your analytical reference standards, temperature and light exposure can make a world of difference. Be sure to check your certificate of analysis for proper storage conditions and precautions.
- If the standard is a mix of analytes, are all of them low or high? If you made a dilution, check your math and measurement techniques for dilutions that were made. Repeat them and verify. Make sure the initial volume used for dilution from the vial is made correctly, as discussed in the blog post Chemical reference standards; don’t just snap and pour.
- If you have any ampules from other lot numbers or vendors, prepare parallel dilutions and compare. Particularly if you have previously done this analysis and are not getting what you expect, obtain another standard and prepare it exactly in the same way and on the same day, alongside the one you are having trouble with. A stability issue can only be confirmed if you have data that shows that you are able to get acceptable results with another lot number or standard from another vendor.
- If you usually analyze this standard in combination with other standards, prepare your test dilutions without adding any other standards to the mix. Because the analytes can interact and affect each others’ stability, this is critical to isolate the issue. If you get to this point and have confirmed an issue with one product and not the other, contact the vendor. If this is a Restek product, contact us in Tech Services for assistance in resolving the issue.
- If your test dilutions demonstrate a problem with all of the lots or sources tested, then there is probably something unique to your analytical system that is causing a low response. If you would like assistance with troubleshooting on your HPLC or GC, feel free to contact our Tech Services group for help at Support@restek.com. We will need to see your operating conditions and settings, as well as chromatograms, so please be prepared to send a copy of those by email.
I hope this has been helpful. Thank you for reading.
I have the privilege of working with a number of talented people here at Restek and when I approached Sharon Lupo about a project last year known affectionately as “The Big Pain” I wasn’t sure how successful she could be.
Think about it: Opioids, Barbiturates, Anti-Depressants, Anti-Epileptics, Hallucinogens, etc. all have vastly different chemical make-ups. How else would they be able to treat the variety of ailments they do, or be able to be abused the way they are? The challenge is not only in the chromatography, but in speed of analysis and detection as well.
With lots of resourcefulness, help from her co-workers, and me mostly staying out of the way, a very comprehensive screening method was developed along with class specific analyses as well. 231 compounds, across ten classes, with detection in ESI(+) and ESI(-), were screened in 10 minutes. Optimized conditions for all the classes have also been completed. So whether you are looking for morphine or PCP, MDMA or THC, we have a method for you.
Sharon isn’t able to attend MSACL 2015 this year, but be sure to check out our presentation of her work at our Monday morning workshop, March 30th, which covers all aspects of this challenging project.
If you have been following this blog series, then you already know that we found numerous (upwards of 64) compounds in electronic cigarette solutions. You also know that we found even more (approximately 82) compounds in e-cigarette vapor. More importantly, you know not to waste your time testing the e-juice, because the vaporization process found in e-cigs results in a vapor with a different chemical profile than the liquid; and results in the production of toxic/carcinogenic VOCs like formaldehyde. What you do not know is how we have been testing our e-cigarette vapor. So without further ado I introduce to you our simple sampling device for collecting electronic cigarette vapor:
So what do we have here? We have an electronic cigarette connected to a thermal desorption (TD) tube and the other end of the TD tube connected to a 50 mL gas tight syringe. To collect a vapor sample from the e-cigarette we simply pull on the gas tight syringe, thereby drawing the e-cig vapor across the TD tube for collection. Subsequent to sampling we place the TD tube in our Markes UNITY for thermal extraction. So there it is in short form.
Now for those of you who like details continue reading on. The TD tube we chose for our work consists of the following 3 sorbents: Tenax TA, Carbograph 1TD, and Carboxen 1003. We chose this tube for its ability to look at C2 to C32 compounds, thus giving us our best chance of seeing as many VOCs and SVOCs. We chose the 50 mL gas tight syringe, because we already knew from the peer reviewed literature that a standard e-cig puff was anywhere from 35 to 70 mL (we chose 40 mL for the record). Lastly, it is important to note that the peer reviewed literature suggested that e-cig vaping topography was usually a puff over a ~4 second period. So obviously we drew our puffs over ~4 seconds. One last important point… the LED lit on the e-cigs when we drew on the syringe, indicating that vaporization was taking place. This is a very important point, because… well… you already know now.
Next time we can cover more on our vapor sampling methodology, compounds of interest, concentrations, and implications.
Need help finding a ferrule to install your column? Part 3: Perkin Elmer GCs
You’re ready to install a column into your GC and realize you do not have ferrules to do the job. 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. A visit to our ferrules home page will provide a general overview of various ferrules offered by Restek. By navigating the page, you can narrow the selection by choosing these parameters. This post will focus on Perkin Elmer GCs.
Perkin Elmer inlets use 1/16 inch fittings to install capillary columns. Some inlets require reducing adaptors as the body of these inlets and large fitting mounted in the GC oven is 1/4 inch. Restek and Perkin Elmer sell 1/4 to 1/16 inch reducing adaptors.
Perkin Elmer FID, ECD, NPD and FPD detectors come with 1/8 inch fittings. To install capillary columns in these detectors you can opt for a 1/8 inch nut and reducing ferrule. Or you can purchase a detector reducing adaptor just like the inlet. Restek and Perkin Elmer sell 1/4 to 1/16 inch reducing adaptors.
Detector Adaptors for Perkin Elmer FID, ECD, NPD and FPD: Ours are supplied with a 1/8 inch nut required to attach.
To install a capillary column into the TCD, make-up gas may be required for low capillary flow rates. Restek does not sell the fittings or adaptors for the TCD.
Our Vespel®/graphite ferrules will work with Perkin Elmer style fittings and nuts. Our 100% graphite ferrules will not.
- Restek does not sell Perkin Elmer style nuts.
- Restek sells a compression style reducing adaptors that will accept 1/16 inch nut. These will accept graphite and Vespel®/graphite capillary ferrules.
- Once you’ve determined which fitting is on your GC you can go to the table in part 1 and match the ferrule ID to capillary column ID and choose the appropriate ferrule.
Perkin Elmer packed column inlets are not on-column. They are equipped with liners (glass or quartz); Restek does not sell this type of packed column inlet liner. The fitting size on both the packed column injector and detectors are 1/8 inch diameter. To connect a 1/8 inch packed column all that is required is a 1/8 inch nut and ferrule.
If you have a 3/16 or 1/4 inch packed column, you will need to purchase from Perkin Elmer the 1/4 inch adaptors for the injector and detector. Then use a 1/4 inch nut and either a 1/4- 3/16 inch reducing ferrule for a 3/16 OD column or a 1/4 ferrule for 1/4 inch OD column
My next post, Part 4 of the series, will discuss Thermo Scientific GC’s ferrules, nuts, and helpful hints. Thank you for reading.
Despite what is sometimes advertised, setting up optimized methods for multiresidue pesticide analysis is typically not “easy peasy” and can be quite time consuming. Luckily, some colleagues are willing to share their method with us.
Thank you Kelli, James, and Jon!*
The downloadable spreadsheet contains retention times, transitions, ionization and collision parameters for our LC Multiresidue Pesticide Kit. The work used a Waters Acquity LC and an AB SCIEX QTRAP® 5500 LC/MS/MS system. Analysis conditions are listed on the last tab. The column used was an Ultra Aqueous C18 (cat# 9178312).
Although conditions may vary on different instruments, this information will dramatically shortcut your own method development. A similar spreadsheet using an LC-QQQ can be found here (see 5th bullet point).
*Kelli Sikorski, PhD, James Wittenberg, PhD, Jon Wong, PhD
You’re ready to install a column into your GC and realize you do not have ferrules to do the job. 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. A visit to our ferrules home page will provide a general overview of various ferrules offered by Restek. By navigating the page, you can narrow the selection by choosing these parameters. This post will cover Bruker/Varian systems.
Although Bruker/Varian GCs can come equipped with many injector options, selection of nuts and ferrules is simpler than my previous post on Agilent ferrules. These injectors all use Bruker/Varian style Capillary nuts and standard 1/16 inch compression ferrules to install capillary columns. The detectors on Bruker/Varian GCs that are designed for capillary columns use the same nuts and ferrules as the injectors.
For chart on ferrule size in relation to column ID see part 1
For table on ferrule material description see part 1
A word on ferrule material choice: I found using Bruker/Varian nuts with 100% graphite ferrules, upon tightening the nut the graphite material will start to extrude out the nut hole.
Bruker/Varian GCs can come equipped with two different packed column ports.
The 1040/1041- On-column Isothermal injector for 0.53mmID capillaries and packed columns. You will need to verify your current installation hardware before you begin. The 1041 comes equipped with 0.53mmID installation hardware. Adaptor kits for 1/8 inch packed columns and 1/4 inch packed columns are sold separately. These kits include adaptors for both Injector and detector sides. Restek does not sell these adaptor kits. Packed columns for this injector should have a void in the inlet side to allow the needle to inject directly into the column.
The 1060/1061 Flash Vaporization Isothermal for 0.53mmID capillaries and packed columns. This inlet has an adaptor with a deactivated glass insert. Restek does not sell this adaptor or inserts. You will need to verify your current installation hardware before you begin. The 1061 comes standard with 0.53mmID installation hardware. Adaptor kits for 1/8 inch packed columns and 1/4 inch packed columns are sold separately. These kits include adaptors for both Injector and detector sides. Restek does not sell these adaptor kits. Packed columns for these inlets can be packed full with no inlet void needed.
- The nuts and ferrules required to install the packed columns would be standard compression ferrules with compression style nuts.
- To install a packed column into a capillary injection port, you would use a “pigtail” setup.
Please refer to part 1 for suggestions on on-column centering adaptor kits.
In summary, the key points to remember are:
- Use Bruker/Varian nut and standard compression ferrules to install capillary columns.
- Know the ID of your column to match with the correct ferrule size.
- For packed columns: know which packed column adaptor you have in your GC.
- Match the correct packed column OD with the ID of the ferrule.
My next post Part 3 of the series, I will discuss Perkin Elmer ferrules, nuts, and helpful hints. Thank you for reading.