Agriculture Reference
In-Depth Information
pro
les. Because of this, monolithic columns can be operated either at much higher
linear velocities or with a combination of gradient and
flow programming, signifi-
-
cantly improving throughput.
The advent of monolithic silica standard- and narrow-bore columns and of several
families of polymer-based monolithic columns has considerably changed the HPLC
field, particularly in the area of narrow-bore columns. By using monolithic columns,
complex mixtures of biological molecules can be ef
ciently separated, and through-
put
cantly
improved. Monolithic columns have been found to be especially useful for separating
larger peptides, proteins, and polycyclic compounds [46]. Highly sensitive proteo-
mics applications are also easily performed using these columns.
in pharmaceutical and biotechnology laboratories has been signi
Core-Shell Columns
It is interesting to note that some manufacturers and a number
of researchers have rediscovered pellicular construction in the form of smaller 1.5
-
2.5
m particle-based packings containing a very thin porous outer layer [29]. Never-
theless, the original pellicular work can be traced back to the late 1960s and was the
packing of choice until the introduction of completely porous 5
μ
μ
m materials in
1972 [46,47].With the reintroduction of pellicularmaterials in combinationwith longer
columns and higher solvent delivery pressures, it is possible to obtain highly ef
-
10
cient
separations of complex proteomic mixtures. Modern porous shell packings are highly
ef
cient (i.e., with improved solute mass transfer kinetics) because their outer micro-
particulate layer is only 0.25
m thick with pores in the 300 Å range. Typically,
thesematerials have surface areas in the 5
-
1.0
μ
10 m
2
/g range. Core
-
-
shell columns offer one
option for users who want higher separation ef
ciency and higher sample throughput
without a UHPLC system. The main disadvantage of core
-
shell columns, relative to
regular columns, is their lower saturation capacity.
2.2.2.2 Mass Spectrometry
Targeted Analysis
The application of MS for food safety analysis can be divided
into targeted and nontargeted analyses. A targeted analysis is a conventional analysis
based on developing a method with standards prior to the analysis and monitoring of
real samples, and does not detect compounds not de
ned in the developedmethod [48].
Themain techniques involve the application of LC
MS, such as using triple quadrupole
mass spectrometry (QqQ-MS), quadrupole linear ion trap mass spectrometry (QLT-
MS), TOFMS, and Orbitrap MS. Selected reaction monitoring (SRM), also called
MRM mode, is still preferred for a quantitative analysis of known or targeted
compounds using QqQ-MS due to its good selectivity, sensitivity, reproducibility,
dynamic range, and quanti
-
ability.
To overcome the limited number of compounds that can be simultaneously
determined, which mainly depends on the scan speed/dwell time, scheduled MRM
TM
or similar techniques (e.g., dynamic MRM mode) have been widely used. Higher
sensitivity and more robustness are achieved by applying these techniques compared
with the more commonly used SRM mode. When these techniques are applied for
an analysis, the whole data acquiring period is divided into different time segments.
The partition of the time segments mainly depends on the retention times of
