Coupling device for desorption of drugs from solid-phase extraction-pipette tips and on-line gas chromatographic analysis

Pipette-tip micro-solid phase extraction based on melamine-foam@polydopamine followed by ultra-high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry for detection of psychotropic drugs in human serum

In this work, pipette-tip micro-solid phase extraction (PT-μSPE) which packed by melamine-foam@polydopamine (MF@PDA) coupled with ultra-high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UHPLC-QTOF) was developed for extraction and determination of psychotropic drugs in serum samples. Considering the operation back pressure, the melamine-foam as carrier material with 3D cross-linked grid structure can provide high permeability and contact surface. MF@PDA was prepared by self-polymerization reaction of dopamine under weak alkaline conditions and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The surface group of PDA containing catechol structure, quinone structure and amine group has multi-interaction with psychotropic drugs which can increase the adsorption capacity. Moreover, the parameters affecting extraction efficiencies such as extraction and desorption cycle, pH value, eluent type, ionic strength and amount of sorbent were investigated. Based on the high sensitivity and accuracy mass measurement by TOF/MS, under the optimized extraction condition, the limits of detection (LOD) of this method were obtained in the range of 0.002-0.1 ng ml^-1. The linearity was ranged from 0.01 ng ml^-1 to 600 ng ml^-1, and all the correlation coefficients (R²) were above 0.993. The spiked recoveries were in the range of 80.04% to 109.18% in real sample test and RSD values obtained from 0.95% to 9.85%. The results demonstrate that MF@PDA-PT-μSPE-UHPLC-QTOF is a sample and reliable method for the detection of psychotropic drugs in serum sample.

Sample treatment based on extraction techniques in biological matrices

The importance of sample preparation methods as the first stage in bioanalysis is described. In this article, the sample preparation concept and strategies will be discussed, along with the requirements for good sample preparation. The most widely used sample preparation methods in the pharmaceutical industry are presented; for example, the need for same-day rotation of results from large numbers of biological samples in pharmaceutical industry makes high throughput bioanalysis more essential. In this article, high-throughput sample preparation techniques are presented; examples are given of the extraction and concentration of analytes from biological matrices, including protein precipitation, solid-phase extraction, liquid–liquid extraction and microextraction-related techniques. Finally, the potential role of selective extraction methods, including molecular imprinted phases, is considered.

Automated micropipette tip-based SPE in quantitative bioanalysis

Background: Automated methodologies using silica-based, monolithic, micropipette tip-based SPE have been developed for the analysis of small molecules in support of both preclinical and first-in-human development studies using LC–MS/MS. The use of micropipette tip-based SPE with the Tomtec Quadra 96® and the evaluation of prototype micropipette tips for use with the Hamilton Microlab® Star robot is outlined. Results: Mixed-mode cation exchange and C18 SPE methods have been developed using human and rat plasma for the extraction of lipophilic and polar analytes. These methods are advantageous as they use low plasma sample, washing and elution volumes and result in a method extraction cycle time of approximately 6.2 min for 96 samples. Conclusion: This significantly reduced extraction time, compared with 96-well plate format SPE, indicates that the sample preparation stage is no longer the rate-limiting stage in performing a selective extraction procedure. Robust and sensitive methods have been developed that have proven to be more cost effective than traditional 96-well plate format SPE methods.

Extraction of amphetamines and methylenedioxyamphetamines from urine using a monolithic silica disk-packed spin column and high-performance liquid chromatography-diode array detection

To overcome the limitations of solid-phase extraction, we developed a device comprising a spin column packed with octadecyl silane-bonded monolithic silica for extracting amphetamines and methylenedioxyamphetamines from urine. Urine (0.5mL), buffer (0.4mL), and methoxyphenamine (internal standard) were directly put into the preactivated column. The column was centrifuged (3000rpm, 5min) for sample loading and washed. The adsorbed analytes were eluted and analyzed by high-performance liquid chromatography, without evaporation. The results were as follows: linear curves (drug concentrations of 0.2-20microg/mL); correlation coefficients >0.99; detection limit, 0.1microg/mL. The proposed method is not only useful for drugs from biological materials but also highly reproducible for the analysis of these drugs in urine.

Simultaneous determination of nikethamide and lidocaine in human blood and cerebrospinal fluid by high performance liquid chromatography

Nikethamide and lidocaine are often requested to be quantified simultaneously in forensic toxicological analysis. A simple reversed-phase high performance liquid chromatography (RP-HPLC) method has been developed for their simultaneous determination in human blood and cerebrospinal fluid. The method involves simple protein precipitation sample treatment followed by quantification of analytes using HPLC at 263 nm. Analytes were separated on a 5 microm Zorbax Dikema C18 column (150 mm x 4.60 mm, i.d.) with a mobile phase of 22:78 (v/v) mixture of methanol and a diethylamine-acetic acid buffer, pH 4.0. The mean recoveries were between 69.8 and 94.4% for nikethamide and between 78.9 and 97.2% for lidocaine. Limits of detection (LODs) for nikethamide and lidocaine were 0.008 and 0.16 microg/ml in plasma and 0.007 and 0.14 microg/ml in cerebrospinal fluid, respectively. The mean intra-assay and inter-assay coefficients of variation (CVs) for both analytes were less than 9.2 and 10.8%, respectively. The developed method was applied to blood sample analyses in eight forensic cases, where blood concentrations of lidocaine ranged from 0.68 to 34.4 microg/ml and nikethamide ranged from 1.25 to 106.8 microg/ml. In six cases cerebrospinal fluid analysis was requested. The values ranged from 20.3 to 185.6 microg/ml of lidocaine and 8.0 to 72.4 microg/ml of nikethamide. The method is simple and sensitive enough to be used in toxicological analysis for simultaneous determination of nikethamide and lidocaine in blood and cerebrospinal fluid.

Simultaneous determination of desloratadine and pseudoephedrine in human plasma using micro solid-phase extraction tips and aqueous normal-phase liquid chromatography/tandem mass spectrometry

Cation-exchange micro solid-phase extraction (SPE) tips and aqueous normal-phase (ANP) chromatography coupled with tandem mass spectrometry were explored for the rapid, selective and sensitive quantitation of desloratadine and pseudoephedrine in human plasma. A novel micro-SPE device was evaluated for analyte capacity, extraction efficiency and its ability to maximize recovery of an analyte of interest from bioanalytical matrices by successive replicates of linked extraction steps. Ion suppression using two different methods with micro-SPE tips was negligible when compared to protein precipitation. The use of ANP chromatography eliminated the need for sample reconstitution following extraction and was found to be highly selective. A reliable chromatography system was developed with a short duty cycle of 2 min/sample. The proposed bioanalytical method required 50 microL of plasma for the determination of desloratadine and pseudoephedrine at limits of quantitation of 0.1 and 1.25 ng/mL, respectively. The analytical method was validated in accordance with the FDA guidance on bioanalytical method validation; selectivity, linearity, reproducibility and accuracy were all acceptable.

Simultaneous determination of ten antihistamine drugs in human plasma using pipette tip solid-phase extraction and gas chromatography/mass spectrometry

Ten antihistamine drugs, diphenhydramine, orphenadrine, chlorpheniramine, diphenylpyraline, triprolidine, promethazine, homochlorcyclizine, cyproheptadine, cloperastine and clemastine, have been found to be extractable from human plasma samples using MonoTip C18 tips, inside which C18- bonded monolithic silica gel was fixed. Human plasma (0.1 mL) containing the ten antihistamines was mixed with 0.4 mL of distilled water and 25 microL of a 1 M potassium phosphate buffer (pH 8.0). After centrifugation of the mixture, the supernatant fraction was extracted to the C18 phase of the tip by 25 repeated aspirating/dispensing cycles using a manual micropipettor. The analytes retained on the C18 phase were then eluted with methanol by five repeated aspirating/dispensing cycles. The eluate was injected into a gas chromatography (GC) injector without evaporation and reconstitution steps, and was detected by a mass spectrometer with selected ion monitoring in the positive-ion electron impact mode. The separation of the ten drugs from each other and from impurities was generally satisfactory using a DB-1MS column (30 m x 0.32 mm i.d., film thickness 0.25 microm). The recoveries of the ten antihistamines spiked into plasma were 73.8-105%. The regression equations for the ten antihistamines showed excellent linearity with detection limits of 0.02-5.0 ng/0.1 mL. The within-day and day-to-day coefficients of variation for plasma were not greater than 9.9%. The data obtained from determination of diphenhydramine and chlorpheniramine in human plasma after oral administration of the drugs are also presented.

Monitoring of drugs and metabolites in whole blood by restricted-access solid-phase microextraction coupled to liquid chromatography–mass spectrometry

Robust biocompatible solid-phase microextraction (SPME) devices were prepared using various alkyldiol-silica (ADS) restricted-access materials (RAM) as the SPME coating. The ADS-SPME approach was able to simultaneously fractionate the protein component from a biological sample, while directly extracting diazepam and the major metabolites N-desmethyldiazepam, oxazepam and temazepam, and overcame the present disadvantages of direct sampling in biological matrices by SPME. The devices were interfaced with an LC-MS system and an isocratic mobile phase was used to desorb, separate, and quantify the analytes. The calculated diazepam, nordiazepam, temazepam, and oxazepam detection limits were 20, 20, 30, and 35 ng/ml in heparinized blood, respectively. The method was confirmed to be linear over the range of 50-1000 ng/ml with an average linear coefficient (R2) value of 0.996. The injection repeatability and intra-assay precision of the method were evaluated over ten injections at concentrations of 50, 200, and 500 ng/ml, resulting in a R.S.D. of ca. 10%. The robustness of the ADS-SPME device was evaluated for future use in in vivo studies, providing many direct extractions and subsequent determination of benzodiazepines in blood. For the extraction of the peptides angiotensin I, II, and III from blood, a novel restricted access material with cation exchange properties was evaluated. The ion-exchange diol silica improved the extraction efficiency of peptides relative to the conventional ADS material with reversed phase extraction centers.

Utility of nonaqueous capillary electrophoresis for the determination of lidocaine and its metabolites in human plasma: a comparison of ultraviolet and mass spectrometric detection

A nonaqueous capillary electrophoresis/electrospray mass spectrometry method for the separation of lidocaine (LID) and two of its metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), has been developed. The separation medium was: 70 mM ammonium formate and 2.0 M formic acid in acetonitrile/methanol (60:40 v/v). With a sheath liquid of methanol/water (80:20 v/v) containing 2% formic acid and positive ion detection, reproducible determinations (8-11% relative standard deviation (RSD)) of lidocaine and its metabolites were performed in spiked human plasma. The limits of detection (LODs) were between 69.1 and 337 nM. The influences of sheath liquid composition, nebulizing gas pressure and drying gas temperature on the separation were examined.

Bio-compatible in-tube solid-phase microextraction capillary for the direct extraction and high-performance liquid chromatographic determination of drugs in human serum

A restricted access material (RAM), alkyl-diol-silica (ADS), was used to prepare a highly bio-compatible solid-phase microextraction (SPME) capillary for the automated and direct in-tube extraction of several benzodiazepines from human serum. The bifunctionality of the ADS extraction phase prevented fouling of the capillary by protein adsorption while simultaneously trapping the analytes in the hydrophobic porous interior. This the first report of a restricted access material utilized as an extraction phase for in-tube SPME. The approach simplified the required apparatus in comparison to existing RAM column switching procedures, and more importantly eliminated the excessive use of extraction solvents. The biocompatibility of the ADS material also overcame the existing problems with in-tube SPME that requires an ultrafiltration or other deproteinization step prior to handling biological samples, therefore further minimizing the sample preparation requirements. The calculated oxazepam, temazepam, nordazepam and diazepam detection limits were 26, 29, 22 and 24 ng/ml in serum, respectively. The method was linear over the range of 50-50 000 ng/ml with an average linear coefficient (R2) value of 0.9998. The injection repeatability and intra-assay precision of the method were evaluated with five injections of a 10-microg/ml serum sample (spiked with all compounds), resulting in an average RSD<7%. The ADS extraction column was robust, providing many direct injections of biological fluids for the extraction and subsequent determination of benzodiazepines.

Determination of cannabinoids by gas chromatography-mass spectrometry and large-volume programmed-temperature vaporiser injection using 25 microl of biological fluid

This paper presents a GC-MS confirmation method, based on large-volume programmed-temperature vaporisation (PTV) injection, for the determination of cannabinoids in plasma samples (or whole blood) with deuterium-labelled internal standards using only 25 microl of biological fluid. The analytes, Delta(9)-tetrahydrocannabinol (THC), 11-hydroxy-Delta(9)-tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-Delta 9-tetrahydrocannabinol (THC-COOH), were enriched by means of solid-phase extraction cartridges containing octadecyl-bonded silica and were, subsequently, methylated. A 20 microl aliquot of an extract in hexane was injected into a PTV in solvent split mode. Method development and the results of the analyses of standard reference material and real samples are presented and discussed. This micro-method is precise and sensitive enough to assess relevant cannabinoid levels in human blood for forensic investigations as well as for clinical applications.

Feasibility of the direct coupling of solid-phase extraction-pipette tips with a programmed-temperature vaporiser for gas chromatographic analysis of drugs in plasma

Solid-phase extraction-pipette tips (SPE-PTs) were used for micro solid-phase extraction of lidocaine and diazepam from plasma. Off-line extraction was followed by on-line desorption. On-line desorption was carried out by direct coupling of the SPE-PTs with the liner of the programmed-temperature vaporiser. This coupling only required shortening of the liner by maximally 16 mm, cutting the SPE-PT, and equipping the remaining part with two O-rings. Due to the heating of the injector the SPE-PTs were heated as well, which resulted in a significant amount of impurities. Pre-heating and pre-washing was performed prior to the extraction to reduce the impurity level. The internal coupling device was applied successfully for the analysis of plasma samples with gas chromatography (GC) and mass-selective detection. Detection limits of 0.75 ng/ml and 2.5 ng/ml were obtained for lidocaine and diazepam, respectively, using 200 microl plasma. Recoveries for both compounds were about 80%. Although it is possible, the internal coupling device was not developed to be used as such. The main goal of this coupling was to show the feasibility of the integration of SPE-PTs with GC and to realize an important step to new automated SPE-GC systems.

Direct LC analysis of five benzodiazepines in human urine and plasma using an ADS restricted access extraction column

An alkyl-diol-silica (ADS) precolumn was used for the direct and on-line extraction of several benzodiazepines from serum and urine. The protein component of the biological sample was flushed through the ADS column, while simultaneously extracting the benzodiazepine compounds in the pores of the ADS stationary phase. The role of hydrophobic interactions in the extraction mechanism was confirmed. Column switching was employed to elute the extracted analytes from the ADS column into a high-performance liquid chromatography reverse-phase C18 column for the isocratic separation and UV detection of the benzodiazepines. Sample preconcentration via large volume injections was possible, improving the limits of detection. The calculated clonazepam, oxazepam, temazepam, nordazepam and diazepam detection limits were 38.8, 24.2, 31.7, 31.3, 45.0 ng/ml in serum, respectively, and 48.4, 24.5, 31.7, 33.1, 52.9 ng/ml for urine, respectively. The method was linear over the range of 50-10000 ng/ml in both matrices with an average linear coefficient (R(2)) value of 0.9918. The injection repeatability and intra-assay precision of the method were evaluated over ten injections, resulting in a percent relative standard deviation <5%. The ADS extraction column was robust, providing many direct injections of biological fluids for the extraction and subsequent determination of benzodiazepines.

Separation of lidocaine and its metabolites by capillary electrophoresis using volatile aqueous and nonaqueous electrolyte systems

The separation of the basic drug lidocaine and six of its metabolites has been investigated both by using volatile aqueous electrolyte system, at low pH and by employing non-aqueous electrolyte systems. In aqueous systems, the best separation of the compounds under the investigated conditions was achieved by using the electrolyte 60 mM trifluoroacetic acid (TFA)/triethylamine (TEA) at pH 2.5 containing 15% methanol. With this electrolyte, all seven compounds were well separated with high efficiency and migration time repeatability. The separations with bare fused-silica capillaries and polyacrylamide-coated capillaries were compared with higher separation efficiency with the latter. On the other hand, near baseline separation of all the seven compounds was also obtained by employing the non-aqueous electrolyte, 40 mM ammonium acetate in methanol and TFA (99:1, v/v), with comparable migration time repeatability but lower separation efficiency relative to the aqueous system.