Environmental Engineering Reference
In-Depth Information
common environmental pollutants (pesticides, explosives, PAHs, etc), HPLC can
analyze amino acids, proteins, nuclei acids, hydrocarbons, carbohydrates, drugs,
antibiotics, steroids, metal-organic species, and a variety of inorganic substances.
In addition to the types of compounds being analyzed by GC and HPLC, a
general comparison of advantages and disadvantages can be made between these
two. One may consider these factors when choosing a specific instrument for a
defined analytical task. Advantages of GC are the following: (a) low cost, fast
analysis, and ease of operation; (b) more sensitive and higher resolution when
capillary columns are used; (c) a variety of columns (stationary phases) and variety
of general and selective detectors to choose from, providing analytical flexibility;
and (d) readily interfaced to mass spectrometer for structural confirmation.
Advantages of HPLC are the following: (a) direct analysis of aqueous sample
without tedious sample preparation and (b) mobile phases of various polarities
provide versatility. Compared to GC, HPLCs are generally more expensive, less
sensitive, and slower. Besides, HPLC instruments are not readily interfaced to mass
spectrometer, and operationally, they are more problematic with hardware.
10.5.2 Development for GC and HPLC Methods
Developing a chromatographic method is to find a combination of instrumental
parameters in order to reach a set of performance goals, such as resolution, detection
limit and linearity, and certainly ruggedness (a rugged method is one that tolerates
minor variations in experimental condition and can be easily run by an average
analyst). The detailed description of chromatographic method development is
beyond the scope of this text. However, a general strategy is suggested for beginners
in this field.
There are many resources available before the analyst actually shoots a
sample. To get started, one should always ask help from their colleague or
senior graduate students who have experience in a particular instrument
method. With the advent of Internet, locating a standard method and the
application notes may be just a few clicks away from your office desk.
Once you have default parameters from a standard method, a similar method
developed by your colleague, or a method reported in the literature, make a
trial injection using a relatively high concentration of mixed standard
solution. The goal at this stage is to make sure the instrument is in working
condition and you get signal at least for some compounds of interest.
Acquiring a ''not-to-do list'' for a particular piece of instrument from a
skilled person, if at all possible, will help you overcome fears of damaging
the instrument. The ''not-to-do'' list will encourage you to explore what is
beyond the textbook and help you quickly get hold of the instrument.
The next step is to modify the parameters of the default method till you
see desired separation and signals of all the test compounds. Knowing
which parameter to change is the key and knowing the reason for this change
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