Application of Monolithic Columns in High Performance Liquid Chromatography

The chromatographic performance of a Chromolith RP-18e column was comprehensively examined for a group of basic drugs (beta-blockers), eluted with isocratic ACN-water mixtures at increasing flow-rate up to 6 mL/min. As the flow-rate increases at fixed mobile phase composition, peak distribution (selectivity) is maintained, but the relative peak widths increase. This reduces the resolution below satisfactory values for closely eluting compounds. With the monolithic column, flow-rate becomes thus an important factor to be optimised, in addition to the mobile phase composition. Since, theoretically, retention factors (k) are independent of the flow-rate, the classical quadratic model relating log k with the solvent content allows the prediction of the retention at any combination of organic solvent content and flow-rate. The small deviations found for the most retained compounds were corrected by including, in the quadratic model, an additional term correlating linearly log k with the flow-rate. Peak shape and resolution changes were predicted by taking advantage of the approximated linear relationships between peak half-widths and retention times, which offered similar coefficients for peaks eluting at different organic solvent contents and flow-rates. The accuracy of the predictions in critical conditions was experimentally verified to be satisfactory.

Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 94%

Interpretive optimisation of organic solvent content and flow‐rate in the separation of β‐blockers with a Chromolith RP‐18e column

Pous-Torres

Torres-Lapası́o

Ruiz-Ángel

et al. 2009

“…These sorbents consist of a continuous porous silica rod with a highly permeable bimodal pore distribution [5], enabling the use of high flow rates without mass transfer limitations. These media have been successfully applied to the separation of various compounds in several biofluids [6] and we have previously reported a simple and rapid LC-MS-based method involving such support [7]. If silica monolithic materials are nowadays widely used for analytical purposes, their utilization as extraction media remains scarce.…”

Section: Introductionmentioning

confidence: 99%

Application of monolithic supports to online extraction and LC‐MS analysis of benzodiazepines in whole blood samples

Bugey

Staub

2007

A column-switching (CS) LC-MS method allowing high-speed determination of benzodiazepines (BZDs) in whole blood is presented. After protein precipitation with ACN followed by evaporation and reconstitution with the loading mobile phase, the online sample clean-up was carried out using a CS device. Two extractive precolumns were evaluated: a conventional restricted access material (RAM) sorbent and a monolithic silica support. Separation was achieved using a Chromolith Performance RP-18e (100 mmx4.6 mm id) monolithic silica column, and detection was performed by atmospheric pressure chemical ionization (APCI) MS. The method with both supports has been fully validated according to an accuracy profile approach. Finally, the monolithic silica column, demonstrating better validation data and a higher robustness than the RAM sorbent, was used for the analysis of several real forensic cases.

“…Therefore, when the pH of the matrix could suitably be buffered, silica monoliths could be used effectively for SPE. The emergence of monolith provides an alternative to existing particle-based SPE cartridges for drug extraction and purification from biological matrices [11,12]. These particle-based cartridges have the inherent drawback of non-uniform packing of particles that creates void spaces in between.…”

mentioning

confidence: 99%

Extraction of ketamine from urine using a miniature silica monolithic cartridge followed by quantification with liquid chromatography tandem mass spectrometry (LC‐MS/MS)

Nema

Chan

2011

The high surface area monolith with reactive hydroxyl group on its surface enables it to function as a miniature solid-phase extraction (SPE) cartridge in size of 1 cm in diameter and 0.5 cm in length. The prepared silica monolith was characterized by Brunauer-Emmett-Teller method, scanning electron microscopy, X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy. Ketamine was selected as model analyte to validate the extraction efficiency of the prepared cartridge. The extracted ketamine from urine sample was quantitated by liquid chromatography tandem mass spectrometry (LC-MS/MS) using positive electrospray ionization. The limit of detection and quantification for ketamine was found to be 0.5 and 1.6 ng/mL, respectively. The analysis exhibited linearity in the range of 10-500 ng/mL with coefficient of correlation >0.99. The recovery was found to be in the range of 89-107% with relative standard deviation (RSD) less than 10%. The prepared cartridge was found robust in extracting ketamine efficiently and repeatedly without any significant deterioration in its performance. Moreover, the batch-to-batch variations in the performance of the prepared cartridges in terms of % ion suppression of the extracts and recoveries of samples were small, suggesting the consistency in the properties of the monolith.