Determination of tetracyclines residues in honey by on-line solid-phase extraction high-performance liquid chromatography

An automated system using on-line solid-phase extraction (SPE) high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection was developed for the determination of tetracyclines (TCs), such as tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC), metacycline (MC), and doxycycline (DC) in honey. One milliliter diluted honey sample was injected into a conditioned C18 SPE column and the matrix was washed out with water for 3 min. By rotation of the switching valve, TCs were eluted and transferred to the analytical column by the chromatographic mobile phase. Chromatographic conditions were optimized. TCs were separated in less than 8 min with a gradient elution using a mixture of 0.8% formic acid and acetonitrile. The UV detection was performed at 365 nm. The conditions for on-line SPE, including solvent and total time for loading sample and washing matrix were also optimized. Time for extraction and separation decreased greatly. For the five kinds of TCs, the limits of detection (LODs) at a signal-to-noise of 3 ranged from 5 to 12 ng g⁻¹. The relative standard deviations (R.S.D.) for the determination of TCs ranged from 3.4 to 7.1% within a day and ranged from 3.2 to 8.9% in 3 days, respectively.     

Determination of imazaquin residues in soil by solid-phase extraction and high-performance liquid chromatography

A method has been developed for the quantitation of imazaquin residues in soil. The herbicide was extracted from soil with methanol-water (2 + 1, v/v) and cleaned up by strong anion-exchange solid-phase extraction cartridges. Analysis was performed by using high-performance liquid chromatography with ultraviolet detection. Average recoveries through the method ranged from 90.7 to 100.6%, with relative standard deviation equal to or lower than 6.6%. The limit of detection was estimated to be 0.0015 mg/kg, and the minimum quantitation concentration of imazaquin in soil was 0.005 mg/kg. This method was successfully applied to evaluate imazaquin residue levels in soil and its dissipation rates in a soybean field in the Xisanqi District of Beijing, People's Republic of China. The dissipation study showed that the half life of imazaquin in soil was 10.37 +/- 0.0135 days at 3 different application rates.     

Determination of forchlorfenuron residues in watermelon by solid-phase extraction and high-performance liquid chromatography

A method using solid-phase extraction for cleanup, followed by high-performance liquid chromatography with ultraviolet detection (HPLC/UV), was developed for the determination of forchlorfenuron residues in watermelon. The pesticide is extracted from the sample with acidic acetonitrile, and the extract is loaded onto a primary-secondary amine (PSA) column. The pesticide is eluted with acetone and determined by HPLC/UV. The PSA column was found to provide effective cleanup, removing the greatest number of sample matrix interferences. The acetonitrile extraction followed by the PSA cleanup provided recoveries of >95%, coefficients of variation (precision) of <10%, and sensitivity of 0.005 mg/kg, in agreement with the directives for method validation in residue analysis. The proposed method was successfully used to determine forchlorfenuron residue levels and dissipation rates in watermelon grown in an experimental greenhouse in Beijing, People's Republic of China.     

Determination of estazolam in plasma by high-performance liquid chromatography with solid-phase extraction.

A high-performance liquid chromatography (HPLC) assay was developed for the determination of estazolam in human plasma. Estazolam and alprazolam as an internal standard were detected by ultraviolet absorbance at 240 nm. Estazolam in plasma was extracted by a rapid and simple procedure based on cyanopropyl bonded-phase extraction. Chromatographic separation was achieved with a reversed-phase C8-5 column using a mobile phase of 0.5% potassium dihydrogenphosphate(pH 4.5)-acetonitrile (70:30, v/v). The determination of estazolam was possible in the concentration range of 1.0 - 200.0 ng/mL. The mean recovery of estazolam added to plasma was 96.1 +/- 1.5% with coefficients of variation of less than 5.5%. This method is applicable for accurately monitoring the plasma level of estazolam in healthy subjects participating in scientific research.     

Determination of gliclazide in serum by high-performance liquid chromatography using solid-phase extraction.

A simple and sensitive high-performance liquid chromatographic method for a routine assay of gliclazide in serum is described. Serum samples spiked with glibenclamide (internal standard) were applied to Bond Elut C18 cartridges. After washing with phosphate buffer (pH 7.5) and water, the cartridge was eluted with 60% methanol. The eluate was evaporated to dryness. The residue was dissolved in methanol and injected onto an octadecyl silica column (5 microns, 150 mm x 4.6 mm I.D.). The mobile phase was 0.04 M potassium dihydrogenphosphate (pH 4.6)-acetonitrile-isopropyl alcohol (5:4:1, v/v). Ultraviolet detection at 227 nm was used. The minimum detectable level of gliclazide was 20 ng/ml.     

固相萃取-高效液相色谱检测葡萄酒中赭曲霉毒素A

使用C18小柱固相萃取, C18反相柱(250 mm×4.6 mm i.d.)分离,V(乙腈):V(水):V(乙酸)＝99:99:2为流动相,荧光检测器(激发波长333 nm,发射波长460 nm)检测,测定葡萄酒中赭曲霉毒素A.其质量浓度在6.25～200 ng/mL范围内呈良好线性,相关系数为0.9997.样品经浓缩60倍后,方法检出限为0.027 ng/mL.对红葡萄酒、干红及白葡萄酒进行了加标回收实验,回收率为80.1%～109.8%.平行7份样品加标回收率相对标准偏差为5.9%.对市售6种葡萄酒进行了赭曲霉毒素A的测定.     

Determination of linear alkylbenzene sulfonates by ion-pair solid-phase extraction and high-performance liquid chromatography

In this paper, the potential use of multiwalled carbon nanotubes (MWCNTs) as solid phase extraction (SPE) adsorbent was evaluated for preconcentration of linear alkylbenzene sulfonates (LAS) using ion-pair (IP)-SPE with tetrabutylammonium hydroxide (TBAH). The LAS homologues present in the aqueous sample were ion-paired with TBAH and the solution was passed through the MWCNT cartridges. The analytes retained in the cartridge were eluted with methanol and the concentrated methanol extract was analysed by HPLC-UV. In order to obtain the satisfactory recovery of LAS homologues, various parameters including the type and amount of the ion-pair reagents, the desorption and enrichment conditions such as the effect of eluent and its volume, pH, the flow rate, the ultrasonic time of sample, and the volume of sample solution were systematically optimized. Under the optimal conditions, LAS homologues could be easily extracted by the proposed SPE cartridge. The favorable limits of detection (LOD) for LAS homologues were in the range from 0.02 to 0.03 μg L⁻¹, and the relative standard deviations (RSDs) were 1.55-2.54% for 10 μg L⁻¹ LAS (n = 6). The proposed method has been successfully applied for the analysis of LAS homologues in aqueous environmental samples. A comparison study with ion-pair solid extraction on MWCNTs, C8 and C18 as adsorbents for LAS demonstrated that ion pair-based solid extraction on MWCNTs adsorbent was advantageous over C8 and C18, the widely used traditional adsorbents.     

Study of semi-automated solid-phase extraction for the determination of acaricide residues in honey by liquid chromatography

A solid-phase extraction (SPE) method followed by a reversed-phase high-performance liquid chromatography (HPLC) procedure is reported for the assay of a wide polarity range acaricide residues in honey. After selection of suitable chromatographic and detection conditions, most steps of the SPE procedure that may affect to the recovery were investigated. Honey sample was buffered at pH 6 and then applied to the preconditioned C₁₈ sorbent. A washing step was performed with 1 ml of a mixture of tetrahydrofuran (THF)–phosphate buffer (10:90, v/v) and finally, the analytes were eluted with 1 ml of THF. The extract was evaporated to dryness, reconstituted in mobile phase and chromatographed on a reversed-phase C₁₈ column with diode array detection. The recoveries of the more polar acaricides were higher than 80% and 60–70% for the more apolar ones. Limits of detection obtained ranged from 1 to 200 ng/g.     

Determination of 4-aminopyridine in serum by solid-phase extraction and high-performance liquid chromatography.

An assay for the determination of 4-aminopyridine in serum has been developed using 3,4-diaminopyridine as internal standard and reversed-phase high-performance liquid chromatography with detection at 244 nm. A mobile phase of acetonitrile-methanol-ethanol-1% ammonium carbonate (75:10:10:5) provided excellent separation of both compounds. Samples were extracted on solid-phase columns. The linearity, precision, recovery and the limit of detection were all sufficient for the routine use of this assay in clinical studies of patients treated with 4-aminopyridine.     

Determination of triazines and dinitroanilines in waters by high-performance liquid chromatography after solid-phase extraction

A rapid and selective method for the simultaneous determination of triazines and dinitroanilines in real water matrices is suggested based on a preliminary adsorption on an RP-18 cartridge, an elution step using acetonitrile and HPLC separation with a Lichrosorb RP- Select B column and UV detection. The washing step cartridge is critical for triazines: terbutryn is eluted with quantitative recovery only after washing with an NH₃ solution. The degree of enrichment of the compounds studied has been determined: triazine recoveries are quantitative, while dinitroaniline recoveries are between 66% and 78% at the lowest fortification level. The detection limits for the ten herbicides are in the range 0.03-0.1 μg/l. The analysis time is 2 h.     

Determination of ethylenediaminetetraacetic acid in sea water by solid-phase extraction and high-performance liquid chromatography

The chelating agent EDTA is widely used, and as a result is showing up widely in the aquatic environment. Here we describe a preconcentration procedure for measuring EDTA concentration in sea water samples by HPLC. The procedure consists of forming an Fe(III) complex followed by solid-phase extraction using an activated carbon cartridge. After the preconcentration, EDTA was quantified by HPLC with ultraviolet detection (260 nm). The enrichment permitted the determination of EDTA at concentrations as low as 1 nM. Good recoveries were obtained for both brackish and full-strength sea water with high repeatability (RSD < 6%). The method was applied to sea water samples taken from near the mouth of the Oyabe River in Japan.     

Determination of alkylphenols and alkylphenol polyethoxylates by reversed-phase high-performance liquid chromatography and solid-phase extraction

A simple, accurate and reproducible reversed-phase high-performance liquid chromatography (HPLC) method was developed for the separation and characterisation of alkylphenols (APs) and alkylphenol polyethoxylates (APEOs), using a C18 octadecyl silica (ODS) column. APs and each APEO oligomer were separated successfully within a reasonable time without gradient elution. An excellent resolution was obtained, even for mixtures of APs and low EO number APEOs, which are otherwise difficult to separate using conventional normal-phase HPLC methods. This method, combined with solid-phase extraction, was highly applicable for the simultaneous determination of alkylphenols and alkylphenol ethoxylates in real samples.     

Determination of sulfophenylcarboxylic acids in marine samples by solid-phase extraction then high-performance liquid chromatography

An analytical method is presented for the determination of sulfophenylcarboxylic acids (SPC) produced by the biodegradation of linear alkylbenzene sulfonates (LAS) in marine samples. Isolation and concentration of the compounds was by solid-phase extraction. The different factors affecting extraction efficiency packing composition, pH, clean-up, ionic strength, and elution solvents--were studied and optimized. With the proposed method C4-C13SPC and C10-C13 LAS recoveries varied between 65% and 105%, with standard deviations between 0.1 and 5, respectively, for 100-mL samples and 100 microg L(-1) concentrations of each homolog. Detection limits within the range 0.5 g L(-1) (for C4SPC) to 1.0 g L(-1) (for C12SPC) were obtained by liquid chromatography with fluorescence detection. This method is the first to be proposed that enables the simultaneous determination of monocarboxylic SPC (C>3) and LAS homologs in marine samples by a simple, sensitive, and specific method giving high recoveries and reproducibility. SPC with from three to twelve carbon atoms in the carboxyl chain have been found in marine water samples.     

Determination of cefotaxime and desacetylcefotaxime in cerebrospinal fluid by solid-phase extraction and high-performance liquid chromatography

A microfluidic analytical system for the separation and detection of organic peroxides, based on a microchip capillary electrophoresis device with an integrated amperometric detector, was developed. The new microsystem relies on the reductive detection of both organic acid peroxides and hydroperoxides at -700 mV (vs. Ag wire/AgCl). Factors influencing the separation and detection processes were examined and optimized. The integrated microsystem offers rapid measurements (within 130 s) of these organic-peroxide compounds, down to micromolar levels. A highly stable response for repetitive injections (RSD 0.35-3.12%; n = 12) reflects the negligible electrode passivation. Such a "lab-on-a-chip" device should be attractive for on-site analysis of organic peroxides, as desired for environmental screening and industrial monitoring.     

Determination of momordicoside A in bitter melon by high-performance liquid chromatography after solid-phase extraction

Summary Momordicoside A has been determined by solid-phase extraction (SPE) on a Envi Carb cartridge (3 mL, 250mg) then high-performance liquid chromatography (HPLC) on a C₁₈ column (4.6 mm×250 mm, 5 μm particle) with acetonitrile-methanol-50mm potassium dihydrogen phosphate buffer, 25:20:60 (v/v), as mobile phase, at a flow rate of 0.8 mL min⁻¹, and UV detection at 208 nm. The analytical method was shown to be highly reproducible, with precision (asRSD) and accuracy (asRME)<10%, both intra-day and inter-day. Absolute recoveries were >90%. The method was applied to the determination of momordicoside A in various tissues from different varieties of bitter melon from different producing areas.     

Determination of benzene metabolites in urine of mice by solid-phase extraction and high-performance liquid chromatography.

A method was developed for quantitative measurement of trans,trans-muconic acid, catechol, hydroquinone and phenol in urine. Hydrolysis of esterified and glucuronized phenolic compounds was effected by specific enzymes. The hydrolysed mixture was purified and separated by solid-phase extraction with an anion exchanger, followed by extraction with diethyl ether. By using a clean-up procedure the natural background from mouse urine could be reduced, so that the detection limit of the metabolites was in the range 3-60 mg/l. Optimization of the chromatographic conditions resulted in a short high-performance liquid chromatography analysis time. Phenol had the longest retention time of about 10 min. The clean-up procedure could also be used for phenylmercapturic acid, an additional benzene metabolite, but for sensitive high-performance liquid chromatographic detection of phenylmercapturic acid other conditions are necessary.     

Determination of sulfonamides in livers using matrix solid-phase dispersion extraction high-performance liquid chromatography

The matrix solid-phase dispersion (MSPD) was applied for extracting seven sulfonamides (SAs) in liver samples. The separation and determination were carried out by high-performance liquid chromatography. The analytes were derivated with fluorescamine and detected with fluorescence detector. The types of dispersion adsorbents for MSPD were examined and the highest recovery was obtained when the diatomaceous earth was used as the dispersion adsorbent and the mass ratio of dispersion adsorbent to sample was 3:1. The acetone was used as the elution solvent. Under the optimal conditions, the linear range for determining the SAs in liver samples was 5.0-1000.0 ng/g. The porcine, chicken and cattle liver samples were analyzed and the average recoveries of seven SAs were higher than 84.6%.     

Determination of tetracyclines in bovine and porcine muscle by high-performance liquid chromatography using solid-phase extraction.

A method is presented for the determination of the three tetracyclines oxytetracycline, tetracycline and chlortetracycline in muscle, spiked at 100 ng/g, using high-performance liquid chromatography (HPLC). The concentration and extraction steps are carried out using Waters Environmental Sep-Pak cartridges. The principal steps involve homogenizing the sample in EDTA-McIlvaine buffer followed by centrifugation and precipitation of the supernatant using trichloroacetic acid. After further filtration and concentration on a Sep-Pak cartridge, the sample is eluted and analysed by HPLC with UV detection and confirmation by diode-array. The column used is a Nova-Pak C18 (4 microns) cartridge (10 cm x 8 mm I.D.). A phosphate-citrate-acetonitrile buffer, utilizing ion suppression, is the mobile phase. The analytes are detectable at levels down to 10 ng/g. The analyte identity can be confirmed at 20 ng/g by the use of diode-array detection and spectral library comparison.     

Determination of amineptine and its main metabolite in plasma by high-performance liquid chromatography after solid-phase extraction

Amineptine and its main metabolite were determined simultaneously in plasma by high-performance liquid chromatography using quinupramine as internal standard. The method comprised adsorption on Extrelut column from alkaline plasma, elution with diethyl ether-methylene chloride, evaporation in the presence of 0.01 M hydrochloric acid and injection of the acid solution onto a mu Bondapak C18 column, using acetonitrile-0.025 M potassium dihydrogenphosphate as mobile phase and ultraviolet detection at 210 nm. Average steady-state concentrations of the two compounds were determined in four patients under treatment regimen (two 100-mg doses of amineptine per day, at 8.00 and 12.00 h). The concentrations determined 20 h after the last dose were undetectable in all cases, whereas the concentrations determined 1 h after the second dose were found to be 780 +/- 96 ng ml-1 for amineptine and 690 +/- 137 ng ml-1 for its metabolite. The technique can also be applied to whole blood with, if necessary, identification on the basis of the ultraviolet spectrum obtained by photodiode-array detection.