Beyond Helium: Carrier Gas Alternatives for Gas Chromatography

63128_LM_Peak Custom eBook_JL V4 (1) Your local gas generation partner Helium Alternatives in Gas Chromatography A Comprehensive Guide Produced by www.peakscientific.com Table of Contents IntroductionAlternatives to Helium 3Comparative AnalysisPerformance comparisons: efficiency, speed, and resolution 4Detailed hydrocarbon analysis (DHA) using ASTM Method D6729 and D6729 Appendix X2 5Analysis of drugs of abuse and explosives using GC-MS: A comparison of helium and hydrogen 7Cost-benefit analysis: the economic advantages of gas generators 9Safety concerns and precautions 10MethodsGas Chromatography Method List 12Method revalidation demonstration using FAMEs 15Technology and Transition GuideHydrogen purification methods: Technology considerations 16A step-by-step guide for converting your GC carrier gas from helium to hydrogen 19FAQFrequently Asked Questions 22Introduction‌‌ Alternatives to Helium Helium is widely used as a carrier gas for gas chromatog- raphy (GC). Alternatives must be sustainable and offer equal, if not better, results. Chromatography has long relied on helium as a prima- ry carrier gas due to its inert nature and reliable results. However, challenges related to helium's cost and avail- ability have prompted a focused reevaluation of potential alternatives over the last decade, with many labs deciding to make the change. Nitrogen is seen as a slow gas and often overlooked as an alternative to helium, though its use would be perfectly valid in multiple GC analyses. With a low optimal linear velocity of 8-14 cms-1 for nitrogen, compared with 25-33 cms-1 for helium (Figure 1), analysis times will be increased when maintaining optimal performance. However, if there is enough resolution between peaks, samples can be run at a higher average linear velocity. This will mean sacrific- ing some theoretical plates, which in practical terms will mean broadened peaks. Hydrogen, on the other hand, is more efficient than helium at higher linear velocities, with an optimal linear velocity range of 38-45 cms-1. This improved efficiency at higher linear velocities potentially allows for increased sample throughput, however, it is not always possible to analyze a sample at a higher linear velocity due to inadequate peak resolution. Matching the linear velocity of hydrogen to that of helium should mean like-for-like analysis, with slightly improved carrier efficiency (see "Method revalidation: the FAMEs example" for more on this). Figure 1. van Deemter curve showing the efficiencies of helium, nitrogen, and hydrogen over a range of flow rates. A primary concern regarding hydrogen use in labs is its flammability; storinghydrogen cylinders can pose signifi- cant health and safety risks. Using generators to produce hydrogen, as well as nitrogen, offers a cost-effective and safer alternative source of gas in the lab. Hydrogen is produced by the electrolysis of deionized water and is supplied to the GC on-demand. The hydrogen generator contains only a low volume of hydrogen at much lower pressure than cylinders, while producing enough gas to supply a whole lab. Nitrogen is produced by removing oxygen, CO2, and hydrocarbons from compressed airviapressure swing adsorption with a carbon-based molecular sieve material. Hydrogen and Nitrogen are two alternative carrier gases. H • • • • High diffusivity Faster linear velocities Shorter analysis Similar separation efficiency as Helium N • • • Hydrogen Nitrogen Best separation efficiencies at lowest velocities Highly abundant Easy to produce Read the full, original article:Cost-effective alternativesto helium for gaschromatographyComparative Analysis‌‌ Performance comparisons: efficiency, speed, and resolution Analyses have repeatedly demonstrated the effective use of nitrogen and hydrogen as alternative carrier gases for many applications without loss of performance. Produc- tion of these gases by generators gives labs a constant, on-demand supply of gas free from the annoyance of running out of gas or moving heavy cylinders, furthering their appeal. In one early comparative analysis, a three-component alkane standard was run using a Shimadzu 2010 GC with a Restek RTX-1 column (30 m x 0.25 mm x 0.25 µm) using cylinder helium and gas generator-produced hydrogen and nitrogen as the carrier gases. The samples were run isothermally (170°C) at the same linear velocity (37.5 cms- 1) to look at the effect of carrier gas on peak area, peak width, theoretical plate count, and resolution. Figure 2 shows that the three carrier gases produced very similar results. Hydrogen and helium give almost identical results, with the peaks in the nitrogen run showing a little band broadening. Although the same linear velocity was used, the alkane peaks from the nitrogen run were slight- ly delayed. The data in table 1 show that all three carrier gases produced the same peak areas for each of the three compounds, demonstrating no effect on sensitivity. As expected, however, running nitrogen at a high linear velocity reduced efficiency, which is demonstrated by the lower number of theoretical plates. This broadens the Figure 2. Chromatogram showing decane, undecane, and dodecane run using helium, nitrogen, and hydrogen carrier gases. Table 1. Peak areas, theoretical plate count, resolution, and peak width of decane, undecane, and dodecane run with helium, nitrogen, and hydrogen carrier gases. peaks, reducing resolution, as shown in the chromatogram and table 1. For analysis of samples with distinct peaks like the al- kane mixture, nitrogen and hydrogen can readily replace helium. Although nitrogen resulted in reduced theoreti- cal plates, it did not impact the overall results. There is a strong case for using nitrogen in GC analyses where high efficiency is not essential. Hydrogen performed very similarly to helium, under- scoring its popularity. In fact, hydrogen has emerged as the most popular alternative to helium, with numerous studies further comparing their performance in different applications. The following two study summaries serve as examples within the petrochemical industry and forensics. These data provide insights into hydrogen's performance in aspects such as efficiency, resolution, and speed in var- ied-and demanding-scientific applications. Read the full, original article:Cost-effective alternativesto helium for gaschromatographyComparative Analysis‌ Detailed hydrocarbon analysis (DHA) using ASTM Method D6729 and D6729 Appendix X2 Detailed hydrocarbon analysis (DHA) is a separation technique used for bulk hydrocarbon characterization and analyzing individual components in the petrochemical industry. Due to the complex nature of gasoline, a long column is typically required to achieve separation, trans- lating to long run times. This study compares gasoline analysis following ASTM D67291 using helium carrier gas and following ASTM D6729-1 appendix X2 using unfil- tered hydrogen carrier gas produced by aPrecision Tracehydrogen generator. Switching from helium to hydrogen reduced the elution time of the final component (n-Penta- decane) from 125 minutes to under 74 minutes. Hydrogen maintained or even improved separation for many com- ponents, including the highly regulated benzene fraction. Toluene and 2,3,3-Trimethylpentane, however, coeluted when using hydrogen, signaling a need for further method optimization. Overall, hydrogen as a carrier gas signifi- cantly reduced analysis times while generally preserving the necessary resolution for critical separations. Read the full, original article:Detailed hydrocarbon anal- ysis (DHA) using ASTM Method D6729 and D6729 Appen- dixX2 Figure 3. Comparison of DHA of total gasoline sample using hydrogen and helium. Figure 4. Comparison of separation of 1-methylcyclopentene and benzene when using hydrogen and helium as carrier gas. Figure 5. Comparison of separation of Toluene and 2,3,3-Trimethylpentane when using hydrogen and helium as carrier gas. Figure 6. Comparison of separation of Tridecane and 1-methylnaphthalene when using hydrogen and helium as carrier gas. Table 2. Designation D 6729-01 standard test method for determination of individual components in spark ignition engine fuels by 100-meter capillary high-resolution gas chromatography. ASTM International 2002. Table 3. Quantitative results of PONA compounds. Comparative Analysis‌ Analysis of drugs of abuse and explosives using GC-MS: A comparison of helium and hydrogen Published by Nnaji, C.N., Williams, K.C., Bishop, J.M. & Verbeck, G.F. (2015) Science and Justice 55: 162-167 In a study led by Dr. Guido Verbeck's group at the Univer- sity of North Texas, the analysis of drugs of abuse (DOA) and explosives was conducted using an ion trap GC-MS, comparing the outcomes with helium and hydrogen as carrier and buffer gases. Most compounds' fragmentation patterns remained unchanged, despite the presence of electron-rich nitrogen and oxygen species, with the ex- ceptions of diazepam and certain explosives. Additionally, the study assessed sensitivity across different ion volume orifice diameters, revealing that the 10 mm ion volume produced the highest intensity for both gases. Given hydrogen's cost-effectiveness and faster analysis time, its comparable performance to helium in this context high- lights its potential benefits for forensics laboratories. Read the full article:Analysis of drugs of abuse andexplosives using GC-MS to compare results when usinghelium andhydrogen Figure 7. Effect of ion volume orifice on signal intensity of cocaine's primary fragment ion (m/z 182.04) when used with helium (Figure 1A) and hydrogen (Figure 1B). Your localgas generation partner‌ The costs of nitrogen cylinders vs. a gas generator Having nitrogen gas cylinders delivered is subject to price increase and additional, often hidden, costs. A gas generator is a more economical and reliable solution for nitrogen gas supply. $ Costs of using nitrogen cylinders $ Employee safety training $ Downtime Increasing nitrogen cylinder costs $ $ Regular deliveries Managing supply stocks Unused nitrogen $ gas in cylinders Producing your own nitrogen with a gas generator $ One-time delivery for installation Annual generator $ service Comparative Analysis‌ Safety concerns and precautions Storing hydrogen cylinders on the premises is prohibited for many laboratories, owing to health and safety restrictions. The most significant risk arising from hydrogen use is a leak into the laboratory environment that raises the hydrogen content to an explosive level. The combination of flammable, high-pressure gas in cylinders presents concerns for handling and storage within the lab. In addition, the size and weight of hydrogen cylinders present hazards to personnel performing cylinder changeouts. Care must be taken, and cylinders should be secured to the wall or bench top using appropriate cylinder holders and restraints. There is an additional risk of leaks when staff change cylinders. Gas generators offer a safer and more sustainable approach. The safety benefit of a generator can be shown with a theoretical example. The lower explosive limit (LEL) for hydrogen is four percent in air. Therefore, the LEL of a small, hermetically sealed laboratory with a volume of 500 m3 can be reached by emptying two 50 L cylinders of Hydrogen. With a large enough leak, this can be achieved in minutes. High-pressure hydrogen can also undergo auto-ignition when released rapidly from a cylinder. Since PEAK Hydrogen generators are designed to contain a minimal amount of Hydrogen (<400 cc), it would take nearly 12 days to reach the LEL in the same lab. They also eliminate the need for personnel to handle large quantities of the flammable, high-pressure gas. The construction of thePrecision Hydrogen Trace generator conforms to CEI / OSHA regulations and it only produces gas when the application places a demand on the unit. The unit also meets the European Electromagnetic Compatibility and Low Voltage Directives and is CE approved. Safety features of Precision Hydrogen Trace generators The PrecisionHydrogen Trace generator has the following safety features to ensure safe and reliable operation: H2 detector option An H2 detector unit can be purchased along with the Precision Hydrogen Trace. The detector is intended for use with a GC and should be placed above the height of the GC outlet. The detector, which can be wall mounted, is connected from the 'In' port at the rear of the unit to the "H2 Detector" port at the rear of the generator. This connection provides the detector unit with power and allows communication between the generator and detector. The detector will sample continuously, and both the detector and the Precision Hydrogen Trace will sound an alarm if dangerous levels of hydrogen are detected. In the rare case of a hydrogen leak, the generator will shut down. Up to four detectors can be connected to one Precision Hydrogen Trace. Beyond the key concern of lack of supply, safety is also a big factor for carrier gases, especially hydrogen, and involving the use of gas cylinders. Read the full, original articles:Hydrogen Safety (Standard and Trace Analysis) andUsing Hydrogen as a Carrier Gas for GC Your local gas generation partner ASTM Methods The list below shows methods which have been rewritten to use Hydrogen or Nitrogen carrier gas for GC as an alternative to Helium. This list is correct as of the date at the foot, however, these methods are being rewritten regularly so if you cannot find your customer method below please contactpmsupport@peakscientific.com. Please note that customers using methods which need helium can also use Precision gas generators for detector or make-up gas. ASTM Methods (Continued) *A indicates methods for which H2 and N2 have not been officially verified, but we are aware of customers using H2 or N2 for the method successfully. USP Methods USP Method 467 EPA Methods Epa Method 8260C 8270C/8270D EPA Methods (Continued) H2 carrier gas and N2 detector gas suitable for RGA analysis Methods‌ Method revalidation demonstration using FAMEs Changing carrier gas from helium to hydrogen does not always present an opportunity for faster sample analysis. Method revalidation can be simplified by keeping the new method as close to the old method as possible, which will limit changes to sample selectivity and resolution whilst maintaining the retention times of analytes. Fatty acid methyl esters (FAMEs) analysis, typically con- ducted using GC-FID, characterizes fat content in prod- ucts like food, biodiesels, and microbes. While hydrogen is attractive for its potential faster analysis, increasing the carrier gas flow rate can cause peak co-elution, affecting resolution. In an analysis of a 38-component standard mixture, switching from helium to hydrogen resulted in co-elution of specific peaks, necessitating method revalidation. The method was successfully revalidated to match the linear velocity of hydrogen to that of the original helium meth- od, which involved reducing the GC head pressure and split flow. After revalidation, the results using hydrogen were almost identical to those using helium. While there was no reduc- tion in analysis time, peak heights increased when using hydrogen, indicating improved efficiency. This demonstrates the possibility of keeping the linear velocity of hydrogen the same as helium, using the same column dimensions, with only minor adjustments to the GC method. Read the full, original article: FAMEs analysis method from helium to hydrogen for GC Figure 8. A shows a section of the total chromatogram for the 38 component FAME standard produced using the original helium method, including poorly resolved peaks 29-33. B shows co-elution of peaks 29-30 and 31-33 when running the sample using hydrogen carrier gas at higher linear velocity. Figure 9. Results of the original method using helium carrier gas (A) and results of the revalidated GC method using hydrogen carrier gas (B). GC method conditions Technology and Transition Guide‌‌ Hydrogen purification methods: Technology considerations Hydrogen generators are becoming an essential compo- nent in many laboratories. There are multiple hydrogen generator manufacturers producing quality instruments that provide ultra-high purity gas through a variety of methods. How do you choose between systems? What do all the acronyms mean? The following is an overview of the technology involved in hydrogen generation, compar- ing the benefits and challenges that arise with each. There are only a few basic mechanisms by which hydro- gen gas can be produced from water. Hydrogen genera- tor systems typically produce purified hydrogen using a two-phase system: hydrogen is first separated from water and then purified. Many hydrogen generators utilize pro- ton exchange membranes (PEM) coupled with a hydrogen purification system, such as palladium-diffusion or pres- sure swing adsorption (PSA) dryers. Water is split into hydrogen and oxygen using an elec- tric current at the PEM, which is a solid polymer electro- lyte. Hydrogen ions traverse the PEM lattice through ion channels that are only permeable to cations, while oxygen ions are retained on the anode side. The post-production hydrogen may contain impurities like moisture and must be purified. Of the four key methods used to purify hydrogen de- scribed below, three use PEM combined with different purification techniques and one uses a combined palladi- um electrolyser. Figure 10. Schematic diagram showing proton exchange membrane function. PEM/palladium diffusion Palladium membrane hydrogen purifiers operate via pres- sure-driven diffusion across palladium membranes. The palladium diffuser can take different forms, including an array of tubes, a coiled tube, or membrane foil. It is com- prised of a palladium and silver alloy material possessing a unique property: when it is heated above 300°C, it allows only monatomic hydrogen to pass through its crystal lat- tice. The hydrogen gas molecules that contact membrane surface dissociate into monatomic hydrogen, pass through the membrane, then recombine into diatomic hydrogen on the other side. Figure 11. PEM/palladium diffusion process Features and benefits Challenges Technology and Transition Guide‌ A step-by-step guide for converting your GC carrier gas from helium to hydrogen This step-by-step guide will provide you with the necessary information to convert your GC's carrier gas supply from helium to hydrogen. Hydrogen gas generators offer a safe, consistent, and reliable source of gas, and are a more conve- nient and greener source than cylinders. Once you are satisfied that your method allows for conversion from helium to an alternative carrier gas, follow the steps in this guide to quickly get up and running with an alternative carrier gas while avoiding some of the common pitfalls of switching carrier gas. If you are unsure if a particular method allows for conversion from helium carrier gas, contact us and we may be able to advise you. Step 1. Review all current method information and instrument conditions Step 2. Perform routine GC maintenance before switching carrier gas Step 3. Install new tubing Step 4. Connect gas supply to GC The gas generators being used to supply your GC should be installed according to site preparation advice from the manufacturer. Ensure that the connections into the GC are leak-free using an electronic leak detector. DO NOT USE LIQUID LEAK DETECTORS since these can cause contam- ination of your gas lines. Detector gas supply Carrier gas supply A general column conditioning guide from RESTEK can be found here. Once the column is conditioned, switch on the detector, connect the column, and allow at least 1 hr stabilization time. System checkout Adjust the linear velocity of the carrier gas to match the value when using helium carrier gas. Running hydrogen at the same linear velocity as helium, with the same oven temperature program, should give you almost identical results. Compare the last chromatogram using helium with the results with hydrogen. The peaks should elute at the same time but may have a slightly different shape.This application note explains the process of switching carrier gas and keeping the linear velocity of the carrier gas the same. Compare the reference chromatogram obtained using helium carrier gas with the new chromatogram to ensure that all peaks have eluted and that their retention times are consistent. If there is plenty of peak separation, you can carry out optimization of the method to increase the linear velocity of the carrier gas and shorten run times. You may be able to halve the analysis time in some methods. Ensure that you can identify all peaks in your mixture. Run calibration standards to revalidate the method. FAQ‌‌ How can I change from cylinders to a generator with limited downtime? The changeover is typically seamless. If you are switching from hydrogen gas cylinders to a generator, existing tubing can be disconnected from the cylinder and connected to the generator using SwageLok fittings. If you are changing from helium to hydrogen, new tubing should always be used. Has any testing been conducted to evaluate the safety of Hydrogen generators? Peak hydrogen generators carry the CE and CSA mark and have been externally tested to IEC standards for labora- tory use and safety requirements for the residual risk of an explosion hazard. The evaluation was conducted under a worst-case scenario by dilution tests and an unoperated fan. The testing showed that the hazard risk for explosion does not exist: the LEL of 4.1 percent hydrogen was not reached under worst-case conditions internally or externally to the generator. Where should I install my generator? The generator can reside safely in the laboratory on the bench, floor, or under the GC auto-sampler. The stackable de- sign of the Peak Precision range allows placement of the generators close to GCs or other applications. The generator should be located on a flat, level surface for operation. Can I put the generator in a cupboard? Adequate airflow must be maintained around the generator to allow the ventilation system to perform efficiently. If the generator is stored in an enclosed space, the environment must be controlled via an air conditioner or extraction fan. The provision must be made to allow the volume of air in the room to be changed five times per hour. The rear of the generator will become warm to the touch during operation-a minimum clearance of 15 cm (6") from other bodies is recommended. The vents should not be obstructed or connected to any application. Safe, forced removal of waste gases has been engineered into the generator to prevent any internal gas or pressure build-up. Can I place the generator outside the laboratory? This is possible as long as the recommended environmental conditions required for normal operation are met. Reduc- ing the length of pipework will reduce costs (if not already installed) and the risk of any potential leaks in the pipework going undetected, improving the safety of the installation. If possible, the generator should be placed near or close (< 10 m) to the GC/application. Do my GCs need to be ventilated? If a customer wishes to use a fume extractor, or to connect tubing between the exhaust of the generator and a fume- hood, this is possible. However, any hydrogen exhausted from the GC will quickly diffuse in the air and presents no danger to laboratory personnel or the environment. If tubing is attached to the exhaust ports of the generator, it is essential that this is monitored frequently, since any kinks could cause a build-up of gas and create additional health and safety issues. The lower explosive limit (LEL) of hydrogen is 4.1 percent and shown not to be reached by a Peak hydrogen gas generator. The majority of laboratory environments will not be completely sealed, with air conditioning in place to allow air movement. If you have any concerns, Peak offers complimentary site evaluations, installation surveys, and demonstrations. Will I need hydrogen sensors in the lab or GC oven? In the laboratory, the amount of hydrogen generated or exhausted into the laboratory is not enough to accumulate and reach the LEL of hydrogen. The risk of a significant build-up of gas in the GC oven is also extremely low with both the external leak safety shutdown feature of the hydrogen generator and the GC inlet safety shutdown feature in place. Should your laboratory, state government, or business policy require regulation, sensors, or monitoring, Peak can offer both external room and internal GC oven monitoring sensors for complete peace of mind. Sounds technical: How difficult are hydrogen gas generators to maintain? Regular maintenance is very simple, cost-effective, and does not require an engineer. Simply refill the deionized water reservoir weekly. Preventive maintenance (PM) is required biannually and involves deionizer cartridge swap-over. Peak also offer user training, Skype tutorials, PowerPoints, detailed user manuals, 24/7 phone technical support and field support.Get in touch . How many GCs can a single hydrogen generator supply? As a rule of thumb, 100 cc will supply two FID detectors. Of course, the required generator will depend on flow rate, carrier gas type, column, other detectors, and unique methods. Use the gas requirement calculator . Or contact us for a consultative solution. ROI-will it really be more cost effective? Calculating the gas, delivery charges, cylinder rental charge, staff downtime time, administration, OHS measures, and training, ROI is typically achieved within 9 to 15 months. Is it difficult to install a hydrogen generator? Not at all. Simply remove packaging, connect an external UV-protected deionized water bottle (at same height or below the generator), connect to an electrical supply (10 Amp) and allow to reach room temperature. Connect to your GC using 1/8" pre-cleaned (gas-purged) refrigerant-grade copper or stainless-steel pipe. What piping do I need? Supply of hydrogen gas should be provided through stainless-steel or analytical-grade-copper tubing using Swagelok compression fittings. It is important to change the tubing that was previously used to supply helium to the GC, since over time, deposits can build up on the inside of the tubing. Hydrogen will carry the deposits to the application, causing higher background signal for a longer period of time. For any connections, Swagelok compression fittings are the recommended solution to connect copper or stain- less-steel tubing. No chemical bonding (such as Loctite), welding or glues should ever be used, since this can introduce volatile organic compounds (VOCs) into the gas supply, which can impact results. When running lines >3 m it may be necessary to use 1/4" piping reduced to 1/8" to supply each GC. This increases the volume considerably and can make installation more difficult. For lines >10 m between the generator and GC, please consult with Peak or your fitting specialists. What water can I use for my hydrogen generator? Peak recommend deionized water (DI) of > 1 megohm resistivity / < 1 µS conductivity purity or better. If MilliQ™ water is available at your facility, this is preferred. Read the full, original article:How does a hydrogen generator work? Your local gas generation partner Produced by www.peakscientific.com Tel +1-800-767-6532 Emailmarketing@peakscientific.com