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Detector

The detector senses a physicochemical property of the analyte and provides a response which is amplified and converted into an electronic signal to produce a chromatogram. Most of the detectors used in GC were invented specifically for this technique, except for the thermal conductivity detector (TCD) and the mass spectrometer. In total, approximately 60 detectors have been used in GC. Detectors that exhibit an enhanced response to certain analyte types are known as "selective detectors".

During the last 10 years there had been an increasing use of GC in combination with mass spectrometry (MS). The mass spectrometer has become a standard detector that allows for lower detection limits and does not require the separation of all components present in the sample. Mass spectroscopy is one of the types of detection that provides the most information with only micrograms of sample. Qualitative identification of unknown compounds as well as quantitative analysis of samples is possible using GC-MS. When GC is coupled to a mass spectrometer, the compounds that elute from the GC column are ionized by using electrons (EI, electron ionization) or a chemical reagent (CI, chemical ionization). Charged fragments are focused and accelerated into a mass analyzer: typically a quadrupole mass analyzer. Fragments with different mass to charge ratios will generate different signals, so any compound that produces ions within the mass range of the mass analyzer will be detected. Detection limits of 1-10 ng or even lower values (e.g., 10 pg) can be achieved selecting the appropriate scanning mode.

Sample preparation techniques

Derivatization

Gas chromatography is primarily used for the analysis of thermally stable volatile compounds. However, when dealing with non-volatile samples, chemical reactions can be performed on the sample to increase the volatility of the compounds. Compounds that contain functional groups such as OH, NH, CO 2 H, and SH are difficult to analyze by GC because they are not sufficiently volatile, can be too strongly attracted to the stationary phase or are thermally unstable. Most common derivatization reactions used for GC can be divided into three types:

  1. Silylation.
  2. Acylation.
  3. Alkylation&Esterification.

Samples are derivatized before being analyzed to:

  • Increase volatility and decrease polarity of the compound
  • Reduce thermal degradation
  • Increase sensitivity by incorporating functional groups that lead to higher detector signals
  • Improve separation and reduce tailing

Advantages and disadvantages

GC is the premier analytical technique for the separation of volatile compounds. Several features such as speed of analysis, ease of operation, excellent quantitative results, and moderate costs had helped GC to become one of the most popular techniques worldwide.

Advantages of gc

  • Due to its high efficiency, GC allows the separation of the components of complex mixtures in a reasonable time.
  • Accurate quantitation (usually sharp reproducible peaks are obtained)
  • Mature technique with many applications notes available for users.
  • Multiple detectors with high sensitivity (ppb) are available, which can also be used in series with a mass spectrometer since MS is a non-destructive technique.

Disadvantages of gc

  • Limited to thermally stable and volatile compounds.
  • Most GC detectors are destructive, except for MS.

Gas chromatography versus high performance liquid chromatography (hplc)

Unlike gas chromatography, which is unsuitable for nonvolatile and thermally fragile molecules, liquid chromatography can safely separate a very wide range of organic compounds, from small-molecule drug metabolites to peptides and proteins.

Relative advantages and disadvantages of GC versus HPLC.
GC HPLC
Sample must be volatile or derivatized previous to GC analysis Volatility is not important, however solubility in the mobile phase becomes critical for the analysis.
Most analytes have a molecular weight (MW) below 500 Da (due to volatility issues) There is no upper molecular weight limit as far as the sample can be dissolved in the appropriate mobile phase
Can be coupled to MS. Several mass spectral libraries are available if using electron ionization (e.g., (External Link) ) Methods must be adapted before using an MS detector (non-volatile buffers cannot be used)
Can be coupled to several detectors depending on the application For some detectors the solvent must be an issue. When changing detectors some methods will require prior modification

Bibliography

  • E. F. Barry, Columns for gas chromatography: performance and selection , Wiley-Interscience, Hoboken, NJ (2007)
  • L. S. Ettre, LCGC , 2001, 19 , 120.
  • D. Filmore, Industry Facts&Figures - American Chemical Society Publications . GC: Mature and moving forward. May, 2003.
  • R. L. Grob and E. F. Barry, Modern practice of gas chromatography , 4 th edition, Wiley-Interscience, Hoboken, N.J.(2004)
  • J. V. Hinshaw, LCG , 2013, 31 , 932.
  • A.T. James, Biochem. J. , 1952, 52 , 242.
  • A. T. James and A. J. P. Martin, Biochem. J. , 1952, 50 , 679.
  • A. T. James, A. J. P. Martin, and G. H. Smith, Biochem. J. , 1952, 52 , 238.
  • A. J. P. Martin and R. L. M Synge, Biochem. J. , 1941, 35 , 1358.
  • G. McMahon, Analytical Instrumentation: A Guide to Laboratory, Portable and Miniaturized Instruments , 1 st edition, Wiley, Hoboken, N.J (2007)
  • H. M. McNair, Basic gas chromatography , Wiley, New York (1998)
  • http://www.chromatographyonline.com/
  • Sigma Aldrich Brochure. Derivatization reagents for selective response and detection in complex matrices. 2011,Sigma-Aldrich Co. Available through http://www.sigmaaldrich.com

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how to find Rutherford scattering parameters angles
saksham Reply
advantages of NAA
Sai Reply
how I can reaction of mercury?
Sham Reply

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Source:  OpenStax, Physical methods in chemistry and nano science. OpenStax CNX. May 05, 2015 Download for free at http://legacy.cnx.org/content/col10699/1.21
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