Trace Level Analysis of Gases with the VeraSpec Trace Atmospheric Pressure Ionization Mass Spectrometery (API-MS) System

Trace level testing of impurities in pure gases is a major aspect in the development and implementation of semiconductor and other advanced technology industrial applications.

Atmospheric pressure ionization mass spectrometry (API-MS) has grown into a significant tool for pure gas analysis, offering part-per-trillion (ppt) level detection of specific impurities in pure gases. For other impurities where API is not a feasible method, electron impact ionization (EI) mass spectrometry can be applied to increase the analysis.

In certain cases, membrane introduction mass spectrometry (MIMS) coupled with an EI source can offer sub part-per-billion (ppb) detection limits for certain parts. Extrel’s VeraSpec Trace has the exclusive capability to unite these methods into one instrument.

VeraSpec Trace system

The VeraSpec Trace system is designed to offer suitable ionization methods for pure gas testing in a single system. The system can be configured for ionization methods, eliminating the requirement of two mass spectrometers, and greatly decreasing the total expenditure. The base system uses either Extrel’s high-performance, closed-source EI ionizer, or the well-established, dependable DC Corona Discharge API source.

The DC Corona Discharge Source is a chemical or soft ionization source that is perfect for observing molecules in the ppt and ppb range. The EI system is taken from Extrel’s MAX300 industrial mass spectrometers, and possesses the same well-established performance seen in those systems, where detection limits are in the low ppb range. The system utilizes a 19 mm tri-filter quadrupole, and is available in a number of mass ranges pinpointed in Table 1. The system is also provided in an MS/MS configuration, the VeraSpec Trace MS/MS.

Table 1. Gas Analysis Systems

*Note: The ionization system of the base system is selected by the customer. Either EI or API can be selected, but not both.

VeraSpec Trace Specifications

The VeraSpec Trace DS is a dual-source model consisting of an API and Extrel’s well-established closed source EI ionizer, fitted with a capillary inlet in the basic configuration. Source selection is achieved using Extrel’s large ion bender for the greatest sensitivity and flexibility. When a membrane inlet is added to the EI system, it pushes the detection limits for applicable analytes into the sub-ppb range in the VeraSpec Trace DS-MIMS system.

Dual Source Performance

One of the most innovative capabilities of the VeraSpec Trace is available in the Dual Source version. While API ionization enables high ion currents resulting in minimal detection limits, the method is limited to molecules with ionization energy that is less than that of the balance gas or any other high concentration part, and have adequate proton affinity to be ionized.

Consequently, every table of lower detection limits for pure gas testing with the aid of API has gaps for parts that cannot be measured. With the VeraSpec Trace DS, the gaps can be filled as shown in Table 2. By adding a high-performance, closed EI source, detection can be made to ppb levels.

Table 2. Mass Range Options

The membrane inlet of the analytes can be preconcentrated, allowing for sub-ppt levels to be accomplished. The VeraSpec Trace gains its strength from Extrel’s research and industrial expertise. The task of the membrane inlets is to allow the VOCs to permeate via the membrane, while water or other liquid phase flows past. The outcome is an instrument with superior detection limits for all of the parts, with the dependability and stability needed in an industrial environment. The VeraSpec Trace has unmatched versatility and capability for trace analysis in a single instrument.

Table 3. Detection limits for some compounds in some bulk gas.

Detection limits marked with * are based on EI ionization tri-filter.

All of the data in Table 4 was taken using a VeraSpec Trace DS MS/MS.

Table 4. Measurement of Impurities in Air with MIMS Option on the VeraSpec Trace

Based on EI with a MIMS inlet.

A Breadth of Gas Analysis

API and EI dual source ionization provides the versatility of having two systems for testing, integrated into one. The VeraSpec Trace can handle difficult atmospheric and gas analysis, ranging from high resolution analysis to CFC detection in atmospheric samples.

Dual Source Ionization

The Extrel VeraSpec Trace enables researchers to use two powerful MS ionization methods simply by pressing a button within the software. When the attractive voltage is on the bottom right pole, it attracts the API ions into the MS (purple traces). When the attractive voltage is switched to the upper right pole, it attracts the EI ions into the system (blue traces).

Lower Detection Limits in Pure Gas

Trace levels of oxygen and carbon dioxide in dry nitrogen were measured in the VeraSpec Trace at a series of levels below 2000 ppt. A multi-point calibration curve was constructed and the detection limits were calculated at at value of 3 (a 99.5% confidence interval). The calibration curves had R2 value of >0.9. The calibration curve was used to compute extremely low detection limits for CO2 of 0.9 ppt, and for O2 of 4.1ppt, showcasing the power of the Extrel APIMS detection scheme.

Applications

The key applications of the VeraSpec Trace system are as follows:

• Atmospheric analysis
• Trace analysis of impurities in bulk gas
• Wind flux measurements
• PTR/MS and CFC detection
• Bulk gas manufacturing QA/QC
• Gas filter and purifier manufacturing QA/QC
• Semi-conductor off-gassing