Tianyu Shi

Determination of biogenic amines in beer with pre-column derivatization by high performance liquid chromatography

Eighteen samples of commercially available Chinese beer were analyzed in order to determine the content of biogenic amines. The method involves pre-column derivatization of the amines with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF) and subsequent analysis by RP-HPLC (reversed phase-high performance liquid chromatography) with diode array detection. The labeled biogenic amines were separated on a Kromasil C18 column (250mmx4.6mm, 5microm) at room temperature and UV detection was applied at 254nm. The separation of seven labeled biogenic amines was achieved within 22min by elution acetonitrile and HAc-NaAc buffers. The method linearity, calculated for each biogenic amine, has a correlation coefficient higher than 0.9925, in concentrations ranging from 2.9micromolL(-1) to 565micromolL(-1). Detection limits of biogenic amines were 0.056-0.87micromolL(-1), at a signal-to-noise ratio of 3. The proposed method has been applied to the quantitative determination of spermine, phenethylamine, spermidine, histamine, tyramine, tryptamine and putrescine in beer with recoveries of 91.9-103.1% and R.S.D. of 2.86-5.63%. Quantitation is relative to external standards. The results showed that each kind of beer examined contained at least three biogenic amines. Putrescine, histamine and tyramine were detected in all samples. Spermidine was detected in 89% of the beers. Spermine, tryptamine and phenylethylamine occurred in 78%, 61% and 44% of the beers examined, respectively. These levels were below the level that may elicit direct adverse reactions for most consumers.

Residue determination of glyphosate in environmental water samples with high-performance liquid chromatography and UV detection after derivatization with 4-chloro-3,5-dinitrobenzotrifluoride.

A pre-column derivatization high-performance liquid chromatographic method for glyphosate analysis has been developed. Derivatization of glyphosate was performed with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF). In pH 9.5 H(3)BO(3)-Na(2)B(4)O(7) media, the reaction of glyphosate with CNBF completed at 60 degrees C for 30min. The labeled glyphosate was separated on a Kromasil C18 column (250mmx4.6mm, 5microm) at room temperature and UV detection was applied at 360nm. The separation of labeled glyphosate was achieved within 15min by gradient elution mode. Compared to other pre-column derivatization, this derivatization was performed more mildly, the derivative was more stable, and the detection limits of a few reagents were higher than CNBF, except 9-fluorenylmethyl chloroformate (FMOC-Cl) using fluorescence and mass spectrometry, however, this reagent avoid to be removed after derivatization like FMOC-Cl. The detection limit of glyphosate was 0.009mgL(-1) (S/N=3) without preconcentration and reach MRL, which is set at the level of 0.1mgL(-1) in China. The method linearity correlation coefficient was 0.9999, in concentrations ranging from 0.3 to 48.5mgL(-1). The proposed method has been applied to the quantitative determination of glyphosate in environmental water with recoveries of 91.80-100.20% and R.S.D. of 2.27-6.80, depending on the sample investigated.

Determination of triazole fungicides in environmental water samples by high performance liquid chromatography with cloud point extraction using polyethylene glycol 600 monooleate.

A preconcentration technique known as cloud point extraction was developed for the determination of trace levels of triazole fungicides tricyclazole, triadimefon, tebuconazole and diniconazole in environmental waters. The triazole fungicides were extracted and preconcentrated using polyethylene glycol 600 monooleate (PEG600MO) as a low toxic and environmentally benign nonionic surfactant, and determined by high performance liquid chromatography/ultraviolet detection (HPLC-UV). The extraction conditions were optimized for the four triazole fungicides as follows: 2.0 wt% PEG600MO, 2.5 wt% Na(2)SO(4), equilibration at 45°C for 10 min, and centrifugation at 2000 rpm (533 × g) for 5 min. The triazole fungicides were well separated on a reversed-phase kromasil ODS C(18) column (250 mm × 4.6 mm, 5 μm) with gradient elution at ambient temperature and detected at 225 nm. The calibration range was 0.05-20 μg L(-1) for tricyclazole and 0.5-20 μg L(-1) for the other three classes of analytes with the correlation coefficients over 0.9992. Preconcentration factors were higher than 60-fold for the four selected fungicides. The limits of detection were 6.8-34.5 ng L(-1) (S/N=3) and the recoveries were 82.0-96.0% with the relative standard deviations of 2.8-7.8%.

Solid-phase extraction and residue determination of glyphosate in apple by ion-pairing reverse-phase liquid chromatography with pre-column derivatization.

A new method for glyphosate residue determination in apple has been developed. A SPE cartridge was used to clean up the samples before derivatization. Glyphosate was derivatized with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF) and quantified by reverse ion-pair liquid chromatography using cetyltrimethylammonium bromide (CTAB) as ion-pair reagent. In pH 9.5 H(3)BO(3)-Na(2)B(4)O(7) medium, the reaction of glyphosate with CNBF was complete after 30 min at 60 degrees C. The stability of the derivative on exposure to light at room temperature in methanol-water was demonstrated. The labeled glyphosate was separated on a Kromasil C(18) column (250 x 4.6 mm, 5 microm) at room temperature and UV detection was applied at 360 nm. Separation was achieved within 15 min in gradient elution mode. The correlation coefficient for the method was 0.9998 at concentrations ranging from 0.1 to 50 microg/g. The calculated recoveries for glyphosate in apple were from 86.00 to 99.55%, and the relative standard deviations (n = 6) were from 1.43 to 6.32. The limit of detection was 0.01 microg/g for glyphosate in apple.

A rapid liquid chromatography method for determination of glufosinate residue in maize after derivatisation

A rapid liquid chromatographic method for glufosinate analysis in maize samples after derivatisation has been developed. The labelled glufosinate was separated on a Kromasil C(18) column (250mm×4.6mm, 5μm) and UV detection was applied at 360nm. The optimisation of derivatisation conditions and the influence of different ion-pair reagents on the separation were discussed. The method linearity correlation coefficient was 0.9998 in concentrations ranging from 0.1 to 20mgL(-1). The level of quantification was set to 0.02mgkg(-1), and reached pesticide EU-MRLs for glufosinate in the maize samples. The proposed method was applied to the quantitative determination of glufosinate in samples with recoveries of 98.0-100.5% and RSDs of 2.13-4.13%.

High-performance liquid chromatographic method for determination of amino acids by precolumn derivatization with 4-chloro-3,5-dinitrobenzotrifluoride

This work presents an high-performance liquid chromatography method for the determination of amino acids after precolumn derivatization with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF) which can readily react with both primary and secondary amines. The precolumn derivatization conditions, including the CNBF concentration, reaction pH, temperature and reaction time were investigated for method optimization. In pH 9.0 borate buffer, the reaction of amino acids with CNBF was carried out at 60 degrees C for 30min, the optimized concentration of CNBF was 70mmol L(-1) and the molar ratio of amino acids to CNBF was 1:5.25. The chromatographic separation of 19 amino acids derivatives was performed on a Kromasil ODS C(18) column (250mm x 4.6mm, 5microm) with good reproducibility, and ultraviolet detection was applied at 260 nm. The mobile phase was a mixture of phase A (acetonitrile) and phase B (acetate buffer, acetonitrile, triethylamine; 82.8:17:0.2, pH 4.9), and the flow rate was 0.4mL min(-1). The separation of all the labeled amino acids was achieved within 45min at room temperature by gradient elution mode. The method linearity, calculated for each amino acid, had a correlation coefficient higher than 0.9979, in concentrations ranging from 9.60 to 3330.00 micromol L(-1). The detection limits of amino acids were 2.40-6.50micromol L(-1), at a signal-to-noise ratio of 3. The proposed method was applied for the determination of amino acids in beer with recoveries of 97.0-103.9% and relative standard deviations of 2.62-4.22%, respectively. This method showed good accuracy and repeatability that can be used for the quantification of amino acids in real samples.

Photodegradation of quinestrol in waters and the transformation products by UV irradiation

Quinestrol is synthetic estrogen used in contraceptive and hormone replacement therapy and occasionally for treating breast cancer and prostate cancer. It can make its way into the environment through sewage discharge and waste disposal produced by human excretions. In this study, the photodegradation kinetics of quinestrol in various conditions was investigated by UV and solar irradiation. The affecting factors were studied including concentration of hydrogen peroxide, different water types, and the initial concentrations of quinestrol. Concurrently, the transformation products and presumed pathways of quinestrol in distilled water by UV irradiation were identified and proposed. The results showed that the degradation of quinestrol in both irradiation conditions followed the pseudo-first-order kinetics. More rapid degradation was observed by UV irradiation (k=0.018 min(-1)) than solar irradiation (k=0.004 h(-1)), and the photodegradation rate of quinestrol depended on the concentration of hydrogen peroxide, the initial concentration of quinestrol and water types. The transformation products of quinestrol in distilled water were identified by gas chromatography/mass spectrometry. When exposed to UV irradiation, quinestrol in aqueous solution was rapidly degraded, giving at least ten photodegradation products. The chemical structures of ten degradation products were identified on the basis of mass spectrum interpretation and literature data.

Adsorption properties and degradation dynamics of endocrine-disrupting chemical levonorgestrel in soils.

Levonorgestrel, a synthetic progesterone used as an oral contraceptive or emergency contraceptive pill, has been shown to be an endocrine-disrupting chemical. To assess the environmental risk of levonorgestrel, batch experiments and laboratory microcosm studies were conducted to investigate the adsorption and degradation of levonorgestrel in five contrasting soils of China. Freundlich and Langmuir models were applied to sorption data to examine the affinity of levonorgestrel for soils with varying physical and chemical properties. The K(f) of levonorgestrel in the tested soils ranged from 10.79 to 60.92 mg(1-n) L(n) kg(-1) with N between 0.69 and 1.23, and the Q(m) ranged from 18.18 to 196.08 mg/kg. The multiple regression analysis was conducted between K(f) and soil properties. Results indicate that total organic carbon plays a dominant role in the adsorption process. Gibbs free energy values less than 40 kJ/mol demonstrate that levonorgestrel sorption on soils could be considered as a physical adsorption. The degradation of levonorgestrel in five soils was fitted by the first-order reaction kinetics model. The half-lives of levonorgestrel were between 4.32 and 11.55 days. The initial concentration and sterilization experiments illustrated that the degradation rate of levonorgestrel in soil was concentration-dependent and microbially mediated. The low mobility potential of levonorgestrel in soils was predicted by the groundwater ubiquity score (GUS) and retardation factor (R(f)).