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PubMed2001

S-naproxen-beta-1-O-acyl glucuronide degradation kinetic studies by stopped-flow high-performance liquid chromatography-1H NMR and high-performance liquid chromatography-UV.

Acyl-migrated isomers of drug beta-1-O-acyl glucuronides have been implicated in drug toxicity because they can bind to proteins. The acyl migration and hydrolysis of S-naproxen-beta-1-O-acyl glucuronide (S-nap-g) was followed by dynamic stopped-flow HPLC-1H NMR and HPLC methods. Nine first order rate constants in the chemical equilibrium between six species (S-nap-g, its alpha/beta-2-O-acyl, alpha/beta-3-O-acyl, alpha/beta-4-O-acyl, and alpha-1-O-acyl-migration isomers, and S-naproxen aglycone) were determined by HPLC-UV studies in 25 mM potassium phosphate buffer, pH 7.40, 25 mM potassium phosphate buffer in D2O pD 7.40, and 25 mM potassium phosphate buffer in D2O pD 7.40/MeCN 80:20 v/v (HPLC-1H NMR mobile phase). In the 25 mM potassium phosphate buffer (pH 7.40) the acyl-migration rate constants (h(-1)) were 0.18 (S-nap-g-alpha/beta-2-O-acyl isomer), 0.23 (alpha/beta-2-O-acyl-alpha-1-O-acyl), 2.6 (alpha-1-O-acyl-alpha/beta-2-O-acyl), 0.12 (alpha/beta-2-O-acyl-alpha/beta-3-O-acyl), 0.048 (alpha/beta-3-O-acyl-alpha/beta-2-O-acyl), 0.059 (alpha/beta-3-O-acyl-alpha/beta-4-O-acyl), and 0.085 (alpha/beta-4-O-acyl-alpha/beta-3-O-acyl). The hydrolysis rate constants (h(-1)) were 0.025 (hydrolysis of S-nap-g) and 0.0058 (hydrolysis of all acyl-migrated isomers). D2O and MeCN decreased the magnitude of all nine kinetic rate constants by up to 80%. The kinetic rate constants for the degradation of S-nap-g in the mobile phase used for HPLC-1H NMR determined using HPLC-UV could predict the results obtained by the dynamic stopped-flow HPLC-1H NMR experiments of the individual acyl-migrated isomers. It is therefore recommended that beta-1-O-acyl glucuronide degradation kinetics be investigated by HPLC-UV methods once the identification and elution order of the isomers have been established by HPLC-1H NMR.

Acetonitriles↗
PubMed1977

The analysis of organic water pollutants by gas chromatography and gas chromatography-mass spectrometry.

Four methods for the analysis of trace levels or organic compounds in water have been discussed: direct aqueous injection, vapor stripping, solvent extraction, and lipophilic adsorption. Table 6 presents a comparison of these techniques. Direct injection is applicable to compounds having a wide range of polarities and volatilities, but it is not a very sensitive technique. For applications in which low sensitivity is acceptable, direct injection offers a very rapid and potentially accurate means of measuring organics in water. Vapor stripping is a factor of 10(6) more sensitive than direct injection, but this is achieved at the expense of simplicity. This method is applicable to compounds of volatilities less than that of eicosane. A subtle operational problem with most vapor stripping techniques is that the contents of the trap are consumed with one analysis; if anything goes awry, the analysis of that trapped sample cannot be repeated. Solvent extraction has a respectable sensitivity (about 0.5 ppb) and operationally it is very simple. Furthermore, aliquots of the resulting extract can be analyzed many times with different techniques if necessary. Because of the evaporation step, very volatile compounds (greater than that of decane) cannot be measured effectively with solvent extraction. The introduction of a solvent into the water carries with it the potential for contamination. Thus, ultrapure solvents must be used and all glassware should be carefully cleaned [96]. Lipophilic adsorption has the unique property of sampling many hundreds of liters of water. Thus, the method is quite sensitive (potentially in the ppt range) and, in addition, it can provide several milligrams of an isolated component. This latter feature is of considerable advantage if one wants to complement GC-MS analyses with infrared or NMR for difficult structural identifications. As a solvent extraction, the evaporation of the final solvent limits the applicability of adsorption methods to compounds with volatilities greater than that of decane. Finally, the importance of avoiding contamination should be emphasized. Many of the compounds encountered in environmental samples are also common laboratory artifacts, for example plasticizers and antioxidants. When one finds such compounds in a water sample, it is absolutely essential to demonstrate that they are indeed present in the water and are not the result of laboratory contamination. The best such demonstration is procedural blank analyses that are indeed blank.

Chromatography, Gas↗