#Food Analytical Methods Journal Full Scan Applications#

Lower energy than ESI, so good for detecting unfragmented molecular ion. Prone to “matrix effects” – unpredictable effects on the analyte signal caused by co-eluting molecules.Alternate for coupling to LC. More limited applicability.Standard technique for coupling to LC. Near universal applicability for molecules approx. Lower energy than EI, so good for detecting unfragmented molecular ions. 50 – 1200 mass range.Alternate for coupling to GC.

Gives potential for portable devices.Atmospheric pressure technique that can also be coupled with LC or other separation techniques. 50 – 1400 mass range particularly good for volatile and labile compounds. Ideal for large biomolecules proteins, DNA fragmentsSample is held on a probe at atmospheric pressure. Simple and quick. Moderate range of applicability for molecules approx. More limited applicability.Standard technique for ionising elements: metals and minerals.Direct introduction from samples spotted on a plate.

Food Analytical Methods Journal Full Scan Applications

LC-MS-MS is the industry standard for detecting trace level adulterants such as melamine or Sudan dyes. If two quadrupoles are used in series (called “triple quadrupole” or “MS-MS”) this gives the optimum sensitivity and selectivity for targeted analysis. The electromagnetic fields in Trap and ToF spectrometers can be varied much faster than in quadrupoles, making them more suitable for full scan applications.Multiple spectrometers can be used in series, to increase selectivity. They can be of the same, or different, separation mechanisms. Once the ion emerges from the first it is broken into smaller fragments, each of which then passes down the second spectrometer. Good for scanning surfaces.Direct analysis of meats, fats (originally developed for pathology/surgery) using a highly charged metal edge (“ion knife”) to cut into the sample. Proprietary technology to Waters Corporation.An electromagnetic field is used to either bend ions through a certain path (magnetic sector or quadrupole spectrometers), trap it for a certain length of time (Ion Trap spectrometers), or time its travel down an acceleration tube (Time of Flight, ToF, spectrometers). Lots of parameters to optimise, depending on the analyte.

So, in principle, the ratio of major-to-minor isotopes could be used to tell the geographic origin of any food. Because isotopes differ in mass, they can be measured by mass spectrometry.The proportion of minor isotopes in the environment is specific to the geographic or geological region. Most elements are a mix of isotopes. Natural carbon, for example, consists of approximately 99% stable 12C, 1% stable 13C, a tiny amount of radioactive 14C., and even smaller amounts of other isotopes. Isotopes can either be radio-isotopes (decay by emitting radiation) or stable (do not decay to any appreciable extent). LC-Q-IM-ToF). This separates using the size and physical shape of the fragment, rather than on mass. Ion mobility detectors are familiar at airport security checks. It is very quick, and so dovetails well with the rapid electronics and computing needed for ToF full scan acquisition.Isotopes are forms of a chemical element that differ only by the number of neutrons in the nucleus. They have the same chemical properties, but different mass.