Determination of Oxytetracycline/Oxytetracycline Hydrochloride in Animal Feed, Fish Feed, and Veterinary Medicinal Products by Liquid Chromatography with Fluorescence Detection: Collaborative Study

A method for determining oxytetracycline (OTC) in animal feed, fish feed, and veterinary medicinal products at medicated use and contamination levels was collaboratively studied. The method is applicable to the analysis of animal feeds and mineral premixes containing levels 2 mg/kg, and fish feed containing levels 10 mg/kg. Oxytetracycline hydrochloride (OTC.HCl) is extracted from ground feed material in acidmethanol solution using mechanical agitation. After centrifugation for 5 min at 1230 g, an aliquot of the extract is diluted with water and/or acidmethanol so that the concentration of OTC.HCl is approximately the same as that in the working standard, and the solutions contain at least 50 water. Injectable veterinary medicinal materials (also called animal remedy materials) are diluted with water and/or extractant to reach the target concentration. The extracts are filtered and analyzed by reversed-phase liquid chromatography with fluorescence detection with excitation at 390 nm and emission at 512 nm. Twenty-eight test samples of medicated feeds, supplements, and drug premixes, including 4 test samples for trace-level analysis, were sent to 17 collaborators in Canada, The Netherlands, and the United States. Results were received from 11 laboratories. The RSDr values (within-laboratory repeatability) ranged from 1.26 to 9.21; RSDR values (among-laboratory reproducibility) ranged from 2.14 to 12.9, and HorRat values ranged from 0.54 to 3.02. It is recommended that this method be adopted AOAC Official First Action.

Determination of Decoquinate in Animal Feeds by Liquid Chromatography: Collaborative Study

The performance characteristics of a liquid chromatographic (LC) method for the analysis of decoquinate (DEC) in supplements, premixes, and complete animal feeds at medicating and trace levels were collaboratively studied. DEC is extracted from ground feed samples with 1 calcium chloridemethanol solution using mechanical agitation for 90 min. After centrifugation for 5 min and dilution (if necessary), an aliquot of the extract is diluted with water. The diluted extracts are filtered and analyzed by reversed-phase LC with fluorescence detection. Suspect positive trace-level samples are confirmed by using an alternate excitation wavelength. Fourteen test samples of medicated feeds, supplement, and medicated premix, along with 8 test samples for trace-level analysis, were sent to 13 collaborators (one in Canada, 4 in Europe, and 8 in the United States). Test samples were analyzed as blind duplicates. Acceptable results were received from 12 laboratories for the medicated test samples and from 13 laboratories for the trace-level samples. Repeatability relative standard deviation estimates ranged from 1.3 to 5.6. Reproducibility relative standard deviations estimates ranged from 2.8 to 6.1, and HorRat values ranged from 0.22 to 0.74.

Zur Struktur von Hydroxy-5-phenyl-furanonen: Lösungs-NMR, Festkörper-13C-NMR und Röntgenstruktur im Vergleich / On the Structure of Hydroxy-5-phenyl-furanone Derivatives: NMR Spectroscopy in Solution and High Resolution Solid State 13C NMR Spectroscopy in Relation to X-Ray Crystallography

The structure of (5H)-2-Amino-3-hydroxy-5-phenyl-furan-4-one (lb) was determined by NMR-spectroscopy in solution and in the solid state. The structure of its oxidation product, 3,4-Dihydro-3,3,4,4-tetrahydroxy-5-phenyl-furan-2(5H)-one (7), given in the literature as 5-Phenyl-2,3,4-(5H)-furan-trione, was determined by NMR spectroscopy and crystal structure analysis. The solid state NMR spectrum of 7 was compared to the spectrum of dehydroascorbic acid

Thermostatted micro-reactor NMR probe head for monitoring fast reactions

A novel nuclear magnetic resonance (NMR) probe head for monitoring fast chemical reactions is described. It combines micro-reaction technology with capillary flow NMR spectroscopy. Two reactants are fed separately into the probe head where they are effectively mixed in a micro-mixer. The mixed reactants then pass through a capillary NMR flow cell that is equipped with a solenoidal radiofrequency coil where the NMR signal is acquired. The whole flow path of the reactants is thermostatted using the liquid FC-43 (perfluorotributylamine) so that exothermic and endothermic reactions can be studied under almost isothermal conditions. The set-up enables kinetic investigation of reactions with time constants of only a few seconds. Non-reactive mixing experiments carried out with the new probe head demonstrate that it facilitates the acquisition of constant highly resolved NMR signals suitable for quantification of different species in technical mixtures. Reaction kinetic measurements on a test system are presented that prove the applicability of the novel NMR probe head for monitoring fast reactions.

Pohnpei, FSM case study in a global health project documents its local food resources and successfully promotes local food for health

This paper presents a summary of Pohnpei, Federated States Micronesia's involvement in a global health study focused on documenting traditional food systems in different parts of the world and providing evidence that local resources are critical for food security, nutrition and health. The Pohnpei study was based in Mand Community, Madolenihmw. The study found that there was a great diversity of foods locally available (381 food items documented), but these were underused. Overweight, obesity, diabetes, and vitamin A deficiency were identified as serious problems. Interventions included community meetings, school activities, and agriculture workshops, cooking classes, charcoal oven development, weight loss and planting competitions, poster campaigns and other relevant mass media. Significant dietary improvements were achieved following the intervention efforts, as well as positive changes in attitude towards local food including: decrease in average daily rice consumption from 846 g/person in 2005 to 544 g/person in 2007 (p = 0.0002); increase in provitamin A carotenoid intake from 227 microg/person in 2005 to 475 microg/person in 2007 (p = 0.02); increased frequency of consumption of local banana (53%), giant swamp taro (476%), local vegetables (130%); and increased dietary diversity (4.8 local food groups consumed in 2005 to 5.5 in 2007). Another positive outcome in Pohnpei was the popularization of the slogan "Let's Go Local."

Validity and reliability of the Migraine-Treatment Optimization Questionnaire

Our aim was to establish the validity and reliability of a patient-rated Migraine Treatment Optimization Questionnaire (M-TOQ) in primary care. Patients who met International Classification of Headache Disorders, 2nd edn criteria for migraine completed a 19-item questionnaire containing candidate items for the M-TOQ, and three questionnaires designed to test convergent/construct validity [Migraine Disability Assessment Scale (MIDAS), Headache Impact Test (HIT)-6 and Migraine-Specific Quality of Life Scale (MSQoL)]. A 15-item (M-TOQ-15) and a five-item (M-TOQ-5) questionnaire were derived. Two hundred and fifty-three adult patients were recruited. Five treatment optimization domains were identified: functioning, rapid relief, consistency of relief, risk of recurrence and tolerability; with Cronbach alphas of 0.70-0.84. The Cronbach alpha for M-TOQ-15 was 0.85, and it correlated well with MIDAS, HIT-6 and MSQoL (r = 0.33-0.44). The Cronbach alpha for M-TOQ-5 was 0.66, and it also correlated well with the three questionnaires (r = 0.33-0.41). The utility of the M-TOQ for assessing treatment benefit in research (M-TOQ-15) and primary care (M-TOQ-5) should be further validated.

Chemical stability of oseltamivir in oral solutions

The stability of oseltamivir in oral aqueous solutions containing the preservative sodium benzoate was studied by a stability indicating HPLC-method. The separation was achieved on a RP-18 ec column using a gradient of mobile phase A (aqueous solution of 50 mM ammonium acetate) and mobile phase B (60% (v/v) acetonitrile/40% (v/v) mobile phase A). The assay was subsequently validated according to the ICH guideline Q2(R1). The extemporaneously prepared "Oseltamivir Oral Solution 15 mg/ml for Adults or for Children" (NRF 31.2.) according to the German National Formulary ("Neues Rezeptur-Formularium") was stable for 84 days if stored under refrigeration. After storage at 25 degrees C the content of oseltamivir decreased to 98.4%. Considering the toxicological limit of 0.5% of the 5-acetylamino derivative (the so-called isomer I) the solution is stable for 46 days. Oseltamivir was less stable in a solution prepared with potable water instead of purified water. Due to an increasing pH the stability of this solution decreased to 14 days. Furthermore a white precipitate of mainly calcium phosphate was observed. The addition of 0.1% anhydrous citric acid avoided these problems and improved the stability of the solution prepared with potable water to 63 days. Sodium benzoate was stable in all oral solutions tested.

Basidiochrome – A Novel Siderophore of the Orchidaceous Mycorrhizal Fungi Ceratobasidium and Rhizoctonia spp

A novel trishydroxamate siderophore, named basidiochrome, was isolated as the principal siderophore from low-iron culture filtrates of Ceratobasidium and Rhizoctonia species which are known as mycorrhizal fungi associated with orchid roots. Ion-exchange chromatography and preparative HPLC yielded a pure compound which contained two components according to GC-MS analysis: L: -N(5)-hydroxy-ornithine and 3-methyl-2-cis-pentenedioic acid (3-methyl-cis-glutaconic acid). FTICR-ESI-MS of both the iron-free and ferric form indicated an elemental composition of C(33)H(47)N(6)O(16)Fe (MW = 839) for the ferric form of basidiochrome. The connectivity was further elucidated by 2D-NMR techniques (HSQC, HMBC, COSY, NOESY) indicating that basidiochrome is a novel linear tripeptide consisting of three L: -N(5)-hydroxy-ornithines each linked to 3-methyl-2-cis-pentenedioic acid residues.

Capillary liquid chromatography–microcoil 1H nuclear magnetic resonance spectroscopy and liquid chromatography–ion trap mass spectrometry for on-line structure elucidation of isoflavones in Radix astragali

Miniaturization and hyphenation of chromatographic separation techniques to nuclear magnetic resonance spectroscopy is being increasingly demanded in the field of biomedical, drug metabolite and natural product analysis. Herein, capillary liquid chromatography was coupled on-line to microcoil 1H nuclear magnetic resonance spectroscopy (capLC-NMR) equipped with a 1.5 microL solenoidal probe for structure elucidation of isoflavones in Radix astragali. The extract was screened by HPLC-UV-MS as the preliminary step and four major peaks were identified tentatively by ion trap mass spectrometry molecular weights and characteristic fragments. Then, stopped-flow capLC-UV-NMR was performed using 33 microg extract injected on-column. The four peaks were parked manually in the micro probe one by one and corresponding 1H NMR spectra were recorded with good resolutions under the applied capLC-NMR conditions (120 and 220 ng injected on-column for peaks 2 and 4, respectively). All aromatic regions of 1H NMR spectra correlated well to the characteristic signals of isoflavone aglycone protons. And the signal corresponding to the anomeric proton of the glucopyranoside of isoflavone glycoside was also obtained for peak 1. Therefore, these four peaks are determined as calycosin-7-O-beta-D-glucopyranoside (1), ononin (2), calycosin (3) and formononetin (4) unambiguously. The capLC-NMR results indicate that this hyphenated technique could be used for the determination of a great variety of natural products from small sample amounts, e.g., only 5 g R. astragali in this study.

Determination and identification of isoflavonoids in Radix astragali by matrix solid-phase dispersion extraction and high-performance liquid chromatography with photodiode array and mass spectrometric detection

The isoflavonoids in Radix astragali were determined and identified by HPLC-photodiode array detection-MS after extraction employing matrix solid-phase dispersion (MSPD). As a new sample preparation method for R. astragali, the MSPD procedure was optimized, validated and compared with conventional methods including ultrasonic and Soxhlet extraction. The amounts of two major components in this herb, formononetin (6) and ononin (2), were determined based on their authentic standards. Four major isoflavonoids, formononetin (6), ononin (2), calycosin (5) and its glycoside (1), and three minor isoflavonoids, (6aR,11aR)-3-hydroxy-9, 10-dimethoxypterocarpan (7), its glycoside (3), and (3R)-7,2'-dihydroxy-3',4'-dimethoxyisoflavone-7-O-beta-D-glycoside (4), were identified based on their characteristic two-band UV spectra and [M + H], [aglycone + H]+ and [A1 + H]+ ions, etc. The combined MSPD and HPLC-DAD-MS method was suitable for quantitative and qualitative determination of the isoflavonoids in R. astragali.

Analysis of silica hydride and surface hydrosilation reactions by solid-state NMR in the preparation of p -chlorobenzamide bonded silica phase

29Si and (13)C CP-MAS NMR spectroscopy was used to follow the conversion of native silica to a p-chlorobenzamide bonded silica material. The benzamide bonded phase was prepared via a hydrosilation reaction of a hydride silica intermediate with p-chloro- N-allylbenzamide. Solid-state NMR was used to show the disappearance of reactive surface hydride species (M(H)) and to identify newly formed bonded chemical species on the silica surface. DRIFT spectroscopy, elemental analysis, and specific surface-area determinations (BET) of the prepared phases are also reported.

Silica-supported TEMPO catalysts: synthesis and application in the Anelli oxidation of alcohols

The application of silica-supported TEMPO as a recyclable catalyst in the Anelli oxidation of alcohols is reported. The catalyst is easily obtained in a one-step reductive amination procedure starting from a commercially available aminopropyl-functionalized silica. Details of the synthesis of the supported catalyst and its analysis by MAS NMR are presented. Various alcohol oxidations according to the Anelli protocol have been carried out and the stability of the applied silica-supported TEMPO has been studied.

Influence of pressure upon coupling pressurized capillary electrochromatography with nuclear magnetic resonance spectroscopy

In this work, the influence of supplementary pressure on the separation efficiency of pressurized capillary electrochromatography (pCEC) was examined. At low pressures of up to 30 bar, which is more than sufficient to prevent bubble formation, no significant loss in separation efficiency is observed. Even at 100 bar, the efficiency of pCEC is still significantly better than without application of an electric field. In addition, analysis times are drastically reduced compared to both capillary electrochromatography (CEC) and capillary HPLC. On the basis of these results, an improved interface for capillary NMR coupling is described and used for the separation and identification of a mixture of unsaturated fatty acid methyl esters. Under these conditions, the analysis time could be shortened by up to a factor of 10 when pCEC is coupled to NMR spectroscopy.

Synthesis, high-performance liquid chromatography-nuclear magnetic resonance characterization and pharmacokinetics in mice of CD271 glucuronide

Retinoic acid-glucuronides are known as retinoids with activity in acne therapy, limited placental transfer and reduced retinoid adverse effects. We synthesized the glucuronide of a novel retinoid, CD271 (adapalene), used for the treatment of moderate acne. The synthesis product ("CD271 glucuronide", CD271G) was purified by preparative HPLC. It undergoes in aqueous solution, like other glucuronides, rapid acyl-migration of the bound aglycone leading to position isomers. Thus characterization of purified CD271G could be only achieved by HPLC-NMR coupling. A subfraction ("CD271GB") consisting essentially of 2'- and 3'-CD271G was used for pharmacokinetic studies. After a single subcutaneous injection at a dosage of 30 mg/kg the substance showed considerable uptake and metabolism to CD271 indicating that CD271GB could serve as a prodrug for CD271.

Synthesis and separation of structural isomers of 2(3),9(10),16(17),23(24)-tetrasubstituted phthalocyanines

The 2(3),9(10),16(17),23(24)-tetrasubstituted metalphthalocyanines 1-7 (M = In, Ni, Zn) were synthesized, as mixtures of four different structural isomers, from the corresponding 4-alkoxy-1,2-dicyanobenzenes and the appropriate metal salts. Separation of the four structural isomers was successfully achieved on a C30 alkyl phase by high-performance liquid chromatography (HPLC). The determination of the point groups of the structural isomers was carried out for 1 and 3, the composition of the structural isomers of 4-7 was accomplished by comparing their retention times and UV/Vis spectra with the data of 1 and 3. For the phthalocyanines 8-10 and the naphthalocyanines 11 and 12 only the C4h and D2h isomers could be separated.

Isolation and identification of clozapine metabolites in patient urine

Biotransformation products of the atypical neuroleptic clozapine were isolated from urine samples of three schizophrenic patients by solid-phase extraction, liquid-liquid extraction for the separation of unpolar and polar metabolites, and thin-layer chromatography followed by final purification by high-performance liquid chromatography. Their structures were elucidated by mass spectrometry and (1)H NMR spectroscopy and in some cases by enzymatic deconjugation. Besides the known metabolites desmethylclozapine, clozapine N-oxide, 8-deschloro-8-hydroxyclozapine, and 8-deschloro-8-hydroxydesmethylclozapine, the unpolar fraction contained 7-hydroxyclozapine and a compound in which the piperazine ring of clozapine was partially degraded to an ethylenediamine derivative. Novel metabolites identified in the polar fraction were the sulfate and glucuronide conjugates of 7-hydroxyclozapine N-oxide, 8-deschloro-8-hydroxyclozapine-O-glucuronide, and the O-glucuronide of N-hydroxydesmethylclozapine; further conjugates were tentatively identified as 9-hydroxydesmethylclozapine-O-sulfate and 6-hydroxyclozapine-O-sulfate. In addition, the previously described conjugates 7-hydroxydesmethylclozapine-O-sulfate, 7-hydroxyclozapine-O-glucuronide and -O-sulfate, 8-deschloro-8-hydroxydesmethylclozapine-O-glucuronide, and the quaternary ammonium glucuronide of clozapine were detected.

Poly(ethylene-co-acrylic acid) stationary phases for the separation of shape-constrained isomers

A new approach for the synthesis of long alkyl chain length stationary phases for use in reversed-phase liquid chromatography is described. Poly(ethylene-co-acrylic acid) copolymers (i.e., (-CH2CH2-)x[CH2CH(CO2H)-]y) with different levels of acrylic acid were covalently bonded to silica via glycidoxypropyl or aminopropyl linkages. 13C cross polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy was used to characterize the new reversed-phase materials. Aspects of shape selectivity were evaluated for six different columns with Standard Reference Material (SRM) 869a, Column Selectivity Test Mixture for Liquid Chromatography. Selectivity for isomer separations was enhanced for stationary phases prepared with poly(ethylene-co-acrylic acid) containing a mass fraction of 5% acrylic acid. The relationship between alkyl conformation and chromatographic properties was studied by 13C magic angle spinning (MAS) NMR measurements, and correlations were made with the composition of the polymer. Finally, the effectiveness of this phase is demonstrated by the separation of several beta-carotene isomers.

Study on the chiral recognition of the enantiomers of ephedrine derivatives with neutral and sulfated heptakis(2,3-O-diacetyl)-β-cyclodextrins using capillary electrophoresis, UV, nuclear magnetic resonance spectroscopy and mass spectrometry

The enantiomers of methylephedrine, pseudoephedrine and ephedrine showed a different migration behavior in capillary electrophoresis in the presence of beta-cyclodextrin (beta-CD), heptakis(2,3-O-diacetyl)-beta-cyclodextrin and heptakis(2,3-O-diacetyl-6-sulfato)-beta-cyclodextrin (HDAS). Utilizing UV, MS and NMR spectroscopy, in particular rotating frame Overhauser experiments, an attempt was made to elucidate the chiral recognition mechanism. In the case of the neutral CDs 1:1 complexes were formed with ephedrine and methylephedrine characterized by the inclusion of the phenyl ring in the cavity and the side chain pointing out of the wider rim. In contrast, manifold complexes were formed with HDAS, which on average are characterized by an upside down inclusion of the phenyl ring in the cavity and the side chain pointing out of the narrow rim. This complex geometry is likely be stabilized by an ion-ion interaction between the positively charged nitrogens of the ephedrine derivatives and the negative charges of HDAS. In addition, an attachment of the ligand to the outside of HDAS and other complex stoichiometries are also possible.

Combined HPLC-MS and HPLC-NMR on-line coupling for the separation and determination of lutein and zeaxanthin stereoisomers in spinach and in retina

The determination and unambiguous identification of carotenoid stereoisomers from biological tissues, avoiding isomerization and oxidation due to the extraction process, is still a major challenge. Particularly, the analysis of lutein and zeaxanthin stereoisomers is of great importance, as these are the main constituents of the macula lutea, the central part of the human retina, and act as possible agents in the prevention and treatment of age-related macular degeneration (AMD). By combining a mild and quick extraction technique such as matrix solid-phase dispersion together with high-performance liquid chromatography (HPLC), the extremely light and oxygen sensitive lutein and zeaxanthin stereoisomers are extracted, enriched, and separated directly from the solid plant or tissue samples, excluding preparation of artifacts. HPLC separations are performed with C30 phases due to their enhanced shape selectivity compared to C18 phases and on-line coupled to mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. By using HPLC-MS with atmospheric pressure chemical ionization, the lutein stereoisomers can be distinguished from the zeaxanthin stereoisomers within one chromatographic run in the upper picogram range, whereas HPLC-NMR coupling allows the unequivocal identification of each stereoisomer with a concentration in the upper nanogram range. This article provides an analytical method for the artifact-free determination of lutein and zeaxanthin stereoisomers directly from the solid biological tissue spinach as a source of carotenoids and retina as the sphere of activity for AMD. In addition, the structures of these stereoisomers were unambiguously elucidated by employing hyphenated analytical techniques.

Planifolin, a new naphthopyranone dimer and flavonoids from Paepalanthus planifolius

A new naphthopyranone dimer (1) named planifolin was isolated from a methylene chloride extract of the capitula of Paepalanthus planifolius. The structure of 1 has been determined by chemical and spectroscopic means. In addition, a known dihydronaphthopyranone glycoside and seven known flavonoids were isolated from an ethanolic extract of the leaves of P. planifolius.

Application of HPLC-NMR coupling using C30 phase in the separation and identification of flavonoids of taxonomic relevance

The on-line separation and identification of two important taxonomic markers for plant species of the Paepalanthus genus, the flavonoids 6-methoxykaempferol-3-O-beta-D-glucopyranoside and 6-methoxykaempferol-3-O-beta-D-6"(p-coumaroyl)glucopyranoside, has been performed with an HPLC-NMR coupling using C30 phase. 1D spectra have been recorded in the stopped-flow mode for the two predominant chromatographic peaks. This is the first application of HPLC-NMR coupling using C30 phase to a taxonomic problem. The technique drastically reduces the required amount of sampling for structure determination.

Separation and identification of twelve catechins in tea using liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry

A method has been developed for the direct microscale determination of 12 catechins in green and black tea infusions. The method is based on liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (LC/APCI-MS). Standard catechin mixtures and tea infusions were analyzed by LC/APCI-MS with detection of protonated molecular ions and characteristic fragment ions for each compound. The identities of eight major catechins and caffeine in tea were established based on LC retention times and simultaneously recorded mass spectra. In addition, monitoring of the catechin-specific retro Diels-Alder fragment ion at m/z 139 throughout the chromatogram provided a unique fingerprint for catechin content in the samples that led to the identification of four minor chemically modified catechin derivatives in the infusions. This report is the first to describe the comprehensive determination of all 12 reported catechins in a single analysis. The utility of LC/APCI-MS for providing routine separation and identification of catechins at femtomole to low-picomole levels without extraction or sample pretreatment, and its potential as a standard analytical tool for the determination of polyphenols in natural products and biological fluids, are discussed.

New stationary phase for liquid chromatography with chemically bonded pinane ligand: synthesis and characterization by nuclear magnetic resonance and high-performance liquid chromatographic investigations

A new bicyclic phase for liquid chromatography was prepared by solution polymerization approaches. To introduce a C4 spacer the starting molecule 3-formylpinane was reduced to the alcohol followed by a substitution of the hydroxy group through a bromide. The obtained halide reacted with magnesium and allyl bromide to the 3-(but-3'-enyl)pinane which was hydrosilylated with trichlorosilane and finally immobilized to silica gels with different pore sizes using the technique of solution polymerization. To elucidate the structure of 3-(but-3'-enyl)pinane high-resolution two-dimensional nuclear magnetic resonance (NMR) spectra were carried out. The new phases were characterized, on the one hand by employing 13C and 29Si solid-state NMR spectroscopy and on the other hand, by separating a standard test mixture consisting of mainly monosubstituted aromatic compounds. The results achieved in chromatography were correlated with the information gained from 29Si CP/MAS NMR measurements.

Contribution of trifluoperazine metabolites to the in vivo (19)F NMR spectrum of rat brain

Fluorine-19 NMR spectra were acquired from extracts of tissues from heads of rats given the antipsychotic drug trifluoperazine (TFP). Contributions to the in vivo (19)F spectra from tissues other than brain were negligible. The in vivo (19)F resonance at -62.3 ppm from CCl(3)F consisted of 6-8 resolved resonances in vitro. Some in vitro resonances were assigned to previously identified TFP metabolites. Multiple resonances in vitro partially explain the relatively large line width seen in vivo for TFP. Unidentified metabolites were observed at about -74 to -75 ppm in a number of spectra of extracts of brain and muscle.

Determination of sulfamethazine in swine and cattle feed by reversed-phase liquid chromatography with post-column derivatization: pre-collaborative study

In-house validation of a liquid chromatographic method for determination of sulfamethazine in swine and cattle feed was performed to verify that the method was ready for collaborative study under AOAC INTERNATIONAL guidelines. In this method, sulfamerazine is added during the extraction procedure and is used as an internal standard to correct for variable recovery of sulfamethazine from a variety of swine and cattle feed matrixes. The determinative step involves the use of post-column derivatization with dimethylaminobenzaldehyde which reacts with the primary amine group on the sulfonamides. Detection is at 450 nm, a wavelength at which most co-extracted matrix materials and other feed additives do not absorb light. The results indicate that the method recovery, precision, and ruggedness meet normal criteria to be ready for a collaborative study. Fortification experiments over a range of sulfamethazine concentrations from 0.006 to 0.26% showed an overall recovery relative to the internal standard of 100 +/- 2%. These studies include both swine and cattle feed matrixes. The mean recovery in the analysis of 3 beef cattle experimental feeds was 98.9%. The method results agreed with the AOAC INTERNATIONAL Official Method for colorimetric analysis of swine feed. Method precision was excellent during in-house validation studies, with coefficients of variation (CVs) ranging from about 0.5 to 3%. The method ruggedness was verified with an overall CV of 3.5%.

Determination of sulfamethazine in swine and cattle feed by reversed-phase liquid chromatography with post-column derivatization: collaborative study

A liquid chromatographic (LC) method for the analysis of sulfamethazine (SMT) in complete swine and cattle feed was collaboratively studied. The method uses post-column derivatization with dimethylaminobenzaldehyde and detection at 450 nm. To 5g finely ground feed, extractant (0.2N HCl + 1.5% diethylamine in 25% methanol), and internal standard solutions are added, and the SMT is extracted by shaking for 1 h. Clarified extract (high-level sample extract diluted to a target concentration of ca 5.5 microg/mL) is chromatographed on a Cla reversed-phase LC column with acetonitrile-2% acetic acid (17 + 83) mobile phase. Sulfamerazine is used as an internal, or surrogate standard to correct for variable recovery of sulfamethazine from a variety of feed matrixes. Six Youden matched-pair samples were sent to 10 collaborators in Korea, Canada, and the United States. Label claims on the commercial feeds ranged from 0.0077 to 0.22% SMT. The SMT mean recovery as determined from the 5 samples with known analyte content was 99.8%. The within-laboratory relative standard deviation (repeatability) ranged from 0.28 to 4.72%. Among-laboratory (including within-laboratory) relative standard deviation (reproducibility) ranged from 1.26 to 4.87%. The authors recommend the method for AOAC INTERNATIONAL Official First Action status.

Characterization of polyalkylvinyl ether phases by solid-state and suspended-state nuclear magnetic resonance investigations

Pure organic polyalkvlvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C4VE) and n-octadecylvinyl ether (C18VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and 1H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of 1H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the 1H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin-lattice relaxation times (T1) as well as accumulation of a 2D wide line separation NMR spectrum.

Hyphenation of high performance liquid chromatography with nuclear magnetic resonance spectroscopy for the characterization of beta-carotene isomers employing a C30 stationary phase

The hyphenation of HPLC together with NMR spectroscopy proves advantageous for the structure elucidation of oxidation- and UV-sensitive compounds such as beta-carotene isomers. In the closed-loop HPLC-NMR system, degradation or isomerization of separated compounds is largely hindered. With the help of 3-microm C30 stationary phases a better separation efficiency towards the different beta-carotene cis/trans isomers could be obtained in comparison to a 5-microm material, resulting in sharper peaks and a better resolution of all compounds. This effect greatly facilitated the structure determination of the isomers by HPLC-NMR coupling. Due to the introduction of a superior stationary phase, the structure of seven cis-isomers of beta-carotene could thereby be determined employing the stopped-flow HPLC-1H-NMR mode.

n-Alkyl fluorenyl phases in chromatography. II. Dynamic behavior and high-performance liquid chromatography applications

The dynamic behavior of two n-hexyl fluorenyl phases (fluorene-6A [3a(Tn)(Qm)y], fluorene-6B [3b(Tn)(Qm)y]) and three n-decyl fluorenyl phases (fluorene-10A [4a(Tn)(Qm)y], fluorene-10B [4b(Tn)(Qm)y], and fluorene-10C [4c(M1)(Qm)y]) is investigated by solid-state nuclear magnetic resonance (NMR) spectroscopy using the dipolar filter technique with both 13C and 1H detection. These results are compared with those from other dynamic measurements, like the relaxation times in the rotating frame (T1pH) and the variation of the contact time (T(CH)). Additionally, another type of a fluorenyl phase [5a(Tn)(Qm)y], which has an aromatic moiety connected to the silica gel by amido couplings, was also investigated by the dipolar filter method. The solid-state NMR dynamic measurements indicate an increased mobility of the n-alkyl fluorenyl phases compared to the amido coupled fluorenyl phase. The lower the ligand density of the studied n-alkyl fluorenyl phases, the higher their mobility. The separation behavior of the respective phases in high-performance liquid chromatography was investigated with samples containing polycyclic aromatic hydrocarbons and nitro explosives. Depending on the amount of the chemically bound aromatic moiety and the length of their n-alkyl spacer groups, pi-pi interactions with the solute molecules are involved in the separation process and cause it to proceed at a different rate. Therefore, n-alkyl fluorenyl phases can be classified as mixed-mode phases.

Liquid chromatography-nuclear magnetic resonance spectroscopy

A general overview of the experimental set-up for performing analytical-scale and nanoliter-scale liquid chromatography-1H nuclear magnetic resonance spectroscopy (LC-1H-NMR) experiments is given. The high power of combining LC with 1H-NMR spectroscopy is demonstrated by two examples, where NMR acquisition was performed either in the continuous-flow mode on the analytical scale or in the stopped-flow mode on the nanoliter scale. Current developments employing the on-line coupling of capillary as well as supercritical fluid separation methods with 1H-NMR spectroscopy together with LC-13C-NMR spectroscopy are discussed.

Separation and identification of various carotenoids by C30 reversed-phase high-performance liquid chromatography coupled to UV and atmospheric pressure chemical ionization mass spectrometric detection

In this paper the application of on-line HPLC-UV-APCI (atmospheric pressure chemical ionization) mass spectrometry (MS) coupling for the separation and determination of different carotenoids as well as cis/trans isomers of beta-carotene is reported. All HPLC separations were carried out under RP conditions on self-synthesized polymeric C30 phases. The analysis of a carotenoid mixture containing astaxanthin, canthaxanthin, zeaxanthin, echinenone and beta-carotene by HPLC-APCI-MS was achieved by scanning the mass range from m/z 200 to 700. For the characterization of a sample containing cis/trans isomers of beta-carotene as well as their oxidation products, a photodiode-array UV-visible absorbance detector was used in addition between the column and the mass spectrometer for structural elucidation of the geometrical isomers. The detection limit for beta-carotene in positive-ion APCI-MS was determined to be 1 pmol. In addition, an extract of non-polar substances in vegetable juice has been analyzed by HPLC-APCI-MS. The included carotenoids could be identified by their masses and their retention times.

Gradient elution capillary electrochromatography and hyphenation with nuclear magnetic resonance

Coupling of gradient capillary electrochromatography (gradient CEC) and capillary zone electrophoresis (CZE) with nuclear magnetic resonance spectroscopy (NMR) was performed using a recently developed capillary NMR interface. This technique was applied for the analysis of pharmaceuticals and food. An analgesic was investigated using isocratic and gradient continuous-flow CEC-NMR. Comparison of the results demonstrated the superiority of gradient CEC over isocratic CEC. Aspartame and caffeine, both ingredients of soft beverages, were separated and analyzed by continuous flow CZE-NMR. The order of elution could be reversed by altering the pH. This reversal led to an increased sample concentration in the NMR detection cell, thus allowing the acquisition of a totally correlated spectroscopy (TOCSY) two-dimensional (2-D) spectrum of the synthetic peptide aspartame.

Reversed-phase high-performance liquid chromatographic identification of lutein and zeaxanthin stereoisomers in bovine retina using a C30 bonded phase

An efficient reversed-phase high-performance liquid chromatographic assay with ultraviolet detection at 450 nm for simultaneous determination of lutein and zeaxanthin stereoisomers in bovine retina is described. The procedure involves rapid and careful one-step hexane extraction of the carotenoids from the homogenized liquid and enrichment by on-line solid phase extraction on a polystyrene cartridge. The substances were eluted at a flow rate of 1 ml/min with acetone-water (85:15, v/v) on a C30 reversed-phase column. C30 phases exhibit superior shape selectivity for the separation of carotenoid stereoisomers compared with conventional C18 phases. For comparison a mixture of iodine-isomerized lutein and zeaxanthin standards was separated.

Directly coupled CZE-NMR and CEC-NMR spectroscopy for metabolite analysis: paracetamol metabolites in human urine

Direct coupling of NMR spectroscopic detection with both capillary zone electrophoresis (CZE) and capillary electrochromatography (CEC) was applied to the separation of metabolites of the drug paracetamol in an extract of human urine. Continuous-flow CZE-NMR and CEC-NMR allowed the detection of the major metabolites, the glucuronide and sulfate conjugates of the drug and the endogenous material hippurate. Identification of these substances was achieved by examination of individual rows of the NMR chromatogram and this also gave estimates of the detection limits. For CEC-NMR, spectra were also obtained in the stopped-flow mode including a two-dimensional TOCSY NMR experiment which afforded confirmatory evidence for paracetamol glucuronide. Characterisation of drug metabolites using NMR spectroscopy is therefore possible with nanolitre sample volumes.