Gradient 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.

Volatile amines from Ci to C(, and ammonia were separated on a PoraPLOT column, with or without a temperature gradient, depending on volatility. The method is applicable to determination of the purity of manufactured amines. Trace analysis of these amines can be performed by capillary GC-FID and of ammonia by GC-ELCD101. 

Refractive index detectors are useless in gradient elution because it is impossible to match exactly the sample and the reference while the solvent composition is changing. Refractive index detectors are sensitive to changes in pressure and temperature (—0.01 °C). Because of their low sensitivity, refractive index detectors are not useful for trace analysis. They also have a small linear range, spanning only a factor of 500 in solute concentration. The primary appeal of this detector is its nearly universal response to all solutes, including those that have little ultraviolet absorption. 

Figure 9.27 Isocratic and gradient HPLC analysis of median eminence (ME) supernatant fraction after incubation with LHRH. Total peptidase activity was assessed in ME and was analyzed by HPLC. Upper HPLC tracing represents a preboiled control, the middle tracing a zero-time incubation, and the lower a 2-hour preincubation. The peptide fragments are indicated in the upper panel by letter (A-D) and the corresponding peaks they represent are shown by the same letter. (From Advis et al., 1982.)...

ASIO L 170 Inorg., org. anions. Isocratic or gradient. Trace level analysis in high ionic strength samples. 

Detectors used in HPLC should have low internal volumes to minimize extracolumn band broadening in addition, they should be sensitive and should respond quickly to concentration changes. Few detectors fulfill all of these requirements. One of the oldest detectors used in HPLC is the refractive index detector, which detects subtle differences between the refractive index of the pure mobile phase and a mobile phase containing the solute. This detector is universal, i.e., it can detect any solute whose refractive index differs from that of the pure solvent. However, its sensitivity is poor, which practically precludes its use in trace analysis. Besides, refractive index detectors are very sensitive to changes in the composition of the mobile phase and to temperature flucmations. The former makes their use in gradient elution impractical the latter requires that the detector is thermostated to at least 0.01°C. 

Figure 3.203 Trace analysis of inorganic and organic anions with an electrolytically generated KOH eluent. Separator column lonPac AS15 column temperature 30°C eluent KOH (EG) gradient 9 mmol/L isocratically for 7 min and then to 46 mmol/L in 11 min flow rate 1.6mL/min detection suppressed...

Figure 10.39 Trace analysis of haloacetic acids standards with ICP-MS as an element-specific detection system. Separator column lonPac AS16 column dimensions 250mmx4mm i.d. eluent NaOH gradient 20mmol/L from 0 to 3 min, then step to 100 mmol/L in 0.1 min, and isocratic at 100 mmol/L for 9 min flow rate 1 mL/min detection ICP-MS ...

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