Well, the season is changing here in the Midwest and sample collection time will soon be upon us. In the laboratory, much like at home, a good spring cleaning goes a long way.
For Volatile Organic Compound (VOC) analysis, multiple cleaning procedures or preventative maintenance techniques should be employed.
Here at Teledyne Tekmar, we focus primarily on U.S. Environmental Protection Agency methodologies and similar global standards, each of which employ Purge and Trap (P&T) as the sample concentration step.
For the determinative methods, USEPA 8260 is probably the most familiar for typical P&T users. There are several other techniques for the sample concentration step, depending upon the matrix and the analytes of interest. For example, if you’re looking for compounds in waste oils, method 3585 may be a more suitable technique. This utilizes a hexadecane extraction, followed by direct injection to the gas chromatograph (GC). Other common techniques include headspace and thermal desorption.
For our spring-cleaning procedure, we will focus exclusively on the P&T concentration technique, known in the 8000 series methods as USEPA 5030 for waters and waste waters and USEPA 5035 for soils and solids. Each of these P&T methods provides its own unique challenges when it comes to clean-up and routine maintenance. For the water only methodologies, both the determinative and preparative techniques are contained in a single method. The primary methods for these analyses are USEPA 524 series for dinking waters and USEPA 624 for wastewaters. Depending on the revision, the P&T parameters are prescribed as well as the hardware employed.
Now that we have covered techniques and methodologies, let’s examine the hardware and what can be cleaned and/or replaced. Typical VOC analysis consist of a P&T in tandem with a gas chromatograph/mass spectrometer (GC/MS) for the USEPA 8260, 524, and 624 methods. Other GC methods incorporate different detectors, including Flame Ionization (FID), Photo Ionization (PID), Thermal Conductivity (TCD), and Electrolytic Conductivity (ELCD). Our spring cleaning will focus on P&T with a GC/MS. Please consult your operation manuals for the other discreet detector configuration options.
For the P&T GC/MS setup, the first piece of the hardware that sees sample is the P&T autosampler. This consists of the sampling device and the volume transfer mechanism. In a typical setup, a needle is inserted into the vial containing sample and an aliquot is removed if liquid, or gas is introduced if a solid. In any event, the needle needs to be cleaned and inspected for any long-term exposure damage. While most systems employ clean-up protocols automatically, it is good practice to manually clean the needle, or replace it if the wear and tear seem excessive. Cleaning with methanol and high-pressure gas will handle most instances of buildup.
The sample is delivered to the P&T by either a syringe or a fixed volume loop. These can be removed and cleaned manually if they are experiencing deteriorative performance. Depending on the material, they can be cleaned with methanol, or replaced if needed. This will hold true for the associated plumbing lines as well. For solids you will need to follow a methanol rinsing of the tubing with a water push and air, to dry the tubing before analysis.
Next, the liquid sample is transferred to the P&T sparger. This piece of glassware may contain a frit to aid in gas dispersion through the sample. If the frit is discolored and exhibits high back pressure, it is best just to replace the glassware. Typical cleaning procedures can be employed, as well as dilute acid washing, if replacement is not an option.
The next component is the trap. This is a consumable item and should be replaced regularly. The heated pathway leading to the trap can be flushed with methanol at ambient temperatures if the contamination from high level samples is bad enough. Checking in with Technical Support on how-to videos is always an option if you are unfamiliar with the process.
Last, the GC/MS needs maintenance too. For the GC, it is always prudent to replace the liner and associated seals along with the split trap. Additionally, a small section of the column should be removed. Each MS manufacturer has procedures for cleaning the source and proper vacuum maintenance. These processes should be performed at this time as well.
Once all these spring-cleaning procedures have been performed, you should be ready to start your routine analysis. Since this cleaning was intensive, the next step usually involves an Initial Demonstration of Capability (IDC), which we will cover in our next blog.
Well, that’s it for now. Happy analyzing, and may all your systems perform at their optimum!
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