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GC-MS vs LC-MS Chemistry: What You Should Know

GC-MS vs LC-MS Chemistry: Facts You Need to Know in Drug Testing

In drug and biological testing, there are two mass spectrometer methods used - Liquid Chromatography-Mass Spectrometry (LC-MS) and Gas Chromatography-Mass Spectrometry (GC-MS). 

LC-MS Chemistry and GC-MS methods are popular and cost effective methods of chemical analysis used in labs across the US. However, if you are a professional in law enforcement, in the clinical analysis field, a healthcare professional, or anyone interested in how chemical testing works, you should know the differences between these two technologies. These two technologies are especially important in drug and disease testing, and which method is used can have clinical and legal implications. Learn more below.

What is GC mass spectrometry?

 How does GC-MS work?


GC-MS, or gas chromatography-mass spectrometry, was originally a method developed for on board chemical analysis during mars probe missions in the 1970s. A GC mass spectrometer is composed of a gas chromatograph that is connected to a mass spectrometer. The gas chromatograph portion of the device is used to analyze and separate compounds in a sample, while the mass spectrometer portion of the device measures the mass to spectrum ratio of ions, which is done as the separated gas moves down the column of the device. By combining data from both pieces of analysis, GC-MS can identify various materials to a much higher degree of precision than data gathered with either device alone. GC-MS has applications in most areas of physical science, including environmental monitoring, criminal forensics, transportation security, food and beverages, and even in space science. Use of the GC-MS principle is the gold standard for chemical analysis across several fields. The only drawback of GC-MS when compared with the newer LC-MS chemistry analysis is that LC-MS is necessary to analyze 85% of natural compounds, restricting GC-MS to petroleum and other manufactured substances for rapid analysis. However, the Gas chromatography mass spectrometry principle still finds wide use in several fields.

How does LC-MS work?

LC-MS, or Liquid Chromatography-Mass Spectrometry, is similar to GC-MS in that it separates samples for analysis. The LC-MS principle is superior for complex natural biological mixtures which GC-MS has difficulty analyzing. After the chromatographic analysis is carried out, the mass spectrometry portion of analysis is carried out in the same way via ionization that enables spectrographic analysis of a sample. This advance in LC-MS chemistry was enabled by the development of electrospray ionization, which enabled the liquid sample to be ionically charged in a nitrogen medium and then analyzed.

How does a Mass Spectrometer work?


Mass spectrometers are devices which measure mass to charge ratio (m/z) of charged particles such as Ions. Mass spectrometers make use of magnetic fields to manipulate the motion of ions produced from a sample and determine their m/z. When using electrospray ionization, the ion source (lasers, light beams, electron beams) converts the neutral fragment molecules into gas phase ions that can then be read by the mass analyzer portion of the spectrometer. Different substances have different m/z profiles and can thus be identified.


What’s the difference between GC-MS and LC-MS?


GC-MS makes use of a system that utilizes a capillary column which contains an inert medium called the liquid phase.  The differences between molecules chemical properties will cause them to separate in this capillary column. This makes a GC-MS chemistry technique ideal for the analysis of volatile materials, such as petroleum byproducts.


LC-MS, on the other hand, makes use of entirely liquid media to separate molecules of differing properties. This is attractive in the analysis of natural chemical compounds since 85% of these substances cannot be analyzed by conventional GC-MS methods. This makes LC-MS the method of choice in police forensics and drug testing.


LC-MS equipment tends to be more expensive than older style GC-MS equipment, given that it is a newer technology, and requires more staff training than to use accurately. However, LC-MS pays for itself in that individual substance amounts in samples can be identified within 3% of the sample amount. Furthermore, LC-MS is necessary for detailed analysis of natural compounds, such as blood, hair, urine, and various naturally occurring drug and disease samples. This has important implications for drug testing, medicine, and forensics, as LC-MS is more accurate when dealing with natural compounds, which includes most drugs and substances derived from the human body. It’s important to keep these facts in mind when comparing LC-MS vs GC-MS.


Use of LC-MS in pain control compliance and drug testing


An expanding area of drug testing is the use of LC-MS testing in pain management. It can be easy to overdose or to fall into addiction when opiates are used incorrectly. During a pain management regimen, weekly testing can be used to make sure that patients are cooperating with doctor’s instructions and that prescribed medications are accounted for, and being used for that patient’s treatment. Further, since medication levels can be measured precisely, clinicians have a better view of how to increase and decrease medication levels to properly treat a patient’s pain while making sure to avoid abuse pitfalls.

LC-MS and GC-MS Takeaways

These takeaways sum up the information in this article:

  • LC-MS and GC-MS are essential tools for chemical analysis across most industries.
  • LC-MS is more expensive and requires more training than GC-MS.
  • LC-MS is essential in medicine, lab drug testing, and criminal forensics, and is better suited for analysis in these areas.
  • LC-MS can be of great benefit in pain management, since weekly urine testing can accurately measure drug levels, avoiding abuse while keeping patients pain under control.

If you want to learn more about GC-MS vs LC-MS, contact us! Countrywide Testing is an expert in the field of clinical testing, and we’d be happy to answer your questions about these technologies.