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Practical Considerations for Quantitative Gas Analysis with Quadrupole Mass Spectrometers

Practical Considerations for Quantitative Gas Analysis with Quadrupole Mass Spectrometers

Many factors must be considered when comparing the overall suitability of different quadrupole-based gas analyzers for any given application and the list can sometimes appear daunting and confusing. This can be due to inconsistencies in the way that different manufacturers choose to define specifications or, in some cases, omit them altogether.

These factors can be categorized into two main areas: (i) inlet interface suitability and (ii) quadrupole mass analyzer suitability. This article aims to remove some of this confusion and define and present those practical specifications which are critical for repeatable and reliable quantitative gas analysis.

The suitability of the inlet and interface determines how well the gas analyzer can capture, condition or transfer the gas sample without altering it and for it to be measured on an appropriate timescale, which could be milliseconds or hours. The inlet and interface can include both the upstream transfer elements and the downstream pumping and gas handling elements.

Quadrupole Mass Spectrometer
Assuming the inlet and interface are properly designed and equal between systems, then the quadrupole mass spectrometer is the critical element determining the overall precision, stability, and detection limits of the gas analyzer. The quadrupole mass spectrometer includes the ionization method, the transmission characteristics, and the quality of the driving electronics.

Precision, stability, and detection limit are often mis-represented in commercial literature. This misrepresentation can be addressed and clarified by directly comparing two different classes of quadrupole analyzers: a 6mm rod diameter, RGA type instrument, typical of many currently on the market, and a higher performance 19mm rod diameter instrument, used in more demanding research and industrial applications. These two systems are compared with nominally identical inlet/transfer conditions, so that only the mass spectrometer performance is under consideration. This presents a direct comparison of the practical range of precision, stability and detection limit in each case so potential users of this powerful analytical technique may be better equipped to make meaningful comparisons between different suppliers.

The MAX300-CAT is typical of the high-end RGA based gas analyzers, based upon 6mm quadrupole rod technology, whereas the MAX300-LG is a higher performing analyzer based on 19mm quadrupole rod technology and more sophisticated electronics.

Detection Limit Comparison
The specified figure of detection limit can be very misleading. Often it will be a calculated figure, or it may reflect data that has been averaged and smoothed for long periods of time to give a best possible case which is often not achievable in practical situations. Nonetheless, the ultimate detection limit is a good starting point to begin to define the practical capabilities of the analyzer.

Speed of Analysis
Analysis speed is a key factor in quantitative gas analysis. Applications such as catalysis, reaction monitoring or kinetics, and evolved gas monitoring all require faster capture of process changes than QA/QC applications, while a breath measurement application needs to report quantitative differences on the millisecond scale. Note that this refers to the ability of the analyzer to measure, with the desired level of accuracy, raw signals and then analyze these in a given timeframe, taking into account spectral interferences, in order to output the result of a single analysis. The rate at which an analyzer scans directly influences this data quality. Slower scanning or more averaging yields more repeatable results and lower detection limits.

Analysis Precision
Analysis precision (or short-term repeatability) represents the standard deviation of analysis results over short time periods. Repeatability can be improved by slowing analysis scan speed or averaging more scans.

Analysis Stability
Analysis stability is a representation of drift or fluctuations over long-term data collection. It is a critical factor which influences longer analyses such as process control, slow heating TGA and thermal analysis, and air monitoring, but also impacts general instrument operation. Stability allows for accurate results over time, less calibration frequency, and confidence in the day-to-day repeatability of the analyzer.

Dynamic Range
Large dynamic measurement range is an essential requirement of quantitative gas analysis and becomes especially apparent in applications such as solvent drying, where species must be monitored from high to low concentrations with accuracy and repeatability.

The MAX300-CAT, a high-end RGA based gas analyzer using 6mm quadrupole rod technology, can demonstrate low detection limits of approximately 5 ppb, using slow scan speeds. The scan speed on this instrument can be increased to a typical quantitative analysis rate of 2 seconds per component, resulting in an increase of detection limits to 0.5 ppm. The MAX300-CAT has a maximum speed of approximately 2-seconds per component in quantitative scans. While this changes the instrument precision, the stability remains constant. The dynamic range of the MAX300-CAT allows for an analysis range from 1×10-6 to 5×10-13 Torr (100% to 0.5 ppm), when scanning at a rate of 2 seconds per analysis component.

The MAX300-LG, a higher performing analyzer based on 19mm quadrupole rod technology and more sophisticated electronics, displays extremely low detection limits of <1 ppb, using slow scan speeds. The scan speed on this instrument can be increased to a typical quantitative analysis rate of 400 milliseconds per component, resulting in a moderate increase of detection limits to <10 ppb. The MAX300-LG has a maximum speed of 5 milliseconds per component in quantitative scans. This instrument has incomparable precision and stability, a result of the large quadrupole and high-performance electronics combination. The MAX300-LG demonstrates a very large dynamic range from the dual detector setup, allowing an analysis range of 1×10-6 to <1×10-14 Torr (100% to <10ppb), while scanning at a rate of 400 milliseconds per component.

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Using a Mass Spec in Semiconductor Fabrication

Consider Using a Mass Spec in Semiconductor Fabrication

Ultra-pure gases are a necessity for semiconductor device fabrication and the continuous monitoring of bulk gas purity can ensure maximum production. Contamination is costly. Semiconductor manufacturers need the ability to continuously verify the purity of process gases in real-time and detect trace contamination at concentrations in the low parts-per-trillion (ppt).

Our ultra-high purity gas analyzers have the speed, sensitivity, and ease-of-use to continuously monitor Nitrogen, Argon, Helium, Oxygen, and Hydrogen supply streams and rapidly report ppt-level contamination to protect the electronics fabrication process. The Process Insights VeraSpecAPIMS combines Atmospheric Pressure Ionization (API) technology with a high-performance mass spectrometer optimized over five decades in industrial gas analysis. Process Insights is the only mass spectrometer manufacturer in the world that utilizes a 19mm, tri-filter quadrupole mass filter in semiconductor gas analysis for the very best performance, reliability, and uptime.


  • Confident supply of UHP production gases
  • One analyzer for all contaminants
  • Fully automated, real-time contamination alerts
  • Reliable 24-7 process protection
  • Maximized wafer yields

Atmospheric pressure ionization is a technique that gives a mass spectrometer the very highest sensitivity for trace gas analysis in UHP samples. A corona discharge needle is used to ionize the molecules of the bulk gas sample. These ions readily transfer this charge to contaminant molecules with lower ionization potentials. The approach yields ionization efficiencies approaching 100%, ensuring exceptional detection limits.

VeraSpec APIMS for Continuous Semiconductor Bulk Gas Purity Verification

While APIMS allows for high ion currents, resulting in low detection limits, the technique is limited to species whose ionization energy is less than that of the bulk gas, or components with sufficient proton affinity to be ionized. The VeraSpec APIMS system combines both EI and API ionization sources. Having two ionization techniques allows for the complete analysis of all components in the pure gas sample with one system.

The Questor5 process control software that drives the VeraSpec APIMS System is designed for continuous gas monitoring in a process environment. The intuitive web-based interface allows the user to check instrument status, review data, or run an acquisition from anywhere on the network, while maintaining government and industry security standards for login and electronic record keeping.

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Flare Compliance at Oil Refineries

Flare Compliance at Oil Refineries

EPA Refinery Sector Rule (RSR) 40 CFR 63 Flare Gas Compliance with Total Composition Monitoring

January 30, 2019 is the compliance deadline for the latest update to the US EPA Refinery Sector Rule (RSR). This will require additional monitoring and gas analysis when regulated material is sent to the flare. The MAX300-AIR, environmental gas analyzer, provides a rapid, speciated analysis of vent gas composition that many refineries are currently using for EPA compliance. According to new requirements in the General Provisions, flares used as Air Pollution Control Devices (APCD) are expected to achieve 98% Hazardous Air Pollutant (HAP) destruction efficiencies. These updated requirements include monitoring of the pilot flame, visible emissions, flare tip velocity, net heating values, and dilution parameters, as well as maintaining a Flare Management Plan and a Continuous Parameter Monitoring System Plan.

The Net Heating Value of the gas in the Combustion Zone (NHVCZ) is of particular importance as it has a direct impact on combustion efficiency. As a result, the RSR update mandates a NHVCZ ≥ 270 Btu/scf, based on a 15-minute block average, when regulated material is sent to the flare for at least 15 minutes. For flares actively receiving perimeter assist air, NHVdil must be greater than or equal to 22 Btu/ft2, when regulated material is sent to the flare. To meet this requirement, continuous direct measurements of refinery vent gas must be made. High variability, sulfur content, and corrosivity can make these samples difficult for many analytical techniques.

The MAX300-RTG 2.0 real-time gas analyzer is currently used at many US refineries for NSPS Subpart Ja sulfur monitoring. The analyzer measures the full, speciated composition of the flare gas and delivers continuous updates of NHV, H2S, and Total Sulfur several times per minute (Fig. 1). Rapid updates of NHV are critical for compliance because the refinery must be able to both monitor and control the gases at the flare tip within the regulated 15-minute block. The additional information provided by full speciation can be used at RSR sites for Ja sulfur compliance, validating or replacing existing sulfur analyzers, as well as for operational control and accurate root cause analysis.

The regulation provides multiple ways to calculate the Net Heating Value of the gas in the Combustions Zone (NHVCZ) for RSR reporting, but all methods use the Net Heating Value of the Vent Gas (NHVVG) as an input. In fact, several parameters, including NHVCZ, NHVdil, and each flare’s specific maximum tip velocity (Vmax), are determined based on NHVVG, making this value one of the key components of reporting compliance and effective flare control. Direct measurements of vent gas composition can be used to calculate NHVVG and high precision gas analysis ensures accurate, actionable NHVVG data (Table 1). When regulated material is sent to the flare, NHVVG changes dramatically as hydrogen and hydrocarbon concentrations in the stream spike and recede. Regardless of the BTU content of the sample, the MAX300-RTG maintains constant, high precision on the NHV parameter due to the inherent repeatability of the gas analysis.

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Fenceline, Air & Flare Gas Monitoring

Fenceline, Air & Flare Gas Monitoring

Environmental Applications for Real-Time Mass Spectrometer Gas Analyzers

By Chuck Decarlo, Business Development & Marketing Manager

See how the recent updates to 40 CFR 60 and 63 have increased EPA regulation of flare gas and fenceline monitoring requirements is prompting the need to adopt real-time gas analysis solutions at many sites, ranging from oil refineries to downstream hydrocarbon manufacturing.

Industrial mass spectrometers provide fast, continuous updates of the necessary compliance parameters as well as additional information for overall process safety and control. This presentation showed many examples and data from fenceline, flare gas, fuel gas and air monitoring environmental applications using a real-time, mass spectrometer gas analyzer.

Mass spectrometry is an analytical technique that utilizes the molecular mass of substances for identification and quantitation. Gas and vapors are ionized inside a vacuum chamber. The ions are then filtered using electric fields generated by the quadrupole. Ions of a particular mass are selected to go to the detector. The composition of the gas sample is calculated from measured ion current and reported to the user in real-time.

By its very nature, a mass spectrometer is a generalist: there is no class of molecules that is unable to analyze and it’s fast.   Also, if you have to measure 80 or 100 sample points spread throughout your facility that would mean many dedicated analyzers, and all of the required maintenance.  A mass spec can do it all.

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Monitoring Gasification with a Mass Spec Gas Analyzer

Monitoring Gasification with a Mass Spec Gas Analyzer

Research in the field of biomass gasification is increasingly important as industry continues to find new uses for syngas. At the Energy & Environmental Research Center (EERC) an Extrel MAX300-RTG process mass spectrometer was used to monitor the exit stream of a Fluid Bed Gasifier. The quadrupole mass spectrometer provided fast, quantitative analysis of the syngas composition.

Over the last several years, concern about the economic and environmental impact of traditional fossil fuel combustion and petrochemicals has led to a search for viable alternatives with gasification emerging as a powerful technique for generating fuel and hydrocarbons. The gasification process makes use of materials such as coal, biomass, and waste to produce synthesis gas, or syngas. Syngas is a combustible mixture of hydrogen, carbon monoxide and carbon dioxide that generally contains a small amount of methane and some trace contaminants. Syngas is used as a fuel source to generate power and heat, or converted into products like hydrogen, for use in fuel cells or fertilizer generation, or liquid fuels via a Fischer-Tropsch reaction.

Gasification and chemical processes utilizing syngas rely upon the ability to obtain information about the composition of the gas stream exiting the reactor. The MAX300-RTG is a 7th generation process mass spectrometer capable of performing quantitative analysis on a wide variety of compounds at concentrations ranging from 100% down to 10 ppb. The 19 mm quadrupole mass filter used by the system allows for high analytical repeatability and long-term stability.

The MAX300-RTG demonstrated that it has the flexibility to quickly characterize and quantify syngas mixtures. It has the sensitivity to detect trace components at ppm levels and below, and the speed to perform each measurement in under 0.4 seconds. The ability to analyze the complete array of syngas components exiting the gasifier, from 100% down to ppm levels, makes the MAX300-RTG an instrument capable of replacing complicated analysis systems involving multiple devices and technologies. The speed of the mass spectrometer means that the MAX300-RTG can be automated to monitor gas composition at several sample points, delivering a complete set of concentrations at 20 seconds per point.

At the EERC, additional sampling at the ports downstream of the reactor could yield important insight into the operation and efficiency of the fixed beds, or be used to analyze hydrogen membrane separation, or a Fischer-Tropsch product. The speed and flexibility of the MAX300-IG, combined with the capability to run 24/7 in rugged and hazardous industrial environments, make it ideal for monitoring production scale gasification and any associated chemical processes downstream. At large facilities that utilize syngas, like ammonia plants, the MAX300-RTG and its predecessors have set the standard for analyzer automation and process control over the last several decades.

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Thermogravimetric Analysis/Mass Spectrometry (TGA-MS)

Thermogravimetric Analysis/Mass Spectrometry (TGA-MS)

An Extrel MAX300-EGA was coupled with a NETZSCH TG 209 F1 Libra to Perform Evolved Gas Analysis

The heated transfer line of the MAX300-EGA™, a quadrupole mass spectrometer designed for evolved gas analysis, was connected to the off-gas port of a NETZSCH® TG 209 F1 Libra® thermobalance. A variety of samples were analyzed and the combination of the two technologies allowed for simultaneous thermal characterization and quantitative analysis of the compounds in the furnace exhaust.

Thermogravimetric analysis (TGA) is a powerful technique that has been used for many years to characterize solid and liquid samples. The mass of the sample material is monitored while it is heated. By using a high precision balance and carefully controlling the heating process, researchers are able to plot mass loss as a function of temperature. TGA is widely used in the study of polymers, pharmaceuticals and petrochemicals to determine degradation temperatures, characterize thermal decomposition, and monitor solvent and moisture content.

Additional information about sample composition and thermal behavior can be obtained by analyzing the gases that leave the material as it is heated. This allows the researcher to determine not only the temperature at which a mass loss occurs, but also the molecular structures involved. Evolved Gas Analysis (EGA) is commonly carried out via a variety of analytical techniques, but in all cases the integrity of the gas stream must be protected. It must be kept hot and moved quickly to the gas analyzer to prevent condensation and chemical interactions.

The NETZSCH TG 209 F1 Libra is a vacuum tight TGA, making it ideal for connecting to a mass spectrometer. The Libra is equipped with an automatic sample changer and can reach temperatures up to 1100°C. It measures sample mass to a resolution of 0.1 μg. The Libra’s heated adapter was connected to the transfer line of the Extrel MAX300-EGA. The interface is differentially pumped for rapid clearing and heated to 200°C to prevent condensation; it provides a low volume, chemically inert sample path from the TGA all the way into the mass spectrometer’s ionizer.

The MAX300-EGA is a quadrupole mass spectrometer optimized for evolved gas analysis in a laboratory setting. It is capable of scanning from 1-500 amu and features the Extrel 19 mm mass filter for high analytical repeatability and long-term stability. The Questor5 software allows the system to perform qualitative analysis for sample characterization, or quantitative analysis, measuring concentrations from 100% down to 10 ppb. In addition to the transfer line, a MAX300-EGA is equipped to import a start-of-heating signal from the TGA and can be configured to perform calculations and trend data or output the data for viewing and manipulation on a different platform.

Polystyrene Decomposition: Detection of High-Mass Fragments

The furnace of the Libra was loaded with 0.94 mg of polystyrene and heated to over 600°C. The breakdown of the sample was monitored to determine the MAX300’s sensitivity to the small signals generated by high-mass hydrocarbons in the off-gas. Although the TGA records the decomposition of the polystyrene as a single weight loss beginning at 290°C, the MAX300 is able to show that the evolution of several compounds has occurred.

It is generally difficult to keep larger molecules from dropping out of an evolved sample once it has left the furnace, but the mass spectrum at 39.75 minutes clearly shows the presence of styrene in the off gas (Fig. 3. B), as well as the much smaller signal generated by methyl styrene.

The mass of each component in the gas was calculated for comparison to data from the TGA’s balance. Even the relatively small, 60 μg, loss that occurred as moisture left the sample was easily measured and quantified by the mass spectrometer. The MAX300 was also able to individually determine the amount of carbon monoxide and carbon dioxide that, combined, resulted in the second mass loss. While the thermal breakdown of calcium oxalate is well documented, the ability of the MAX300 to perform similar quantitative separations can be used to better understand a complex decomposition featuring the simultaneous evolution of multiple unknown compounds.

Further Applications for the MAX300-EGA

The data gathered from the effluent of the TGA 209 F1 Libra indicates that the MAX300-EGA is a powerful tool for evolved gas analysis. The sensitivity, resolution and quantitation demonstrated during the tests indicate the instrument’s potential for other evolved gas applications. In its standard configuration or equipped with the 300 or 400°C transfer line upgrades, the MAX300-EGA could be used to quantify solvent loss in a pharmaceutical sample, detect trace VOCs, or monitor the gas exiting a microreactor.

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