Development and validation of a sensitive method for hydromorphone in human plasma by normal phase liquid chromatography-tandem mass spectrometry

Impact assessment of metabolite instability in the development and validation of LC-MS/MS bioanalytical assays for measurement of rosuvastatin in human plasma and urine samples

During bioanalytical assay development and validation, maintaining the stability of the parent drug and metabolites of interest is critical. While stability of the parent drug has been thoroughly investigated, the stability of unanalyzed metabolites is often overlooked. When an unstable metabolite is known or suspected to interfere with measurement of the parent drug or other metabolites of interest through back-conversion or other routes, additional tests with these unstable metabolites should be conducted. Here, the development and validation of two assays for quantification of rosuvastatin, one in human plasma and one in human urine, was reported. To this end, additional sets of quality control samples were added during assay validation to ensure the reliability of the assays. Acid treatment of samples is shown to be necessary for rosuvastatin quantification. In this regard, stability issues caused by the metabolite, rosuvastatin lactone, may have been overlooked if assay development and validation had only considered the parent drug, rosuvastatin. These assays represent a case study for how to develop and validate assays with unstable metabolites. Taken together, unstable metabolites should be included in all applicable stability tests.

Long-Term Stability of Hydromorphone in Human Plasma Frozen at −20°C for Three Years Quantified by LC-MS/MS

The long-term stability of drugs under normal laboratory storage conditions (−20°C) for years is important for research purposes, clinical re-evaluation, and also for forensic toxicology. To evaluate the stability of the analgesic opioid hydromorphone, 44 human frozen plasma samples of a former clinical trial were reanalyzed after at least three years. Blood samples were disposed using solid-phase extraction with an additional substitution of stable isotope labelled hydromorphone as an internal standard. Hydromorphone concentrations were determined by ultra-performance liquid chromatography (UPLC) with gradient elution, followed by tandem mass spectrometry with electrospray ionization. Calibration curves demonstrated linearity of the assay in the concentration range of 0.3–20 ng/mL hydromorphone. The limit of detection of the hydromorphone plasma concentration was 0.001 ng/mL, and the lower limit of quantification was 0.3 ng/mL. Intra- and interassay errors did not exceed 16%. The percentage deviation of the measured hydromorphone plasma concentrations between the reanalysis and the first analysis was −1.07% ± 14.8% (mean ± SD). These results demonstrate that hydromorphone concentration in human plasma was stable when the samples were frozen at −20°C over three years. This finding is of value for re-evaluations or delayed analyses for research purposes and in pharmacokinetic studies, such as in forensic medicine.

Bioanalytical hydrophilic interaction chromatography: recent challenges, solutions and applications

Hydrophilic interaction chromatography (HILIC) has, in recent years, been shown to be an important supplement to reversed-phase liquid chromatography for polar analytes. HILIC, in conjunction with tandem mass spectrometry (MS/MS), has been steadily gaining acceptance in the analysis of polar compounds from complex biological matrices. This hyphenated technique offers the advantages of improved sensitivity by employing high organic content in the mobile phase, shortened sample preparation time with direct injection of the organic-solvent extracts of biological samples and the potential for ultra-fast analysis because of low-column backpressure. This article reviews recent challenges presented by HILIC, advancements in the better understanding of retention characteristics of analytes with different mobile- and stationary-phase compositions and solutions to ion suppression and interference problems encountered in HILIC–MS/MS assays. Applications of HILIC–MS/MS are summarized, including those for pharmacokinetic studies, metabolic studies, therapeutic drug monitoring and clinical diagnostics.

Succinylmonocholine analytics as an example for selectivity problems in high-performance liquid chromatography/tandem mass spectrometry, and resulting implications for analytical toxicology

The determination and quantitation of drugs in biological matrices using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) is becoming increasingly popular in analytical toxicology, while at the same time a growing awareness for the limits of this technique can be observed. Our group previously developed a rapid HPLC/ESI-MS/MS method for the detection and quantitation of succinylcholine (SUX) and succinylmonocholine (SMC) using ion-pairing extraction of samples with subsequent separation by gradient chromatography on a Synergi Hydro RP C18 column (4 microm, 150 x 2 mm). Identification of analytes was achieved in the multiple reaction monitoring (MRM) mode, using two characteristic ion transitions each, the respective analytes' retention time as well as co-elution of stable isotopic analogues. In both native serum as well as urine an interference with the main MRM transition of SMC was found to co-elute with this analyte, thus severely compromising the identification and quantitation of this target analyte. The interference was further shown to be eliminated from serum and urine by exposure to alkaline conditions and hence proven to share a key physicochemical property with SMC. The observed absence of the second and third most intense ion transitions of SMC in the unknown substance was the only useful distinction between both compounds.The detailed presentation of selectivity problems encountered during method development is intended to initiate further discussion on this yet underrepresented issue in HPLC/MS/MS. The present work emphasizes the need to monitor more than just one ion transition to confidently rule out signal interferences, ensure correct analyte identification as well as quantitation, and thus avoid false-positive results. In this context, the employment of minor MRM transitions for the quantitation and identification of a given analyte is presented as a satisfactory solution to HPLC/MS/MS selectivity problems, and proposed as a possible alternative to previously published approaches.

A 96-well single-pot liquid–liquid extraction, hydrophilic interaction liquid chromatography–mass spectrometry method for the determination of muraglitazar in human plasma

A single-pot liquid-liquid extraction (LLE) with hydrophilic interaction liquid chromatography/tandem mass spectrometry (HILIC/MS/MS) method has been developed and validated for the determination of muraglitazar, a hydrophobic diabetes drug, in human plasma. To 0.050 ml of each plasma sample in a 96-well plate, the internal standard solution in acetonitrile and toluene were added to extract the compound of interest. The plate was vortexed, followed by centrifugation. The organic layer was then directly injected into an LC/MS/MS system. Chromatographic separation was achieved isocratically on a Thermohypersil_Keystone, Hypersil silica column (3 mmx50 mm, 3 microm). The mobile phase contained 85% of methyl t-butyl ether and 15% of 90/10 (v/v) acetonitrile/water with 0.3% trifluoroacetic acid. Post-column mobile phase of 50/50 (v/v) acetonitrile/water containing 0.1% formic acid was added. Detection was by positive ion electrospray tandem mass spectrometry on a Sciex API 4000. The standard curve, ranged from 1 to 1000 ng/ml, was fitted to a 1/x weighted quadratic regression model. This single-pot LLE approach effectively eliminated time-consuming organic layer transfer, dry-down, and sample reconstitution steps, which are essential for a conventional liquid-liquid extraction procedure. The modified mobile phase was more compatible with the direct injection of the commonly used extraction solvents in LLE. Furthermore, the modified mobile phase improved the retention of muraglitazar, a hydrophobic compound, on the normal phase silica column. The validation results demonstrated that this method was rugged and suitable for analyzing muraglitazar in human plasma. In comparison with a revised-phase LC/MS/MS method, this single-pot LLE, HILIC/MS/MS method improved the detection sensitivity by more than four-fold based upon the LLOQ signal to noise ratio. This approach may be applied to other hydrophobic compounds with proper modification of the mobile phase compositions.

An automated and fully validated LC-MS/MS procedure for the simultaneous determination of 11 opioids used in palliative care, with 5 of their metabolites

A fully validated liquid chromatographic procedure coupled with electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) is presented for quantitative determination of the opioids buprenorphine, codeine, fentanyl, hydromorphone, methadone, morphine, oxycodone, oxymorphone, piritramide, tilidine, and tramadol together with their metabolites bisnortilidine, morphine-glucuronides, norfentanyl, and nortilidine in blood plasma after an automatically performed solid-phase extraction (SPE). Separation was achieved in 35 min on a Phenomenex C12 MAX-RP column (4 microm, 150 x 2 mm) using a gradient of ammonium formiate buffer (pH 3.5) and acetonitrile. The validation data were within the required limits. The assay was successfully applied to authentic plasma samples, allowing confirmation of the diagnosis of overdose situations as well as monitoring of patients' compliance, especially in patients under palliative care.

Bioanalytical liquid chromatography tandem mass spectrometry methods on underivatized silica columns with aqueous/organic mobile phases

This review article summarizes the recent progress on bioanalytical LC-MS/MS methods using underivatized silica columns and aqueous/organic mobile phases. Various types of polar analytes were extracted by using protein precipitation (PP), liquid/liquid extraction (LLE) or solid-phase extraction (SPE) and were then analyzed using LC-MS/MS on the silica columns. Use of silica columns and aqueous/organic mobile phases could significantly enhance LC-MS/MS method sensitivity, due to the high organic content in the mobile phase. Thanks to the very low backpressure generated from the silica column with low aqueous/high organic mobile phases, LC-MS/MS methods at high flow rates are feasible, resulting in significant timesaving. Because organic solvents have weaker eluting strength than water, direct injection of the organic solvent extracts from the reversed-phase solid-phase extraction onto the silica column was possible. Gradient elution on the silica columns using aqueous/organic mobile phases was also demonstrated. Contrary to what is commonly perceived, the silica column demonstrated superior column stability. This technology can be a valuable supplement to the reversed-phase LC-MS/MS.

Direct injection of solid-phase extraction eluents onto silica columns for the analysis of polar compounds isoniazid and cetirizine in plasma using hydrophilic interaction chromatography with tandem mass spectrometry

Isoniazid and cetirizine do not retain well on reversed-phase columns due to their high polarity. Silica columns, when operated under hydrophilic interaction conditions, do provide excellent retention of these compounds. We have developed simple and proof of concept analytical methods for the analysis of isoniazid and cetirizine in animal and human plasma, respectively. Both methods employed the approach of direct injection of solid-phase extraction (SPE) organic eluents onto silica columns for analysis, thus eliminating evaporation and reconstitution steps that are typically needed for reversed-phase liquid chromatographic analysis. Isoniazid was extracted from animal plasma samples using a Waters Oasis HLB 96-well plate and then eluted with acetonitrile, while cetirizine was extracted from human plasma with a Waters MCX mu-Elute plate and then eluted with acetonitrile containing 5% concentrated ammonium hydroxide. The direct injection of the SPE eluent onto the analytical column was necessary since significant loss of isoniazid was found during the evaporation and reconstitution steps. The method for isoniazid also enabled ultra-fast analysis due to the relatively low back-pressure exhibited by silica columns even under high flow conditions. Both methods show good linearity, accuracy and precision covering the range of 10-2000 ng/mL of isoniazid, and 1-1000 ng/mL of cetirizine in plasma. Substantial time savings were realized as a result of both the elimination of the evaporation and reconstitution steps and the fast chromatographic analysis.

A sensitive LC/MS/MS method using silica column and aqueous-organic mobile phase for the analysis of loratadine and descarboethoxy-loratadine in human plasma

A sensitive method using liquid chromatography with tandem mass spectrometric detection (LC/MS/MS) was developed and validated for the simultaneous analysis of antihistamine drug loratadine (LOR) and its active metabolite descarboethoxy-loratadine (DCL) in human plasma. Deuterated analytes, i.e. LOR-d(3) and DCL-d(3) were used as the internal standards (I.S.). Analytes were extracted from alkalized human plasma by liquid/liquid extraction using hexane. The extract was evaporated to dryness under nitrogen, reconstituted with 0.1% (v/v) of trifluoroacetic acid (TFA) in acetonitrile, and injected onto a 50 x 3.0 mm I.D. 5 microm, silica column with an aqueous-organic mobile phase consisted of acetonitrile, water, and TFA (90:10:0.1, v/v/v). The chromatographic run time was 3.0 min per injection and flow rate was 0.5 ml/min. The retention time was 1.2 and 2.0 min for LOR and DCL, respectively. The tandem mass spectrometric detection was by monitoring singly charged precursor-->product ion transitions: 383-->337 (m/z) for LOR, 311-->259 (m/z) for DCL, 388-->342 (m/z) for LOR-d(3), and 316-->262 (m/z) for DCL-d(3). The low limit of quantitation (LLOQ) was 10 pg/ml for LOR and 25 pg/ml for DCL. The inter-day precision of the quality control (QC) samples was 3.5-9.4% relative standard deviation (R.S.D.). The inter-day accuracy of the QC samples was 99.0-107.9% of the nominal values.

Liquid/liquid extraction using 96-well plate format in conjunction with hydrophilic interaction liquid chromatography-tandem mass spectrometry method for the analysis of fluconazole in human plasma

A bioanalytical method using automated sample transferring, automated liquid/liquid extraction (LLE) and hydrophilic interaction liquid chromatography-tandem mass spectrometry was developed for the determination of fluconazole in human plasma. Samples of 0.05 ml were transferred into 96-well plate using automatic liquid handler (Multiprobe II). Automated LLE was carried out on a 96-channel programmable liquid handling workstation (Quadra 96) using methyl-tetra butyl ether as the extraction solvent. The extract was evaporated to dryness, reconstituted, and injected onto a silica column using an aqueous-organic mobile phase. The chromatographic run time was 2.0 min per injection, with retention times of 1.47 and 1.44 min for fluconazole and internal standard (IS) ritonavir, respectively. The detection was by monitoring fluconazole at m/z 307-->238 and IS at m/z 721-->296, respectively. The standard curve range was 0.5-100 ng ml(-1). The inter-day precision and accuracy of the quality control samples were <7.1% relative standard deviation and <2.2% relative error.

Enhanced resolution triple-quadrupole mass spectrometry for fast quantitative bioanalysis using liquid chromatography/tandem mass spectrometry: investigations of parameters that affect ruggedness

In order to increase sample analysis throughput, the use of fast liquid chromatography in quantitative bioanalysis based on liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) has become prevalent. Therefore, it is important to increase the specificity of such bioanalytical methods. This can be done by enhancing both the chromatographic and mass resolving power. Increasing the mass spectrometric resolving power to minimize interference from endogenous compounds in the biological matrix is the subject of this paper. We present the results of our experience with developing and validating SRM-based, enhanced resolution bioanalytical methods using a new triple-quadrupole mass spectrometer with enhanced resolution capability. We have shown that SRM bioanalytical methods using better than unit-mass resolution (Q1 FWHM = 0.2 Th, Q3 FWHM = 0.7 Th) can be developed which are as rugged as unit resolution methods (Q1 FWHM = 0.7 Th, Q3 FWHM = 0.7 Th). The enhanced resolution methods require more attention to detail than unit resolution methods. For instance, the mass setting for precursor ion selection is more critical because the mass peak is narrower. Because of this, enhanced resolution methods may be more easily influenced by temperature changes in the laboratory. We have shown that there is good correlation between the shift in the precursor ion mass and the ambient temperature. Other studies carried out to investigate the effects on mass peak shape and response (both in the SIM and SRM mode) as the result of varying the FWHM revealed some interesting results. For instance, the decrease in response with the decrease in the FWHM was larger using SRM compared to that using SIM. However, the decrease in both SRM and SIM response with decreasing FWHM was significantly smaller compared with the decrease obtained using an older generation instrument. We demonstrate that, at concentrations near the limit of detection, the signal specificity can be improved by using an enhanced resolution method. To compare the performance of an enhanced resolution method against a unit resolution method under optimized mass spectrometric conditions, we analyzed calibration standards and quality control samples using a lower limit of quantitation that could be easily achieved by either method. Under these conditions, the two methods were essentially the same, demonstrating that the enhanced resolution method is as accurate, precise and rugged as the unit resolution method. We propose system suitability procedures, based on precursor ion scan, product ion scan, SRM with fractional mass changes, or SIM with a narrow scan width, for the updating of the SRM set masses before the start of analysis. We also recommend that Q1 SRM masses be determined during and at the end of analysis in order to ascertain whether or not the precursor masses have shifted during the course of the analysis.

Development and validation of a liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the determination of ribavirin in human plasma and serum

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the analysis of antiviral agent ribavirin in human plasma and serum. The samples (0.1 ml) were extracted from the matrix using a simple protein precipitation procedure. The supernatants were evaporated to dryness, reconstituted and injected onto the LC/MS/MS system. The chromatography separation was achieved on a silica column operated with an aqueous-organic mobile phase. The use of a silica column not only provided adequate retention for the extremely polar compound of ribavirin, but also enhanced electrospray ionization sensitivity with the use of high percentage organic solvent in the mobile phase. The method has been validated over the concentration range of 10-10000 ng/ml ribavirin in human plasma and serum. Bamethan was used as the internal standard. The protein precipitation extraction has been automated based on 96-well format with the use of robotic liquid handlers to improve the overall throughput of the analysis.

Simultaneous development of six LC-MS-MS methods for the determination of multiple analytes in human plasma

Traditional sequential single analyte method development is both time-consuming and labor-intensive. In this report, a concept of simultaneously developing multiple liquid chromatography coupled with tandem mass spectrometry (LC-MS-MS) methods were proposed. Mass spectrometric and chromatographic conditions as well as sample preparation methods for all analytes were optimized concurrently. Mass spectrometric conditions for six analytes, i.e. clonidine (CLO), albuterol (ALB), fentanyl (FEN), ritonavir (RIT), naltrexone (NAL), and loratadine (LOR), were established simultaneously using the Sciex Analyst software. LC-MS-MS sensitivities obtained using gradient elution methods on reversed-phase Inertsil ODS3 and normal phase Betasil silica columns were compared. Sample extraction methods using protein precipitation, liquid/liquid extraction, or solid-phase extraction (SPE) were evaluated. Recovery of analytes was determined. Matrix effects and interference due to endogenous compounds were investigated. Selection of a potential internal standard was discussed.

Simultaneous determination of hydrocodone and hydromorphone in human plasma by liquid chromatography with tandem mass spectrometric detection

A rapid, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS-MS) method has been developed and validated for the simultaneous analysis of hydrocodone (HYC) and its metabolite hydromorphone (HYM) in human plasma. A robotic liquid handler and a 96-channel liquid handling workstation were used to aliquot samples, to add internal standard (I.S.), and to extract analytes of interest. A 96-well mixed-mode solid-phase cartridge plate was used to extract the analytes and I.S. The chromatographic separation was on a silica column (50 x 3 mm, 5-microm) with a mobile phase consisting of acetonitrile, water and trifluoroacetic acid (TFA) (92:8:0.01, v/v). The run time for each injection was 2.5 min with the retention times of approximately 2.1 and 2.2 min for HYC and HYM, respectively. The tandem mass spectrometric detection was by monitoring singly charged precursor-->product ion transition 300-->199 (m/z) for HYC, and 28-->185 (m/z) for HYM. The validated calibration curve range was 0.100-100 ng/ml, based on a plasma volume of 0.3 ml. The correlation coefficients were greater than or equal to 0.9996 for both HYC and HYM. The low limit of quantitation (LLOQ) was 0.100 ng/ml for both HYC and HYM with signal-to-noise ratio (S/N) of 50 and 10. respectively. The deuterated analytes, used as internal standards, were monitored at mass transitions 303-->199 (m/z) for HYC-d3 and 289-->185 (m/z) for HYM-d3. The inter-day (n= 17) precision of the quality control (QC) samples were < or = 3.5% RSD (relative standard deviation) for HYC and < or = 4.7% RSD for HYM, respectively. The inter-day accuracy of the QC samples were < or = 2.1% RE (relative error) for HYC and < or = 1.8% RE for HYM. The intra-day (n=6) precision and accuracy of the QC samples were < or = 2.6% RSD and < or = 3.0% RE for HYC, and < or = 4.7% RSD and < or = 2.4% RE for HYM. There was no significant deviation from the nominal values after a 5-fold dilution of high concentration QC samples by blank matrix. The QC samples were stable when kept at room temperature for 24-h or experienced three freeze-thaw cycles. The extraction recoveries were 86% for HYC and 78% for HYM. No detectable carryover was observed when a blank sample was injected immediately after a 2500 ng/ml sample that was 25-fold more concentrated than the upper limit of quantitation (ULOQ).

Simultaneous assay of sildenafil and desmethylsildenafil in human plasma using liquid chromatography-tandem mass spectrometry on silica column with aqueous-organic mobile phase

A liquid chromatography-tandem mass spectrometry method was developed for the analysis of sildenafil (SIL) and its metabolite desmethylsildenafil (DMS) in human plasma. Samples were accurately transferred to 96-well plates using a liquid handler (Multiprobe II). Solid-phase extraction was carried out on a 96-channel programmable liquid handling workstation (Quadra 96) using a C8 and cation-exchange mixed-mode sorbent. The extract was injected onto a silica column with an aqueous-organic mobile phase, a combination that was novel for improving the method sensitivity. The low limit of quantitation was 1.0 ng/ml for both SIL and DMS. The method was validated to meet the criteria of current industrial guidance for quantitative bioanalytical methods.

Ultrafast liquid chromatography/tandem mass spectrometry bioanalysis of polar analytes using packed silica columns

Ultrafast liquid chromatography/tandem mass spectrometry (LC/MS/MS) bioanalysis was demonstrated with the use of packed silica columns operated under elevated flow rates. A special effort has been made to achieve ultrafast analysis without sacrificing chromatographic resolution. Two multiple analyte/metabolites assays, (1) morphine/morphine-6-glucuronide(M6G)/morphine-3-glucuronide(M3G) and (2) midazolam/1'-hydroxymidazolam/4-hydroxymidazolam, were used to demonstrate the speed, sensitivity, peak shape and separation of the ultrafast methods utilizing silica columns. In both methods adequate chromatographic separation was a necessity because quantitation results would be otherwise compromised due to cross interference between different selected reaction monitoring (SRM) transitions. Baseline resolutions between morphine, M6G and M3G in human plasma extracts were achieved within 30 s on a 50 x 3 mm Betasil silica column operated at 4 mL/min of isocratic acetonitrile/water mobile phase. The total injection-to-injection cycle time was 48 s with a simple, single-autosampler/single-column setup, when a Shimadzu SIL-HT autosampler was used. Baseline resolution between 1'-hydroxymidazolam and 4-hydroxymidalolam in monkey plasma extracts was achieved within 33 s using similar conditions. Due to the absence of carry-over in this case, no rinsing of the injection needle was necessary, resulting in a cycle time of only 39 s/sample. These ultrafast methods were successfully used to analyze extracted biological samples and proved to be reproducible, reliable and generated equivalent pharmaco-kinetic (PK) results to those obtained by regular flow LC/MS/MS analysis to support discovery PK studies.

An automatic 96-well solid phase extraction and liquid chromatography-tandem mass spectrometry method for the analysis of morphine, morphine-3-glucuronide and morphine-6-glucuronide in human plasma

A bioanalytical method using automated sample transferring, automated solid phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS-MS) was developed for morphine (MOR), and its metabolites morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) in human plasma. Samples of 0.25 ml were transferred into 96-well plate using automatic liquid handler (Multiprobe II). Automated SPE was carried out on a 96-channel programmable liquid handling workstation (Quadra 96) using a C(18) sorbent. The extract was injected onto a silica column using an aqueous-organic mobile phase. The chromatographic run time was 3.5 min per injection, with retention times of 1.5, 2.0 and 2.6 min for MOR, M6G, and M3G, respectively. The detection was by monitoring MOR at m/z 286-->152, M6G and M3G at m/z 462-->286. The deuterated internal standards were monitored at m/z 289-->152 for MOR-d(3), and m/z 465-->289 for M6G-d(3) and M3G-d(3). The standard curve range was 0.5-50 ng ml(-1) for MOR, 1.0-100 ng ml(-1) for M6G, and 10-1000 ng ml(-1) for M3G. The inter-day precision and accuracy of the quality control samples were <8% relative standard deviation (RSD) and <7% relative error (RE) for MOR, <5% RSD and <2% RE for M6G, and <2% RSD and <4% RE for M3G.

A strategy for a post-method-validation use of incurred biological samples for establishing the acceptability of a liquid chromatography/tandem mass-spectrometric method for quantitation of drugs in biological samples

Validated liquid chromatography/tandem mass spectrometric (LC/MS/MS) methods are now widely used for quantitation of drugs in post-dose (incurred) biological samples for the assessment of pharmacokinetic parameters, bioavailability and bioequivalence. In accordance with the practice currently accepted within the pharmaceutical industry and the regulatory bodies, validation of a bioanalytical LC/MS/MS method is performed using standards and quality control (QC) samples prepared by spiking the drug (the analyte) into the appropriate blank biological matrix (e.g. human plasma). The method is then declared to be adequately validated for analyzing incurred biological samples. However, unlike QC samples, incurred samples may contain an epimer or another type of isomer of the drug, such as a Z or E isomer. Such a metabolite will obviously interfere with the selected reaction monitoring (SRM) transition used for the quantitation of the drug. The incurred sample may also contain a non-isomeric metabolite having a molecular mass different from that of the drug (such an acylglucuronide metabolite) that can still contribute to (and hence interfere with) the SRM transition used for the quantitation of the drug. The potential for the SRM interference increases with the use of LC/MS/MS bioanalytical methods with very short run times (e.g. 0.5 min). In addition, a metabolite can potentially undergo degradation or conversion to revert back to the drug during the multiple steps of sample preparation that precede the introduction of the processed sample into the LC/MS/MS system. In this paper, we recommend a set of procedures to undertake with incurred samples, as soon as such samples are available, in order to establish the validity of an LC/MS/MS method for analyzing real-life samples. First, it is recommended that the stability of incurred samples be investigated 'as is' and after sample preparation. Second, it is recommended that potential SRM interference be investigated by analyzing the incurred samples using the same LC/MS/MS method but with the additional incorporation of the SRM transitions attributable to putative metabolites (multi-SRM method). The metabolites monitored will depend on the expected metabolic products of the drug, which are predictable based on the functional groups present in the chemical structure of the drug. Third, it is recommended that potential SRM interference be further investigated by analyzing the incurred samples using the multi-SRM LC/MS/MS method following the modification of chromatographic conditions to enhance chromatographic separation of the drug from any putative metabolites. We will demonstrate the application of the proposed strategy by using a carboxylic acid containing drug candidate and its acylglucuronide as a putative metabolite. Plasma samples from the first-in-man (FIM) study of the drug candidate were used as the incurred samples.

Liquid chromatography/tandem mass spectrometric bioanalysis using normal-phase columns with aqueous/organic mobile phases - a novel approach of eliminating evaporation and reconstitution steps in 96-well SPE

Bioanalytical methods using automated 96-well solid-phase extraction (SPE) and liquid chromatography with electrospray tandem mass spectrometry (LC/MS/MS) are widely used in the pharmaceutical industry. SPE methods typically require manual steps of drying of the eluates and reconstituting of the analytes with a suitable injection solvent possessing elution strength weaker than the mobile phase. In this study, we demonstrated a novel approach of eliminating these two steps in 96-well SPE by using normal-phase LC/MS/MS methods with low aqueous/high organic mobile phases, which consisted of 70-95% organic solvent, 5-30% water, and small amount of volatile acid or buffer. While the commonly used SPE elution solvents (i.e. acetonitrile and methanol) have stronger elution strength than a mobile phase on reversed-phase chromatography, they are weaker elution solvents than a mobile phase for normal-phase LC/MS/MS and therefore can be injected directly. Analytical methods for a range of polar pharmaceutical compounds, namely, omeprazole, metoprolol, fexofenadine, pseudoephedrine as well as rifampin and its metabolite 25-desacetyl-rifampin, in biological fluids, were developed and optimized based on the foregoing principles. As a result of the time saving, a batch of 96 samples could be processed in one hour. These bioanalytical LC/MS/MS methods were validated according to "Guidance for Industry - Bioanalytical Method Validation" recommended by the Food and Drug Administration (FDA) of the United States.

Importance of injection solution composition for LC-MS-MS methods

For the first time, the influence of the injection solution composition on the quality of LC-MS-MS methods, in terms of column efficiency and peak shape, was systematically investigated. Various types of compounds, including polar ionic acidic, polar ionic basic and non-polar neutral compounds, were prepared in different solutions ranging from 100% water to 100% acetonitrile. Different volumes of these solutions were injected onto either C18 or silica columns connected to tandem mass spectrometry. The mobile phases consisted of acetonitrile, water, and small amounts of volatile acid or buffer. On silica columns, the influence of injection solution on the peak shape and column efficiency was straightforward. The sharpest peaks and the highest column efficiency were obtained with 100% acetonitrile as the injection solvent. On C18 columns, this type of influence was less clear due to the dual retention mechanism of the bonded phase and of the residual silanol groups. On C18 column, retention due to residual silanol groups was significant even with a mobile phase containing less than 50% acetonitrile. Poor peak shape was observed when the injection solution had a stronger eluting strength than mobile phase, particularly for early eluting peaks.

Novel liquid chromatographic-tandem mass spectrometric methods using silica columns and aqueous-organic mobile phases for quantitative analysis of polar ionic analytes in biological fluids

Use of silica stationary phase and aqueous-organic mobile phases could significantly enhance LC-MS-MS method sensitivity. The LC conditions were compatible with MS detection. Analytes with basic functional groups were eluted with acidic mobile phases and detected by MS in the positive ion mode. Analytes with acid functional groups were eluted with mobile phases at neutral pH and detected by MS in the negative ion mode. Analytes poorly retained on reversed-phase columns showed good retention on silica columns. Compared with reversed-phase LC-MS-MS, 5-8-fold sensitivity increases were observed for basic polar ionic compounds when using silica columns and aqueous-organic mobile phase. Up to a 20-fold sensitivity increase was observed for acidic polar ionic compounds. Silica columns and aqueous-organic mobile phases were used for assaying nicotine, cotinine, and albuterol in biological fluids.

Increased throughput in quantitative bioanalysis using parallel-column liquid chromatography with mass spectrometric detection

The feasibility of quantitative bioanalysis by parallel-column liquid chromatography in conjunction with a conventional single-source electrospray mass spectrometer has been investigated using plasma samples containing a drug and its three metabolites. Within a single chromatographic run time, sample injections were made alternately onto each of two analytical columns in parallel at specified intervals, with a mass spectrometer data file opened at every injection. Thus, the mass spectrometer collected data from two sample injections into separate data files within a single chromatographic run time. Therefore, without sacrificing the chromatographic separation or the selected reaction monitoring (SRM) dwell time, the sample throughput was increased by a factor of two. Comparing the method validation results obtained using the two-column system with those obtained using the corresponding conventional single-column approach, the methods on the two systems were found to be equivalent in terms of accuracy and precision. The parallel-column system is simple and can be implemented using existing laboratory equipment with no additional capital outlays. A parallel-column system configured in this manner can be used not only for the within-a-run analysis of two samples containing two different sets of chemical entities, but also for the within-a-run analysis of two samples containing the same set of chemical entities.

A highly automated 96-well solid phase extraction and liquid chromatography/tandem mass spectrometry method for the determination of fentanyl in human plasma

A high-throughput bioanalytical method based on automated sample transfer, automated solid phase extraction, and fast liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis, has been developed for the determination of the analgesic fentanyl in human plasma. Samples were transferred into 96-well plates using an automated sample handling system. Automated solid phase extraction (SPE) was carried out using a 96-channel programmable liquid-handling workstation using a mixed-mode sorbent. The extracted samples were then dried down, reconstituted and injected onto a silica column using an aqueous/organic mobile phase with tandem mass spectrometric detection. The method has been validated over the concentration range 0.05-100 ng/mL fentanyl in human plasma, based on a 0.25-mL sample size. The assay is sensitive, specific and robust. More than 2000 samples have been analyzed using this method. The automation of the sample preparation steps not only increased the analysis throughput, but also facilitated the transfer of the method between different bioanalytical laboratories of the same organization.