Development of an effective extraction process for coenzyme Q10 from Artemia

A method for extracting coenzyme Q₁₀ (CoQ₁₀) from Artemia was developed. 1 g of fresh Artemia was incubated with 75 % acetic acid at (30 ± 2)°C for 24 h, followed by three consecutive extractions with a mixture of 5 mL of hexane and 5 mL of ethanol, then analysis by a validated high-performance liquid chromatography with a diode-array detector. The calibration curve for CoQ₁₀ was linear in a range of 1–50 μg mL^?1. The limits of detection and quantification were 0.3 μg mL^?1 and 1.1 μg mL^?1, respectively. Mean recoveries were 94–100 % with a high precision of below 10 %. The method developed was found to be simple, efficient and the time required for releasing CoQ₁₀ from Artemia was short. The method provides not only low energy consumption but is also practical for industrial applications.     

Quantitative determination of 8-hydroxy-2′-deoxyguanosine as a biomarker of oxidative stress in thalassemic patients using HPLC with an electrochemical detector

A simple and robust HPLC method with electrochemical detection was developed for the quantitative determination of 8-hydroxy-2′-deoxyguanosine (8-OHdG), a DNA damage product excreted in urine. Sample cleanup was carried out using solid-phase extraction (SPE) prior to chromatographic separation. 8-OHdG was well separated on an Eclipse XDB®-C18 column (150 × 4.6 mm i.d., 5 μm) with an Eclipse XDB®-C18 guard column (12 × 4.6 mm i.d., 5 μm). Two mobile phases containing methanol and 10 mM sodium formate (pH 4.5) at a ratio of 10: 90 and 50: 50 v/v, respectively, were used. The retention time of 8-OHdG was 9.8 ± 0.5 min. The recovery of 8-OHdG was found to be 97.2 ± 3.3% (n = 6). Intraday and interday precisions of the method were 4.0 ± 2.9% (n = 6) and 6.6 ± 1.7% (n = 6), respectively. The detection limit was 5 ng/mL. Preliminary investigation showed that the mean value of 8-OHdG, normalized with the amount of creatinine in the sample, from the thalassemic group was significantly higher than that from healthy subjects (211 ± 214 ng/mg creatinine vs. 31.4 ± 32.2 ng/mg creatinine, respectively), indicating oxidative stress.     

Membraneless vaporization unit for direct analysis of solid sample

A new apparatus, called ‘membraneless vaporization’ (MBL-VP) unit was designed and developed for direct analysis of solid samples. Solid analyte was converted into a gaseous form which then reacts with an indicator reagent. Change in absorbance was used to quantitate the analyte. Stirring with a magnetic bar was employed to facilitate the evaporation of the gas. Unlike the pervaporation technique, hydrophobic membrane was not required for this MBL-VP technique.Application of the membraneless technique for direct determination of calcium carbonate in calcium supplements, has shown to be very precise (R.S.D. = 2.5% for 0.16 mmol CO₃²⁻), with detection limit of 0.5 mg CaCO₃. Results by this method agreed well with flame atomic absorption spectrometric method. Sample throughput was 20 samples h⁻¹.     

Solidification of floating organic droplet microextraction for determination of seven insecticides in fruit juice,vegetables and agricultural runoff using gas chromatography with flame ionization and mass spectrometry detection

Liquid microextraction employing solidification of the floating organic droplet, with vortexing and heating to optimize extraction efficiency, was developed for the determination of seven insecticides in fruit juice, vegetables, and agricultural runoff water. The extracts were analyzed by gas chromatography with both flame ionization and mass spectrometry detection for the determination of chlorpyrifos, prothiofos, profenofos, ethion, λ‐cyhalothrin, permethrin, and cypermethrin, respectively. Using 20 μL of 1‐undecanol in 10 mL of aqueous solution containing 1% w/v sodium chloride provided preconcentration factor of 500. The enrichment factor of the analytes was in the range of 355 to 509 with extraction recovery >71%. The linearity ranges were 4–200 μg/kg for gas chromatography with flame ionization detection and 1–100 μg/kg for gas chromatography with mass spectrometry, with limits of detection ranging from 0.04 to 1.2 μg/kg, which are lower than the international maximum residue limits for vegetables and fruit juice. Intra‐day and inter‐day precisions are less than 5.4 and 7.0% relative standard deviation, respectively. The method was successfully applied to the determination of the seven insecticides in samples of vegetables, fruit juice and agricultural runoff, with recoveries ranging from 61.7 to 120.8%. The extraction method is simple, efficient and environmentally friendly.     

Characterization of biodiesel and biodiesel blends using comprehensive two-dimensional gas chromatography

In this work the development of a comprehensive 2-D GC flame ionization detection (GC x GC FID) method for biodiesel fuels is reported. This method is used for the analysis of fatty acid methyl esters (FAMEs) in both biodiesel (B100) and biodiesel blend (B5) samples. The separation of FAME was based on component boiling point in the first dimension and polarity in the second dimension by using a BPX5/BP20 column set to provide a measure of 'orthogonality' in the 2-D space. Here the columns are coupled with a cryogenic modulator operating in a novel temperature programmed mode (T(M)) whereby the cryotrap is progressively incremented in temperature as the oven temperature is increased. The final method employs eight cryotrap temperature settings. The developed GC x GC method is able to successfully characterize and identify both B100 and B5 FAME components, which are produced from a variety of vegetable oils, animal fats and waste cooking oils, with high precision. The method is capable of analysing FAME with carbon numbers C4-C24, and is particularly suitable to characterize various types of biodiesel, making it possible to differentiate the origin and type of FAME used in the biodiesel samples.     

Monolithic and packed particle materials for in-line pre-concentration in capillary electrophoresis for 4-hydroxy-3-methoxy-methamphetamine and terbutaline

In-line solid-phase extraction (SPE) for capillary electrophoresis (CE) was investigated using a synthesized monolith and a commercial packing material. Terbutaline (TER) and 4-hydroxy-3-methoxy-methamphetamine (HMMA) with benzyl alcohol as the electroosmotic flow marker were employed as model compounds. Two types of methacrylate-based monoliths, namely methacrylic acid-ethylene dimethacrylate and butylmethacrylate-ethylene dimethacrylate were examined. Preliminary results indicated that a non-aqueous separating medium is more suitable for these methacrylate monoliths than a purely aqueous medium (non-reproducible elution). However, coupling of the methacrylic acid-ethylene dimethacrylate with non-aqueous capillary electrophoresis could not provide good precision for the three model compounds. A packed-silica C18 SPE was also adopted by simply packing the C18 particles in situ in the separation capillary. Using an aqueous running buffer (10 mM phosphate buffer (PPB), pH 7), acceptable precision could be obtained with this type of SPE material. With a 10 min loading time and 20 min total analysis time, the pre-concentration factors were 333 and 1000 for TER and HMMA, respectively. The %RSD were less than 4.5 and 0.3 for the peak areas and migration times, respectively, for both HMMA and TER (n=20).     

Separation of alpha-, beta-, gamma-, delta-tocopherols and alpha-tocopherol acetate on a pentaerythritol diacrylate monostearate-ethylene dimethacrylate monolith by capillary electrochromatography

This work reports the first use of a monolith with method development for the separation of tocopherol (TOH) compounds by CEC with UV detection. A pentaerythritol diacrylate monostearate-ethylene dimethacrylate (PEDAS-EDMA) monolithic column has been investigated for an optimised condition to separate alpha-, beta-, gamma- and delta-TOHs, and alpha-tocopherol acetate (TAc). The PEDAS-EDMA monolith showed a remarkably good selectivity for separation of the TOH isomers including the beta- and gamma-isomers which are not easily separated by standard C8 or C18 particle-packed columns. Retention studies indicated that an RP mechanism was involved in the separation on the PEDAS-EDMA column, but polar interactions with the underlying ester and hydroxyl groups enhanced the separation of the problematic beta- and gamma-isomers. Separation of all the compounds was achieved within 25 min using 3:10:87 v/v/v 100 mM Tris buffer (pH 9.3)/methanol/ACN as the mobile phase. The method was successfully applied to a pharmaceutical sample with recoveries from 93 to 99%. Intraday and interday precisions (%RSD) for peak area and retention time were less than 2.3. LODs for all four TOHs and TAc were below 1 ppm.     

Comprehensive two-dimensional gas chromatography improves separation and identification of anabolic agents in doping control

The application of comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS) for the analysis of six anabolic agents (AAs) in doping control is investigated in this work. A non-polar–polar column configuration with 0.2 μm film thickness (d_f) second dimension (²D) column was employed, offering much better spread of the components on ²D when compared to the alternative 0.1 μm d_f²D column. The proposed method was tested on the “key” AA that the World Anti-Doping Agency (WADA) had listed at the low ng mL⁻¹ levels (clenbuterol, 19-norandrosterone, epimethendiol, 17α-methyl-5α-androstane-3α,17β-diol, 17α-methyl-5β-androstane-3α,17β-diol and 3′-OH-stanozolol). The compounds were spiked in a blank urine extract obtained by solid-phase extraction, hydrolysis and liquid–liquid extraction; prior to analysis they were converted to the corresponding trimethylsilyl (TMS) derivatives. The limit of detection (LOD) was below or equal to the minimum required performance limit (MRPL) of 2 ng mL⁻¹ defined by WADA, and the correlation coefficient was in the range from 0.995 to 0.999. The method allows choosing an ion from the full mass spectra which shows the least interference from the matrix and/or the best sensitivity; this can only be done if full scan mass spectral data are available. The advantage of GC × GC over classical one-dimensional GC (1D GC), in terms of separation efficiency and sensitivity, is demonstrated on a positive urine control sample at a concentration of 5 ng mL⁻¹. The obtained similarity to the in-house created TOFMS spectra library at this level of concentration was in the range from 822 to 932 (on the scale from 0 to 999). Since full mass spectral information are recorded, the method allows the retro-search of non-target compounds or new “designer steroids”, which cannot be detected with established GC–MS methods that use selected ion monitoring (SIM) mode.     

Evaluation of World Anti-Doping Agency criteria for anabolic agent analysis by using comprehensive two-dimensional gas chromatography–mass spectrometry

This work presents the validation study of the comprehensive two-dimensional gas chromatography (GC×GC)–time-of-flight mass spectrometry method performance in the analysis of the key World Anti-Doping Agency (WADA) anabolic agents in doping control. The relative abundance ratio, retention time, identification and other method performance criteria have been tested in the GC×GC format to confirm that they comply with those set by WADA. Furthermore, tens of other components were identified with an average similarity of >920 (on the 0–999 scale), including 10 other endogenous sterols, and full mass spectra of 5,000+ compounds were retained. The testosterone/epitestosterone ratio was obtained from the same run. A new dimension in doping analysis has been implemented by addressing separation improvement. Instead of increasing the method sensitivity, which is accompanied by making the detector increasingly “blind” to the matrix (as represented by selected ion monitoring mode, high-resolution mass spectrometry (MS) and tandem MS), the method capabilities have been improved by adding a new “separation” dimension while retaining full mass spectral scan information. Apart from the requirement for the mass spectral domain that a minimum of three diagnostic ions with relative abundance of 5% or higher in the MS spectra, all other WADA criteria are satisfied by GC×GC operation. The minimum of three diagnostic ions arises from the need to add some degree of specificity to the acquired mass spectrometry data; however, under the proposed full MS scan method, the high MS similarity to the reference compounds offers more than the required three diagnostic ions for an unambiguous identification. This should be viewed as an extension of the present criteria to a full-scan MS method.     

A membraneless gas diffusion unit: design and its application to determination of ethanol in liquors by spectrophotometric flow injection

This work presents new design of a gas diffusion unit, called ‘membraneless gas diffusion (MGD) unit’, which, unlike a conventional gas diffusion (GD) unit, allows selective detection of volatile compounds to be made without the need of a hydrophobic membrane. A flow injection method was developed employing the MGD unit to determine ethanol in alcoholic drinks based on the reduction of dichromate by ethanol vapor. Results clearly demonstrated that the MGD unit was suitable for determination of ethanol in beer, wine and distilled liquors. Detection limit (3S/N) of MGD unit was lower than the GD unit (GD: 0.68%, v/v; MGD: 0.27%, v/v). The MGD design makes the system more sensitive as mass transfer is more efficient than that of GD and thus, MGD can perfectly replace membrane-based designs.