Reduced graphene oxide as an efficient sorbent in microextraction by packed sorbent: Determination of local anesthetics in human plasma and saliva samples utilizing liquid chromatography-tandem mass spectrometry.

Herein, reduced graphene oxide (RGO) has been utilized as an efficient sorbent in microextraction by packed sorbent (MEPS). The combination of MEPS and liquid chromatography-tandem mass spectrometry has been used to develop a method for the extraction and determination of three local anesthetics (i.e. lidocaine, prilocaine, and ropivacaine) in human plasma and saliva samples. The results showed that the utilization of RGO in MEPS could minimize the matrix effect so that no interfering peaks at the retention times of the analytes or internal standard was observed. The high extraction efficiency of this method was approved by mean recoveries of 97.26-106.83% and 95.21-105.83% for the studied analytes in plasma and saliva samples, respectively. Intra- and inter-day accuracies and precisions for all analytes were in good accordance with the international regulations. The accuracy values (as percentage deviation from the nominal value) of the quality control samples were between -2.1 to 13.9 for lidocaine, -4.2 to 11.0 for prilocaine and between -4.5 to -2.4 for ropivacaine in plasma samples while the values were ranged from -4.6 to 1.6 for lidocaine, from -4.2 to 15.5 for prilocaine and from -3.3 to -2.3 for ropivacaine in human saliva samples. Lower and upper limit of quantification (LLOQ, ULOQ) were set at 5 and 2000 nmol L-1 for all of the studied drugs. The correlation coefficients values were ≥0.995. The limit of detection values were obtained 4 nmol L-1 for lidocaine and prilocaine, and 2 nmol L-1 for ropivacaine.

A convenient TLC method for the identification of local anesthetics.

A TLC method for the separation of seven local anesthetics and the related antiarrhythmic drug procainamide was developed. Spraying the plates with cobalt(II) thiocyanate solution, followed by spraying with Ehrlich's reagent allowed a clear distinction between the drugs, except for the couple articaine/prilocaine. Articaine could be distinguishedfrom prilocaine and other local anesthetics by a colour reaction with copper(II) sulphate solution.

1H-NMR studies of drugs with chiral solvating agent: the direct enantiomeric purity determination of the chiral anesthetic, prilocaine.

Chiral recognition of prilocaine was obtained on a 400 MHz 1H-NMR spectrometer by fast diastereomeric interactions with the chiral solvating agent (S)-(+)-2,2,2-trifluoro-1-(9-anthryl) ethanol (TFAE). Assignment of absolute configuration was based on relative field position of the resolved enantiomeric signals. Influence of temperature, substrate concentration and solvating agent to substrate molar ratio on enantiomeric resolution were studied and evaluated. Optimization of experimental conditions provided two significant resolved signals for quantitative use. Utilizing the relative intensities of the resolved enantiomeric signals of the methine proton attached to the stereogenic center assigned to (S)-(+)- and (R)-(-)-prilocaine, the analysis of synthetic mixtures of the enantiomers by the proposed NMR method resulted in assay values which agreed closely with the known quantities of each enantiomer in the tested mixtures. The mean +/- SD recovery values for the (S)-(+)-enantiomer was 99.9 +/- 0.2% of added antipode (n = 7). The optically pure enantiomers were used to establish the minimum amount detected by the proposed NMR spectroscopic method.

Enantioseparation of anaesthetic drugs by capillary zone electrophoresis using cyclodextrin-containing background electrolytes.

The enantiomers of five racemic anaesthetic drugs were resolved with cyclodextrins using capillary zone electrophoresis. Parameters which affected the chiral resolution, such as type and concentration of cyclodextrin, temperature, and addition of organic modifier were investigated. The results show that the enantiomeric discrimination of the solutes is influenced by the structural shape of the solute molecules, separation temperature, and type of cyclodextrin. It was found that alpha-cyclodextrin was the best enantioselector for resolution of prilocaine and ketamine, while the enantiomers of mepivacaine, ropivacaine, and bupivacaine were resolved with beta-cyclodextrin and/or modified beta-cyclodextrins, i.e., methyl- and 2-hydroxypropyl-beta-cyclodextrin, as chiral selectors. The length of the alkyl chain on the amino group of the drug molecule had a strong effect on the enantioresolution of mepivacaine, ropivacaine, and bupivacaine. Baseline separation of racemic ketamine was achieved with alpha- and methyl-beta-cyclodextrin at 15 degrees C. Addition of 5 M urea to the running buffer containing beta-cyclodextrin at high concentrations resulted in the enantioseparation of prilocaine, mepivacaine, and ketamine. Enantioresolution was improved upon the addition of 10% methanol to the buffer containing urea and beta-cyclodextrin. Generally, the complex formed between the S-enantiomers and modified beta-cyclodextrins was stronger than the corresponding R-forms. An exception was prilocaine where the R-form gave a more stable complex both with alpha- and beta-cyclodextrin.

Enantioseparation of local anaesthetic drugs by capillary zone electrophoresis with cyclodextrins as chiral selectors using a partial filling technique.

The enantiomers of prilocaine were successfully resolved with alpha-cyclodextrin, and those of mepivacaine and bupivacaine, with methyl-beta-cyclodextrin as chiral selectors, by means of capillary zone electrophoresis (CZE) employing a partial filling technique. By this separation mode, a discontinous separation zone is formed in the capillary. Prior to application of the actual drug substance, the capillary is partially filled with the separation solution. During the enantioseparation both ends of the capillary are dipped into the running buffer solution, i.e., without chiral selector. The consumption of chiral selector is thus very low, less than a microliter per run. The repeatibility of the electrophoretic mobility of the enantiomers was better than 1.2% relative standard deviation (RSD). The effect of the length of the separation zone on the resolution of the enantiomers was studied. The application time of the chiral selector, instead of the selector concentration, was varied in order to improve and regulate the enantioresolution and reduce consumption of the chiral selector as much as possible. It was found that the enantioseparations were directly affected by the length of the separation zone, and there was a minimal plug length where complete enantioresolution was achieved.