Jianqiang Li

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%.

Biodegradation and chiral stability of fipronil in aerobic and flooded paddy soils.

Microbiological degradation of the racemic mixture, the enantiopure R- and S-fipronil was examined under both aerobic and flooded conditions in three Chinese paddy soils. The degradation kinectics and enantiomer fraction (EF) were determined by means of high-performance liquid chromatography (HPLC) with chiral Chiralcel OD-H column, while desulfinyl, sulfone and sulfide derivatives were monitored by reversed phase HPLC with diode array detection (DAD). The degradation/transformation of enantiomers of fipronil in the three live soils under aerobic and flooded conditions generally complied with the first-order kinetics (R2 > or = 0.94). The calculated t1/2 values of the enantiomers of fipronil ranged between 21 and 34 days for aerobic incubation experiments and between 8 and 19 days under flooded conditions incubation, respectively. The calculated EF values of fipronil during the incubation time were all close to 0.5, indicating that the degradation/transformation of fipronil was almost nonenantioselective. The main metabolites of fipronil formed in the incubation experiments were sulfone and sulfide derivatives by oxidative and reductive processes, respectively. The oxidative pathway seemed more active. Under flooded conditions, S-fipronil was preferentially degraded in the three soil samples used. The main metabolite was determined as fipronil sulfide. In control experiments, almost no removal of enantiomers of fipronil was observed indicating that the degradation of fipronil in the paddy soil used was attributed to microbial mediated processes under both aerobic and flooded conditions. In addition, no enantiomerization of fipronil was observed in the soil samples examined under both aerobic and flooded conditions. These results for major differences in the degradation of the enantiomers as well as the formation of toxic metabolites may have some implications for better environmental and ecological risks assessment for chiral pesticides.

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.

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.

Ion-pairing high-performance liquid chromatography determination of amitrole in apple after solid-phase extraction and precolumn derivatization

AbstractA novel method based on solid-phase extraction was studied for the extraction of amitrole (3-amino-1,2,4-triazole), and its residue determination in apples has been developed. The samples were derivatized with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF). The derivatization conditions and the influence of elution composition on the separation were investigated. In pH 9.5 H3BO3–Na2B4O7 media, the reaction of amitrole with CNBF was complete at 60°C after 30xa0min. The separation of derivatized amitrole was achieved at room temperature within 13xa0min by gradient elution mode with cetyltrimethylammonium bromide in mobile phase as ion-pair reagent. The method correlation coefficient was 0.9996, in concentrations ranging from 1.66 to 415xa0mgxa0L−1. The calculated recoveries of the proposed method were from 94.17% to 105.67%, and relative standard deviations were 1.57% to 6.44% in the application to the quantitative determination of amitrole in apples. The detection limit of amitrole was 0.10xa0mgxa0L−1 with a signal-to-noise ratio of 3.n FigureResidue determination of amitrole in apple by ion-pairing high-performance liquid chromatography

Development and validation of a HPLC method for determination of levonorgestrel and quinestrol in rat plasma

Levonorgestrel and quinestrol, commonly known as EP-1, has long been used in the control of wild rodents. Up to the present time, however, no method for simultaneous quantification of levonorgestrel and quinestrol in rat plasma has been reported. In the present study, a sensitive reverse-phase high-performance liquid chromatography with ultraviolet detection (RP-HPLC-UV) method for quantification of levonorgestrel and quinestrol in rat plasma has been developed. It uses a Kromasil ODS C(18) column and acetonitrile-0.1% formic acid (85 : 15, v/v) mobile phase at ambient temperature. The plasma sample was prepared by hexane-isoamyl alcohol extraction (90 : 10, v/v). The flow rate and detection wavelength were 1.0 mL/min and 230 nm. The correlation coefficients were greater than 0.9995 within 0.08-50 microg/mL for levonorgestrel and 0.12-50 microg/mL for quinestrol, and the limits of detection were 0.02 and 0.05 microg/mL for levonorgestrel and quinestrol, respectively. Average recovery ranged from 92.5 to 96.3% and inter-day RSDs were less than 7.56%. This method can be applied to the further pharmacokinetic study of levonorgestrel and quinestrol in rat plasma.