Application Note #3

In-situ Mass Spectrometry for Process Analysis

Description of Technique:

In traditional on-line process analysis, instrumentation is placed permanently on line to measure specific process components over a well-defined concentration range in a known matrix. Issues such as ruggedness, long-term reliability, ease of maintenance, and ability to interact with process control systems are often of equal or greater importance than some analytical measurement issues. Conversely, the goal of in-situ process analysis is to place measurement technology temporarily on line in a chemical process to assist in short term projects such as process startups and optimization. In-situ analysis projects are often used to characterize a process prior to specification of a permanent on-line analyzer. In-situ applications should be designed to be information rich, flexible, and quickly implemented, with consideration given to analytical attributes such as sensitivity and reproducibility. In-situ projects often reveal unknown information about the process chemistry and operation.

Although mass spectrometry has been used for on-line process analysis for many years, process mass spectrometers tend to lack flexibility, particularly with respect to the data acquisition and analysis systems. Thus, they are generally unsuitable for in-situ analysis. Our solution to this problem is to customize the well-developed commercial benchtop quadrupole mass spectrometers for information-rich, in-situ process analysis. These mass spectrometers possess excellent analytical attributes and flexible data systems that can be configured for a variety of applications. In addition, they are relatively low cost and can be assembled in a reliable and easy-to-service package.

Figure 1: Sampling and Instrumental Block Diagram

Example Applications

Characterization and optimization of vapor-phase chemical processes
Vent-control system optimization and characterization of process vents
Characterization of organics in aqueous process streams
Ambient air or fenceline monitoring
Evaluate the operation and performance of new environmental control, recovery, and remediation devices
Semiconductor gas system monitoring and troubleshooting
In-situ residual gas analysis of semiconductor manufacturing tools

Description of Instrumentation and Sampling System

Most process analytical system failures are due to to the sampling system or interface, not the analytical instrument or method. For this reason, each new application should be evaluated very carefully to design an appropriate sampling strategy for analytes under each process condition and matrix. We have experience in successfully implementing a variety of sampling systems, depending on the nature of the process. Examples of inlet systems that can be used for in-situ MS applications are listed in Table 1 below.

**Table 1: Representative In-Situ Mass Spectrometry Inlet Systems**
Inlet System	Typical Application
Membrane	Ambient air, aqueous streams
Capillary or crimped-tube	Qualitative or semi-quantitative analysis of either high-pressure or vacuum processes
Valved injection,Transfer-Line GC-MS	Quantitative analysis of high pressure processes
Variable restrictor with bypass loop	Quantitative analysis of vacuum processes

The sampling and inlet system delivers a representative process sample to the mass spectrometer, which collects mass spectra every few seconds in either continuous scan or selected-ion monitoring modes. After collection of each spectrum the data system extracts abundance data for each of the target masses, and then passes the mass/abundance data to a trend plotting and archiving subsystem. Depending on the rate at which the process changes, the system can either signal average to improve signal to noise, or trend plot the raw data to keep up with a quickly changing process stream.

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