Retention time supercritical fluid chromatography

The separation and estimation of diloxanide furoate and metronidazole in solid dosage forms was reported by Bhoir et al., using packed column supercritical fluid chromatography [38], A JASCO Cig colunm (10 pm particle size, 25 cm x 4 mm) was used at 40°C, with an injection volume of 20 pL. The mobile phase consisted of 26% methanol in CO2 (flow rate of 2 mL/min), and operated at a pressure of 17.6 MPa. When detected on the basis of its ultraviolet absorbance at 230 nm, the retention time for the drug was 1.6 minutes. The linear region of the calibration graph was reported to be 20-70 pg/mL. 

Cosolvent-modifled supercritical fluids are also used routinely in supercritical fluid chromatography (SFC) to modify solute retention times (11-20). In these reports, cosolvents are used to alter the mobile and stationary phase chemistries (16t17t20). However, distinguishing between such effects in a chromatography... 

The checkers determined enantiomeric purity by supercritical fluid chromatography (SFC) using a Chiralpak AD (4.6 x 250 mm) column. Eluent carbon dioxide (300 Bar) modifier methanol (24%) flow rate 1.5 mL/min detection UV (210 nm). Retention times were as follows "diphenylcyclopentanone (3.9 min) (R)-diphenylcyclopentanol (5.9 min) (S)-diphenylcyclopentanol (10.4 min). 

Supercritical fluid chromatography can be used as a qualitative or quantitative technique. Qualitative information allows a substance to be identified on the basis of retention time comparisons between a standard and the sample. When used quantitatively, the SFC can employ external or internal standards to generate a standard curve. Then, the peak area of the sample peak on the chromatogram can be used to obtain a concentration. An example of an SFC instrument is shown in Figure 3.35. 

A number of experimental techniques have been described for the determination of isotherms based on frontal analysis, frontal analysis by characteristic point, elution by characteristic point, and perturbation methods [12,21,27,169,176-179]. Most authors report single-component isotherm results. Multiple-component isotherm data are more complicated because all components are simultaneously in competition for the sorption sites on the stationary phase. The retention time and peak shapes of any solute is dependent on the concentration and properties of all other solutes in the mixture [12,170,180]. For multicomponent mobile phases in liquid and supercritical fluid chromatography this includes each component of the mobile phase. 

Porous graphitic carbon (section 4.2.5) is an inert but highly retentive sorbent under supercritical fluid chromatography conditions. Supercritical carbon dioxide is a weak eluent for porous graphitic carbon and even compounds such as naphthalene are difficult to elute in a reasonable time [72]. Low molecular mass polar compounds generally have poor peak shapes, but in this case most likely due to limited solubility in tbe mobile phase rather than undesirable interactions with active sites on the stationary phase. The flat surface of porous graphitic carbon leads to preferential adsorption of... 

Prednisolone has been analysed by capillary supercritical fluid chromatography in equine urine extract and was identified by matching retention time of pure standard. Supercritical fluid carbon dioxide was used as the mobile phase in conjunction with a methylpolysiloxane stationary phase capillary column and a flame ionization detector. SFC can thus be successfully applied for the estimation of prednisolone without derivatization (118). 

In special cases, polar gases such as ammonia, formic acid and water are doped into the carrier gas to improve the analyte s solubility in the carrier gas. In both supercritical fluid and liquid chromatography, the analyte solubility in the carrier liquid affects the retention time. The carrier liquid is called the eluent and/or the mobile phase. The prediction of retention times in liquid chromatography is very difficult due to the lack of a solubility prediction method. However, the retention can be predicted by computational chemical methods using model phases. ... 

Hsieh et al. (2006a) demonstrated the use of packed-column supercritical fluid chromatography (SFC) combined with atmospheric pressure chemical ionization (APCI)—tandem mass spectrometry (MS/MS) for the analysis of metabolic stability samples. For the SFC step, the mobile phase is liquid carbon dioxide with some organic modifiers added to adjust the retention time of the analytes. In this report, the primary organic modifier was methanol, and the authors described how the percentage of methanol in the mobile phase varied the retention of the analytes and affected the relative response of the test compounds in the APCI source. The authors also demonstrated that the results obtained by the SFC—APCI—MS/MS assay were equivalent to those obtained by a conventional HPLC—APCI—MS/MS assay, as shown in Figure 12.3. 

Figure 21. Supercritical fluid chromatography (SFC) Schematic chromatogram (tR.i or tR,2 = retention time of substance 1 or 2 te.i or Ib,2 = base width of subst ince 1 or 2 to = retention time of a non-retained substance see [13]).

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