Microanalysis of propofol in human serum by semi-microcolumn high-performance liquid chromatography with UV detection and solid-phase extraction

Propofol detection for monitoring of intravenous anaesthesia: a review

This paper presents a review of established and emerging methods for detecting and quantifying the intravenous anaesthetic propofol in solution. There is growing evidence of numerous advantages of total intravenous anaesthesia using propofol compared to conventional volatile-based anaesthesia, both in terms of patient outcomes and environmental impact. However, volatile-based anaesthesia still accounts for the vast majority of administered general anaesthetics, largely due to a lack of techniques for real-time monitoring of patient blood propofol concentration. Herein, propofol detection techniques that have been developed to date are reviewed alongside a discussion of remaining challenges.

An Overview of Analytical Methods for the Estimation of Propofol in Pharmaceutical Formulations, Biological Matrices, and Hair Marker

Propofol (PFL) owing to its excellent inhibitory property of neurotransmitters in CNS by positive modulation of ligand gated ion channels to an integrated chloride channeled GABA_A thereby acts as a general anesthetic. It differs from other general anesthetics chemically and pharmacologically as it has lesser side effects compared to other general anesthetics and is most commonly used. The present review focuses on two aspects (a) various analytical methods used in quantification of Propofol in pharmaceutical formulations and (b) various analytical methods used to determine Propofol in biological matrices and some biological markers like hair and end tidal nasal air for forensic purpose to estimate drug concentration in suspected cases. Here the various analytical methods are developed using different parameters and validation of employed methods are discussed. Estimated parameters like the linearity, LOQ (Limit of quantification), % recovery, slope, intercept, validation are discussed for the individual method. The critical quality attributes like the wavelength of detection, columns, flow rate, gas flow, and the sample preparation methods for the determination of PFL by bioanalytical methods are also discussed. Type of electrode, mechanism involved and the potential voltage applied for a particular electrochemical method are also discussed.

Application of a benchtop colorimetric method for quantification of blood propofol levels

Quantification of plasma propofol (2,6-diisopropylphenol) in the context of clinical anaesthesia is challenging because of the need for offline blood sample processing using specialised laboratory equipment and techniques. In this study we sought to refine a simple procedure using solid phase extraction and colorimetric analysis into a benchtop protocol for accurate blood propofol measurement. The colorimetric method based on the reaction of phenols (e.g. propofol) with Gibbs reagent was first tested in 10% methanol samples (n = 50) containing 0.5-6.0 µg/mL propofol. Subsequently, whole blood samples (n = 15) were spiked to known propofol concentrations and processed using reverse phase solid phase extraction (SPE) and colorimetric analysis. The standard deviation of the difference between known and measured propofol concentrations in the methanol samples was 0.11 µg/mL, with limits of agreement of - 0.21 to 0.22 µg/mL. For the blood-processed samples, the standard deviation of the difference between known and measured propofol concentrations was 0.09 µg/mL, with limits of agreement - 0.18 to 0.17 µg/mL. Quantification of plasma propofol with an error of less than 0.2 µg/mL is achievable with a simple and inexpensive benchtop method.

Rapid determination and continuous monitoring of propofol in microliter whole blood sample during anesthesia by paper spray ionization-mass spectrometry

Propofol is a widely used intravenous anesthetic agent in sedation and general anesthesia. To improve the safety and maintain the depth of anesthesia, it is important to develop a rapid, sensitive, and reliable method to monitor the concentration of propofol in blood during anesthesia continuously. Here, we present a novel strategy based on paper spray ionization-mass spectrometry (PSI-MS) to detect propofol. Samples (in 10 μL) were mixed with methanol as protein precipitation solvent and 2,6-dimethylphenol as internal standard. Protein micro-precipitation was achieved with methanol by vortexing and centrifuging for 5 s each, and propofol was extracted to the supernatant. PSI-MS was performed in negative ionization mode, and MS signal lasted for 1 min. The analysis of a single sample was completed within 2 min. The area ratios of propofol to internal standard were calculated for quantification. Limit of detection of 5.5 ng mL^-1 and limit of quantification of 18.2 ng mL^-1 were achieved for propofol in whole blood. Calibration curve was linear in the range of 0.02-10 μg mL^-1. The developed method was used successfully in monitoring the propofol concentration in 3 patients' whole blood during anesthesia, showing its further application in controlling and feeding-back target concentration infusion. Graphical abstract.

A sensitive liquid chromatography method for analysis of propofol in small volumes of neonatal blood

WHAT IS KNOWN AND OBJECTIVE

Sampling volumes of blood from neonates is necessarily limited. However, most of the published propofol analysis assays require a relatively large blood sample volume (typically ≥0.5 mL). Therefore, the aim of the present study was to develop and validate a sensitive method requiring a smaller sample volume (0.2 mL) to fulfill clinically relevant research requirements.

METHODS

Following simple protein precipitation and centrifugation, the supernatant was injected into the HPLC-fluorescence system and separated with a reverse phase column. Propofol and the internal standard (thymol) were detected and quantified using fluorescence at excitation and emission wavelengths of 270 nm and 310 nm, respectively. The method was validated with reference to the Food and Drug Administration (FDA) guidance for industry. Accuracy (CV, %) and precision (RSD, %) were evaluated at three quality control concentration levels (0.05, 0.5 and 5 µg/mL).

RESULTS AND DISCUSSION

Calibration curves were linear in the range of 0.005-20 µg/mL. Intra- and interday accuracy (-4.4%-13.6%) and precision (0.2%-5.8%) for propofol were below 15%. The calculated LOD (limit of detection) and LLOQ (lower limit of quantification) were 0.0021 µg/mL and 0.0069 µg/mL, respectively. Propofol samples were stable for 4 months at -20°C after the sample preparation. This method was applied for analyzing blood samples from 41 neonates that received propofol, as part of a dose-finding study. The measured median (range) concentration was 0.14 (0.03-1.11) µg/mL, which was in the range of the calibration curve. The calculated median (range) propofol half-life of the gamma elimination phase was 10.4 (4.7-26.7) hours.

WHAT IS NEW AND CONCLUSION

A minimal volume (0.2 mL) of blood from neonates is required for the determination of propofol with this method. The method can be used to support the quantification of propofol drug concentrations for pharmacokinetic studies in the neonatal population.

Selective and Accurate Determination Method of Propofol in Human Plasma by Mixed-Mode Cation Exchange Cartridge and GC-MS

A gas chromatography-mass spectrometry (GC-MS) method for the determination of propofol in human plasma has been developed and validated. Propofol was extracted from human plasma by using mixed-mode cation exchange/reversed-phase (MCX) cartridges. As propofol easily volatilizes during concentration, 100% methanol was injected directly into GC-MS to elute propofol. Despite avoiding concentration process of the eluted solution, lower limit of quantization (LLOQ) of propofol was 25 ng/mL. The validated method exhibited good linearity (R (2) = 0.9989) with accuracy and precision -5.8%~11.7% and 3.7%~11.6%, respectively. The other validation parameters, recovery and matrix effect, ranged from 96.6% to 99.4% and 95.3% to 101.4%, respectively. Propofol standard was quantified to evaluate possible loss due to the concentration processes, nitrogen gas and centrifugal vacuum. These two concentration processes resulted in notable decrease in the quantity of propofol, signifying avoiding any concentration processes during propofol quantification. Also, to confirm suitability of the developed method, authentic human plasma samples were analyzed. The selective assay method using MCX cartridge and GC-MS facilitated quantification of propofol in plasma sample accurately by preventing any losses due to the concentration processes.

Fully automated analytical procedure for propofol determination by sequential injection technique with spectrophotometric and fluorimetric detections

In this work, an application of an enzymatic reaction for the determination of the highly hydrophobic drug propofol in emulsion dosage form is presented. Emulsions represent a complex and therefore challenging matrix for analysis. Ethanol was used for breakage of a lipid emulsion, which enabled optical detection. A fully automated method based on Sequential Injection Analysis was developed, allowing propofol determination without the requirement of tedious sample pre-treatment. The method was based on spectrophotometric detection after the enzymatic oxidation catalysed by horseradish peroxidase and subsequent coupling with 4-aminoantipyrine leading to a coloured product with an absorbance maximum at 485 nm. This procedure was compared with a simple fluorimetric method, which was based on the direct selective fluorescence emission of propofol in ethanol at 347 nm. Both methods provide comparable validation parameters with linear working ranges of 0.005-0.100 mg mL(-1) and 0.004-0.243 mg mL(-1) for the spectrophotometric and fluorimetric methods, respectively. The detection and quantitation limits achieved with the spectrophotometric method were 0.0016 and 0.0053 mg mL(-1), respectively. The fluorimetric method provided the detection limit of 0.0013 mg mL(-1) and limit of quantitation of 0.0043 mg mL(-1). The RSD did not exceed 5% and 2% (n=10), correspondingly. A sample throughput of approx. 14 h(-1) for the spectrophotometric and 68 h(-1) for the fluorimetric detection was achieved. Both methods proved to be suitable for the determination of propofol in pharmaceutical formulation with average recovery values of 98.1 and 98.5%.

Rapid detection of propofol in whole blood using an automated on-line molecularly imprinted pretreatment coupled with optical fibre detection

Here we present a validated rapid detection system for propofol, an anaesthetic with a narrow therapeutic window, in whole blood. This method utilises an on-line molecularly imprinted polymer solid-phase extraction, rather than the traditional C18 solid-phase extraction, coupled to fluorescence optical fibre detection. The linearity was assessed from 0.10-15 μg mL(-1) of propofol in whole blood, and the coefficients were greater than 0.995. The absolute recoveries of propofol were 95.81, 97.56 and 97.93% at three different concentrations. The inter-batch precision ranged from 4.3% to 8.1%, and the accuracy value ranged from 102.5% to 104.4%. The developed method was successfully applied to measure propofol concentrations in simulated whole blood samples. The entire analysis procedure lasted only 5 minutes, and the results showed no statistical difference between the new on-line method and a validated high-performance liquid chromatography method. The new on-line method, however, is faster and more convenient for the clinical real-time detection of propofol than previously reported methods.

Enhanced anesthetic propofol biochips by modifying molecularly imprinted nanocavities of biosensors

This paper presents enhanced performance of anesthetic propofol biosensors by modifying molecularly imprinted nanocavities of biosensors. In this work, the relationship between molecularly imprinted nanocavities and performance of molecularly imprinted polymer (MIP) films is investigated. The morphological control of imprinted nanocavities on molecularly imprinted biosensors is done by adjusting polymer composition and polymerization process. The newly developed MIP biosensors are characterized using our developed microfluidic biochips and optical microsystems. Experimental results show that the sizes of molecularly imprinted nanocavities were reduced to 10 to 14 nm from 10 to 25 nm. The roughness of the MIP film surface was reduced to 2.5 nm from 6.6 nm. Smaller imprinted nanocavities have better molecular separation performance. The specificity and linearity of the anesthetic biosensors could be enhanced by adjusting morphology of imprinted nanocavities. The linearity and the sensitivity of the microfluidic biochip with an improved on-chip MIP biosensor have been enhanced from 0.9341 to 49.5 mV/mm².ml/μg, respectively, to 0.9782 and 176.9 mV/mm².ml/μg. The anesthetic propofol biosensor presented in this study is applicable to numerous fluidic-based disposable biochips.

Headspace-SPME-GC/MS as a simple cleanup tool for sensitive 2,6-diisopropylphenol analysis from lipid emulsions and adaptable to other matrices

Due to increased regulatory requirements, the interaction of active pharmaceutical ingredients with various surfaces and solutions during production and storage is gaining interest in the pharmaceutical research field, in particular with respect to development of new formulations, new packaging material and the evaluation of cleaning processes. Experimental adsorption/absorption studies as well as the study of cleaning processes require sophisticated analytical methods with high sensitivity for the drug of interest. In the case of 2,6-diisopropylphenol - a small lipophilic drug which is typically formulated as lipid emulsion for intravenous injection - a highly sensitive method in the concentration range of μg/l suitable to be applied to a variety of different sample matrices including lipid emulsions is needed. We hereby present a headspace-solid phase microextraction (HS-SPME) approach as a simple cleanup procedure for sensitive 2,6-diisopropylphenol quantification from diverse matrices choosing a lipid emulsion as the most challenging matrix with regard to complexity. By combining the simple and straight forward HS-SPME sample pretreatment with an optimized GC-MS quantification method a robust and sensitive method for 2,6-diisopropylphenol was developed. This method shows excellent sensitivity in the low μg/l concentration range (5-200μg/l), good accuracy (94.8-98.8%) and precision (intraday-precision 0.1-9.2%, inter-day precision 2.0-7.7%). The method can be easily adapted to other, less complex, matrices such as water or swab extracts. Hence, the presented method holds the potential to serve as a single and simple analytical procedure for 2,6-diisopropylphenol analysis in various types of samples such as required in, e.g. adsorption/absorption studies which typically deal with a variety of different surfaces (steel, plastic, glass, etc.) and solutions/matrices including lipid emulsions.

Clinical effects and lethal and forensic aspects of propofol

Propofol is a potent intravenous anesthetic agent that rapidly induces sedation and unconsciousness. The potential for propofol dependency, recreational use, and abuse has only recently been recognized, and several cases of accidental overdose and suicide have emerged. In addition, the first documented case of murder using propofol was reported a few months ago, and a high profile case of suspected homicide with propofol is currently under investigation. A number of analytical methods have been employed to detect and quantify propofol concentrations in biological specimens. The reported propofol-related deaths and postmortem blood and tissue levels are reviewed. Importantly, limitations of propofol detection are discussed, and future considerations are presented. Because propofol has the potential for diversion with lethal consequences, the forensic scientist must have a basic understanding of its clinical indications and uses, pharmacologic properties, and detection methods. In addition, medical institutions should develop systems to prevent and detect diversion of this potential drug of abuse.

A rapid and simple HPLC method for the analysis of propofol in biological fluids

A selective and sensitive high-performance liquid chromatographic method for the analysis of propofol in biological samples was developed. Propofol and thymol (internal standard) were analysed on a Purospher RP-18 endcapped (75 mmx4 mm, 3 microm) stationary phase using acetonitrile and water (65:35, v/v) as eluents at a flow rate of 0.6 mL/min. The excitation and emission wavelengths were 276 and 310 nm, respectively. Sample treatment consisted of deproteinization by acetonitrile containing the internal standard and direct injection of the supernatant. Mean analytical recovery were 105% (CV 2.0%) at concentrations ranging from 0.05 to 10 mg/L. The quantification limit was 3 ng/mL for a 500 microL sample plasma volume and 5 ng/mL for a 500 microL blood sample. The intra-day and inter-day precisions were lower than 5.5% for three concentrations assessed (0.05, 1.0 and 10.0 mg/L). Considering the column size and the flow rate, the separation was achieved with an analysis time less than 6 min with a reduced consumption of solvent. This rapid HPLC method using a simple treatment procedure is sensitive enough for monitoring propofol in human biological samples.

Rapid measurement of blood propofol levels: a proof of concept study

OBJECTIVE

Despite many advantages over traditional volatile anaesthetic techniques, propofol total intravenous anaesthesia (TIVA) makes up a small percentage of general anaesthetics administered. One of the reasons for this is the absence of a clinically useful method for measuring blood propofol concentrations. We have designed and tested a prototype system for rapidly measuring blood plasma levels of propofol using solid phase extraction (SPE) methodology, coupled with colorimetric and spectrometric techniques.

METHODS

Multiple venous blood samples were taken from 17 subjects during induction of anaesthesia with propofol. Samples were analysed in duplicate on both the prototype system and using High Performance Liquid Chromatography (HPLC). The prototype monitor response was calibrated against known methanol-based propofol standards and an estimate of the plasma concentration of propofol derived from regression analysis of the standard responses.

RESULTS

Bland Altman analysis from a total of 87 samples gave 95% limits of agreement between the two methods of -0.34 to 0.42 microg mL(-1) (with no significant bias). The mean absolute prediction error was 8.9(7.5)%. The run time per sample on the prototype system was 4.5 min, including sample preparation.

CONCLUSION

The results show that this methodology may be suitable for rapid and accurate clinical monitoring of propofol levels during general anaesthesia.

Development of a rapid and sensitive LC–ESI/MS/MS assay for the quantification of propofol using a simple off-line dansyl chloride derivatization reaction to enhance signal intensity

A rapid, selective and sensitive method was developed for the determination of propofol concentration using an off-line dansyl chloride derivatization step to enhance signal intensity. The method consisted of a protein precipitation extraction followed by derivatization with dansyl chloride and analysis by liquid chromatography ionspray tandem mass spectrometry (LC-ESI/MS/MS). The separation was achieved using a 100 mm x 2 mm C8 analytical column combined with an isocratic mobile phase composed of 80:20 acetonitrile: 0.5% formic acid in water. Signal intensity of the propofol-dansyl chloride derivative was increased up to 200-fold as compared to the underivatized propofol in positive electrospray mode. An analytical range of 20-20,000 ng/mL was used in the calibration curve of plasma and blood samples. The novel method met all requirements of specificity, sensitivity, linearity, precision, accuracy and stability. A pharmacokinetic study was performed in rats and the novel analytical method was used as a routine analysis to provide enhanced measurements of plasma and blood concentrations of propofol. Blood and plasma pharmacokinetic results show that a very important fraction of propofol distributes into red blood cells. In conclusion, a rapid and sensitive LC-ESI/MS/MS method using a derivatization agent was developed to enhance signal intensity of propofol. Routine analysis with the novel method provided accurate results and enhanced the detection levels of plasma and blood concentrations of propofol to better characterize the in vivo biodisposition of propofol.