Air assisted dispersive liquid-liquid microextraction with solidification of the floating organic droplets (AA-DLLME-SFO) and UHPLC-PDA method: Application to antibiotics analysis in human plasma of hospital acquired pneumonia patients.

An ultra high-performance liquid chromatographic (UHPLC) method with PDA detection was developed and validated for the simultaneous quantification of metronidazole, meropenem, ciprofloxacin, linezolid and piperacillin in human plasma and applied to patients suffering from hospital acquired pneumonia (HAP). The method uses an air assisted dispersive liquid-liquid microextraction for sample preparation. All parameters in the extraction step, including selection of extractant, amount of extractant, ionic strength, pH, and extraction cycles, were investigated and optimized. Chromatography was carried out using a Poroshell 120 SB C18 (50 × 2.1 mm I.D. 2.6 µm particle size) column and a gradient mobile phase consisting of ammonium acetate buffer (10 mM, pH 4.0) (eluent A); and a mixture of acetonitrile-methanol in a ratio (80/20)(eluent B). Ulifloxacin was used as internal standard. The method demonstrated good linearity with correlation coefficients, r2 > 0.9995 for the drugs, as well as high precision (RSD% ≤ 9.87%), accuracy ranged from -8.14% to +8.98. The enrichment factor (EF) obtained ranged within 87 and 121. During the validation, the concentrations of the analytes were found to be stable after 3 freeze-thaw cycles and for at least 24 h after extraction. Subsequently, this method was used to quantify the drugs in patients with HAP in order to establish if the dosage regimen given was sufficient to eradicate the infection at the target site.

Meropenem, levofloxacin and linezolid in human plasma of critical care patients: A fast semi-automated micro-extraction by packed sorbent UHPLC-PDA method for their simultaneous determination.

An ultra high-performance liquid chromatographic (UHPLC) method with PDA detection was developed and validated for the simultaneous quantification of meropenem, linezolid, and levofloxacin in human plasma and applied in human plasma of critical care patients. A semi-automated microextraction by packed sorbent (MEPS) for sample preparation was used. All parameters in the extraction step (pH, sample volume, sample dilution and number of aspiration - ejection cycles) and in the desorption step (percentage of acetonitrile in the solvent of elution and number of aspirations of elution solvent through the device) were statistically significant when the recovery was used as response. The method showed good linearity with correlation coefficients, r2>0.9991 for the three drugs, as well as high precision (RSD%<10.83% in each case). Accuracy ranged from -7.8% to +6.7%. The limit of quantification of the three drugs was established at 0.01µg/mL for linezolid and levofloxacin and 0.02µg/mL for meropenem. Linezolid, meropenem, levofloxacin and the internal standard were extracted from human plasma with a mean recovery ranged from 92.4% to 97.4%. During validation, the concentration of meropenem, linezolid and levofloxacin was found to be stable after 3 freeze-thaw cycles and for at least 24h after extraction. This method will be subsequently used to quantify the drugs in patients to establish if the dosage regimen given is sufficient to eradicate the infection at the target site.

Development of a dried blood spot HPLC-PDA method for the analysis of linezolid and ciprofloxacin in hospital-acquired pneumonia patients.

This study developed a high performance liquid chromatography (HPLC) method involving dried blood spotting (DBS) as a sampling method for the therapeutic drug monitoring of antimicrobial combination therapy with linezolid and ciprofloxacin. DBS for standards, quality control samples, and patient samples was excised and then extracted using a mixture of methanol/water/formic acid 80:20:0.1 (v/v/v), respectively. Linezolid (LZD) and ciprofloxacin (CPR) were measured by HPLC using a Kinetex EVO C18 (100 × 4.6 mm I.D. 2.6 µm particle size). Mobile phase consisted of 10 mM ammonium acetate (A) and a mixture of acetonitrile and methanol (B), both containing 0.1% triethylamine, in gradient elution. Detection was carried out at 251 nm for linezolid (LZD) and 277 for ciprofloxacin (CPR). Ulifloxacin was used as an internal standard. The internal standard, LZD, and CPR were eluted in 7.90, 7.18, and 8.89 min, respectively. Total run-time was 20 min. Calibration curves were constructed in the range of 0.05-30 µg/mL for LZD and 0.02-10 µg/mL for CPR, respectively. The intra- and inter-day precision (RSD values) did not exceed 9.43%, the intra- and inter-day accuracy (accuracy %) ranged between 96.2 and 106.2%. Haematocrit (Hct) effects were investigated to obtain a linear correlation between haematocrit values and volume of blood. Copyright © 2017 John Wiley & Sons, Ltd.

Continuous-Flow N-Heterocyclic Carbene Generation and Organocatalysis.

Two methods were assessed for the generation of common N-heterocyclic carbenes (NHCs) from stable imidazol(in)ium precursors using convenient and straightforward continuous-flow setups with either a heterogeneous inorganic base (Cs2CO3 or K3PO4) or a homogeneous organic base (KN(SiMe3)2). In-line quenching with carbon disulfide revealed that the homogeneous strategy was most efficient for the preparation of a small library of NHCs. The generation of free nucleophilic carbenes was next telescoped with two benchmark NHC-catalyzed reactions; namely, the transesterification of vinyl acetate with benzyl alcohol and the amidation of N-Boc-glycine methyl ester with ethanolamine. Both organocatalytic transformations proceeded with total conversion and excellent yields were achieved after extraction, showcasing the first examples of continuous-flow organocatalysis with NHCs.