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Analytical Equipments at RAL

 

Gas Chromatography (GC)

Gas Chromatography (GC) is an instrumental technique used to analyse organic compounds. The compounds with sufficient volatility and thermal stability could be analysed using GC. The samples that come in different matrices such as water, soil, fertilizer, etc are extracted into organic solvents, separated from interfering substances and concentrated before introducing to the instrument. Once the sample is injected into the instrument it enters to the separation column with the carrier gas. Inside the column the compound gets separated into various components. The detector measures the components that exit from the column. Different detectors will give different types of selectivity.

In our lab we use GC with various detectors to conduct analysis of volatile organic and chlorinated organic compounds such as pesticides, polychlorinated biphenyls, solvents, anti-oxidants and natural product extracts, etc..

 

GC-FID/ECD (Gas Chromatograph-Flame Ionization Detector/Electron Capture Detector)

 

FID and ECD are two common detectors that have good sensitivity, thermal stability and a wide range of linearity. The basic principle of FID is the ionization of the organic compound by burning the compounds in hydrogen air flame.

The detection of compounds by ECD is based on the reduction of the background current by the sample.

FID is the detector used for many applications such as solvents and petrochemicals. Pesticides and polychlorinated biphenyls are detected by ECD.

 

GC /NPD (Gas Chromatograph/Nitrogen-phosphorus detection)

 

Nitrogen Phosphorus detector is used to detect organic compounds containing nitrogen and phosphorus. As in FID, NPD also uses hydrogen air flame to get the compound ionized. However NPD has a rubidium or caesium chloride alkali bead which is heated by a coil. The surface of this bead can adsorb the partially combusted N and P compounds. Due to this selectivity and sensitivity NPD is widely used in pesticide analysis.

 

GC/MS (Gas Chromatograph – Mass Spectrometer)

 

GC/MS is composed of two analytical instruments, Gas Chromatograph and Mass Spectrometer. Here the compounds that come out from the GC column are fragmented by the electron impact of the MS. Those charged fragments are detected and with the subsequent spectrum obtained molecules could be identified.  

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High Performance Liquid Chromatography (HPLC)

 

HPLC is an instrumental analytical technique to separate compounds into their components. Unlike in normal liquid chromatography where the liquid passes through the column under gravity, HPLC uses high pressure to pass the sample mixture through the column packed with a solid adsorbent material. As in other chromatographic techniques, separation of the sample into its constituents occurs according to their affinity to the mobile and stationary phase. The eluting components that come out from the column is detected by detectors.

At RAL, we use three types of HPLC in our analytical work.

 

HPLC- DAD (High Performance Liquid Chromatograph – Diode Array Detection)

 

Diode Array Detector is the most commonly used detector to record UV and visible spectra of the sample elute from HPLC. The advantage of DAD over UV-VIS detector is DAD has multiple photodiode arrays to obtain information over a wide range of wave lengths at one time.

In RAL, this instrument is basically used to analyse pesticides, food toxins and pharmaceuticals.

 

HPLC- FLD (High Performance Liquid Chromatograph - Fluorescence Detector)

 

HPLC- FLD has high level of sensitivity, selectivity and repeatability. Usually the FLD is used when the sample has little or no visible absorbance.

 

HPLC- RID (High Performance Liquid Chromatograph – Refractive Index Detector)

 

HPLC-RID is considered as a universal detector were it uses to analyse compounds with low or no visible adsorption. RI detector is less sensitive than other detectors. The result is dependent on charges in RI of eluting components in the mobile phase.

 

LCMS-MS (QTRAP) (Liquid Chromatograph - Tandem Mass Spectrometer (QTRAP)

 

LCMSMS (QTRAP) is one of the recently added high end instruments to our lab. LCMS-MS is usually a high performance liquid chromatograph combined with two mass spectrometric analyzers. Here the injected sample which gets separated into different components in the LC column is directed into the ion source where analytes get ionized. The resulting ions are then separated in the first mass analyzer and further fragmented by a collision cell and those fragments are detected in the second mass analyzer. The results of LCMS-MS have more accuracy and precision together with better selectivity. Further QTRAP function offers a higher and deeper selectivity and sensitivity by secondary fragmentation of initially fragmented analytes in the second mass analyzer.

LCMS-MS is mainly used for analysis of polar organic compounds in the lab.

 

Atomic Absorption Spectrophotometer (AAS)

 

Atomic Absorption Spectrophotometer is a scientific instrument used to detect metals in solutions. Here the sample is fragmented into small metal atoms using an atomizer. These metal atoms interact with radiation of a pre-set wavelength which can be measured and interpreted. AAS can determine metals in parts per million to parts per billion concentration ranges with speed and affordable cost.

 

AAS-GTA (Atomic Absorption Spectrophotometer – Graphite Tube Atomizer)

 

GTA is used to atomize the sample using electro thermal energy and compressed inert gases. GTA method is more sensitive than the flame atomization method.

 

AAS- VGA (Atomic Absorption Spectrophotometer- Vapor Generation Assembly)

 

Hydride generation techniques are specialized in solutions of specific elements. The technique provides a means of introducing samples containing arsenic, antimony, tin, selenium, bismuth, and lead into an atomizer in the gas phase. With these elements, hydride atomization enhances detection limits by a factor of 10 to 100 compared to alternative methods. Hydride generation occurs by adding an acidified aqueous solution of the sample to a 1% aqueous solution of sodium borohydride, all of which is contained in a glass vessel. The volatile hydride generated by the reaction that occurs is swept into the atomization chamber by an inert gas, where it undergoes decomposition. This process forms an atomized form of the analyte, which can then be measured by absorption or emission spectrometry.

 

ICPMS (Inductively Coupled Plasma Mass Spectrometer)

 

ICPMS is the latest addition to the Residual Analysis Laboratory. It is also an analytical technique used for elemental analysis. ICPMS is a type of mass spectrometer which is combined with inductively coupled Plasma. This instrument has the capability to detect metals at concentrations as low as one pat in 1015

 

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Last Updated on Tuesday, 30 May 2017 08:57

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