Mobile trace analysis

LC/MS-APCI in the positive ion mode was used for trace analysis of TATP [20]. Chromatographic separation was carried out with a C18 (150 X 2.0 mm, 3 (Xm particle size) column, with a mobile phase of methanol—water (70 30) with 5 mM ammonium acetate buffer, at flow rates between 0.1 and 0.2mL/min. Samples were injected as acetonitrile solutions. 

Precision of flow rates from solvent delivery systems Precision in LC analysis Improved sensitivity for trace analysis Recirculation of mobile phase UV and EC detection Baseline drift Rl detection Conductivity detection Summary... 

Because of the very popular reverse-phase mode of LC, water is probably the most popular solvent used in mobile phases. With today s instruments, chemists are now capable of detecting and measuring trace elements down to the level of fractional parts per billion. Typically, however, the thresholds of trace analysis are imposed by problems external to the instrument itself. 

The mobile phase should be of highest purity with regard to the respective analyte ion or ions. The detection limit of a given ion depends on its concentration in the eluent the higher this concentration is, the worse is the limit. Water of HPLC quality can have rather high concentrations of iron and of other ions even if its conductivity is as low as 1 j,S cm It may be necessary to use a water quality designed for inorganic trace analysis." ... 

Figure 5.13. A good vs. a bad blank chromatogram from a gradient trace analysis for impurity testing of pharmaceuticals. The ghost peaks from the blank injection are derived mostly from the trace contaminants in the weaker mobile phase, which are concentrated during column equilibration. Reprint with permission from reference 16.

In summary, more effective and successful HPLC assays can be accomplished by following some of the best practices in mobile phase preparation, strategies in qualitative, quantitative, and trace analysis, and some of the standard operating procedures in HPLC system and data system operation. 

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