Gas chromatography, liquid chromatography, and mass spectroscopy flow control
Chromatography and spectroscopy are two major techniques used to perform quantitative and qualitative analysis of gas and liquid samples. Various sample analyzers based on these methods have been developed, differentiated by features and specifications such as:
- Type(s) of detectors used
- Type(s) of phase chemical used
- Operating temperature and pressure conditions
- Ionization method (in mass spectroscopy)
Based on differences in sophistication, the cost of analyzers can range from a few thousand dollars to over a million. The main subcategories of the different types of analyzers include:
In the following, we highlight how Alicat mass flow controllers improve flow regulation, helping to design more valuable analyzer systems.
Gas chromatography (GC)
In gas chromatography, samples are separated in their volatile phases using carrier gases passed in a heated chamber through a column, or a stationary phase, which then hit a detector for analysis. By using this technique, the individual components of a sample are able to be identified and characterized in more depth or simply separated out for further analysis, such as in gas chromatography mass spectrometry systems (GC-MS). Many variations of this technique exist to conduct different types of analysis while the fundamental principles described remain the same.
Using Alicat devices in GC
It is critical to maintain consistent, low flow rates for mobile carriers. Alicat mass flow controllers therefore add value in gas chromatography systems by providing more accurate, repeatable, automated control of mobile carrier/carrier gas flow rates than do traditional control options such as rotameters.
For mass flow control in gas chromatography, Alicat’s MC-Series and CODA KC-Series offer the following specifications and features:
- Full scale ranges down to 0.5 SCCM with a 0.01% – 100% controllable range for MC-Series; 40 g/h with a 2% – 100% of full scale control range for CODA KC-Series
- MC-Series NIST-traceable accuracy of ±0.6% of reading or ±0.1% of full scale, whichever is greater; CODA KC-Series NIST-traceable gas accuracy of ±0.5% of reading or ±0.05% of full scale, whichever is greater
- Warm-up times less than 1 sec
Liquid chromatography (LC)
In high pressure liquid chromatography (HPLC), a sample is separated into individual components using a high pressure liquid mobile carrier. In contrast to gas chromatography, where the sample must be volatile to work with the inert carrier gas, liquid chromatography requires that the sample be soluble to work with the mobile carrier liquid. Just as in gas chromatography, in liquid chromatography the sample is sent through a heated chamber column, or stationary phase, resulting in the separation of different components which then hit a detector.
Using Alicat devices in LC
Just as in gas chromatography systems, CODA KC-Series allows for continuous, accurate, repeatable, mobile carrier flow control during liquid chromatography, as CODA devices are compatible with both gases and liquids. Alicat’s CODA KC-Series include the following additional features which are beneficial for liquid chromatography systems:
- Operating pressures up to 4000 PSIA
- Compatibility for various mobile carrier fluids with an aggressive or unknown composition
- NIST-traceable liquid accuracy of ±0.2% of reading or ±0.05% of full scale, whichever is greater
- Repeatability of ±0.05% of reading or ±0.025% of full scale, whichever is greater
Mass spectroscopy (MS)
Mass spectroscopy describes the process of determining the mass-to-charge ratio of ions, identifying the molecular weight of different components in a sample. This technique is often combined with gas or liquid chromatography, where the chromatography stage separates individual components of a sample and the mass spectrometry stage identifies those components, assessing the distribution, or weight, of different components in the sample mix.
Using Alicat devices in MS
Mass flow controllers such as Alicat’s MC-Series or CODA KC-Series can be used to control the ionization of samples in mass spectroscopy, particularly via the electrospray ion source technique. In this process, nebulizer gases are controlled using a mass flow controller which is mixed with sample fluid, such as the liquid exiting from a liquid chromatography system, forming an aerosol spray which is then vaporized by a drying gas that is also controlled using another mass flow controller.
Since the drying and nebulizer flow rates must be consistent to one another, using mass flow devices such as MC-Series or KC-Series help to better regulate the nebulizer and drying gases, improving the accuracy of mass spectrometry and allowing for more precise measurements.
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