Process Analyzers

1. Gas Chromatograph (GC)                             

Origins of Gas Chromatography

The development of GC as an analytical technique was pioneered by Martin and Synge 1941; they suggested the use of gas-liquid partition chromatograms for analytical purposes.

When dealing with liquid-liquid partition chromatography, they predicted that the mobile phase need not be a liquid but may be a vapor. Very refined separations of volatile substances on a column in which a permanent gas is made to flow over a gel impregnated with a non-volatile solvent would be much faster and thus, the columns much more efficient and separation times much shorter.

The concept of gas chromatography was envisioned in the early forties but unfortunately little notice was taken of the suggestion.

Why Choose Gas Chromatography

The two main chromatographic techniques used in modem analytical chemistry are Gas Chromatography (GC) and High Performance Liquid Chromatography (HPLC).

HPLC uses a liquid mobile phase to transport the sample components (analytes) through the column, which is packed with a solid stationary phase material.

In contrast, gas chromatography uses a gaseous mobile phase to transport sample components through either packed columns or hollow capillary columns containing a polymeric liquid stationary phase. In most cases, GC columns have smaller internal diameter and are longer than HPLC columns. GC has developed into a sophisticated technique since the pioneering work of Martin and James In 1951, and is capable of separating very complex mixtures of volatile analytes.

Gas Chromatography Separation Mechanism

In Gas Chromatography (GC) the mobile phase is a gas and the stationary phase is either a solid - Gas solid chromatography (GSC) or an immobilized polymeric liquid - Gas Liquid Chromatography (GLC). Of the two types of GC, GLC is by far the most common as will be seen.

The Gas Chromatograph

Instrumentation for Gas chromatography has continually evolved since the inception of the technique in 1951 and the introduction of the first commercial systems in 1954.

Most modern commercial GC systems operate in the following way:

• An Inert carrier gas, such as helium, is supplied from gas cylinders to the GC where the pressure is regulated using manual or electronic (pneumatic) pressure controls
• The regulated carrier gas is supplied to the inlet and subsequently flows through the column and into the detector
• The sample is injected into the (usually) heated injection port where it is volatilized and carried into the column by the carrier gas
• The sample is separated inside the column - usually a long silica based column with small internal diameter. The sample separates by differential partition of the analytes between the mobile and stationary phases, based on relative vapor pressure and solubility in the immobilized liquid stationary phase
• On elution from the column, the carrier as and analytes pass into a detector, which responds to some physicochemical property of the analyte and generates an electronic signal measuring the amount of analyte present
• The data system then produces an integrated chromatogram
• Gas chromatography uses ovens that are temperature programmable. The temperature of the GC oven typically ranges from 5°C to 400°C but can go as low as -25°C with cryogenic cooling         

GC Advantages and Disadvantages

Gas chromatography has several important advantages which are listed opposite.

GC techniques produce fast analyses because of the highly efficient nature of the separations achieved - this will be studied further in the Band Broadening Section. It can be argued that modern GC produces the fastest separations of all chromatographic techniques. A column has been produced to separate 970 components within a reasonable analysis time-proving that very complex separations may be carried out using GC.

By using a combination of oven temperature and stationary phase chemistry (polarity) very difficult separations may also be carried out-including separations of chiral and other positional isomers.

GC is excellent for quantitative analysis with a range of sensitive and linear detectors to choose from.

GC is however limited to the analysis of volatile samples. Some highly polar analytes can be derivatized to impart a degree of volatility, but this process can be difficult and may incur quantitative errors.

Advantages

• Fast analysis
• High efficiency-leading to high resolution
• Sensitive detectors (ppb)
• Non-destructive - enabling coupling to Mass Spectrometers (MS) - an instrument that measures the masses of individual molecules that have been converted into ions, i.e. molecules that have been electrically charged
• High quantitative accuracy (<1% RSD typical)
• Requires small samples {<1 mL)
• Rugged and reliable techniques
• Well established with extensive literature and applications

Disadvantages

• Limited to volatile samples
• Not suitable for samples that degrade at elevated temperatures (thermally labile)
• Not suited to preparative chromatography
• Requires MS detector for analyte structural elucidation (characterization)
• Most non-MS detectors are destructive

Typical GC Application

Since the development of GC instruments in the early to mid 1950's, GC has found applications in a host of industrial, environmental, pharmaceutical and biotechnology analytical laboratories.

Modern GC techniques are able to sample from a wide variety of matrices, inducing solids, liquids and permanent gases.

High temperature applications using specially designed columns are able to analyze relatively non-volatile substances and Cool-on-Column injection techniques allow the sampling of moderately thermally labile materials.

Purge and trap and headspace auto sampling techniques are now well established and are able to desorbs or extract samples collected in the most inhospitable of environments, such as the emission stacks of industrial plants.

Detector technology for GC is able to detect very small amounts of pesticides for example, from environmental samples and GC-MS techniques allow structural elucidation of even the most complex analytes.

Pharmaceutical

In the pharmaceutical industry GC is used to analyze residual solvents in both raw materials (drug substance) and finished products (drug product). Biopharmaceutical applications include urine drug screens for barbiturates and underivatized drugs and for ethylene oxide in sterilized products such as sutures.

Food/flavors/Fragrances

The food Industry uses GC for a wide variety of applications including quality testing and solvents testing. The Flavors and Fragrances industries use GC for quality testing and fingerprinting of fragrances for characterization.

Petrochemical

GC applications Include natural gas analysis or refineries, gasoline characterization and fraction quantitation, aromatics in benzene, etc. Geochemical applications include mapping of oil reserves and tracing of reservoirs etc.

Chemical/Industrial

Chemical / Industrial uses include determination of product content, determination of purity, monitoring production processes, etc. GRS are used to detect organic acids, alcohols, amines, esters, and solvents.

Environmental

Environmental GC applications include detection of pollutants such as pesticides, fungicides, herbicides, purgeable aromatics, etc. Industrial environmental protection applications include stack and waste emissions as well as water discharges.

2. Continues Gas Analyzer(CGA)                         

Using various measurement principles to provide precise continuous analysis of Process gas down to low PPM levels.

Continuous Gas Analyzers use in an extremely wide variety of applications is proof of their quality, reliability and measuring accuracy.

Two Measuring method is used for different application:

Continuous gas analysis – extractive

Continuous gas analysis – in-situ

We can refer to below items as some examples of this category : 

• H2S Analyzer
• O2 Analyzer
• CO2 nalyzer
• H2 Analyzer

3. Liquid Analyzer     

These Analyzers are used for monitoring process chemistry including water quality, providing process optimization and control. Applications are in chemical process, power, refining, food & beverage, pharmaceutical and water & wastewater

1. 1. Retractable

This category includes all parameters and components which are important to measure in liquids such as

• PH
• ORP
• Conductivity
• Turbidity
• Dissolved Oxygen
• Chlorine

1. 2. Steam and Water Analysis System(SWAS)

1. 3. Lab Sampler