Monday, October 8, 2012

Gas chromatography mass spectrometry equipment

There are various options when it comes to Gas Chromatography Mass Spectrometry (GC-MS) equipments. The options range in price and footprint depending on the sensitivity required and the manufacturer of the instrument.

Agilent (Hewlett-Packard) lead the industry when it comes to Gas Chromatography Mass Spectrometry (GC-MS) equipments. Agilent's GC-MS have the quality and sensitivity while the price still being affordable compared to other manufacturers.

Some of the other Gas Chromatography Mass Spectrometry (GC-MS) equipment manufacturers are  Shimadzu, Perkin-Elmer, Thermo-Finnigan,

There are several types of mass spectrometer detectors

The most common type of mass spectrometer (MS) associated with a gas chromatograph (GC) is the quadrupole mass spectrometer, sometimes referred to by the Hewlett-Packard(now Agilent) trade name "Mass Selective Detector" (MSD). Another relatively common detector is the ion trap mass spectrometer. Additionally one may find a magnetic sector mass spectrometer, however these particular instruments are expensive and bulky and not typically found in high-throughput service laboratories. Other detectors may be encountered such as time of flight (TOF), tandem quadrupoles (MS-MS) (see below), or in the case of an ion trap MSn where n indicates the number mass spectrometry stages.

[edit]GC-tandem MS

When a second phase of mass fragmentation is added, for example using a second quadrupole in a quadrupole instrument, it is called tandem MS (MS/MS). MS/MS can sometimes be used to quantitate low levels of target compounds in the presence of a high sample matrix background.
The first quadrupole (Q1) is connected with a collision cell (q2) and another quadrupole (Q3). Both quadrupoles can be used in scanning or static mode, depending on the type of MS/MS analysis being performed. Types of analysis include product ion scan, precursor ion scan, selected reaction monitoring (SRM) (sometimes referred to as multiple reaction monitoring (MRM)) and neutral loss scan. For example: When Q1 is in static mode (looking at one mass only as in SIM), and Q3 is in scanning mode, one obtains a so-called product ion spectrum (also called "daughter spectrum"). From this spectrum, one can select a prominent product ion which can be the product ion for the chosen precursor ion. The pair is called a "transition" and forms the basis for SRM. SRM is highly specific and virtually eliminates matrix background.


After the molecules travel the length of the column, pass through the transfer line and enter into the mass spectrometer they are ionized by various methods with typically only one method being used at any given time. Once the sample is fragmented it will then be detected, usually by an electron multiplier diode, which essentially turns the ionized mass fragment into an electrical signal that is then detected.
The ionization technique chosen is independent of using full scan or SIM.

[edit]Electron ionization

By far the most common and perhaps standard form of ionization is electron ionization (EI). The molecules enter into the MS (the source is a quadrupole or the ion trap itself in an ion trap MS) where they are bombarded with free electrons emitted from a filament, not unlike the filament one would find in a standard light bulb. The electrons bombard the molecules, causing the molecule to fragment in a characteristic and reproducible way. This "hard ionization" technique results in the creation of more fragments of low mass to charge ratio (m/z) and few, if any, molecules approaching the molecular mass unit. Hard ionization is considered by mass spectrometrists as the employ of molecular electron bombardment, whereas "soft ionization" is charge by molecular collision with an introduced gas. The molecular fragmentation pattern is dependant upon the electron energy applied to the system, typically 70 eV (electron Volts). The use of 70 eV facilitates comparison of generated spectra with library spectra using manufacturer-supplied software or software developed by the National Institute of Standards (NIST-USA). Spectral library searches employ matching algorithms such as Probability Based Matching[5] and dot-product[6] matching that are used with methods of analysis written by many method standardization agencies. Sources of libraries include NIST,[7] Wiley,[8] the AAFS,[9] and instrument manufacturers.

[edit]Cold electron ionization

The "hard ionization" process of electron ionization can be softened by the cooling of the molecules before their ionization, resulting in mass spectra that are richer in information[10][11]. In this method named cold electron ionization (Cold-EI) the molecules exit the GC column, mixed with added helium make up gas and expand into vacuum through a specially designed supersonic nozzle, forming a supersonic molecular beam (SMB). Collisions with the make up gas at the expanding supersonic jet reduce the internal vibrational (and rotational) energy of the analyte molecules, hence reducing the degree of fragmentation caused by the electrons during the ionization process[10][11]. Cold-EI mass spectra are characterized by an abundant molecular ion while the usual fragmentation pattern is retained, thus making Cold-EI mass spectra compatible with library search identification techniques. The enhanced molecular ions increase the identification probabilities of both known and unknown compounds, amplify isomer mass spectral effects and enable the use of isotope abundance analysis for the elucidation of elemental formulae[12].

[edit]Chemical ionization

In chemical ionization a reagent gas, typically methane or ammonia is introduced into the mass spectrometer. Depending on the technique (positive CI or negative CI) chosen, this reagent gas will interact with the electrons and analyte and cause a 'soft' ionization of the molecule of interest. A softer ionization fragments the molecule to a lower degree than the hard ionization of EI. One of the main benefits of using chemical ionization is that a mass fragment closely corresponding to the molecular weight of the analyte of interest is produced.

In positive chemical ionization (PCI) the reagent gas interacts with the target molecule, most often with a proton exchange. This produces the species in relatively high amounts.
In negative chemical ionization (NCI) the reagent gas decreases the impact of the free electrons on the target analyte. This decreased energy typically leaves the fragment in great supply.

Gas chromatography vs Liquid chromatography

Gas Chromatography and Liquid Chromatography are two of the most common techniques used in most Analytical Chemistry Labs.

Gas chromatography (GC), is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture (the relative amounts of such components can also be determined). In some situations, GC may help in identifying a compound. In preparative chromatography, GC can be used to prepare pure compounds from a mixture.

Liquid chromatography (LC) is a separation technique in which the mobile phase is a liquid. Liquid chromatography can be carried out either in a column or a plane. Present day liquid chromatography that generally utilizes very small packing particles and a relatively high pressure is referred to as high performance liquid chromatography (HPLC).

The biggest difference between the two techniques is, as the name suggests, whether the sample is liquid or gas when it gets to the column. Due to this reason, liquid chromatography is often used when the sample cannot be volatilized to a gas to be analyzed by gas chromatography.

Chemistry lab equipment list with pictures

A list of commonly used analytical chemistry instruments with pictures and a brief description.

Analytical Chemistry Lab Equipments

Inductively Coupled Plasma – Optical Emission Spectrophotometer (ICP-OES)
Inductively Coupled Plasma – Optical Emission Spectrophotometer (ICP-OES)
This instrument detects trace metal using inductively coupled plasma to produce excited atoms and ions that emit electromagnetic radiation at wavelengths characteristic of a particular element. The intensity of the emission indicates the concentration of the element within the sample.
Inductively Coupled Plasma/Mass Spectrometer (ICP/MS)
This instrument is used for analysis of routine and complex matrix samples where very low detection limits are required.
High-Pressure Liquid Chromatography Inductively Coupled Plasma/Mass Spectrometer (HPLC ICP/MS)
High-Pressure Liquid Chromatography Inductively Coupled Plasma/Mass Spectrometer (HPLC ICP/MS)
This instrument is used for speciation of arsenic and other metals.
Gas Chromatography Fourier Transform Infrared Spectrometer (GC/FTIR)
This technology is used to separate and identify complex mixtures of organic compounds.
Gas Chromatograph (GC)
Gas Chromatograph (GC)
The gas chromatograph separates and analyzes compounds that can be vaporized without decomposition. Typical uses include testing the purity of a particular substance, separating the different components of a mixture, and determining the relative amounts of components.
Gas Chromatograph/Mass Spectrometer (GC/MS)
The GC/MS combines the features of gas-liquid chromatography and mass spectrometry to identify substances. It can identify trace elements in materials that were previously thought to have disintegrated beyond identification.
Gas Chromatograph/Liquid Chromatograph/Mass Spectrometer/Mass Spectrometer (GC/LC/MS/MS)
Gas Chromatograph/Liquid Chromatograph/Mass Spectrometer/Mass Spectrometer (GC/LC/MS/MS)
This instrument analyzes the molecular and ionic composition of solid, liquid, and gaseous chemical compounds by combining gas chromatography (to separate and identify compounds) with mass spectrometry (to determine the molecular weight and ionic components of individual compounds).
Isotope Ration Mass Spectrometer (IRMS)
Isotope Ration Mass Spectrometer (IRMS)
This mass spectrometer allows the precise measurement of mixtures of stable isotopes.
Ion Chromatography/Hydride Generation/Atomic Fluorescence Spectrophotometer (IC/HG/AFS)
Ion Chromatography/Hydride Generation/Atomic Fluorescence Spectrophotometer (IC/HG/AFS)
This instrument allows separation of ions and polar molecules based on the charge properties of the molecules.
Ion Chromatograph (IC)
This chromatograph measures concentrations of major anions (such as fluoride, chloride, nitrate, nitrite, and sulfate) and major cations (such as lithium, sodium, ammonium, potassium, calcium and magnesium) in parts per billion.
High-Pressure Liquid Chromatograph (HPLC)
This chromatograph uses a liquid mobile phase to separate components of a mixture as it is dissolved in a solvent and forced to flow through a chromatographic column under high pressure.
Isotope Ration Mass Spectrometer (IRMS)
Capillary Ion Analyzer (CIA)
This instrument is used to analyze small ionic species by applying an electric field to the sample in a capillary filled with an electrolyte.
Accelerated Solid-Phase Extraction (ASPE) System
Accelerated Solid-Phase Extraction (ASPE) System
This instrument uses a separation process to remove solid or semisolid compounds from a mixture of impurities based on their physical and chemical properties. The ASPE can isolate analytes from a wide variety of matrices.
Scintillation Counters
Scintillation Counters
Scintillation counters are used for analyzing radioisotope-labeled samples.

Science lab equipment names with pictures

If you are looking for a list of science lab equipments with pictures, you have come to the right place. A list of commonly used chemistry lab equipments in basic chemistry college labs with picture. This includes general chemistry I and II, basic organic chemistry and quantitative analysis labs. Leave a comment and let us know if we missed anything.

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