It is widely acknowledged that the purity of a carrier gas is critical for the performance, longevity and maintenance of analytical instruments - “contaminants in gases can significantly impact your analysis. Oxygen, hydrocarbons, and moisture can cause loss of sensitivity and accuracy of the GC and damage your column.” (1) Variations in the sensitivities of samples may cause high baseline noise in analytical results due to water moisture and oxygen, which could distort the sample results.
To identify the appropriate hydrogen source for the operation, it is essential to understand the purity of different hydrogen supply methods, this will have a significant impact on the performance of analysis conducted.
In addition to stable results, the use of research grade (or better) high purity hydrogen can provide various other benefits. “Oxygen is known for causing column stationary phase and inlet liner degradation in analytical instruments, further damaging the decomposition of labile analytes.” (2)
Removing contaminants like oxygen is vital to GC performance because “as the column is heated, very rapid degradation of the stationary phase occurs. This results in the premature onset of excessive column bleed, peak tailing for active compounds and/or loss of efficiency (resolution) by the time oxygen damage is discovered, significant column damage has already occurred. In less severe cases, the column may still be functional but at a reduced performance level. In more severe cases, the column is irreversibly damaged.” (3)
The purity of the carrier gas is a critical factor to consider to obtain stable results and to extend the service life of the GC column. Understanding the supply of a carrier gas and the variability that is introduced into a process is critical.
In general, there are two methods to supply hydrogen to laboratories:
- Bulk hydrogen delivery usually sourced from large natural gas reformation plants and stored in cylinders or tube trailers for easier delivery
- On-site hydrogen generation via water electrolysis
The bulk delivery method has been in practice for decades, and has proven to be a reliable hydrogen source for the laboratory market. The purity content of bulk hydrogen and the cost for guaranteed high purity are the key factors to consider when choosing a hydrogen source for gas chromatography applications.
Water moisture, nitrogen, oxygen, carbon monoxide, carbon dioxide, and hydrocarbon are some of the most common contaminants present in bulk hydrogen delivery, negatively affecting analyses. (4)
It is necessary to take appropriate measures to mitigate these contaminants to control the performance of analytical instruments and ensure accurate results. Packaging, distribution, and purification methods all affect the purity of the gas supplied to the customer.
The variability of purity, and in certain cases the reliability of supply, has prompted several lab managers and chemists to consider generating their own hydrogen via water electrolysis. On-site hydrogen generation via water electrolysis delivers a research grade pure hydrogen source for use as a carrier gas, providing users with complete control over cost and supply.
Hydrogen generated via Proton Exchange Membrane (PEM) water electrolysis technology is free from impurities other than oxygen, nitrogen, and water moisture in trace amounts that are well below levels that have a negative impact on the sample results or column life. As a result, the hydrogen is allowed to maintain a consistent level of purity.
Testing was performed by two third-party laboratories to examine the output of a hydrogen gas generator producing 99.99999% pure hydrogen to be employed as a carrier gas for GC analysis. As mentioned earlier, the carrier gas purity is a key factor as it not only impacts the sample results in analytical testing but also the longevity of analytical instruments employed.
Water moisture and oxygen output levels were the target contaminants in the analysis. A Proton OnSite® model G600-HP was the hydrogen generator used. A Delta-F DF-550 Nanotrace Oxygen Analyzer, with a detection level down to 0.2 ppb and resolution of 0.1 ppb, was used to measure the oxygen and a GE Moisture Monitor Series 35 IS was used to measure the water moisture output.
Guaranteed Ultra High Purity and Consistent Results
Proton’s water electrolysis system's enabling feature is the proton exchange membrane (PEM), which allows only positive ions and water to cross between compartments. As the membrane also acts as the electrolyte in the cell, the system does not require harmful liquid electrolytes such as concentrated potassium hydroxide.
During PEM water electrolysis, pure deionized water (H2O) is split into its components, hydrogen (H2) and oxygen (O2), on either side of this membrane. When a DC voltage is applied to the electrolyzer, water fed to the anode or oxygen electrode are oxidized to oxygen and protons, while electrons are released.
The protons (H+ ions) then pass through the PEM to the cathode, or hydrogen electrode, where they are reduced to hydrogen gas upon reaction with the electrons from the other side of the circuit.
The two reactions that occur in the cell are as follows:
2H2O → 4H+ + 4e- +O2
4H+ + 4e- → 2H2
The only possible components of the streams are hydrogen, oxygen and water moisture (Figure 1).
Figure 1. Proton Exchange Membrane (PEM) Illustration
The hydrogen generator used in this experiment utilizes Proton Exchange Membrane (PEM) technology with a high differential pressure design, generating hydrogen at 8 barg and oxygen at ambient pressure in a safe and efficient manner. This significant pressure difference eliminates the chance of oxygen entering the hydrogen stream, ensuring superior unity safety and producing ultra high pure hydrogen for analytical applications.
Figure 2 shows that the average oxygen levels measured from the output of the hydrogen gas generator was less than 0.55 ppb after achieving a stable baseline. Figure 3 displays the water content testing results, showing the hydrogen gas generator performance at approximately 20 ppb.
With oxygen below 1 ppb and water moisture content below 20 ppb, the total impurities are less than 50 ppb. Therefore, the hydrogen gas purity of the G600-HP is around 99.999995%, approaching 99.999999%.
Figure 2. O2 output results from G600-HP
Figure 3. Water content results from G600-HP
Efficiency is a critical factor for laboratories when testing a sample. High purity hydrogen can benefit analysis. Based on the ability to reduce band broadening, high purity carrier gas enables lower detection limits. Sharp peaks can be obtained with high purity hydrogen, simplifying the process and improving the performance.
When performing trace analysis on samples with extremely low concentrations, a high purity carrier gas must be relied on to ensure a stable reading. There are many advantages when introducing a high purity carrier gas into GC testing.
In addition to high sensitivity, faster analysis, and lowered baseline noise, hydrogen generated on-site with a high purity hydrogen generator offers additional benefits. “Ensuring gas hygiene is one of the most important steps you can take to optimize GC system performance. Impure gases can introduce contaminants, or cause installation delays, premature instrument failure, and flawed results.” (5)
“All but the 6.0 grades of gas are qualified by statistical quality control. Generally, 10% or fewer of the cylinders in a fill batch will be analyzed to verify gas quality....The problem with per cylinder guarantees is that the analytical costs incurred by the gas supplier to ensure the gas quality of each cylinder are passed along to the customer.” (4)
When it is determined that certified high purity gas is required for a lab, the cost associated with this requirement becomes an issue. “The inefficient use of increasingly expensive and rare gas can go right to your bottom line.” (5) Alternatively, many labs prefer to purchase uncertified cylinder gases.
In doing so, gas chromatography manufacturers often suggest that laboratories purchase gas traps, such as moisture traps, oxygen traps, and hydrocarbon traps and contamination traps, as a final line of defense, to filter impurities and purify the inlet carrier gas, resulting in additional consumable expenses.
Laboratory professionals can benefit from producing high purity hydrogen on-site in both certified and uncertified gas cylinder sourcing, achieving better control over their gas purity and costs associated with hydrogen supply to their GC analyses.
“The general principle is that your GC gases should be free of the impurities that would interfere with your specific analysis or would degrade your chromatographic equipment.” (4) On-site hydrogen generators that employ PEM technology use only DI water and electricity, so their output does not contain any impurities except trace amounts of oxygen, nitrogen, and water moisture.
The G600-HP produces research grade hydrogen with less than 20 ppb water moisture and less than 1 ppb oxygen, eliminating the need for laboratories to purchase purification tools, such as gas traps, which further increase the cost of their processes. “This reduces the risks of column damage, sensitivity loss, and instrument downtime.” (1)
Extended Column Life
Using hydrogen as a carrier gas for gas chromatographs can be very beneficial, especially in extending the service life of the column as it enables a faster analysis due to the higher linear velocity of hydrogen. Using hydrogen also keeps the column temperature low due to the speed of the separations.
Column life is a quintessential aspect of maintaining sound analytical instruments and ensuring stable readings. The use of inappropriate carrier gas makes columns susceptible to many contaminants. The presence of contaminants not only threaten the condition of the analytical instruments, but also the testing results.
“With extended use, columns may accumulate absorptive debris or experience a loss of surface deactivation that leads to increased polar peak tailing and subsequent loss of resolution as well as compromised minimum detectable levels,” (6) making it vital for laboratory professionals to secure a safe and dependable high purity carrier gas for analytical testing.
The purity of the carrier gas used is directly related to the performance and longevity of analytical instruments. Aimed to extend detector life, prevent column damage, and improve the quality and reliability of GC separations, results show that high purity hydrogen supports analytical testing while significantly reducing the possibility of column degradation.
In fact, research grade hydrogen eliminates common contaminants such as water moisture and oxygen from the sample. When constantly exposed to oxygen and moisture, specifically at elevated temperatures, severe damage occurs to the capillary columns.
Therefore, many laboratory professionals rely on moisture and oxygen traps to protect their analytical instruments and increase the column life. (2) The purity requirements are based on the function of the gas, and the sensitivity of the specific detector and the analysis.
For instance, the presence of oxygen in the carrier gas will reduce the column life by contributing to stationary phase degradation. In order to select an appropriate carrier gas, one must know what impurities present and at what levels these contaminants will interfere with the analysis. “Packed and capillary columns may respond differently to the active impurities in the carrier gas. This difference in response depends on the extent of cross-linking, phase loading, age and condition of the column, and typical temperatures the column is exposed to.” (4)
The analytical data discussed in this article highlights the importance of the purity of a carrier gas for laboratories performing GC sample analyses. With on-site gas generators producing research grade hydrogen, gas chromatographers can obtain many benefits in their analyses, such as improved efficiencies, faster analyses, and lower operating costs.
Additionally, the extended column life and reliability of supply are the other benefits offered to laboratories performing GC analytical testing. Proton OnSite’s G600-HP is an affordable system that eliminates the challenges faced by laboratory professionals when using high purity carrier gas sourced from delivered cylinders for their GC analyses. Therefore, the G600-HP is a valuable research grade hydrogen source that supports analytical testing and improves analysis performance.
- “Delivering Clean Gases For Accurate Analyses.” Agilent Technologies, Inc.. Agilent Technologies, Inc., 12 June 2013. Web. 16 Oct. 2015.
- “Maintaining your Agilent GC and GC/MS Systems.” LCGC Chromatography Online. Agilent Technologies, Inc., 15 Feb. 2005. Web. 16 Oct. 2015.
- “Major Causes of Column Performance Degradation .” Agilent Technologies, Inc. . Agilent Technologies, Inc., 7 Aug. 2007. Web. 16 Oct. 2015
- “Frequently Asked Questions about Chromatographic Gases.” Air Products. Agilent Technologies, Inc., 2003. Web. 16 Oct. 2015.
- Lynam, Ken. “No Interference.” Lab Manager. Agilent Technologies, Inc., 9 May 2012. Web. 16 Oct. 2015.
This information has been sourced, reviewed and adapted from materials provided by Proton OnSite.
For more information on this source, please visit Proton OnSite.