Synthesis of zinc oxide powders in plasma–solution systems

A new method is proposed for the synthesis of powdered zinc oxide with the use of a plasma–solution system. The chemical and phase compositions and the morphology of the synthesized powders have been determined. It has been found that the calcination of powders obtained in the plasma–solution system leads to the formation of ZnO.     

Liquid chromatography–mass spectrometric determination of plasmalogens in human plasma

A new liquid chromatography–mass spectrometry (LC/MS) method has been developed for the quantitative analysis of plasmalogens in human plasma using a nonendogenous plasmalogen (1-O-1′-(Z)-tricosenyl-2-oleoyl-rac-glycero-3-phosphocholine, PLS 23:0/18:1) as an internal standard. 1-O-1′-(Z)-Tricosenyl glyceryl ether was prepared by reacting lithioalkoxyallyl with 1-iodoeicosane as the key intermediate in the formation of PLS 23:0/18:1. In LC/MS analyses, PLS 23:0/18:1 generated significant fragment ions in positive and negative modes. In positive ion mode, the [M+H]⁺ of PLS 23:0/18:1 yielded unique fragments with cleavages at the sn-1 and sn-2 positions of the glycerol backbone. In negative ion mode, the [M+CH₃COO]⁻ of PLS 23:0/18:1 resulted in characteristic fragmentation at the sn-2 and sn-3 positions. 1-O-1′-(Z)-Hexadecenyl-2-linoleoyl-rac-glycero-3-phosphocholine (PLS 16:0/18:2) and 2-arachidonoyl-O-1′-(Z)-hexadecenyl-rac-glycero-3-phosphocholine (PLS 16:0/20:4) were chemically synthesized as PLS 23:0/18:1. The calibration curves obtained for PLS 16:0/18:2 and PLS 16:0/20:4 were linear throughout the calibration range (0.04–1.60 pmol). The LOD (S/N = 5:1) was 0.008 pmol and the LOQ (S/N = 6:1) was 0.01 pmol for both PLS 16:0/18:2 and PLS 16:0/20:4. Plasma concentrations of PLS 16:0/18:2 and PLS 16:0/20:4 were 4.0 ± 1.3 μM and 3.5 ± 1.2 μM (mean ± SD), respectively, in five healthy volunteers.     

Validated HPLC–MS–MS method for determination of azithromycin in human plasma

A validated, highly sensitive, and selective HPLC method with MS–MS detection has been developed for quantitative determination of azithromycin (AZI) in human Na₂EDTA plasma. Roxithromycin (ROX) was used as internal standard. Human plasma containing AZI and internal standard was ultrafiltered through Centrifree Micropartition devices and the concentration of AZI was determined by isocratic HPLC–MS–MS. Multiple reaction monitoring mode (MRM) was used for MS–MS detection. The calibration plot was linear in the concentration range 2.55–551.43 ng mL⁻¹. Inter-day and Intra-day precision and accuracy of the proposed method were characterized by R.S.D and percentage deviation, respectively; both were less than 8%. Limit of quantification was 2.55 ng mL⁻¹. The proposed method was used to determine the pharmacokinetic profile of AZI (250-mg tablets).     

Computerized simulation of solute–particle vaporization in an inductively coupled plasma

Recent experiments involving aerosol introduction into the inductively coupled plasma have shown that intact droplets and solute particles cause enormous fluctuations in analyte emission and mass-spectral signals. Here, particle-vaporization kinetics are simulated as a detailed function of the operating conditions, fundamental properties and spatial location in the inductively coupled plasma, and as a function of several of the properties of the particles themselves: diameter, chemical composition and size distribution. These simulations portray the particle vaporization as proceeding nominally linearly with respect to the particle radius when the particles are small, but roughly quadratically with radius when the particles are very large. Further, the heat- and mass-transfer-limited rates of vaporization are roughly equal for the typical gas-temperature range in the plasma tail flame, so that at any height either process might limit the rate of vaporization. This similarity gives rise to a dynamic, competitive picture of plasma vaporization kinetics.     

Liquid chromatographic–electrospray mass spectrometric determination of cyclosporin A in human plasma

A rapid, sensitive and selective liquid chromatography–mass spectrometry (LC–MS) assay has been developed for determination of cyclosporin A (CyA) in human plasma; cyclosporin B (CyB) was used as internal standard (IS). The method utilized a combination of a column-switching valve and a reversed-phase symmetry column. The mobile phase was a 25:75 (v/v) mixture of 10% aqueous glacial acetic acid and acetonitrile. Running time per single run was less than 10 min. Sample preparation included C₈ SPE of human plasma spiked with the analyte and internal standard, evaporation of the eluate to dryness at 50°C under N₂ gas, and finally reconstitution in the mobile phase. Detection of cyclosporin A and the IS was performed in selected ion-monitoring mode at m/z 601.3 and 594.4 Da for CyA and IS, respectively. Quantitation was achieved by use of the regression equation of relative peak area of cyclosporin to IS against concentration of cyclosporin. The method was validated according to FDA guideline requirements. The linearity of the assay in the range 5.0–400.0 ng mL^–1 was verified as characterized by the least-squares regression line Y=(0.00268±1.9×10^–4)X+(0.00078±1.8×10^–3), correlation coefficient, r=0.9986±1.1×10^–3 (n=48). Intra and inter-day quality-control measurements in the range 5.0–350.0 ng mL^–1 revealed almost 100% accuracy and 9% CV for precision. The mean absolute recovery of CyA was found to be 84.01±9.9% and the respective relative recovery was 100.3±9.19. The limit of quantitation (LOQ) achieved was 5 ng mL^–1. Eventually, stability testing of the analyte and IS in plasma or stock solution revealed that both chemicals were very stable when stored for long or short periods of time at room temperature or –20°C.     

Qualitative detection of desmopressin in plasma by liquid chromatography–tandem mass spectrometry

This work describes a liquid chromatography–electrospray tandem mass spectrometry method for detection of desmopressin in human plasma in the low femtomolar range. Desmopressin is a synthetic analogue of the antidiuretic hormone arginine vasopressin and it might be used by athletes as a masking agent in the framework of blood passport controls. Therefore, it was recently added by the World Anti-Doping Agency to the list of prohibited substances in sport as a masking agent. Mass spectrometry characterization of desmopressin was performed with a high-resolution Orbitrap-based mass spectrometer. Detection of the peptide in the biological matrix was achieved using a triple-quadrupole instrument with an electrospray ionization interface after protein precipitation, weak cation solid-phase extraction and high performance liquid chromatography separation with an octadecyl reverse-phase column. Identification of desmopressin was performed using three product ions, m/z 328.0, m/z 120.0, and m/z 214.0, from the parent ion, m/z 535.5. The extraction efficiency of the method at the limit of detection was estimated as 40% (n = 10), the ion suppression as 5% (n = 10), and the limit of detection was 50 pg/ml (signal-to-noise ratio greater than 3). The selectivity of the method was verified against several endogenous and synthetic desmopressin-related peptides. The performance and the applicability of the method were tested by analysis of clinical samples after administration of desmopressin via intravenous, oral, and intranasal routes. Only after intravenous administration could desmopressin be successfully detected.     

Metallomics in drug development: characterization of a liposomal cisplatin drug formulation in human plasma by CE–ICP–MS

A capillary electrophoresis inductively coupled plasma mass spectrometry method for separation of free cisplatin from liposome-encapsulated cisplatin and protein-bound cisplatin was developed. A liposomal formulation of cisplatin based on PEGylated liposomes was used as model drug formulation. The effect of human plasma matrix on the analysis of liposome-encapsulated cisplatin and intact cisplatin was studied. The presence of 1 % of dextran and 4 mM of sodium dodecyl sulfate in HEPES buffer was demonstrated to be effective in improving the separation of liposomes and cisplatin bound to proteins in plasma. A detection limit of 41 ng/mL of platinum and a precision of 2.1 % (for 10 μg/mL of cisplatin standard) were obtained. Simultaneous measurements of phosphorous and platinum allows the simultaneous monitoring of the liposomes, liposome-encapsulated cisplatin, free cisplatin and cisplatin bound to plasma constituents in plasma samples. It was demonstrated that this approach is suitable for studies of the stability of liposome formulations as leakage of active drug from the liposomes and subsequent binding to biomolecules in plasma can be monitored. This methodology has not been reported before and will improve characterization of liposomal drugs during drug development and in studies on kinetics.

Determination of lesinurad in rat plasma by a UHPLC–MS/MS assay

Lesinurad is an oral inhibitor of urate-anion exchanger transporter 1 and has been approved by the US Food and Drug Administration for combination therapy with a xanthine oxidase inhibitor for the treatment of hyperuricemia associated with refractory gout. In the present study, a sensitive and specific ultra high-performance liquid chromatography with tandem mass spectrometry assay was established and verified for the determination of lesinurad in rat plasma and was described in details for the first time. Chromatographic separation of lesinurad and diazepam (internal standard, IS) was performed on a Rapid Resolution HT C18 column (3.0 × 100 mm, 1.8 µm) using methanol–water (70:30, v/v) as the mobile phase at a flow rate of 0.3 mL/min. Lesinurad and IS were extracted from plasma by liquid–liquid extraction using ethyl acetate. The mass spectrometric detection was carried out using an electrospray ionization source in positive mode. Multiple reaction monitoring was used for quantification of the precursor to product ion at m/z 405.6 → 220.9 for lesinurad and m/z 285.1 → 192.8 for IS. The assay was well validated for selectivity, accuracy, precision, recovery, linearity, matrix effects, and stability. The verified method was applied to obtain the pharmacokinetic parameters and concentration–time profiles for lesinurad after oral/intravenous administration in rats. The study might provide an important reference and a necessary complement for the qualitative and quantitative evaluation of lesinurad.     

Quantification of clomiphene metabolite isomers in human plasma by rapid-resolution liquid chromatography–electrospray ionization–tandem mass spectrometry

Since the 1960s, clomiphene citrate is used for ovulation induction. Since nonresponse to clomiphene therapy is still not well understood, interindividual variability of clomiphene metabolism has been considered to be a plausible explanation. Therefore, a comprehensive, rapid, sensitive, and specific analytical method for the quantification of (E)- and (Z)-isomers of clomiphene and their putative N-desethyl, N,N-didesethyl, 4-hydroxy, and 4-hydroxy-N-desethyl metabolites, and the N-oxides in human plasma has been newly developed, using HPLC-tandem mass spectrometry and stable isotope-labeled internal standards. All standards other than the parent drug were synthesized in our laboratory. Following protein precipitation analytes were separated on a ZORBAX Eclipse plus C18 1.8 μm column with a gradient of 0.1% formic acid in water and 0.1% formic acid in acetonitrile and detected on a triple quadrupole mass spectrometer with positive electrospray ionization in the multiple reaction monitoring mode. Lower limit of quantification for metabolites ranged from 0.06 ng/mL for clomiphene-N-oxides to 0.3 ng/mL for (E)-N-desethylclomiphene. The assay was validated according to FDA guidelines. Plasma levels of clomiphene and its metabolites were measured in two women after single-dose treatment with clomiphene.     

The calculation of Cs and Rb conductivities in the region of liquid–plasma transition

The conductivity and thermal conductivity of Cs and Rb are calculated in the liquid phase and in the region between the plasma (gas) and the liquid states. The last area is located at the temperatures higher than the critical one, near the critical point. The Ziman formalism originated from the liquid metal theory was used for the calculations. The results of present calculations were compared with available experiments and calculations of other researchers. It was found that the liquid state formalism can be applied to expanded liquid Cs and Rb at densities higher than the critical one, but another type of models is necessary at lower densities.     

Determination of tandospirone in human plasma by a liquid chromatography–tandem mass spectrometry method

A rapid, sensitive, and selective liquid chromatography–tandem mass spectrometry method for the detection of tandospirone in human plasma is described. It was employed in a pharmacokinetic study. The analyte and internal standard diphenhydramine were extracted from plasma using liquid–liquid extraction, then separated on a Zorbax XDB C₁₈ column using a mobile phase of methanol–water–formic acid (80:20:0.5, v/v/v). The detection was performed with a tandem mass spectrometer equipped with an electrospray ionization source. Linearity was established in the concentration range of 10.0-5,000 pg/ml. The lower limit of quantification was 10.0 pg/ml. The intraday and interday relative standard deviation across three validation runs over the entire concentration range was less than 13%. Accuracy determined at three concentrations (25.0, 200, and 4,000 pg/ml for tandospirone) ranged from 94.4 to 102.1%. Each plasma sample was chromatographed within 3.4 min. The method proved to be highly selective and suitable for bioequivalence evaluation of different formulations containing tandospirone and clinical pharmacokinetic investigation of tandospirone.     

SPMMTE and Q-TOF–UPLC–MS for monitoring of atenolol and atorvastatin in human plasma using pentafluoro phenyl column

Iron nanocomposite adsorbent was prepared by green technology with 90% yield. The prepared iron nanocomposite adsorbent was used in solid-phase micromembrane tip extraction (SPMMTE) sample preparation technique. Analysis of atenolol and atorvastatin was performed in human plasma using SPMMTE and Q-TOF–UPLC–MS methods. New generation Acquity UPLC HSS penta fluoro phenyl (2.1?×?75?mm²; 1.8?µm) column was used with acetonitrile–0.1% formic acid in water (50:50 v/v) as mobile phase. The flow rate was 0.2?mL?min^?1 with electrospray mass detection. The limits of detection were 0.2 and 0.4?ng active mass for atenolol and atorvastatin, while the limits of quantification were 1.0 and 2.0?ng active mass, respectively. The values of the retention times were 3.224 and 3.907 for atorvastatin and atenolol. The values of the separation and resolution factors were 1.31 and 1.71, respectively. The peaks were sharp with base lined separation within 4.2?min. The developed SPMMTE and Q-TOF–UPLC–MS methods were reproducible, fast, precise, robust, rugged, and economic for the analyses of atenolol and atorvastatin in human plasma. The reported methods can be applied for monitoring of the reported drugs at trace level.     

Particle size characterization of titanium dioxide in sunscreen products using sedimentation field-flow fractionation–inductively coupled plasma–mass spectrometry

Sedimentation field-flow fractionation–inductively coupled plasma–mass spectrometry (SdFFF-ICP-MS) was successfully applied to investigate particle size distribution of titanium dioxide (TiO₂) in sunscreen samples after hexane extraction to remove organic components from the samples. Three brands of sunscreen products of various sun protection factor (SPF) value were used as samples. Different particle size distribution profiles were observed for sunscreen samples of various brands and SPF values; however, the particle size distributions of titanium dioxide in most sunscreen samples investigated in this work were larger than 100 nm. The titanium dioxide concentrations were higher for the products of higher SPF values. By comparing the results obtained from online SdFFF-ICP-MS and those from the off-line ICP-MS determination of titanium after acid digestion, ICP-MS was found to effectively atomize and ionize the titanium dioxide particle without the need for acid digestion of the samples. Therefore, the online coupling between SdFFF and ICP-MS could be effectively used to provide quantitative information of titanium dioxide concentrations across particle size distribution profiles.     

Doping control analysis of seven bioactive peptides in horse plasma by liquid chromatography–mass spectrometry

In recent years, there has been an ongoing focus for both human and equine doping control laboratories on developing detection methods to control the misuse of peptide therapeutics. Immunoaffinity purification is a common extraction method to isolate peptides from biological matrices and obtain sufficient detectability in subsequent instrumental analysis. However, monoclonal or polyclonal antibodies for immunoaffinity purification may not be commercially available, and even if available, such antibodies are usually very costly. In our study, a simple mixed-mode anion exchange solid-phase extraction cartridge was employed for the extraction of seven target peptides (GHRP-1, GHRP-2, GHRP-6, ipamorelin, hexarelin, CJC-1295, and N-acetylated LKKTETQ (active ingredient of TB-500)) and their in vitro metabolites from horse plasma. The final extract was subject to ultra-high-performance liquid chromatographic separation and analysed with a hybrid high-resolution mass spectrometer. The limits of detection for all seven peptides were estimated to be less than 50 pg/mL. Method validation was performed with respect to specificity, precision, and recovery. The applicability of this multi-analyte method was demonstrated by the detection of N-acetylated LKKTETQ and its metabolite N-acetylated LK from plasma samples obtained after subcutaneous administration of TB-500 (10 mg N-acetylated LKKTETQ) to two thoroughbred geldings. This method could easily be modified to cover more bioactive peptides, such as dermorphin, β-casomorphin, and desmopressin. With the use of high-resolution mass spectrometry, the full-scan data acquired can also be re-processed retrospectively to search for peptides and their metabolites that have not been targeted at the time of analysis. To our knowledge, this is the first identification of in vitro metabolites of all the studied peptides other than TB-500 in horses.

Simultaneous and sensitive LC–MS/MS determination of tetrahydrocannabinol and metabolites in human plasma

Cannabis is not only a widely used illicit drug but also a substance which can be used in pharmacological therapy because of its analgesic, antiemetic, and antispasmodic properties. A very rapid and sensitive method for determination of ?⁹-tetrahydrocannabinol (THC), the principal active component of cannabis, and two of its phase I metabolites in plasma has been developed and validated. After solid-phase extraction of plasma (0.2 mL), the clean extracts were analyzed by tandem mass spectrometry after a 5-min liquid chromatographic separation. The linear calibration ranges were from 0.05 to 30 ng?mL^?1 for THC and 11-nor-?⁹-carboxy-tetrahydrocannabinol (THC-COOH) and from 0.2 to 30 ng?mL^?1 for ?⁹-(11-OH)-tetrahydrocannabinol (11-OH-THC). Imprecision and inaccuracy were always below 7 and 12 % (expressed as relative standard deviation and relative error), respectively. The method has been successfully applied to determination of the three analytes in plasma obtained from healthy volunteers after oral administration of 20 mg dronabinol.     

Simulation of droplet heating and desolvation in inductively coupled plasma—part II: coalescence in the plasma

A numerical model is developed to consider for the first time droplet coalescence along with transport, heating and desolvation in an argon inductively coupled plasma (Ar ICP). The direct simulation Monte Carlo (DSMC) method and the Ashgriz–Poo model are used, respectively, to compute droplet–droplet interactions and to determine the outcome of droplet collisions. Molecular dynamics (MD) simulations support the use of the Ashgriz–Poo coalescence model for small droplet coalescence. Simulations predict spatial maps of droplet number and mass densities within an Ar ICP for a conventional nebulizer-spray chamber arrangement, a direct injection high efficiency nebulizer (DIHEN), and a large bore DIHEN (LB-DIHEN). The primary findings are: (1) even at 1500 W, the collisions of the droplets in the plasma lead primarily to coalescence, particularly for direct aerosol injection; (2) the importance of coalescence in a spray simulation exhibits a complex relationship with the gas temperature and droplet size; (3) DIHEN droplets penetrate further into the Ar ICP when coalescence is considered; and (4) droplets from a spray chamber or the LB-DIHEN coalesce less frequently than those from a DIHEN. The implications of these predictions in spectrochemical analysis in ICP spectrometry are discussed.     

Validated HPLC–MS–MS method for simultaneous determination of atorvastatin and 2-hydroxyatorvastatin in human plasma—pharmacokinetic study

Cholesterol-reducing statin drugs are the most frequently prescribed agents for reducing morbidity and mortality related to coronary heart disease. In this publication a validated, highly sensitive, and selective isocratic HPLC method is reported for quantitative determination of the major statin drug atorvastatin (ATV) and its metabolite 2-hydroxyatorvastatin (HATV). Detection was performed with an electrospray ionization triple-quadrupole mass spectrometer equipped with an ESI interface operating in positive-ionization mode. Multiple reaction monitoring (MRM) was used for MS–MS detection. The calibration plot was linear in the concentration range 0.10–40.00 ng mL⁻¹ for both ATV and HATV. Inter-day and intra-day precision and accuracy of the proposed method were characterized by measurement of relative standard deviation (RSD) and percentage deviation, respectively; both were less than 8% for both analytes. The limit of quantitation was 0.02 ng mL⁻¹ for ATV and 0.07 ng mL⁻¹ for HATV. The method was used for pharmacokinetic study of ATV and HATV. Pharmacokinetic data for all analytes are also reported.     

Study on the excitation mechanism 1. Non-Boltzmann–Saha distributions in the inductively coupled plasma

This work has further shown that the collisional–radiative multi-level model for the analyte atom and ion could be approximated by the step-wise series model. The non-Boltzmann and non-Saha factors of Ca for 48 levels corresponding to radiative decay, radiative recombination, Penning ionization and absorption processes, respectively, as well as to their mutual processes occurring at the axial channel of inductively coupled plasma and at an observation height of 15 mm above the load coil, were calculated. It was found that the high level relative to low level is over populated.     

High-performance liquid chromatographic determination of diltiazem in human plasma after solid-phase and liquid–liquid extraction

A selective, sensitive, and accurate high-performance liquid chromatographic method for determination of diltiazem in plasma samples has been developed and validated. The effects of mobile phase composition, buffer concentration, mobile phase pH, and concentration of organic modifiers on retention of diltiazem and internal standard were investigated. Solid-phase and liquid–liquid extraction were examined and proposed for isolation of the drug and elimination of endogenous plasma interferences. A 5 m Lichrocart Lichrospher 60 RP-select B chromatographic column was used; the mobile phase was acetonitrile–0.025 mol L^–1 KH₂PO₄ (pH 5.5), 35:65 ( v / v) at a flow-rate of 1.5 mL min^–1. The detection wavelength was 215 nm. The calibration plots were linear in the concentration range 20.0–500.0 ng mL^–1. The method has been implemented to monitor diltiazem levels in patient samples.     

Rapid and simple determination of selenium in blood serum by inductively coupled plasma–mass spectrometry (ICP–MS)

An inductively coupled plasma mass spectrometer (ICP-MS) with a rapid sample-preparative procedure was used for the determination of selenium in blood serum. Blood serum was prepared by dilution in an acidic solution consisting of nitric acid (1%), X-triton (0.1%) and 1-butanol (0.8%). A calibration curve was established for 1-40 microg mL(-1) (r(2)>0.99). The limit of detection was 0.5 microg mL(-1). Repeatability and intermediate precision were satisfactory with relative standard deviations (RSD) of 2.0% and 3.2%, respectively. This method was easily applied to reference materials with satisfactory accuracy. Good correlation (r(2)=0.96) was observed between ICP-MS and atomic absorption spectrometry (AAS) for the determination of (82)Se in blood serum from 23 patients. These results suggest that the sample preparative procedure coupled with ICP-MS can be used for the routine determination of (82)Se in human blood serum.