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--- atmos:535:projects:hewlett_packard_5890_series_ii_gc-ms [2008/12/09 07:16] – loganen3
+++ atmos:535:projects:hewlett_packard_5890_series_ii_gc-ms [2020/01/29 17:25] (current) – external edit 127.0.0.1
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+====== Gas Chromatograph/Mass Spectrometer ======
+  * Manufacturer - Hewlett Packard
+  * Model Number - HP 5890 II
+       * Shown with Autosampler (on right)
+{{:atmos:535:projects:tekmar2.jpg|}}
+======Theory======
+     * Six Basic Principles in Performing Gas Chromatography:
+          * Flow Controller
+          * Sample Introduction Device
+          * Column
+          * Oven
+          * Detectors
+          * Computer Interface (Data Management)
+====Gas Chromatography====
+          * Process involves the physical separation of compounds in a mixture by injecting the mixture into a tube (column) that contains a silica based inert compound.  The mixture is called the mobile phase and the silica compound is known as the stationary phase.  A carrier gas is used to flush the mobile phase through the column.  The stationary phase will pass some compounds and slow down others.
+          * Compounds in mixture are identified by their retention times.
+               * Retention time is the time it takes for the individual compound to pass through the entire column.
+====Mass Spectrometry====
+          * Mass spectrometry deals with shattering compounds into component ions by passing sample through an ionization (high voltage) source.
+          * The ions are separated by a large magnetic or electric field.  The ions are then collected in "traps" and then analyzed.  A charge to mass ratio is calculated and a mass spectra is generated.
+{{:atmos:535:projects:ms.png|}}
+======Interface and Equipment======
+{{:atmos:535:projects:gcsetup.png|}}
+====GC Column====
+          * Capillary tube of length between 1 to 100 m and thickness range of 0.25 to 5 mm
+          * Column is either packed with silicone based stationary phase or inside is coated with the material.
+{{:atmos:535:projects:column.png|}}
+====Hardware====
+     * Nitrogen Gas Cylinder
+          * Carrier gas for mobile phase, non-reactive and inert to sample being tested
+     * Hydrogen Gas Cylinder
+          * Used to combust sample at the end of the analysis
+     * Plumb Lines
+          * To connect cylinders to GC/MS
+     * Vacuum Pump
+          * Used for MS which operates under low pressure conditions
+====Computer Interface====
+     * The GC/MS can either be run automatically or manually.
+          * Both require use of computer program.
+               * PC and software are Windows based.
+               * Software contains program that controls oven temperature such that the oven starts at a low temperature and ramps up to a higher temperature at different heating rates.
+======Calibration======
+     * Calibration standard is made of a pure compound (e.g. bromofluorobenzene) and is used for quality control of the GC/MS.
+     * The compound has a specific retention time and a specific mass spectra.
+     * Quality control is usually done at after a fixed number, usually 20, of samples have been analyzed.
+     * Quality assurance is done whenever the instrument cannot be calibrated.
+          * QA steps include:
+               * Changing the check standard - an aged check standard can affect accuracy of instrument
+               * Conditioning the column - bake the column to a temperature of 300<sup>o</sup>C to remove contaminants
+               * Replacing the column - cracks and fissures
+               * Checking the carrier gas flow rate - mobile phase may be going faster or slower than normal
+               * Replacing the entire instrument - GC oven may be irreparable, internal plumbing damaged, etc
+======Purpose and Performance======
+     * A combined GC/MS has the ability to detect minute quantities of a solute contained within a larger volume of solvent.  For example, a properly calibrated GC/MS can quantify organic contaminants, such as volatile organic carbons (VOC) on the order of parts per billion present within large volumes of soil, water or air.
+          * This is useful in environmental sampling especially when looking for compounds that adversely affect human health.
+          * Liquid or air samples on the order of milliliters can be sampled.
+               * If using the direct inject method, microliters of sample are usually used.
+     * Sample Injection
+          * Non-Direct Inject
+               * Usually done with help of autosampler.
+               * Nitrogen gas is bubbled into a tube containing sample to draw out the volatile parts of the mixture.
+                    * Semi or non-volatile compounds are not usually sampled by GC.
+               * Mixture is held in a trap until GC signals the computer to start the oven program.
+               * Mixture is injected into the inlet of both the GC and MS at the same time.  Both instruments collect data at the same time.
+               * As the compound is sent through and out of the column, the MS shatters each compound into ions as they are ejected and quantifies their mass spectra.
+               * At the end of the column, there is a flame ionizing detector, FID, which combusts the sample with the aid of hydrogen gas.
+                    * The GC quantifies the amount of burn and the time of ionization to render a retention time and concentration.
+          * Direct Inject
+               * Analyst will start computer program and inject sample at same time rather than using autosampler.
+======Data=====
+{{:atmos:535:projects:scan2.jpg|}}
+     * Top picture shows the chromatogram.
+          * Chromatogram shows peaks for each compound in the mixture according to retention time.  It also shows concentrations of the compounds.
+          * Integrated area of peak is the concentration.
+     * Bottom picture shows the mass spectra.
+          * Using the reference spectra library that comes with the GC/MS software, an analyst can identify each peak by clicking on the highest point of the peak.
+          * At the end of the mass spectra is the molecular weight of the ion.
+               * For example, chloroform is a chlorinated VOC with molecular weight of 119.5 g/mol.  The ion molecular weight will be somewhere between 116 and 118 g/mol.  The discrepancy is due to isotopes of carbon and chlorine.
+======Usage and Deployment======
+     * Liquid samples are collected in bottles and air samples are collected in bags.
+          * Air samples can be direct injected into GC/MS from the bag instead of by autosampler or syringe as with liquid samples.
+          * Does not perform real time sampling.
+          * In a production laboratory setting, a GC/MS can be dedicated to performing emergency sampling which requires a fast turn around.
+          * Most samples that are being tested for VOCs have an average sampling time of 30 minutes from injection to the end of the analysis.
+     * GC/MS is designed to be used in a stationary environment.
+          * Complex setup of GC, MS, computer interface, carrier gas cylinders, and plumbing make it difficult to use in a mobile setting (e.g. aircraft).
+          * Less sophisticated instruments can be used in mobile platforms.
+               * Martian land rover has onboard GC/MS but uses much less sophisticated sampling techniques due to space constraints.
+     * Fields Other Than Environmental and Space Science GC/MS Is Used for
+          * Forensic Science
+          * Toxicology
+          * Drug Screening
+          * Pesticides
+     * Power Consumption
+          * GC/MS can be used on standard 120 V (220 V if 50 Hz cycling alternating current) power line but requires high current for MS.
+          * 800 W power consumption
+     * Cost
+          * $40,000 for GC/MS combination
+          * $1000 for PC and software
+          * $500 for gas cylinder - lasts approximately three weeks with 24 hour consumption
+======Acknowledgments and References=====
+     * GMI, Inc - [[http://www.gmi-inc.com/Products/HP%205890%20GC.htm]]
+     * University of North Dakota, Chemistry Department, Abbott Hall GC/MS Lab
+     * HP 5890 GC/Agilent 5973 MS User Manual
+     * TestAmerica Labs, Inc (Formerly Severn Trent Labs), Edison, New Jersey