BLBS102-c02 BLBS102-Simpson March 21, 2012 11:54 Trim: 276mm X 219mm Printer Name: Yet to Come
36 Part 1: Principles/Food AnalysisGC separates (partitions) and analyzes molecules of inter-
est such as lipids and carbohydrates, which can be volatilized
(naturally or chemically) without decomposition or creation of
chemical artifacts. The volatilized compounds are injected into
the GC, vaporized, and carried through a column by an inert gas,
where they differentially interact with the inner lining of the col-
umn. Their rate of release from the column lining is based on
their attraction with the column lining, and after being released,
they are carried to the detector that electronically records the
amount of time each substance has taken to travel through the
column. MS, on the other hand, determines the elemental com-
position of a sample, such as the gaseous effluent from a gas
chromatograph. Molecules are ionized, creating both charged
molecules as well as their various fragments. These charged
substances are accelerated through an electromagnetic field that
filters the ions based on a predetermined mass size. The ions are
then counted by a detector that sends the information to a com-
puter, which generates a “graph” showing both the number of
the various ion fragments with their different masses and their
relative amounts. Each chemical has a specific fragmentation
pattern, just like a human fingerprint or iris pattern.
GC–MS is used for substances that are thermally stable (up to
300 ◦C) and relatively volatile at temperatures less than 300◦C,
whereas liquid chromatography–MS (LC–MS or HPLC–MS) is
used for chemicals that are not volatile and/or degrade at tem-
peratures above room temperatures. Nonvolatile chemicals can
be made volatile with derivatizing agents, but not all derivatizing
agents and solvents are compatible with various components of
GC or HPLC equipment. Both GC–MS and LC–MS provide
the much-needed sensitivity than either equipment used alone.
Conventional tests such as Kjeldahl or Dumas can determine
if a sample contains any substances that can be categorized as
proteins, carbohydrate, lipid, etc., but these single methods are
not able to specifically identify the substance of interest. The
main advantage of using these two analytical tools in tandem
(GC–MS) is that together they positively identify (confirm) the
presence of any chemical in a sample with no false positive re-
sults even to levels as low as 5 ppb (Tareke et al. 2002). Using
the analogy of a puzzle, single tests such as Kjeldahl or Dumas
provide one piece to the puzzle, whereas GC–MS provides the
entire picture. Both single and tandem analytical approaches are
valid but before starting any analysis, one has to determine what
information is needed and which analytical test(s) would best
provide that information to the meet the criteria of identification,
accuracy, and sensitivity.
Currently, food applications of GC–MS is primarily limited
to detect the presence of contaminants such as pesticides, insec-
ticides, etc., in fruits and vegetables produced around the world,
as their use in the agricultural industry is not globally standard-
ized. This reality has made GC–MS a valuable tool in the area
of food safety and quality assurance.
Foods and beverages contain many aromatic compounds such
as esters, fatty acids, alcohols, aldehydes, terpenes, etc., which
may be naturally present or formed during processing, and the
presence or absence of specific compounds may be of interest
to researchers, food product developers, food inspectors etc. As
stated above, GC–MS is mainly used to detect the presence orabsence of pesticides in foods, but it can easily be expanded to
detect contaminants arising from the spoilage or adulteration of
food. GC–MS detected the presence of pesticides in pet food
from China in 2007 (FDA 2007) as well as the presence of
melanine in Chinese baby food in 2008. Both Kjeldahl and
Dumas would have shown the presence of much higher than ex-
pected nitrogen content, and hence protein content, in the con-
taminated pet food and melamine adulterated baby food. The
higher than expected protein content would have raised the sus-
picions of analysts, but further expensive and time-consuming
tests would need to have been completed. In this case, GC–MS
clearly demonstrated the presence of pesticides in the pet food
and was also able to differentiate between the nitrogenous milk
proteins and the nitrogen from the melanine.
In the world of expensive foods, GC–MS is an effective tool
in the detection of food adulteration. Some food delicacies such
as caviar, bird’s nests, saffron, and truffles as well as other ex-
pensive food commodities such as coffee, tea, olive oil, balsamic
vinegar, honey, maple syrup, etc., are commonly adulterated to
levels that may not be detectable by conventional tests, and vi-
sual inspection may not raise the suspicions of food inspectors or
consumers. Ruiz-Matate et al. (2007) reported the development
of a GC–MS method to detect the adulteration of honey with
commercial syrups. Honey can be adulterated with inexpensive
sugar syrups such as high-fructose corn syrup or inverted syrups.
Using GC–MS, they discovered, and were also the first to report,
the presence of di-fructose in the four syrup samples but not in
any of the honey samples. Hence, the presence of di-fructose
in any honey sample would indicate possible adulteration of
the honey. Likewise, Plessi et al. (2006) used GC–MS to dis-
cover the presence of nine phenolic antioxidant compounds in
balsamic vinegar, an internationally and nationally recognized
commodity that has country of origin status in the European
Union (European Council Regulation 813/2000). These pheno-
lic acids certainly contribute to the unique sensory qualities of
the balsamic vinegar from Modena and may very well be used
as specific identification markers indicating country, and region,
of origin.
As adulteration can be fatally dangerous as well as compro-
mise the integrity of the genuine food product, constant vigilance
by advanced analytical methods such as GC–MS is critically
necessary.REFERENCES
AOAC International. 1995.Official Methods of Analysis, 16th edn.
AOAC International, Gaithersburg, MD.
AOAC Official Method 992.03. 1995. Vitamin E activity (all-rac-
α"-tocopherol) in milk and milk-based infant formula. Liquid
chromatographic method. In: MP Bueno (ed.)Official Methods
of Analysis of AOAC International, 16th edn. AOAC International,
Arlington, VA, pp. 50-4–50-5.
AOAC Official Method 992.04. 1995. Vitamin A (retinol isomers)
in milk and milk-based infant formula. Liquid chromatographic
method. In: MP Bueno (ed.)Official Methods of Analysis of AOAC
International, 16th edn. AOAC International, Arlington, VA,
pp. 50-1–50-2.