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Quick-Start Guide to LPGC

How to Know if It’s Right for Your Analysis and Get Started Quickly

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Determining if LPGC is Right for You

Interested in trying LPGC in your lab but aren’t sure if it will work for you? We can help with that! Restek recommends reviewing a few factors about your analysis to determine if it’s amenable to LPGC.

One factor to consider regarding your analysis is critical separations. If there are no critical separations, the analysis is generally amenable to LPGC. If there are critical separations in your conventional GC-MS analysis and those resolutions are important to maintain, then some additional considerations need to be weighed before switching to LPGC. Since the LPGC technique trades resolution for speed, applications requiring the same or better resolution of critical pairs may not be amenable. However, if your critical pairs are not isobars, the spectral resolving power of the MS can be used to separate them while speeding up your analysis times! This means LPGC can work for your analysis and result in significant speed gains (Figure 1).

Another factor to consider is the sample capacity and the increase in sensitivity (or S/N) that can result. If you’re already running a fast GC method (for example using a 10 m x 0.10 mm ID column), LPGC can provide more sample capacity than the smaller ID columns (short, narrow-bore columns) that are typically used. So, if you have a fast run but would like more sample capacity, LPGC is a good option!  Additionally, since LPGC allows for more sample capacity and narrower peaks, using LPGC can result in higher S/N, better sensitivity, and the ability to reach lower detection limits. 

Figure 1: LPGC-MS analysis of arylamines is 3.3x faster and uses 81% less helium compared to conventional GC-MS.

 

Installing and Optimizing Your LPGC Column Kit

Once you’ve determined if LPGC will work for you, you’re ready to select your LPGC kit from our broad catalog offering, install it, and optimize your run conditions! Here’s a quick rundown of what you’ll need to do: 

  1. Select your LPGC kit from our website. To explore our offering of LPGC kits, visit www.restek.com, and search for "LPGC" with "Products" selected in the dropdown menu of the search bar.
  2. Install your LPGC kit – it’s as easy as a column change! 
    1. Simply remove your conventional GC column, and then install the LPGC kit with the restrictor column at the inlet.
    2. Give the installation a leak check using our electronic leak detector (cat.# 28500). 
  3. Optimize your run conditions for LPGC.
    1. Flow: To achieve the optimal flow for LPGC, set the flow rate using only the dimensions of the restrictor column at the oven’s initial temperature. For LPGC kits with a 0.53 mm ID analytical column, the optimal flow rate is 1.5-2.5 mL/min with helium. For LPGC kits with a 0.32 mm ID analytical column, the optimal flow rate is 0.9-1.1 mL/min with helium.
      1. The ideal flow rate is a balance between how fast the MS can work, how fast you want to perform the analysis, and the level of sensitivity needed. 
      2. For 0.53 mm ID columns, higher flows result in lower responses due to overloading the pump. However, the pump will be able to keep up with the vacuum up to a flow of about 6 mL/min.
      3. For 0.32 mm ID columns, higher flows than the ideal range can cause the pump to lose vacuum, especially at higher temperatures. 
    2. Temperature: The temperature program may need to be adjusted when converting from conventional GC to LPGC. A rapid heating program is required for LPGC with the optimal ramp set at 30-35 °C per minute. The start and end temperatures can also be lowered because the flow rate will be higher than a conventional GC column. LPGC takes advantage of a low-pressure system (using the MS to pull vacuum on the analytical column) to increase flow, making analytes elute faster at lower temperatures. 
      1. If your GC is having trouble keeping up with these oven ramp rates, try our GC Accelerator (cat.# 23849). 
  4. Start your run! 
    1. Be prepared to observe your analysis and optimize your conditions again based on initial data, if necessary. Don’t forget, coelution may occur as resolution is decreased with LPGC since it is a tradeoff for a faster run. If the coelutions are not isobars, use the spectral resolving power of the MS to analyze them!

With this simplified setup, you can start processing more samples per shift, have more time for instrument maintenance, or even put off that next big capital investment on a new instrument to accommodate your workload.

To learn more about the benefits of LPGC, visit www.restek.com/lpgc

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