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Think you must use RFID-tagged lamps? Think again!

The recent addition of RFID tags to detector lamps allows automatic reference and usage data collection to your system software. This is convenient but comes at a cost: up to 40% more for an OEM-tagged lamp compared to a Restek replacement lamp. At the time of the writing of this blog post, Restek does not offer RFID-tagged lamps. But if you don’t need the bookkeeping feature, simply disable the tag requirement in your system software and save some money.

To allow the use of a non-tagged lamp in Lab Advisor, follow these instructions:

At your Lab Advisor home screen, choose “System Information > Instrument Control” from the left navigation column. A module list appears in the main window. Click on the detector module. Expand the “Controls” menu. Click on the “Special Commands” triangle at the bottom. Turn the “Lamp tag required” option off (circled option). A non-tagged lamp will not attempt to light if this option is ON. Be sure to click the “Save Session Results” button at the bottom of the screen. That’s it!

LabAdvisor SS Circle

The software can still count your hours. Simply reset the counter in the “EMFs” menu option.

Lab Advisor EMFsCircle

Except for the tag, Restek lamps are manufactured to meet OEM specifications and have stood the test of time in field use. We have been offering lamps for more than 15 years. In the rare case that you experience an issue with a Restek lamp, return it for a replacement. 100% satisfaction guarantee is Pure Satisfaction.


Pesticide analysis for cannabis flower: method and data overview

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Sara in her Restek Chromatography Mastermind shirt.

blog trace group photo 1Pesticides in cannabis has been a hot topic lately and we have been getting many requests for help with this analysis. We did work on pesticide residue testing in cannabis about 6 years ago. At that time, we were limited to testing our methods with a small amount of seized material. Recently, we have been able to work with great collaborators, Shimadzu Scientific Instruments and Trace Analytics, to do more comprehensive method development and partial validation. Trace Analytics is a testing laboratory servicing the medical and recreation cannabis inustry in Spokane, Washington since 2015. With the help of our collaborators and availability of bulk samples, we were able to revisit method development and perform a partial validation. This would not have been possible without the hard work of all of the team members; Jeff Dahl, Caitlin Johnson, Derek Laine, Sara Minier, Amanda Rigdon, Gordon Fagras, and  Jack Cochran.

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Amanda and Derek doing some creative plumbing


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Sara, Caitlin and Julie too busy to look at the camera.

We developed a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) sample preparation method (stay tuned for a more discussion in a future blog) paired with LC-MS/MS analysis using a Shimadzu LCMS-8050 with Prominence HPLC. QuEChERS is designed to be generic and work for a wide variety of pesticides with diverse chemical properties. This is one of the reasons why QuEChERS is so popular for food safety testing. This approach takes advantage of the selectivity and sensitivity of LC-MS/MS allowing us to use a “good enough” sample preparation. QuEChERS is much less intensive than what would be needed if a non-MS/MS based method was used…another reason why it is popular.


We used a 1 µL injection to help with early eluting pesticides peak shapes since the extraction solvent is acidified acetonitrile and the initial mobile phase is mainly water. This also helps maintain column and instrument cleanliness allowing many injections to be made before maintenance is needed. At least two MS/MS transitions were monitored for each analyte.

Take a look at the method details of our sample prep protocol and analysis method.


We tested three different cannabis flower matrices. They included orange kush flower, permafrost flower and then a composite. The composite sample was simply a combination of flower and sugar leaves from several strains. We did this so we had enough “pesticide-free” sample to perform all of the spiking experiments.  Each matrix was spiked at three levels (50, 200, 1000 µg/kg “dry” weight) with the Restek Oregon pesticide standard (more information in “sample prep protocolpage 2). These levels were chosen based on current and proposed regulatory limits from various states. Each spike level was performed in triplicate. The spiking scheme is shown in the table below. Triplicate data allows us to determine average recovery and relative standard deviation (RSD) for each level in each matrix as well as across the three matrices. Matrix-matched calibration was used for quantitation and both method and instrument internal standards were used.

cannabis spiking scheme2





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1.5 grams flower with water and acetonitrile





The data shown here is for “dry” flower material and so we used a reduced sample amount (1.5 g) and a hydration step. Adding water is critical for the extraction chemistry to work properly. The AOAC QuEChERS extraction salts were used for the salting out step of the extraction. After the extraction step, we chose to use the “universal” formulation of the dispersive solid phase extraction (dSPE) to remove unwanted coextracted compounds. This formula contains 50 mg/mL extract each of primary secondary amine (PSA) and octadecyl (C18) sorbents and a moderate level of graphitized carbon black (GCB) (7.5 mg GCB per mL of extract). GCB removes chlorophyll which can cause instruments to become dirty if injected.


For more information on QuEChERS, see these other blogs: QuEChERS – Where to start?, QuEChERS 3 part series and Shortcut: AOAC QuEChERS protocol.

Take a look at recovery values and RSDs table.



Highlights of the data:

  • For the large majority of pesticides, in all three matrices AND at all three spike levels, recovery was between 70-120% which is the desirable range for the food safety industry. It is expected that difficult pesticides or detection at very low levels may produce recovery below this range. In most of these cases, RSD values were less than 20% for a single matrix (n=9) and across all three matrices (n=27). This data indicates that this method is appropriate for multi-residue pesticide analysis in cannabis flower.
  • There are some of the Oregon pesticides that are more amenable to GC analysis and we would suggest using GC-MS/MS testing of the extracts to cover bifenthrin, cyfluthrin, dichlorvos, MGK-264, and permethrin. We were able to determine recovery at the highest spike level (1000 ppb) with LC-MS/MS for bifenthrin, dichlorvos, MGK-264 and they fell within the 70-120% recovery and less than 20% RSD so this indicates that the sample preparation method is suitable.
  • Abamectin, widely known by the trade name Avid, is a popular insecticide used to treat spider mites which are known to attack cannabis plants. Abamectin is heat sensitive and so the hot LC-MS/MS interface used for other pesticides caused the abamectin signal to be low. Abamectin can be tested with different LC-MS/MS interface parameters to obtain maximum signal and detect it a low levels. However, even using the multi-residue method, we were able to confirm recovery of 85% (7% RSD, n= 9) for the 1000 ppb level.
  • Spiromesifen is an insensitive compound and detectability could be improved by increasing the injection volume for LC-MS/MS or by using GC-MS/MS analysis.
  • Spinosad and spiroxamine show slightly lower recovery values ranging from 60% and higher but these recovery values are generally consistent with less than 20% RSD across all spike levels and matrices (only one exception). These compounds are slightly basic and recovery may be lower than other pesticides because acidic extraction conditions are used during sample preparation.
  • Overall, this method is a great approach for multi-residue pesticide testing in cannabis as demonstrated by the acceptable recovery of nearly all of the almost 60 pesticides we tested.

Stay tuned for more information and details about pesticide analysis in cannabis.

Check out more blogs on cannabis and our webpage


Need Help with QuEChERS: #AskRestek Twitter Q&A session

Just wanted to let everyone know we will be hosting a #AskRestek Twitter Q&A session about QuEChERS next week at 3:00 p.m. EST (12:00 noon PST) on Tuesday, May 3.

QuEChERS is a great approach for sample preparation with lots of benefits. It is also very flexible which is nice but that can also make things a bit confusing. My colleagues Mike Chang and Jonathan “Munch” Keim… yes, the famous “Door Prize Guy” from NACRW will be the panelists. Mike Chang is our Sample Preparation Product Marketing Manager and Munch is the Education Program Manager. I will be on hand to help out with technical questions since i have used QuEChERS extensively.

Check out more details and instructions for attending the Q&A session here.

For more information about QuEChERS, check out these blogs and webpage.


Mike and Munch

Is it OK to use THF (tetrahydrofuran) on my HPLC?

Well, it might be. In the early days of HPLC, THF was commonly used as a mobile phase solvent. It has eluting strength similar to acetonitrile, but just slightly stronger. Since it technically is an ether and is very miscible with water, it is sometimes useful with reverse phase HPLC. It also provides additional options for ternary mixes when methanol/water or acetonitrile/water mobile phases are not able to produce a fine tuned separation.

Like many organic solvents, there are some possible health hazards associated, which you can read about here. THF has a very low boiling point (66C) and emits fairly noxious fumes at room temperature, making it quite unpleasant to work with. You definitely need to use this in a hood.

A more concrete to reason to limit usage of THF for HPLC mobile phase is that it does have a tendency to swell PEEK (polyetheretherketone) material and may contribute to degradation over time. A side effect of the swelling could be increased system pressure, which may become an issue. The use of PEEK tubing and fittings has increased dramatically over the years, due to its ease of usage compared to stainless steel parts. However, THF should not be used with PEEK tubing, unless it is present only at low levels. I have read varying opinions on how much THF one should try using. Personally, I would prefer to stay less than 10% if using PEEK tubing. There is also the possibility that THF at higher levels can degrade other plastic-like materials, for example, pump seals. When using THF, it always best to check with the instrument manufacturer to ensure the proper seals are being used. Some pump seals are designed only for use with aqueous solutions and weaker organic solvents (these would be ones designated as “aqueous” or “reverse phase”).

As far as detection methods go, THF is OK to use for UV detection methods. Since its UV cutoff is around 212 nm, it usually does not produce interference. However, it is important to use HPLC-grade THF to avoid interference from stabilizers that often are used with other solvent grades. It is also important to make sure the THF is fresh, as the formation of peroxides over time will increase the UV background. Usage of THF for PDA and fluorescence detection is fairly similar and the same precautions exist. Some of the same concerns about purity, stabilizers and peroxides apply to most detection methods, including refractive index (RI) detectors.

Using THF with mass spec detectors presents some unique concerns. Agilent and Waters both suggest that its use for LC/MS should be very limited and special precautions should be taken:

Use of THF with LC/MS (Agilent)

Solvents and Caveats for LC/MS (Waters)

ThermoScientific mentions similar precautions for Charged Aerosol Detectors below:

Optimizing and Monitoring Solvent Quality for UV-Vis Absorption, Fluorescence and Charged Aerosol Detectors (ThermoScientific)


I hope you have found this information useful. Thank you for reading.

Analysis of N2O (nitrous oxide) via GC: an update

2011-jaap-pasfoto4-smallNitrous oxide (N2O), is commonly known as “laughing” gas, but is also used as a component in fuels in rockets and as an aerosol propellant. N2O is itself a stable gas and can be analyzed relative easy via gas chromatography. Often it is confused with “nitric oxide”, (NO). NO is a very reactive gas. When oxygen is preset, it will immediate oxidize into NO2. NO2 can be easily recognized as it has a dark brown color. Also NO2 shows reactivity, meaning that the analysis of NO and NO2 via gas chromatography is not commonly done, see for details: http://blog.restek.com/?p=4583

N2O elutes as a sharp peak from alumina.

Nitrous oxide on Alumina BOND / Na2SO4 Column: 30m x 0.53mm Rt Alumina BOND / Na2SO4; Helium, 4 mL/min; Oven: 40ºC; sample: 60µl; Detector: PlasmaDetek PED; sample: 5.4 ppm N2O.Chromatogram courtesy: L. Paradis, LDetec.

Recently a summary of N2O analysis was published by Separation science. Separations are shown on different adsorbents like, Porous polymer, Alumina, Molsieve 5A and ShinCarbon materials.

Full Article can be found here: http://www.sepscience.com/Information/Archive/All-Articles/4365-/Analysis-of-Gases-via-Gas-Chromatography-Part-1-Nitrous-Oxide

Especially the alumina PLOT is interesting (Fig.1) as often CO2 is present and can interfere with the N2O measurement. CO2 is adsorbed completely by Alumina, resulting is a single N2O peak. CO2 can be removed periodically by conditioning at 200C.



Preserving the First Dimension Separation in GCxGC

I mentioned in a recent blog post that to maximize peak capacity in GCxGC the first dimension separation needs to be preserved by having a very short second dimension separation (short modulation time), often on the order of 2 sec or less, even.  While maximizing peak capacity can be very important when trying to characterize a complex sample (e.g., for metabolomics or discovering emerging contaminants in the environment), maintaining the first dimension separation through short modulation times is even more critical when isomers are to be determined individually, including for mass spectrometry.  That’s because isomers that coelute in the first dimension for GCxGC are very rarely separated in the second dimension.  The second dimension column, no matter the alternate selectivity, is just too short.

The problem outlined above, first dimension coelution caused by a longer modulation time in GCxGC, and its solution, a faster modulation time to preserve the first dimension separation, are illustrated in the figure below.  See how the tetrachlorobenzenes coelute when the modulation time is 2 sec?  The peaks eluting from the first dimension column are “piling up” at the modulator, which might be OK if they were separated in the second dimension, but they are not.  Modulate faster = preservation of the first dimension separation, in GCxGC.  The general rule of thumb is modulate (slice) the first dimension peak at least 3 times.

Mod time

Restek at BFR2016 in Toronto – APGC of Brominated Flame Retardants Using Helium and Nitrogen Carrier Gases

In only a few short weeks, I will be giving a presentation on the analysis of brominated flame retardants at BFR2016 in Toronto.  My colleagues and I used an atmospheric pressure ionization mass spectrometer with gas chromatography on an Rtx-1614  (15m x 0.25mm x 0.10µm) column to look at polybrominated diphenyl ethers (PBDEs) in various samples.  First though, we explored optimizing the chromatography for speed, while using efficient helium carrier gas.  But we also looked at employing nitrogen carrier gas, since the APGC instrument we used can easily handle nitrogen carrier with no loss in sensitivity like would occur with the typical vacuum-pumped electron ionization MS system.  By employing a selective GC column like the Rtx-1614, you can get the same analysis times (and PBDE retention times!) for helium and nitrogen carrier gases and still meet necessary separation criteria (e.g., separation of Br4 PBDE congeners 49 and 71 as per EPA Method 1614).  Both helium and nitrogen approaches were facilitated by the EZGC Method Translator and Flow Calculator.

Check out the abstract and the preliminary program and I hope to see you at the conference.

Peak Capacity and Selectivity in Gas Chromatography

I recently had the pleasure of hearing Professor Taduesz Gorecki from the University of Waterloo lecture on comprehensive two-dimensional gas chromatography (GCxGC).   One of his chief areas of research is on the GCxGC modulator, which is essentially the “injector” for the second dimension column in this multidimensional chromatography approach.  A twist on the usual process from Taduesz involved “stop-flow” modulation, where the column flow in the first dimension is halted while the injection and separation occur for the second dimension.  Where the usual second dimension columns and separations in GCxGC are super short (sometimes L less than 1 m and time less than 2 sec) to preserve the first dimension separation, “stop-flow” modulation allows longer second dimension separations (and longer second dimension columns to improve them).  The first and second dimension separations are more independent of each other than in traditional GCxGC.

GCxGC in general, and especially stop-flow GCxGC, generate very large peak capacities versus one-dimensional GC, up to an order-of-magnitude higher.  But in his lecture Tadeusz reminded us that without good choices of stationary phase selectivity in both dimensions, that peak capacity won’t be fully realized.  I can easily demonstrate that with some recent work I did for an upcoming lecture at the 40th International Symposium on Capillary Chromatography and 13th GCxGC Symposium.  Note in the figure below how the Stabilwax column in the second dimension pulls apart the diesel, placing the aromatic analytes further away (higher) from the aliphatic compounds (line of peaks at the bottom of the contour plot).  However, the Rtx-200 (a trifluoropropylmethyl phase) does not have the necessary selectivity to allow full use of the 2D space.  Never fear; I exploited that space later by analyzing an environmental sample containing PAHs, pesticides, PCBs, explosives, and priority pollutants.  Sometimes it’s all about having selectivity choices in GCxGC, and that’s where Restek excels.

Diesel on Wax and 200

Split Injection Makes for Easier Polar Solvent GC Work versus Splitless Injection

As anyone who’s doing QuEChERS knows, analyzing acetonitrile extracts on nonpolar GC columns (like Rxi-5ms, e.g.) using splitless injection can be problematic because of the classic solvent – stationary phase mismatch.  To avoid split peaks we usually have an initial GC oven temperature slightly above the 82°C boiling point of acetonitrile (MeCN), but this causes tailing of early eluting peaks as they are not focused using the “solvent effect” or cold trapping.  Life is much easier if we can do split injection at, say, a ratio of 10:1, since instead of, e.g., 1 microliter, we now have approx. 0.1 microliter of polar solvent going onto our nonpolar GC column.  Of course you need to pay attention to the hit on your LODs and LOQs, but with more sensitive MS/MS instruments being developed every year, split injection for pesticide residue work is becoming practical.  Given that approx 10 times less extract goes onto the column and into the MS source, system uptime is greatly improved, too.  A Sky Precision split liner with wool and “shoot-and-dilute” GC (split injection GC) makes life easier!

Split MeCN

Don’t Forget to Change Your GC Inlet Bottom Seal and Trim Your GC Column as Part of Your Maintenance Routine!

While doing PAH analysis for dirty samples with splitless GC I saw increased peak tailing and loss of response, so I did what anybody would do: changed my GC inlet liner.  In this case I used a Sky single taper inlet liner with wool.  Unfortunately when I did my next standard analysis, not much was improved.  While sometimes an inlet liner change is indeed enough to restore performance, in this case it wasn’t, and so I changed the gold dual vespel ring inlet seal at the inlet bottom and trimmed the column slightly.  Problem solved!

PAH 01PAH 02