Simple and practical high-performance liquid chromatographic assay of propofol in human blood by phenyl column chromatography with electrochemical detection

Propofol detection and quantification in human blood: the promise of feedback controlled, closed-loop anesthesia

The performance of a membrane-coated voltammetric sensor for propofol (2,6-diisopropylphenol) has been characterized in long term monitoring experiments using an automated flow analytical system (AFAS) and by analyzing human serum and whole blood samples by standard addition. It is shown that the signal of the membrane-coated electrochemical sensor for propofol is not influenced by the components of the pharmaceutical formulation of propofol (propofol injectable emulsion). The current values recorded with the electrochemical propofol sensor in buffer solutions and human serum samples spiked with propofol injectable emulsion showed excellent correlation with the peak heights recorded with an UV-Vis detector during the HPLC analysis of these samples (R(2) = 0.997 in PBS and R(2) = 0.975 in human serum). However, the determination of propofol using the electrochemical method is simpler, faster and has a better detection limit (0.08 ± 0.05 μM) than the HPLC method (0.4 ± 0.2 μM). As a first step towards feedback controlled closed-loop anesthesia, the membrane-coated electrochemical sensor has been implemented onto surface of an intravenous catheter. The response characteristics of the membrane-coated carbon fiber electrode on the catheter surface were very similar to those seen using a macroelectrode.

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.

Toward feedback-controlled anesthesia: voltammetric measurement of propofol (2,6-diisopropylphenol) in serum-like electrolyte solutions

Propofol is a widely used, potent intravenous anesthetic for ambulatory anesthesia and long-term sedation. The target steady state concentration of propofol in blood is 0.25-10 μg/mL (1-60 μM). Although propofol can be oxidized electrochemically, monitoring its concentration in biological matrixes is very challenging due to (i) low therapeutic concentration, (ii) high concentrations of easily oxidizable interfering compounds in the sample, and (iii) fouling of the working electrode. In this work we report the performance characteristics of an organic film coated glassy carbon (GC) electrode for continuous monitoring of propofol. The organic film (a plasticized PVC membrane) improved the detection limit and the selectivity of the voltammetric sensor due to the large difference in hydrophobicity between the analyte (propofol) and interfering compounds of the sample, e.g., ascorbic acid (AA) or p-acetamidophenol (APAP). Furthermore, the membrane coating prevented electrode fouling and served as a protective barrier against electrode passivation by proteins. Studies revealed that sensitivity and selectivity of the voltammetric method is greatly influenced by the composition of the PVC membrane. The detection limit of the membrane-coated sensor for propofol in PBS is reported as 0.03 ± 0.01 μM. In serum-like electrolyte solutions containing physiologically relevant levels of albumin (5%) and 3 mM AA and 1 mM APAP as interfering agents, the detection limit was 0.5 ± 0.4 μM. Both values are below the target concentrations used clinically during anesthesia or sedation.

Electrochemical quantification of 2,6-diisopropylphenol (propofol)

2,6-Diisopropylphenol (propofol) is a potent anesthetic drug with fast onset of the anesthetic effect and short recovery time for the patients. Outside of the United States, propofol is widely used in performing target controlled infusion anesthesia. With the long term vision of an electrochemical sensor for in vivo monitoring and feedback controlled dosing of propofol in blood, different alternatives for the electrochemical quantification of propofol using diverse working electrodes and experimental conditions are presented in this contribution. When the electrochemical oxidation of propofol takes place on a glassy carbon working electrode, an electrochemically active film grows on the electrode surface. The reduction current of the film is proportional to the propofol concentration and the accumulation time. Based on these findings a stripping analytical method was developed for the detection of propofol in acidic solutions between 0 and 30 μM, with a detection limit of 5.5±0.4 μM. By restricting the scanned potential window between 0.5 V and 1.0 V in cyclic voltammetric experiments, the formation of the electrochemically active polymer can be prevented. This allowed the development of a direct voltammetric method for assessing propofol in acidic solutions between 0 and 30 μM, with a 3.2±0.1 μM (n=3) detection limit. The stripping method has a better sensitivity but somewhat worse reproducibility because the electrode surface has to be renewed between each experiment. The direct method does not require the renewal of the electrode surface between measurements but has no adequate selectivity towards the common interfering compounds.

Gas chromatography–mass spectrometric assay for propofol in cerebrospinal fluid of traumatic brain patients

A sensitive gas chromatography-mass spectrometry method for measuring propofol in cerebrospinal fluid is described, validated and applied to four patients after traumatic brain injury. The limit of quantitation was 2 microg/L using a volume of 0.5 mL. The inter- and intra-assay coefficients of variation were 5.9 and 5.1%, respectively. The assay covers the linear concentration range of 2-50 microg/L, which is relevant in clinical pharmacokinetic studies when propofol is used in the Intensive Care Unit as a sedative agent or to lower the intracranial pressure.

Mass spectral fragmentation of the intravenous anesthetic propofol and structurally related phenols

Propofol (2,6-diisopropyl phenol) is a widely used intravenous anesthetic. To define its pharmacokinetics and pharmacodynamics, methods for its quantitation in biological matrixes have been developed, but its pattern of mass spectral fragmentation is unknown. We found that fragmentation of the [M - H](-) ion (m/z 177) of propofol in both APCI MS/MS and ESI MS/MS involves the stepwise loss of a methyl radical and a hydrogen radical from one isopropyl side chain to give the most intense product ion, [M -H - CH(4)](-), at m/z 161. This two-step process is also the preferred mode of fragmentation for similar branched alkyl substituted phenols. This mode of fragmentation of the [M - H](-) ion is supported by three independent lines of evidence: (1) the presence of the intermediary [M - H - CH(3)](-) radical ion under conditions of reduced collision energy, (2) the determination of the mass of the predominant [M - H - CH(4)](-) product ion by high resolution mass spectrometry, and (3) the pattern of product ions resulting from further fragmentation of the [M - H - CH(4)](-) product ion. Phenols with a single straight chain alkyl substituent, in contrast, undergo beta elimination of the alkyl radical irrespective of the length of the alkyl chain, yielding the most intense product ion at m/z 106. This product ion represents a special case of a stable intermediary radical for the two-step process described for branched side chains, because further elimination of a hydrogen radical from the beta carbon is not possible.

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

OBJECTIVE

To develop a simple analytical method for monitoring the low serum levels of propofol found when administered for the sedation of patients in the intensive care unit (ICU).

METHODS

A high-performance liquid chromatographic method (HPLC) was used with UV detection. Solid-phase extraction (SPE) cartridges and a semi-microcolumn (TSK gel ODS-80Ts, 2.0 mm i.d. x 25 cm, 5 microm) were used to improve sensitivity. Propofol in the eluate obtained from the SPE cartridge was concentrated to about five times the initial concentration.

RESULTS

The sensitivity using the semi-microcolumn was amplified by about three-fold. The assay showed a good linearity with a quantification limit 20 ng/mL. Intra- and inter-assay coefficients of variation were less than 2.2% and 10.0%, respectively. The mean recoveries ranged from 97.6 to 109.5%.

CONCLUSION

The HPLC method described should be useful for measuring the low serum propofol levels found when the drug is used for ICU sedation.

The advantages of cell lysis before blood sample preparation by extraction for HPLC propofol analysis

Propofol (2,6-diisopropylphenol) is a short-acting drug with a large volume of distribution and high body clearance. It is suitable both for the induction of anaesthesia by bolus injection and the maintenance of anaesthesia by repeated injections or a continuous infusion. Examining the drug concentration its analysis in whole blood is recommended. This results from the fact that propofol molecules strongly bind with plasma proteins and cellular blood constituents and blood composition variations are observed between individuals or in different disease states or resulting from transfusion etc. In most cases the HPLC analysis follows the extraction of samples. The degree of propofol binding with blood cells can be different, depending on the blood type, and it can change in time, which may affect the results of the analysis. The paper discusses and shows the necessity of blood cell lysis before the extraction procedure. The cell lysis makes possible to determine the total amount of propofol in blood independently of the degree of propofol binding with cellular blood constituents and its changes.

High-performance liquid chromatographic assay to detect hydroxylate and conjugate metabolites of propofol in human urine

This paper describes a HPLC method for the simultaneous detection of phase I (2,6-diisopropyl-1-4-quinol and 2,6-diisopropyl-1-4-quinone) and phase II (4-(2,6-diisopropyl-1-4-quinol)-sulphate, 1-(2,6-diisopropyl-1-4-quinol)-glucuronide, 4-(2,6-diisopropyl-1-4-quinol)-glucuronide, and propofol-glucuronide) metabolites of propofol in human urine samples. Separation was based on a simple mobile phase and a reversed-phase chromatographic column. Metabolite identification was performed by UV spectrum on a diode-array detector and by LC-APCI-MS. The identification was also carried out using in vitro incubation mixtures (cytosol and microsomes prepared from liver) from several species: human, rat and rabbit. This assay was performed using UV, fluorescence and electrochemical detection modes. Each of these was analyzed and discussed.

Propofol directly depresses lumbar dorsal horn neuronal responses to noxious stimulation in goats

PURPOSE

We tested the hypothesis that propofol, acting in the brain, would either enhance, or have no effect, on lumbar dorsal horn neuronal responses to a noxious mechanical stimulus applied to the hindlimb. We recorded the response of lumbar dorsal horn neurons during differential delivery of propofol to the brain and torso of goats.

METHODS

Goats were anesthetized with isoflurane and neck dissections performed which permitted cranial bypass. A laminectomy was made to allow microelectrode recording of lumbar dorsal horn neuronal activity. Isoflurane was maintained at 0.8+/-0.1% to both head and torso throughout the study. During cranial bypass propofol was separately administered to the torso (1 mg x kg(-1), n = 7; 3.75 mg x kg(-1), n = 8) or cranial (0.04 mg x kg(-1), n = 7; 0.14 mg kg(-1), n = 8) circulations.

RESULTS

Propofol administered to the torso depressed dorsal horn neuronal responses to noxious stimulation: low dose: 500+/-243 to 174+/-240 impulses x min(-1) at one minute post-injection, P<0.001; high dose: 478+/-204 to 91+/-138 impulses x min(-1) at one minute post-injection, P<0.05). Propofol administered to the cranial circulation had no effect: low dose: 315+/-150 to 410+/-272 impulses x min(-1), P>0.05; high dose: 462+/-261 to 371+/-196 impulses x min(-1), P>0.05.

CONCLUSIONS

These data indicate that propofol has a direct depressant effect on dorsal horn neuronal responses to noxious stimulation, with little or no indirect supraspinal effect.

Chromatographic assay and pharmacokinetic studies of propofol in human serum

A high-performance liquid chromatographic system with automated precolumn extraction was developed for the determination of propofol in human serum. Propofol of directly injected serum sample was enriched on a protein-coated mu Bondapak phenyl precolumn while serum constituents such as proteins and salts were eluted to waste. Thereafter, using an on-line column-switching system, the drug was quantitatively transferred and separated on a second analytical column followed by spectrophotometric determination at 270 nm. Good precision, accuracy and linearity were obtained over a range of 30-3000 ng/mL propofol in human serum. The developed method proved to be fast, simple, reproducible, reliable and therefore convenient for propofol monitoring from serum. The recovery of propofol in serum samples from the lowest to the highest concentration ranged from 96.84 to 100.16% (n = 5). The assay was applied to study the pharmacokinetic of the drug in six women undergoing elective caesarean section under general anaesthesia induced with a single intravenous bolus dose of propofol (2.5 mg/kg).

Direct high-performance liquid chromatography determination of propofol and its metabolite quinol with their glucuronide conjugates and preliminary pharmacokinetics in plasma and urine of man

Propofol (P) is metabolized in humans by oxidation to 1,4-di-isopropylquinol (Q). P and Q are in turn conjugated with glucuronic acid to the respective glucuronides, propofol glucuronide (Pgluc), quinol-1-glucuronide (Q1G) and quinol-4-glucuronide (Q4G). Propofol and quinol with their glucuronide conjugates can be measured directly by gradient high-performance liquid chromatographic analysis without enzymic hydrolysis. The glucuronide conjugates were isolated by preparative HPLC from human urine samples. The glucuronides of P and Q were present in plasma and urine, P and Q were present in plasma, but not in urine. Quinol in plasma was present in the oxidised form, the quinone. Calibration curves of the respective glucuronides were constructed by enzymic deconjugation of isolated samples containing different concentrations of the glucuronides. The limit of quantitation of P and quinone in plasma are respectively 0.119 and 0.138 microg/ml. The limit of quantitation of the glucuronides in plasma are respectively: Pgluc 0.370 microg/ml, Q1G 1.02 microg/ml and Q4G 0.278 microg/ml. The corresponding values in urine are: Pgluc 0.264 microg/ml, Q1G 0.731 microg/ml and Q4G 0.199 microg/ml. A pharmacokinetic profile of P with its metabolites is shown, and some preliminary pharmacokinetic parameters of P and Q glucuronides are given.

Determination of diprivan in urine by a supported liquid membrane technique and liquid chromatography-electrochemical detection

A supported liquid membrane technique was used for the extraction and enrichment of propofol in a spiked sample of urine. An acidic solution of propofol and thymol as an internal standard was passed over the membrane and after enrichment the acceptor solution was analyzed by LC with an electrochemical detector. The acceptor and donor pH, flow-rate, and volume of donor and different membrane solvents were varied to optimize the extraction efficiency. The detection limit for 100 ml of a spiked urine sample was 10 ppt of propofol.

Microdetermination of propofol in plasma by a rapid and sensitive liquid chromatographic method

A direct and sensitive liquid chromatographic method for the determination of propofol in 50 microliters of plasma is described. The separation of the drug and internal standard (methyldopa) was achieved using a 4 microns particle size C1R cartridge (10 cm x 8 mm i.d.) in conjunction with a radial compression system and a C18 precolumn module. The mobile phase consisted of 0.01 M sodium acetate solution (adjusted to pH 3 with acetic acid)-acetonitrile-methanol (37:47.25:15.75, v/v/v) at a flow rate of 2 ml min-1. The compounds were detected in the effluent spectrofluorimetrically with excitation and emission wavelengths of 276 and 310 nm, respectively. After the internal standard had been added, the sample was diluted with 50 microliters of hydrochloric acid and centrifuged prior to injection into the chromatograph. The peaks of both propofol and internal standard under these conditions were sharp and symmetrical, and the retention times were 8.2 and 5.15 min, respectively. The peak-height ratio (drug/internal standard) varied linearly (r > 0.9959) with concentration in the ranges 0.002-0.1 and 0.1-10 micrograms ml-1 and the relative standard deviation was consistently < 5.6%. There was no interference in the assay from the endogenous substance or other concomitantly used drug. This method is currently being used for monitoring propofol in intensive care patients and investigating its pharmacokinetics.

High-performance liquid chromatographic assay of propofol in human and rat plasma and fourteen rat tissues using electrochemical detection

This paper describes a sensitive HPLC-electrochemical detection analytical method for determining the concentration of the intravenous anesthetic, propofol, in human or rat plasma or serum and a variety of rat tissues. Internal standard and drug are extracted from serum or plasma and other tissues with pentane. 2,6-tert.-Butylmethylphenol is used as internal standard. It includes a novel steam distillation procedure for separating the highly lipophilic propofol from skin and fat. The plasma/serum assay has a precision of 1-4% (C.V.) in the range 10 ng/ml to 1 microgram/ml and permits the assay of assay of 5 ng/ml from 0.1 ml of plasma/serum. The tissue procedure allows the estimation of 50 ng/g in 0.1 g of tissue for most of the major organs with less than 2% (C.V.) precision. This assay was used to measure propofol concentrations in plasma/serum and tissue samples in support of a project to develop a physiological pharmacokinetic model for propofol in the rat.

Quantitation of propofol in whole blood by gas chromatography-mass spectrometry

A gas chromatographic-mass spectrometric assay, using selected-ion monitoring (GC-MS-SIM) with thymol as internal standard, was developed for quantitating propofol, an intravenous anaesthetic. The method described is rapid and sensitive for the determination of propofol in whole blood. The sensitivity of the present method is 10 ng/ml. The recovery of propofol added to human whole blood in the concentration range 10-10,000 ng/ml ranged between 95 and 100%. A single extraction procedure was used with chloroform-ethyl acetate. The assay allowed the detection of two metabolites formed during propofol metabolism: 2,6-diisopropyl-1,4-quinone and 2,6-diisopropyl-1,4-quinol.

The first fatal 2,6-di-isopropylphenol (propofol) poisoning in Singapore: a case report

The propofol levels in the blood and tissues of a 37-year-old Chinese male suspected of having fatally self-administered an intravenous dose of 1600 mg of propofol (12.3-15.4 times the dose required for the induction of anaesthesia) were determined by headspace gas chromatography. The blood (femoral), liver, kidney and brain propofol levels were 2.5 micrograms/ml, 22 micrograms/g, 3.6 micrograms/g and 11.3 micrograms/g, respectively. The blood propofol level in the present case is 11.4 times and the liver propofol level is 15.7 times that of the first propofol overdose reported in the literature.

Determination of plasma propofol levels using gas chromatography-mass spectrometry with selected-ion monitoring

Propofol (2,6-diisopropylphenol, I.C.I. 35,868) is a rapid-acting, intravenous anesthetic agent recently introduced for the induction and maintenance of general anesthesia. This paper describes a gas chromatographic-mass spectrometric procedure using selected-ion monitoring for the determination of plasma propofol levels. The drug and the internal standard (thymol) were extracted from plasma into diethyl ether-pentane, and derivatized to their trimethylsilyl derivatives before analysis. The reproducibility of the daily standard curves had coefficients of variation ranging from 2.7% to 10.2%. The precision of the assay yielded a coefficient of variation ranging from 4.5% to 5.6%, and the concentration means for the seeded control samples were found to be within -1.6% to +0.6% of the theoretical values for propofol. No interfering peaks have been observed in application of this procedure to either normal volunteer or patient samples. The minimum detectable level under the conditions described was 0.20 ng propofol/ml plasma. This assay and a high-performance liquid chromatographic assay with fluorescence detection were both used to measure plasma propofol concentrations in 89 human plasma samples, and the correlation between the two methods was excellent.

Quantitation of propofol in plasma by capillary gas chromatography

A rapid, accurate and sensitive gas chromatographic method is described for measuring plasma concentrations of propofol. The technique required only 200 microliters of plasma and a single extraction process, using chloroform containing pentadecane (500 ng/ml) as an internal standard. Quantitation was achieved on an SGE BP-1 fused-silica capillary column (25 m x 0.33 mm I.D., 0.5 micron film thickness) with flame ionization detector. The peak response was linear over a wide concentration range (10-10,000 ng/ml) and the limit of quantitation was 10 ng/ml. The absolute recoveries were over 96% (n = 3). The method is applicable for both research and routine plasma level monitoring.

Rapid and sensitive pre-column extraction high-performance liquid chromatographic assay for propofol in biological fluids

A completely automated high-performance liquid chromatographic system is described for the determination of the phenolic anaesthetic propofol. The method is based on pre-column extraction in a closed system allowing direct injection of biological samples without any sample pretreatment. The assay is sensitive (limit of quantification is 5 ng/ml serum), reliable (the variability within a series is 2%) and rapid (results are available after 6 min).