GC / MS

Gas Chromatography Mass Spectrometer (GC/MS)

ASTM 6420

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GC/MS is an analytical method that combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC/MS include drug detection, fire investigation, environmental analysis, explosives investigation, and identification of unknown samples. GC/MS can also be used in airport security to detect substances in luggage or on human beings. Additionally, it can identify trace elements in materials that were previously thought to have disintegrated beyond identification.

GC/MS has been widely heralded as a “gold standard” for forensic substance identification because it is used to perform a specific test. A specific test positively identifies the actual presence of a particular substance in a given sample. A non-specific test merely indicates that a substance falls into a category of substances. Although a non-specific test could statistically suggest the identity of the substance, this could lead to false positive identification.

The GC/MS is composed of two major building blocks: the gas chromatograph and the mass spectrometer. The gas chromatograph utilises a capillary column which depends on the column’s dimensions (length, diameter, film thickness) as well as the phase properties (e.g. 5% phenyl polysiloxane). The difference in the chemical properties between different molecules in a mixture and their relative affinity for the stationary phase of the column will promote separation of the molecules as the sample travels the length of the column. The molecules are retained by the column and then elute (come off) from the column at different times (called the retention time), and this allows the mass spectrometer downstream to capture, ionise, accelerate, deflect, and detect the ionised molecules separately. The mass spectrometer does this by breaking each molecule into ionised fragments and detecting these fragments using their mass-to-charge ratio.

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These two components, used together, allow a much finer degree of substance identification than either unit used separately. It is not possible to make an accurate identification of a particular molecule by gas chromatography or mass spectrometry alone. The mass spectrometry process normally requires a very pure sample while gas chromatography using a traditional detector (e.g. Flame ionisation detector) cannot differentiate between multiple molecules that happen to take the same amount of time to travel through the column (i.e. have the same retention time), which results in two or more molecules that co-elute. Sometimes two different molecules can also have a similar pattern of ionised fragments in a mass spectrometer (mass spectrum). Combining the two processes reduces the possibility of error, as it is extremely unlikely that two different molecules will behave in the same way in both a gas chromatograph and a mass spectrometer. Therefore, when an identifying mass spectrum appears at a characteristic retention time in a GC/MS analysis, it typically increases certainty that the analyse of interest is in the sample.

 

Why we need to know?

  • Environmental monitoring and clean-up
    GC/MS is becoming the tool of choice for tracking organic pollutants in the environment. The cost of GC/MS equipment has decreased significantly, and the reliability has increased at the same time, which has contributed to its increased adoption in environmental studies. There are some compounds for which GC/MS is not sufficiently sensitive, including certain pesticides and herbicides, but for most organic analysis of environmental samples, including many major classes of pesticides, it is very sensitive and effective.
  • Criminal forensics
    GC/MS can analyze the particles from a human body in order to help link a criminal to a crime. The analysis of fire debris using GC/MS is well established, and there is even an established American Society for Testing Materials (ASTM) standard for fire debris analysis. GCMS/MS is especially useful here as samples often contain very complex matrices and results, used in court, need to be highly accurate.
  • Law enforcement
    GC/MS is increasingly used for detection of illegal narcotics, and may eventually supplant drug-sniffing dogs. It is also commonly used in forensic toxicology to find drugs and/or poisons in biological specimens of suspects, victims, or the deceased.
  • Sports anti-doping analysis
    GC/MS is the main tool used in sports anti-doping laboratories to test athletes’ urine samples for prohibited performance-enhancing drugs, for example anabolic steroids.
  • Security
    A post–September 11 development, explosive detection systems have become a part of all US airports. These systems run on a host of technologies, many of them based on GC/MS. There are only three manufacturers certified by the Federal Aviation Administration (FAA) to provide these systems one of which is Thermo Detection (formerly Thermedics), which produces the EGIS, a GC/MS-based line of explosives detectors. The other two manufacturers are Barringer Technologies, now owned by Smith’s Detection Systems, and Ion Track Instruments, part of General Electric Infrastructure Security Systems.
  • Food, beverage and perfume analysis
    Foods and beverages contain numerous aromatic compounds, some naturally present in the raw materials and some forming during processing. GC/MS is extensively used for the analysis of these compounds which include esters, fatty acids, alcohols, aldehydes, terpenes etc. It is also used to detect and measure contaminants from spoilage or adulteration which may be harmful and which are often controlled by governmental agencies, for example pesticides.
  • Astrochemistry
    Several GC/MS have left earth. Two were brought to Mars by the Viking program. Venera 11 and 12 and Pioneer Venus analysed the atmosphere of Venus with GC/MS. The Huygens probe of the Cassini-Huygens mission landed one GC/MS on Saturn’s largest moon, Titan. The material in the comet 67P/Churyumov-Gerasimenko will be analysed by the Rosetta mission with a chiral GC/MS in 2014.
  • Medicine
    Dozens of congenital metabolic diseases also known as Inborn error of metabolism are now detectable by new-born screening tests, especially the testing using GC/MS. GC/MS can determine compounds in urine even in minor concentration. These compounds are normally not present but appear in individuals suffering with metabolic disorders. This is increasingly becoming a common way to diagnose IEM for earlier diagnosis and institution of treatment eventually leading to a better outcome. It is now possible to test a new-born for over 100 genetic metabolic disorders by a urine test at birth based on GC/MS.In combination with isotopic labeling of metabolic compounds, the GC/MS is used for determining metabolic activity. Most applications are based on the use of 13C as the labeling and the measurement of 13C-12C ratios with an Isotope Ratio Mass Spectrometer (IRMS); an MS with a detector designed to measure a few select ions and return values as ratios.

 

STANDARD AND SPECIFICATION FOR RECOVERED WASTE OIL

Waste oil that has been processed by recovery facilities and met the standard and specification of recovered waste oil as in Table 1 below can be considered as non-scheduled waste. For waste oil that has been processed but does not meet the standard and specification of recovered waste oil as in Table 1 below still categorised as scheduled waste.

Table 1: Standard and Specification of Recovered Waste Oil

Poly-aromatic hydrocarbons
Benzo(a)pyrene

10 mg / I kg (10 ppm) maximum

Dibenz(ah)anthracene

10 mg / I kg (10 ppm) maximum

Benz(s)anthracene

100 mg / I kg (10 ppm) maximum

Benzo(b)fluoranthene

100 mg / I kg (10 ppm) maximum

Benzo(k)fluanthene

100 mg / I kg (10 ppm) maximum

Chrysene

100 mg / I kg (10 ppm) maximum

Indeno(123-cd)pyrene

100 mg / I kg (10 ppm) maximum

*ppm – parts per million