手性溶剂-NMR法测定2,4-滴丙酸对映体纯度的定量分析

研究了手性溶剂法测定2,4-滴丙酸的^1H、^13C谱,在满足NMR准确定量所要求的分离度和信噪比的条件下,能准确测定手性化合物的对映体纯度。比较了以对映体百分含量（R％）和对映体过量（ee）表示手性农药的对映体纯度的差别,发现以对映体百分含量代替对映体过量来表示手性农药的对映体纯度更为准确。     

Isotopic labeling for determination of enantiomeric purity by 2H NMR spectroscopy

The use of 2H NMR spectroscopy as a tool for the analysis of enantiomeric purity is reported. Enantiopure isotopically chiral substrates bearing a monodeuterated methylene unit were prepared; introduction of an additional asymmetric center leads to diastereomers which can be distinguished by 2H NMR on a standard spectrometer. The assays allow for simple semiquantitative analysis of asymmetric transformations.     

Establishment of an analytical method for accurate purity evaluations of acylcarnitines by using quantitative 1H NMR spectroscopy

Accreditation and Quality Assurance - Recently, it has become possible to examine metabolism abnormalities by detecting increases in specific acylcarnitines in blood tests of newborn babies using...     

Pristine single-walled carbon nanotube purity evaluation by using 1H NMR spectroscopy

Proper purity characterization of single-walled carbon nanotubes (SWCNTs) is an increasingly hot topic in the area of carbon nanotechnology. There are inconsistencies in purity characterization of SWCNT from manufacturers and in the literature. Purity of “as received,” oven dried, and NaHCO₃-washed SWCNTs of three commercially available brands (NanoLab, SWeNT, and HiPco) is explored by using a consistent methodology via proton nuclear magnetic resonance (¹H NMR) spectroscopy comparison, across three NMR solvents: DMSO-d ₆, CDCl₃, and D₂O. Important insights into the purity of commercially available SWCNT and the importance of washing (cleaning) samples before use are offered.     

Quantitative evaluation of amino acids using microwave accelerated hydrolysis

Summary An improved method for the quantitative determination of amino acids using HPLC, after preliminary derivatisation with o-phthalaldehyde, is described. Separation was carried out on a LiChrospher RP-18 column, using gradient elution and a fluorescence detector. Hydrolysis was performed with 6M HCl or with 3M p-toluenesulphonic acid depending on the amount of carbohydrates in the sample. In addition, the time required for total hydrolysis was shortened from 24 hours to 15 minutes by the use of a microwave oven. The results with these two hydrolytic methods are compared with regard to the extent of peptide bond cleavage and the percentage of decomposition of amino acids in a test mixture.     

Simple31P NMR method for the determination of the enantiomeric purity of chiral O-alkylalkylthiophosphonic acids

The³¹P-(¹H) NMR spectra of bis(alkylalkoxythiophosphoryloxy)phosphonites may be utilized to determine the enantiomeric purity (p) of O-alkylalkylthiophosphonic acids with the application of the Oro equation, p= (Q – Q)/(Q + Q), where Q is the integral intensity of the d, -form, and Q is the integral intensity of the meso forms.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2225–2228, October, 1989.     

Direct determination of enantiomeric purity of FMOC amino acids with high performance liquid chromatography

Summary Analytical methods are described which allow a direct determination of enantiomeric purity of seventeen FMOC amino acids commonly used in peptide synthesis. The corresponding ester derivatives can be separated directly on cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel-OD). The methods are suitable for primary as well as secondary FMOC amino acids. The presence of a highly sensitive fluorescence moiety within the molecule, in combination with large separation factors (-values between 1.5–2.2) allowed for a general detection limit below 0.05%. In several cases the antipode has been determined in the ppm-range. An interesting result has been observed with respect to the elution order of the FMOC amino acid esters. The elution order of the Trp enantiomers is opposite to that obtained with the other amino acids. This is contrary to the generally held belief that elution order is identical within a homologous series of racemates when chromatographed under identical conditions on the same chiral stationary phase. In addition, the inversion of elution of the Pro enantiomers depending on the estertype indicates a competition of different separation mechanisms.     

The determination of steric purity of amines and amino acids by gas chromatography and mass spectrometry

Amines and amino acids have been condensed with a mixture of N-TFA-R-prolyl chloride and n-TFA-S-[1-²H]-prolyl chloride and the resulting four diastereoisomers have been separated by gas chromatography into two peaks. The amount of each diastereoisomer formed was then determined by chemical ionization mass spectrometry. The steric purity of the enantiomeric mixture can be calculated from these values. The method is not dependent on the diastereoisomer formation going to completion.     

Quantitative determination of amino acids in functional foods by microchip electrophoresis

Microchip electrophoresis (MCE), a first-generation micrototal analysis system, has emerged during the miniaturization phase of food analysis. Based on the micellar electrokinetic chromatography mode, a simple and fast MCE method with light emitting diode-induced fluorescence detection was developed for quantitative analysis of amino acids in three different kinds of functional foods, viz. sports beverages, jelly-form beverages, and tablet-form functional foods. In contrast to the glass microchip, we improved the separation of amino acids on a poly(methyl methacrylate) (PMMA) chip by addition of cationic starch derivatives. 4-fluoro-7-nitro-2,1,3-benzoxadiazole, which has a short labeling time for amino acids, was used as the fluorescently labeled dye. This MCE method takes less than 10 min of total analysis time including sample preparation and analysis of amino acids in functional foods on a PMMA chip. The results show that this approach has the potential to be a fast and simple method for amino acid analysis in functional foods.     

An efficient method for the determination of enantiomeric purity of racemic amino acids using micellar chromatography,a green approach

A simple, sensitive and green micellar liquid chromatographic method (RP-HPLC) was developed for enantioseparation of four racemic amino acids, namely, (RS)-selenomethionine, (RS)-methionine, (RS)-cysteine and (RS)-penicillamine. An aqueous solution of sodium dodecyl sulfate and Brij-35 was prepared and used as mobile phase for HPLC analysis. Activated esters of (S)-ibuprofen, (S)-ketoprofen and (S)-levofloxacin were synthesized by reacting them with N-hydroxybenzotriazole. These esters were characterized by UV, IR, ¹HNMR, HRMS and elemental analysis. These chiral reagents (activated esters) were used for the synthesis of diastereomeric derivatives of the chosen amino acids. The diastereomeric derivatives were separated on a C₁₈ column by micellar liquid chromatography. Chromatographic conditions were optimized by varying concentration of surfactant in aqueous solution, and by varying the concentration and pH of the buffer. The green assessment score was calculated for the developed method (78, an excellent green method score). In addition, density functional theory calculations were performed, using Gaussian 09 rev. A.02 and hybrid density functional B3LYP with a 6-31G* basis set program, in order to develop lowest energy optimized structures of diastereomeric derivatives. The method was validated according to International Conference on Harmonization guidelines and the retention factor (k), selectivity factor (α), resolution factor (R_S) and limit of detection (0.295 ng ml⁻¹) and limit of quantification (0.896 ng ml⁻¹) were calculated.     

Quantitative 1H NMR method for the routine spectroscopic determination of enantiomeric purity of active pharmaceutical ingredients fenfluramine, sertraline, and paroxetine

Determining the enantiomeric purity of chiral therapeutic agents is important in the development of active pharmaceutical ingredients (API). A strategy for determining the enantiomeric purity of three APIs was developed using nuclear magnetic resonance (NMR) and the chiral solvating agent (CSA) 1,1-bi-2-naphthyl (1). While chiral chromatography is widely used to evaluate enantiomeric purity, it can sometimes suffer from tedious sample preparation obviating rapid measurements that are sometimes needed during the manufacture of such agents. The techniques described herein provide comparable enantiomeric purity results with those obtained with traditional chiral HPLC and other published methods for these compounds. Chiral analysis of standard samples of methylbenzylamine enantiomeric mixtures using 1 were found to be quantitative to approximately 1% minor enantiomer. Enantiomeric purity determination by NMR utilizing chiral solvating agents do not require special instrumental techniques, chemical derivatization or standards and is therefore ideally suited for rapid routine analysis. As a result, the technique demonstrated is commonly used in our laboratory as a complementary or alternative method to chiral HPLC or optical rotation measurements for routine determination of enantiomeric purity.     

Quantitative determination of glyphosate in human serum by 1H NMR spectroscopy

The determination and quantification of glyphosate in serum using (1)H NMR spectroscopy is reported. This method permitted serum samples to be analysed without derivatization or any other sample pre-treatment, using 3-trimethylsilyl 2,2',3,3'-tetradeuteropropionic acid (TSP-d(4)) as a qualitative and quantitative standard. Characterization of the herbicide N-(phosphonomethyl)glycine was performed by analysing chemical shifts and coupling constant patterns. Quantification was performed by relative integration of CH(2)-P protons to the TSP-d(4) resonance peak. The method was tested for repeatability (n=5) and yielded coefficients of variation of 1% and 3%, respectively: detection and quantification limits were also determined and were 0.03 and 0.1mmol/L, respectively. The method was applied to the quantification of glyphosate in a case of acute poisoning.     

3,5-dinitrobenzoyl amino acid esters. Broadly applicable chiral solvating agents for NMR determination of enantiomeric purity.

Methyl esters of N-(3,5-dinitrobenzoyl)-amino acids have been used as chiral solvating agents to induce NMR spectral nonequivalence between the enantiomers of a broad array of solutes.     

A stereodivergent approach to amino acids, amino alcohols, or oxazolidinones of high enantiomeric purity

(-)-Menthone, an inexpensive chiral auxiliary, was used to prepare both enantiomers of alpha-amino acids, amino alcohols, or oxazolidinones. The sequence includes the S(N)2' displacement by a cuprate reagent and a Curtius rearrangement as key steps.     

Quantitative determination of singlet oxygen generated by excited state aromatic amino acids, proteins, and immunoglobulins

Singlet oxygen quantum yields generated by excited state aromatic amino acids (tryptophan, tyrosine, phenylalanine), N-acetylated amino acids (N-acetyl-tryptophan, N-acetyl-tyrosine, N-acetyl-phenylalanine), and from selected proteins and immunoglobulins have been quantified by time-resolved phosphorescence measurements. A small, but significant, quantum yield found for proteins and immunoglobulins demonstrates that molecular oxygen can diffuse through the polypeptide matrix and can be sensitized by residues buried within the folds of protein structure.     

Quantitative high-performance liquid chromatographic determination of sulfur amino acids in protein hydrolysates

A rapid, quantitative high-performance liquid chromatographic procedure for the determination of methionine and cystine after oxidation to methionine sulfone and cysteic acid is described. The Dns derivatives of the amino acids are separated by reversed-phase chromatography with a phosphate buffer-acetonitrile gradient and detected by UV absorption at 254 nm. The procedure is validated by confirming the methionine and cystine content of ribonuclease A. The average yields of cysteic acid and methionine sulfone from triplicate analyses of ribonuclease A were 98.1% (±3.3) and 106.1% (±2.4) of the theoretical values, respectively.     

An uncertainty budget for the determination of the purity of glyphosate by quantitative nuclear magnetic resonance (QNMR) spectroscopy

An uncertainty budget is presented for the results of measurements of purity of the agrochemical glyphosate using ¹H and ³¹P quantitative nuclear magnetic resonance (QNMR) spectroscopy. The budget combines intralaboratory precision from repeated independent measurements of a batch, and other Type A and Type B effects. Consideration of correlation of uncertainties in ratios of mass determinations has been included. Expanded uncertainties of the purity for single determinations of purity by ¹H and ³¹P QNMR are 0.66% and 0.82% (95% confidence interval, k=2), respectively.     

Quantitative determination of carboxylate by infrared spectroscopy: application to humic acids

The carboxylate content has been determined by infrared (IR) spectroscopy in different commercial salts of carboxylic acids and also in commercial and isolated samples of soil humic acids. A linear standard curve using anhydrous sodium salicylate has been obtained from the plot of carboxylate (COO^–) concentration vs. the weight of the IR band area, using the COO^– antisymmetric stretch vibration at 1580 cm^–1. Parallel determinations of carboxy groups by the commonly used Ca(OAc)₂ method with related carboxylic acids and humic acids in the H⁺ form has been carried out for comparison. A much better sensitivity and a similar accuracy was obtained. This method is furthermore much faster, simpler and more economical, and offers in some cases a better applicability.     

Direct determination of enantiomeric purity using CPL spectroscopy

The dependency of the Circular Polarization of the Luminescence (CPL) on the handedness of the excitation light potentially provides a means to determine enantiomeric purity. In literature two procedures have been outlined for such determinations, but as yet they have not been experimentally tested. These procedures, along with a third one we propose here, are evaluated from theory and confronted with experiment. It appears that the CPL technique provides a valuable tool for the determination of enantiomeric purity. The scope and limitations of the method are discussed.