High-Performance Liquid Chromatographic Method for Determination and Pharmacokinetic Study of Chlorogenic Acid in the Plasma of Rats After Administration of the Chinese Medicinal Preparation Luying Decoction

A simple and sensitive high-performance liquid chromatographic method has been developed for determination of chlorogenic acid in rat plasma. Chlorogenic acid was extracted from plasma samples with methanol. HPLC analysis of the extracts was performed on a C₁₈ column (250 mm × 4.6 mm i.d., 5 µm particles). The mobile phase was acetonitrile −1% formic acid (9:91, v/v). The calibration plot was linear over the range 0.0420–2.10 µg mL⁻¹ and the lower limit of quantification was 0.0420 µg mL⁻¹. The method was reproducible and reliable with intra-day precision better than 8.2%, inter-day precision better than 9.1%, accuracy within ±8.3%, and mean extraction recovery above 84.4%. The validated method was successfully applied to pharmacokinetic studies of chlorogenic acid in rat plasma after administration of Luying decoction.     

Determination of Lead, Chromium, Manganese and Zinc in Slurries of Botanical and Biological Samples by Electrothermal Atomic Absorption Spectrometry Using Tungsten-Containing Chemical Modifiers

Lead, Cr, Mn and Zn in slurries of botanic and biological samples were determined by electrothermal atomic absorption spectrometry (ETAAS) using W, Ir, NH₄H₂PO₄, W and NH₄H₂PO₄, Ir and NH₄H₂PO₄, W and Ir, and W + Ir + NH₄H₂PO₄ chemical modifiers in an 0.2% (v/v) Triton X-100 plus 0.2% (v/v) nitric acid mixture. Zeeman effect background correction was performed and platforms inserted into graphite tubes were used. Comprehensive comparative studies were carried out with respect to pyrolysis and atomization temperatures, atomization and background absorption profiles, characteristic masses, detection limits and accuracy of the determinations in the presence and absence of modifiers. The mixture of W + Ir + NH₄H₂PO₄ was found to be preferable for the determination of Pb, Cr, Mn and Zn in slurry samples. The pyrolysis temperatures of the analytes were increased up to 1250 °C for Pb, 1000 °C for Zn, 1400 °C for Cr and Mn by using W + Ir + NH₄H₂PO₄ with an 0.2% (v/v) Triton X-100 plus 0.2% (v/v) nitric acid mixture used as diluent solution. The optimum masses of the mixed modifier components were found to be 20 µg W + 4 µg Ir + 50 µg NH₄H₂PO₄. The characteristic masses of Pb, Cr, Mn and Zn obtained are 16.3, 5.6, 0.1 and 1.1 pg, respectively. The detection limits of Pb, Cr, Mn and Zn based on integrated absorbance for 0.5% (m v⁻¹) slurries were found to be 0.14, 0.06, 0.02 and 0.01 µg g⁻¹, respectively. The slurries of botanic and biological certified and standard reference materials were analyzed with and without the modifiers. Depending on the sample type, the percent recoveries increased from 63 up to 104% for analytes when using the proposed modifier mixture.     

A Comparative Study of Homemade C18 and Commercial C18 Sorbents for Preconcentration of Lead by Minicolumn Solid Phase Extraction

A comparative study of commercial C₁₈ chemically immobilized on silica and homemade C₁₈, as sorbents for Pb complexed with O,O-diethyl-dithiophosphate (DDTP) in a flow injection preconcentration system is reported. The homemade C₁₈ sorbent was obtained by sorption of poly(methyloctadecylsiloxane) (PMODS) on the silica support followed by immobilization using thermal treatment. The method follows the concept of green chemistry, since there are no toxic residues after synthesis. The complexed Pb was formed in 1.0molL^–1 HCl medium and retained on the minicolumn filled with the sorbents. The elution was carried out using ethanol, and the richest 210µL fraction was collected and analyzed by flame atomic absorption spectrometry. Chemical and flow variables were optimized for each sorbent. The results demonstrated that the performance of the proposed homemade C₁₈ sorbent for preconcentration of Pb complexed with DDTP is very similar to commercial C₁₈ chemically bonded on silica. By processing 25mL, the enrichment factors were 129 and 125 for commercial C₁₈ and homemade C₁₈, respectively. The limit of detection for commercial and homemade C₁₈ was 0.2µgL^–1 and 0.6µgL^–1, respectively. The relative standard deviation (RSD) was lower than 1.2% for both sorbents for a Pb concentration of 100µgL^–1. The method was also applied successfully to the analysis of water samples, and the accuracy was tested by recovery measurements on spiked samples and biological reference material.     

Simultaneous Determination of Cefepime and the Quinolones Garenoxacin, Moxifloxacin and Levofloxacin in Human Urine by HPLC-UV

A liquid chromatographic method with a C₁₈ column and acetonitrile/0.1 M phosphoric acid/ sodium hydroxide buffer (pH 3.0)/0.01 M n-octylamine (pH 3.0) as mobile phase in gradient mode has been developed and optimised for the simultaneous determination of the cephalosporin cefepime and the quinolones garenoxacin, levofloxacin and moxifloxacin. Identification and quantification was carried out with a diode-array UV detector, with working wavelengths of 256 nm for cefepime, 292 nm for levofloxacin, 294 nm for moxifloxacin and 282 nm for garenoxacin. The mobile flow-rate and sample volume injected were 1 mL min⁻¹ and 20 µL, respectively. The retention times and detection limits for each antibiotic were 4.9 min and 1.9 µg mL⁻¹ for cefepime, 7.5 min and 2.2 µg mL⁻¹ for levofloxacin, 8.9 min and 2.7 µg mL⁻¹ for moxifloxacin and 10.7 min and 1.8 µg mL⁻¹ for garenoxacin, respectively. The method was applied to the determination of the four molecules in spiked samples of human urine.     

Determination of some selected polycyclic aromatic hydrocarbons in environmental samples by high-performance liquid chromatography with fluorescence detection

Summary Analytical methods for the determination in environmental samples, of some selected Polycyclic Aromatic Hydrocarbons (PAH's), which are included on the EPA Priority Pollutant list, have been developed and evaluated. The methodology involves the extraction of PAH's from water samples by solvent extraction with dichloromethane. Solid samples were ultrasonically extracted with acetone/hexane and the extract was cleaned up on a silica gel/alumina column. The concentrated and cleaned up extracts were analysed by HPLC on a polymeric C₁₈ column using a gradient of acetonitrile/water as the mobile phase and fluorescence detection. Typical detection limits lie in the range of 1–30 ng ml^–1 of the analytes, but after sample pretreatment detection limits of 10–300 ng l^–1 were obtained. The extraction, clean-up and HPLC methodology was applied to the determination of selected PAH's in coal washings samples and the method was validated by the quantification of PAH's in a natural contaminated and a spiked sediment.     

Sensitive Determination of DNA by Resonance Light Scattering with Pentamethoxyl Red

A novel sensitive method for the determination of nucleic acid (DNA) using the resonance light scattering (RLS) spectra of pentamethoxyl red has been developed. It is based on the effects on the resonance light scattering of Pentamethoxyl Red. The effective factors and the optimum conditions were studied, and the enhanced intensity of RLS is in proportion to the concentration of nucleic acids in the range of 0–2.54 µg mL⁻¹ for ct-DNA, 0–4.54 µg mL⁻¹ for hs-DNA. The limits of detection are 1.1 and 2.1 ng mL⁻¹, respectively. Most foreign substances do not interfere in the determination, and the method has good selectivity and high sensitivity. It has been applied to the determination of DNA in synthetic samples and in real samples with satisfactory results.     

Simultaneous determination of gibberellic acid, indole-3-acetic acid and abscisic acid in wheat extracts by solid-phase extraction and liquid chromatography-electrospray tandem mass spectrometry

A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed for simultaneous determination of three representative phytohormones in plant samples: gibberellic acid (GA₃), indole-3-acetic acid (IAA) and abscisic acid (ABA). A solid-phase extraction (SPE) pretreatment method was used to concentrate and purify the three phytohormones of different groups from plant samples. The separation was carried out on a C₁₈ reversed-phase column, using methanol/water containing 0.2% formic acid (50:50, v/v) as the isocratic mobile phase at the flow-rate of 1.0 mL min⁻¹, and the three phytohormones were eluted within 7 min. A linear ion trap mass spectrometer equipped with electrospray ionization source was operated in negative ion mode. Selective reaction monitoring (SRM) was employed for quantitative measurement. The SRM transitions monitored were as 345 → 239, 301 for GA₃, 174 → 130 for IAA and 263 → 153, 219 for ABA. Good linearities were found within the ranges of 5–200 μg mL⁻¹ for IAA and 0.005–10 μg mL⁻¹ for ABA and GA₃. Their detection limits based on a signal-to-noise ratio of three were 0.005 μg mL⁻¹, 2.2 μg mL⁻¹ and 0.003 μg mL⁻¹ for GA₃, IAA and ABA, respectively. Good recoveries from 95.5% to 102.4% for the three phytohormones were obtained. The results demonstrated that the SPE-LC–MS/MS method developed is highly effective for analyzing trace amounts of the three phytohormones in plant samples.     

Preparation of a Novel Fluorescence Probe of Terbium Composite Nanoparticles and its Application in the Determination of Ascorbic Acid

Novel Tb/acetylacetone (acac)/poly (acrylic acid) (PAA) composite nanoparticles were successfully synthesized using the ultrasonic method. The nanoparticles are water soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. They were used as fluorescence probes in the determination of ascorbic acid (Vc) based on the fluorescence quenching of nanoparticles in the presence of ascorbic acid. The method is based on the complexation between ascorbic acid and nanoparticles in the absence of the oxidant. The influence of different buffers and concentration of the nanoparticles on the relative fluorescence intensity was tested, and Tris-HCl buffer solution proved to be the best. Under the optimum conditions, a liner calibration graph was obtained over the Vc concentration range of 0.05–10 µg mL⁻1. The corresponding detection limit is 0.008 µg mL⁻¹ and the relative standard deviation is 1.4% for 0.5 µg mL⁻¹ (n=7). The method proved to be simple, rapid, and specific, and the recovery and relative standard deviation are very satisfactory. A mechanism explaining the process is also presented.     

Rapid and sensitive method for the determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with UV–Vis detection

A high-performance liquid chromatography (HPLC) method for the determination of acetaldehyde in fuel ethanol was developed. Acetaldehyde was derivatized with 0.900 mL 2,4-dinitrophenylhydrazine (DNPHi) reagent and 50 L phosphoric acid 1 mol L^–1 at a controlled room temperature of 15°C for 20 min. The separation of acetaldehyde-DNPH (ADNPH) was carried out on a Shimadzu Shim-pack C₁₈ column, using methanol/LiCl_(aq) 1.0 mM (80/20, v/v) as a mobile phase under isocratic elution and UV–Vis detection at 365 nm. The standard curve of ADNPH was linear in the range 3–300 mg L^–1 per injection (20 L) and the limit of detection (LOD) for acetaldehyde was 2.03 g L^–1, with a correlation coefficient greater than 0.999 and a precision (relative standard deviation, RSD) of 5.6% (n=5). Recovery studies were performed by fortifying fuel samples with acetaldehyde at various concentrations and the results were in the range 98.7–102%, with a coefficient of variation (CV) from 0.2% to 7.2%. Several fuel samples collected from various gas stations were analyzed and the method was successfully applied to the analysis of acetaldehyde in fuel ethanol samples.     

Determination of sulfonylurea herbicides in water using solid-phase extraction followed by liquid chromatography with electrospray ion trap mass spectrometry

A method has been developed for confirmation and quantitation of ten sulfonylurea herbicides (nicosufuron, thifensulfuron-methyl, metsulfuron-methyl, sulfometuron-methyl, chlorsulfuron, ethametsulfuron-methyl, tribenuron, bensulfuron-methyl, pyrazosulfuron-ethyl and chlorimuron-ethyl) in water samples. Herbicides were extracted from water by off-line solid-phase extraction (SPE). Different types of absorbents were evaluated: silica-based ODS-C₁₈ and two polymeric sorbents, Cleanert HXN and Oasis HLB. Analyte determination and quantitation was performed by liquid chromatography with electrospray mass spectrometry (LC-ESI-MS) instrumentation, equipped with ion trap mass filter. Confirmatory analysis was carried out by LC/MS/MS. MS data acquisition was performed by a single or two-ion extracted ion monitoring program. The ten herbicides were measured in fortified tap water. Average recoveries of the nine analytes (except for tribenuron) from water samples were in the range of 77–109%, and the RSD ranged from 0.3 to 14.5%. The limit of detections (LODs) varied from 6 to 34.8 ng/L.     

Bimodal normal distribution model for binding of trivalent europium by soil fulvic acid

Complexation of trivalent europium by a well characterized soil fulvic acid was investigated by equilibrium dialysis titration method ([FA]=24 mg·dm^–3, [Eu] _t =9.0·10^–7–3.5·10^–6 mol·dm^–3, pH 6.0). The concentrations of the fulvate bound and free europium were measured radiometrically using¹⁵²Eu as a tracer. The experimental results were evaluated using a bimodal normal distribution model and a plot with two overlapping normal distributions was obtained which gave two means logK (µ_I=7.0, _I=1.1; µ_II=4.9, _II=0.5) values for binding of europium by two classes of sites in fulvic acid. A multiligand model was assumed for fulvic acid, based upon the Eu(III) luminescence studies (⁷F₀⁵D₀ excitation) on many organic acids as model ligands.     

In-field determination of nanomolar nitrite in seawater using a sequential injection technique combined with solid phase enrichment and colorimetric detection

A novel sequential injection method for the determination of nitrite at nanomolar level in seawater samples has been developed. The pink azo compound was formed based on the Griess reaction and quantitatively adsorbed onto a Sep-Pak C18 cartridge. The enriched azo compound was rinsed with water and ethanol (28%, v/v) in turn, and then eluted with an eluent containing 26.6% (v/v) ethanol and 0.108 mol L⁻¹ H₂SO₄. Finally the azo compound was measured using a spectrophotometer at 543 nm. Under the optimized conditions, the linear calibration ranges were 0.71–42.9 nmol L⁻¹ for a 150-mL sample and 35.7–429 nmol L⁻¹ for a 15-mL sample. The relative standard deviation of 8 measurements was 1.44% for 14.3 nmol L⁻¹ nitrite. For the 150 mL sample, the detection limit was estimated to be 0.1 nmol L⁻¹. The throughput of the method was about 4 samples per hour. The proposed method has been successfully applied to the in-field determination of nanomolar concentrations of nitrite in seawater.     

Sorption-desorption of radiocesium on various sorbents in presence of humic acid

In general, the amount of radiocesium sorbed by the five sorbents with 0.01 mol·dm^–3 NaCl was in order zeolite > NiFeCN–SiO₂ > montmorillonite > aerogel > silica gel. Addition of humic acid solution to the sorbents depressed the sorption of cesium by all sorbents, except for NiFeCN–SiO₂ was not seen, with the greatest effect showing to the aerogel. The presence of humic acid resulted in an enhanced desorption of cesium from zeolite, NiFeCN–SiO₂ and to a lesser extent from montmorillonite and silica gel. The order of cesium retention following desorption for both sorbent and sorbent/humic-acid mixtures was zeolit > NiFeCN–SiO₂ > montmorillonite > silica gel. The presence of humic acid resulted in decreasing of distribution coefficient values for both sorption and desorption processes.     

Direct acetylation followed by solid-phase disk extraction and GC-ITDMS for the determination of trace phenols in water

Summary A rapid, accurate and sensitive method is described for the analysis of phenolic compounds, including phenol, alkylphenols, halogenated phenols and nitrophenols in tap, ground and river water samples. The method consists in direct acetylation of the aqueous phenols with acetic anhydride, extraction of the phenol acetates with a C₁₈ disk and analysis by gas chromatography with an ion-trap detector mass spectrometer. Using this method, the sample preparation time was approximately 1.5 h for six 1-L water samples, and recoveries for most of the phenolic compounds studied were more than 80% at concentration levels of 0.1 and 1.0g L^–1. The detection limits were in the range 2 to 15 ng L^–1 for phenol, alkylphenols and halogenated phenols, and 25 to 50 ng L^–1 for nitrophenols.     

Application of solid-phase extraction for determination of phenolic compounds in barrique wines

A fast, selective and sensitive chromatographic method has been developed for determination of gallic, protocatechuic, p-hydroxybenzoic, vanillic, caffeic, syringic, p-coumaric, benzoic, ferulic, sinapic, cinnamic, and ellagic acids and p-hydroxybenzaldehyde, vanillin, syringaldehyde, 2-furfural, 5-methylfurfural, and 5-methoxyfurfural. The compounds from untreated wine samples were pre-concentrated and cleaned using solid-phase extraction on RP-105 polymeric sorbent. The cartridge was conditioned with methanol and water. Co-extracted ballast substances were rinsed from the sorbent with 0.1 mol L^–1 hydrochloric acid–methanol, 1:4 (v/v). Retained phenolic compounds were selectively eluted with diethyl ether. A linear mobile phase gradient containing 0.3% acetic acid and methanol was used for final baseline chromatographic separation on a Hypersil BDS C18 column. Limits of detection (LOD=3s_bl) in the range 5.2 to 181.2 g L^–1, resolution (R) better than 1.7, and repeatability of 2.7–5.1% (RSD for real samples) were achieved. The method was applied for quantification of individual phenolic compounds in barrique wines.     

Solid phase extraction for sample preparation in trace analysis of ionogenic compounds by capillary isotachophoresis

Various sorbents recommended for solid phase extraction (SPE) in sample preparation procedures were studied for use in combination with capillary isotachophoresis (ITP). They were very efficient in achieving trace concentration levels (low ppb, i.e., low parts per 10⁹) for different types of ITP analytes present in environmental and biological matrices. A macroporous carbon sorbent was convenient for sample preparation in ITP analysis of short chain fatty acids (C₄–C₉) in drinking water. Chelating sorbents based on hydroxyalkyl methacrylate matrix with salicylate, thioglycolate and 8-hydroxyquinolinate functionalities were found to be very suitable for preconcentration of heavy metals with an inherent sample clean-up. An octadecyl-bonded silica sorbent enabled in ITP a photometric detection of -aminobutyrate (labeled with a 2,4,6-trinitrophenyl group) at concentrations considerably lower than required for the determination of this amino acid in cerebrospinal fluid (5·10^–8 mol/l).     

New chromatographic method for separation and determination of denatured alphaS1-, alphaS2-, beta- and kappa-caseins by hydrophobic interaction chromatography

A procedure based on solid-phase extraction (SPE) has been developed for the simultaneous preconcentration of three widely used herbicides and seven of their most common degradation products. The compounds studied were atrazine and its metabolites, desethylatrazine, desethyldesisopropylatrazine (DEDIA), 2-hydroxyatrazine, desethyl-2-hydroxyatrazine and desisopropyl-2-hydroxyatrazine (DIHA), terbutryne and its metabolite 2-hydroxyterbutylazine, and chlorotoluron and its metabolite 3-chloro-4-methylphenylurea. A HPLC system with diode array detection was used for the separation, identification and quantification of all these analytes. In the SPE preconcentration step, different types of sorbent were studied: C₁₈ on silica and polymeric sorbents (Oasis and LiChrolut EN), the best results being obtained with the styrene–divinylbenzene cartridge and when the elution was performed with methanol and ethyl acetate. The detection limits obtained were between 0.1 μg l⁻¹ for DIHA and DEDIA and 0.02 μg l⁻¹ for the other analytes. The method used permitted the determination of these herbicides in drinking water at the concentration levels demanded by current legislation. The proposed method was used to evaluate the presence and evolution with time of these herbicides and their degradation products in samples of surface and ground waters from agricultural zones of the provinces of Salamanca and Zamora (basins of the Rivers Guareña and Almar), Spain.     

Preconcentration and determination of boron in milk,infant formula,and honey samples by solid phase extraction-electrothermal atomic absorption spectrometry

This work presents alternative procedures for the electrothermal atomic absorption spectrometric determination of boron in milk, infant formulas, and honey samples. Honey samples (10% m/v) were diluted in a medium containing 1% v/v HNO₃ and 50% v/v H₂O₂ and introduced in the atomizer. A mixture of 20 µg Pd and 0.5 µg Mg was used for chemical modification. Calibration was carried out using aqueous solutions prepared in the same medium, in the presence of 10% m/v sucrose. The detection limit was 2 µg g^− 1, equivalent to three times the standard error of the estimate (s_y/x) of the regression line. For both infant formulas and milk samples, due to their very low boron content, we used a procedure based on preconcentration by solid phase extraction (Amberlite IRA 743), followed by elution with 2 mol L^− 1 hydrochloric acid. Detection limits were 0.03 µg g^− 1 for 4% m/v honey, 0.04 µg g^− 1 for 5% m/v infant formula and 0.08 µg mL^− 1 for 15% v/v cow milk. We confirmed the accuracy of the procedure by comparing the obtained results with those found via a comparable independent procedure, as well by the analysis of four certified reference materials.     

Coupled liquid-liquid extraction and column switching LC for the determination of a new antihistaminic H1 drug in human urine

Summary Mizolastine (SL 85.0324) is a new antihistaminic H₁ benzimidazole derivative which is excreted into urine almost completely metabolized; about 2% of the unchanged drug is excreted as conjugated compound which requires enzymatic deconjugation before analysis. Since the existing methods for plasma samples do not work on deconjugated human urine due to interferences, a new method was developed. The method is based on a diethyl-ether extraction of mizolastine and an internal standard from alkalinized urine. The ether extract is back-extracted with an aqueous buffer (pH=2.6), this extract is neutralized (pH=6.5) and an aliquot injected into a C₁₈ pre-column where clean up and preconcentration take place. The analytes are then desorbed from the pre-column and transferred to the analytical column. The analytical column is a C₁₈ type specially seactivated for basic compounds with an eluent of acetonitrile/phosphate solution (pH=4.5), 40/60, v/v, at a flow rate of 1 ml min^–1. Detection is at 285 nm. The method is linear in the range 10–500 ng ml^–1 with a lower limit of detection of 10 ng ml^–1. The precision and accuracy, evaluated during intra-day and inter-day assays, are satisfactory for pharmacokinetic investigations.     

Continuous Ultrasound-Assisted Leaching of Phenoxyacid Herbicides in Soil and Sediment with in-situ Sample Treatment

Summary Ultrasound, water and Na₂EDTA·2H₂O have been used for continuous leaching with in-situ sample treatment of acid herbicides (namely, bentazone, 2,4-D, trichlopyr, 2,4,5-T and 2,4,5-Tp) from different types of soil (namely, clayey, slimy, sandy, organic and limy) and one sediment. The subsequent steps for quantitation of the leached analytes (namely, preconcentration, individual chromatographic separation and UV detection) were performed using a flow injection manifold that permits automation of the overall process. The main factors contributing to the leaching efficiency—namely, ultrasound radiation amplitude, probe position, percentage of duty cycle of ultrasound exposure, extractant flow-rate and temperature of the water bath in which the extraction cell is immersed—were optimized by means of a central composite design. Also, the kinetics of the leaching step with Na₂EDTA·2H₂O was studied. In all cases, the recoveries of the target analytes were higher than 92%. The detection and quantification limits were 10 and 30 ng g^–1, respectively, for all analytes, but trichlopyr (detection and quantification limits 5 and 12 ng g^–1, respectively). The relative standard deviations for repeatability range between 2.8–5.3%.