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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

Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
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Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
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Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
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what is nanomaterials​ and their applications of sensors.
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what is system testing?
AMJAD
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