, I I
figure 11.14 HPLC separation of 11 heterocyclic amine standards with thermospray MS detection. The lowest panel shows the chromatogram observed with UV detection, whereas the upper panels show the chromatograms observed in various mass selective detection channels. (From Kataoka, H., J. Chromatogr., 774, 121-142, 1997.)
subsequently generate ionized fragments. In other cases, chemical ionization (CI) is applied. In CI, ion-molecule reactions take place between reagent gas ions and sample molecules. As a result, molecular ions, adduct ions, and fragment ions can be generated. Chemical ionization provides better sensitivity and selectivity than EI, but the number of applications is relatively low compared with EI.
The GC-MS instruments used range from simple linear quadrupoles to multisector analyzers with EI and positive/negative CI capabilities that allow for the achievement of low detection limits, because of increasing selectivity and detection limits parts per trillion (ppt). However, high-resolution mass spectrometry (HRMS) is recommended when an enhancement of the selectivity of MS detection is required, because this technique has the capacity of matrix-interfering compounds. In recent years, the use of MS instruments with quadrupole ion-trap (GC-ITMS-MS) or time-of-flight mass analyzers (TOF-MS) has come to play an important role in environmental analysis.
The new-generation sensitive detection instruments are ideal for combining with high-speed GC or comprehensive two-dimensional gas chromatography (GC X GC), the two most promising recent developments in GC, for the identification and quantification of complex environmental samples, which require an extremely fast acquisition rate.128
GC-MS bas been recognized as the method of choice in a wide series of environmental analyses because of its superiority in selectivity and sensitivity.129 However, these methods have some inherent problems related to the difficulty in handling low molecular weight (LMW) amines because of their high water solubility and volatility.61 Moreover, in GC analysis, amines are likely to be adsorbed and decompose in the column, and readily give tailed elution peaks.64
The direct GC determination of some underivatized AAs, particularly nitro-substituted anilines, requires optimal deactivation of the GC system and careful choice of experimental conditions to
Was this article helpful?