Postcolumn Infusion as a Quality Control Tool for LC-MS-Based Analysis

Postcolumn infusion has been widely used to study the matrix effect of analytical methods based on liquid chromatography coupled to mass spectrometry (LC-MS). Nevertheless, this methodology is usually only applied during a method development or validation. With this application note, we aim to demonstrate that the continuous use of postcolumn infusion can be also a very useful tool to monitor the quality of LC-MS analyses and easily detect flaws in the analytical method performance. Here we propose a protocol that can be transferred to other LC-MS platforms, and we show some real situations in bioanalysis in which postcolumn infusion proved to be extremely helpful in, for example, the evaluation of a sample treatment or the detection of unexpected sources of the matrix effect.

Bioanalytical chromatographic method validation according to current regulations, with a special focus on the non-well defined parameters limit of quantification, robustness and matrix effect

Method validation is a mandatory step in bioanalysis, to evaluate the ability of developed methods in providing reliable results for their routine application. Even if some organisations have developed guidelines to define the different parameters to be included in method validation (FDA, EMA); there are still some ambiguous concepts in validation criteria and methodology that need to be clarified. The methodology to calculate fundamental parameters such as the limit of quantification has been defined in several ways without reaching a harmonised definition, which can lead to very different values depending on the applied criterion. Other parameters such as robustness or ruggedness are usually omitted and when defined there is not an established approach to evaluate them. Especially significant is the case of the matrix effect evaluation which is one of the most critical points to be studied in LC-MS methods but has been traditionally overlooked. Due to the increasing importance of bioanalysis this scenario is no longer acceptable and harmonised criteria involving all the concerned parties should be arisen. The objective of this review is thus to discuss and highlight several essential aspects of method validation, focused in bioanalysis. The overall validation process including common validation parameters (selectivity, linearity range, precision, accuracy, stability…) will be reviewed. Furthermore, the most controversial parameters (limit of quantification, robustness and matrix effect) will be carefully studied and the definitions and methodology proposed by the different regulatory bodies will be compared. This review aims to clarify the methodology to be followed in bioanalytical method validation, facilitating this time consuming step.

Simultaneous determination of imperatorin and its metabolite xanthotoxol in rat plasma by using HPLC-ESI-MS coupled with hollow fiber liquid phase microextraction

The objective of the present study was to develop a new method for the simultaneous quantitation of imperatorin and its metabolite xanthotoxol in rat plasma. The samples were prepared with hollow fiber liquid phase microextraction (HF-LPME). The optimized extraction procedure was acquired by assessing extraction solvent, length of the fiber, agitation rate, extraction temperature and time. A comparison of sample pretreatment ways between HF-LPME and deproteinization with methanol was performed, which demonstrated less ion suppression and better sensitivity of HF-LPME. Analytes were separated on a C18 column with a gradient elution consisted of methanol and water containing 1mmol/L ammonium acetate. The detection was accomplished by electrospray ionization (ESI) source operating in the positive ionization mode. Selected-multiple-reaction monitoring (SMRM) scanning was employed, which guaranteed a higher sensitivity compared with MRM mode. Calibration curves were linear over investigated ranges with correlation coefficients greater than 0.9979. Precision varied from 0.26% to 14%, and the accuracy varied within ±5.5%. The developed method was successfully applied to the pharmacokinetic research of imperatorin and its metabolite xanthotoxol after oral administration of imperatorin to rats.