A comparative study of several HPLC methods for determining free amino acid profiles in honey

A study of the viability of three derivatizing reagents for obtaining amino acid profiles in honey through high performance liquid chromatography (HPLC) is presented. A method using diode array detection based on a reaction with diethyl ethoxymethylene malonate (DEMM) and two other methods using fluorescence detection based on derivatization with fluorenylmethyl chloroformate (FMOC-Cl) and 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) have been developed. The three methods yield detection limits close to the ppb level, but vary in relation to other analytical characteristics. The use of methyl chloroformate derivatives allows the profile to be obtained with the greatest sensitivity within a short time frame. On applying such methods to honey samples of diverse botanical origin, we observe that the proline values obtained are always lower than those found using the official spectrophotometric method, thereby underlining the advisability of using HPLC methods to reduce uncertainty in these results.     

Chiral separation of some triazole pesticides by supercritical fluid chromatography

The enantiomeric separation of six triazole pesticides: cyproconazole, propiconazole, diniconazole, hexaconazole, tebuconazole and tetraconazole, using supercritical fluid chromatography and the Chiralpak AD column, is presented in this work. The effect of different organic modifiers such as methanol, ethanol and 2-propanol on the retention and resolution was studied as well as the presence of additives in the mobile phase. The results obtained were highly successful, all the compounds were enantiomerically separated and in most of the cases the analysis time was close to 10 min. The type of organic modifier that provided the best results depended on the compound.     

Use of semipreparative supercritical fluid chromatography to obtain small quantities of the albendazole sulfoxide enantiomers

The semipreparative separation of the albendazole sulfoxide enantiomers using chiral supercritical fluid chromatography is presented in this work. For this purpose, a modular SFC chromatograph was adapted to work at semipreparative scale and a Chiralpak AD (250 x 10 mm) column was used. Different injection volumes were evaluated in order to obtain high purities and throughputs. Using the maximum load, it was possible to obtain 37 mg/h of the first eluted enantiomer with a purity of 99.9%, and 36.5 mg/h of the second eluted enantiomer with a purity of 95%.     

Multistep mass spectrometry of heterocyclic amines in a quadrupole ion trap mass analyser

The fragmentation of heterocyclic amines (HAs) in an ion trap was studied by means of the infusion of methanolic solutions containing the compounds under assay, and using an atmospheric pressure chemical ionization (APCI) as ion source. The MS(n) spectra obtained for compounds included in the same family, either aminoimidazoazaarenes (AIAs) or carbolines, were compared in order to propose fragmentation pathways for each HA. Moreover, labelled AIAs were used to establish the mechanisms. The protonated molecule was always obtained, but subsequent fragmentation was different for both families. In the case of AIAs, major product ions came from the fragmentation of the aminoimidazole moiety, thus the base peak in MS(2) corresponded to the loss of the methyl group, and losses of C(2)NH(3) and CN(2)H(2) were also observed. Further fragmentation occurred in the heterocyclic rings, mainly with losses of HCN and CH(3)CN. For carbolines, the most important product ions came from the loss of ammonia, except for harman and norharman, the loss of a methyl group for methylated carbolines or the loss of diverse fragments from the heterocyclic rings. In some cases, ion-molecule reactions into the ion trap were observed. For instance, for AalphaC or MeAalphaC one ion originating from these reactions corresponded to the base peak.     

Rapid and sensitive method for determining free amino acids in honey by gas chromatography with flame ionization or mass spectrometric detection

This paper describes a rapid, sensitive and specific method for determination of free amino acids in honey involving a new reaction of derivatization and gas chromatography (GC) with flame ionization (FID) and mass spectrometric (MS) detection. The method allows the determination of 22 free amino acids in honey samples in a short time: 8 and 5 min for GC-FID and GC-MS, respectively. Quantitation was performed using Norvaline as internal standard, with detection limits ranging between 0.112 and 1.795 mg/L by GC-FID and between 0.001 and 0.291 mg/L by GC-MS in the selected-ion monitoring mode. The method was validated and applied to a set of 74 honey samples belonging to four different botanical origins: eucaliptus, rosemary, orange and heather. The statistical treatment of data shows a correct classification of different origins over 90%.     

Determination of phenolic compounds in water samples by on-line solid-phase extraction—supercritical-fluid chromatography with diode-array detection

Summary The eleven Environmental Protection Agency (EPA) priority phenolic compounds have been determined by solid-phase extraction (SPE) coupled on-line to supercritical-fluid chromatography (SFC) with diodearray detection. The variables affecting chromatographic separation were optimized and the analytes were separated at 40 °C in two diol columns connected in series; a gradient of methanol, as modifier, and CO₂ was used as mobile phase. Under these conditions, all the compounds studied were separated to baseline in less than 13 min. PLRP-S and LiChrolut EN were tested as sorbents in a 10×3 mm i.d. laboratory-packed precolumn for solid-phase extraction. An ion-pair reagent, tetrabutylammonium bromide (TBA), was used in the extraction process to increase break-through volumes. The performance of the method was checked with tap and river waters and the pre-concentration of 20 mL of sample in a PLRP-S pre-column enabled phenolic compounds to be determined at low μg L⁻¹ levels with limits of detection ranging between 0.4 and 2 μg L⁻¹. The repeatability and reproducibility between days (n=3) for real samples spiked at 10 μg L⁻¹ were lower than 10%.     

From calcium interaction to calcium electrochemical detection by [(C5H5)Fe(C5H4COCH=CHC6H4NEt2)] and its two novel structurally characterized derivatives

[(C(5)H(5))Fe(C(5)H(4)COCH=CHC(6)H(4)NEt(2))] (1) has been electrochemically evaluated toward different cations in solution. Calcium sensing by this compound and its two new derivatives [(C(5)H(5))Fe(C(5)H(4)CO(CH=CH)(2)C(6)H(4)NMe(2))] (2) and [(C(5)H(5))Fe(C(5)H(4)CH=CHCOCH=CHC(6)H(4)NEt(2))] (3) that exhibit a conjugated link between the ferrocene unit and the nitrogen atom has been thoroughly examined. Compounds 2 and 3 have been structurally characterized by single-crystal X-ray diffraction studies. The three related protonated species [1H][BF(4)] (4), [2H][BF(4)] (5), and [3H][BF(4)] (6) have been isolated in a good yield. NMR experiments clearly established that calcium interaction occurs in the vicinity of the carbonyl group, and mass spectrometry studies confirmed that this interaction, which involves several ligand-Ca(2+) adducts, is complex. A combination of electrochemical and NMR experiments highlighted an original salt influence on the electrochemical calcium sensing result.     

Simple isotopic product rules valid for absolute and integrated infrared intensities

Microwave spectra of CH¹⁸ OCOOH, CHOC¹⁸ OOH, CHOCO¹⁸ OH, ¹³ CHOCOOH and CHO¹³ COOH are reported and have been used in combination with data on CHOCOOH and CHOCOOD to determine the molecular structure as r(C=O)_ald. = 1.174 ± 0.006 Å, r(C=O)_acid = 1.203 ±0.006 Å, r(C—O) = 1.313 ± 0.010 Å, r(C—C) = 1.535 ± 0.005 Å, r(O—H) = 0.948 ± 0.004 Å, r(C—H) = 1.104 ±0.010 Å, ald. = 123.7 ± 0.4<, 相似文献