Bronkhorst

MEMS technology to support compact gas chromatography equipment

November 28, 2017 Dion Oudejans

Semiconductor chip technology is enhancing our lives in many ways. Emerged from semiconductor technology, MEMS chip technology is also present in devices around you in the form of sensors that add functionality. Think of your smartphone that captures your voice and senses the smartphone position, orientation and movement by means of Micro Electro Mechanical Systems (MEMS). Adding those features is barely impacting the physical dimensions of a smartphone and it still fits in your hand and pocket.

This blog is about instrument miniaturization by MEMS chip technology and discusses the benefits of miniaturized gas flow instruments for application in the field of gas chromatography analysis and headspace sampling in specific. As a product manager for MEMS-based instruments at Bronkhorst High-Tech, I can see the benefits of miniaturization by MEMS technology in such applications.

Laboratory

Miniaturization by MEMS chip technology

Bronkhorst developed the so called  IQ+FLOW product line with instruments based on MEMS chip technology. The product line consists of miniaturized gas flow and pressure meters and controllers, which are suitable for many applications. For instance, analysis equipment in laboratories benefit from the reduced size of the these flow instruments, compared to regular flow instruments.

In this case, MEMS chip technology is an enabler for miniaturization. Additionally, Bronkhorst provides a service to develop customer specific solutions. Hereby, further miniaturization in case of a combination of instruments can be possible. Please have a look at our blog The trend towards miniaturization in flow solutions.

Advantages of miniaturization

In a laboratory environment, it is advantageous to work with desktop-sized equipment. Advantages of increasing functionalities in table top equipment are: reduced space requirements, enhanced ease of operation and often reduced cost of ownership.

Gas chromatography equipment is a good example of a concentration of functionalities on a small footprint. Many types of gas composition and vapour composition can be analysed with high accuracy and for very low concentration levels. Additionally, there is a certain degree of automation involved. This is all within arm’s reach of a laboratory analyst.

principle gas chromatography
Principle gas chromatography

Gas chromatography

The goal of gas chromatography analysis is to identify and measure the concentration of gas components in an analytical gas sample. Within the gas chromatograph, there can be different arrangements of gas streams, injections, splits, columns and detectors. Within these arrangements, there is often a need for gas flow or pressure control. The picture shows a gas flow controller for the carrier gas stream (red) and a pressure controller for the split flow stream (yellow).

The principle of gas chromatography involves a controlled carrier gas stream that passes an injector, column and detector. A sample gas is injected for a short period of time, creating a gas sample plug. The gas sample plug is separated into gas components across the column, which become visible as peaks during detection. The picture on the right shows an example of a gas chromatography output signal.

output signal diagram gas chromatography
Output signal diagram gas chromatography
headspace sampling
Dynamic headspace sampling units

Headspace sampling

Let’s zoom in on dynamic headspace sampling units that are used in combination with gas chromatographs. Headspace sampling is a method that is named after the gas space in a chromatography vial containing a liquid sample. The liquid sample can be a solvent, containing material to be analysed. For example, materials like: volatile organic compounds in environmental samples, alcohols in blood, residual solvents in pharmaceutical products, plastics, flavor compounds in beverages and food, coffee, fragrances in perfumes and cosmetics.

This is explained in the picture. The headspace is the gas space above the liquid sample in a chromatography vial. Dynamic headspace sampling is performed by purging the gas space and the adsorbent. The adsorbent collects the sample gas. After transport, the adsorbent is purged again to release the sample gas into a gas chromatograph.

Where a gas flow controller comes into play is at purging the headspace with a constant Helium or Nitrogen flow for a pre-determined period of time at a specified temperature between 10 - 200 °C. The gas flow, containing the headspace sample gas, passes an adsorbent that collects the headspace sample gas.

The adsorbent is usually made of Tenax TA material. Now, the adsorbent is transported to the inlet of a gas chromatograph. While the adsorbent is heated between 20 - 350°C, a controlled Helium or Nitrogen gas flow passes the adsorbent to release the headspace sample gas into the inlet of the gas chromatograph. The gas chromatograph does its job to analyse the sample. Different signal peaks in time show the different components and their concentration.

IQ+flow gas flow meter

IQ+FLOW gas flow meters and pressure controllers

For flow instruments, a number of specifications are important in headspace sampling and gas chromatography in general. The IQ+FLOW product line addresses these specifications with small instrument size, fast response, good repeatability, low power, low cost of ownership and the excellent support that you can expect from Bronkhorst.

The future of MEMS technology

Nowadays, MEMS chip technology is in many products around you. Bronkhorst is committed to look ahead and find applications that can be enhanced with MEMS chip technology, also in the field of gas chromatography. Feel free to contact us for questions. We will keep you informed!