Reaction monitoring using HPLC

To a rapidly stirred mixture of abs dioxane and abs EtOH (40 1) at 95 °C, containing 4-pyrrolidi-nopyridine (0.1-1 equiv of the OPfp ester) and Pd/C, a soln of the peptide pentafluorophenyl ester in abs dioxane (one-tenth of the total volume used above, to yield a 1-2 mM soln) was added dropwise at 95 °C over 5 h, while simultaneously passing H2 through the soln. After completion of the reaction (monitored by HPLC), the mixture was cooled to rt, filtered, and the solvent was removed under reduced pressure. The crude cyclization product was purified by standard procedures. 

The product from Step 2 was dissolved in methyl alcohol and the reaction monitored by HPLC (Waters 600E) using a Zorbax column (ODS) under the conditions of L = 230 nm, 2ml/min, 20% CH3CN 80% water (initial) to 80% CH3CN 20% water, and changed linearly from 9-17 minutes. A single peak was isolated within 5.8 minutes. 

Oxosanguinarine (35) has been isolated from the mother liquor after the crystalization of 33 and identified by mp. and spectral data [119]. The formation of 0x0- and dibydrosanguinarine was proved in an independent experiment hen the composition of the alkaline reaction mixture was monitored using HPLC. As the compounds 35 (a lactam) and 36 (a substituted naphthylamine) are virtually non-basic species they were readily... 

More recently, the reaction advancement of resole syntheses (pH = 8 and 60°C) was monitored using high-performance liquid chromatography (HPLC), 13C NMR, and chemical assays.55,56 The disappearance of phenol and the appearances of various hydroxymethyl-substituted phenolic monomers and dimers have been measured. By assessing the residual monomer as a function of reaction time, this work also demonstrated the unusually high reactivity of 2,6-dihydroxymethyl-phenol. The rate constants for phenolic monomers toward formaldehyde substitution have been measured (Table 7.6). 

Figure 5.58 Reconstructed LC-MS-MS ion chromatograms for selected-reaction monitoring of methoxyfenozide using the m/z 367 to m/z 149 transition from the continual post-column infusion of a standard solution of analyte during the HPLC analysis of a...

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

Figure 50.1. Comparison of conversion vs. time for the reaction of Scheme 50.1 using HPLC sampling of product concentration to in situ monitoring by FTIR spectroscopy and reaction calorimetry.

The formation of final oxidation products such as 8-oxodGuo 44, 8-oxo-dAdo 48, 5-HMdUrd 12 and 5-FordUrd 13 is monitored using the highly specific method of HPLC-MS/MS [17]. Application of this powerful technique as described in the next section has also been extended to the quantitative measurement of the main DNA photoproducts that arise from the reaction... 

The amount of TiO was varied, and the assembly was tested for its photocata-lytic activity using degradation of 2,4-xylidine as test reaction probe. The decrease in the concentration of xylidine and the corresponding increase in oxalate concentration were monitored through HPLC. A pseudo-first order kinetics was ob served in the photodegradation process based on the Langmuir-Hinshelwood mechanism. An inverse correlation was observed between the kinetic rate constant and the obtained Light-Induced Optoacoustic Spectroscopy (LIOAS) frequency maxima. 

The metabolites of interest in urine are separated using reverse-phase HPLC combined with electrospray ionization (ESI)-MS/MS, and detection is performed using multiple-reaction monitoring. Stable-isotope-labeled reference compounds are used as internal standards. 

---