Measurement of emulsion stability by pulsed nuclear magnetic resonance (NMR)

The stability of emulsions can be measured rapidly and accurately using pulsed nuclear magnetic resonance (NMR).     

Cottonseed oil estimation by pulsed nuclear magnetic resonance technique

Seed asymmetry and moisture associated with the seeds are known to affect seed oil estimation by pulsed nuclear magnetic resonance (NMR) technique employing free induction decay or single spin echo (SE) pulse sequence. UsingGossypium (cottonseeds) as experimental material, it is shown that transverse relaxation times (T₂) of seed oil, in different varieties of seeds, measured in vivo, are not the same. The mean T₂ value of tetraploid seeds is found to be significantly higher than that of diploids. The effect of T₂ variation and other problems on oil estimation by the free induction decay and SE methods can be avoided by using the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence to monitor the signal intensities of a certain number of selected echoes and processing them to yield the extrapolated signal intensity at zero time. The oil content values thus estimated are found to agree well with those obtained by Soxhlet method. The agreement between the two methods might depend upon the presence of gossypol and other pigments present in the samples. Neither delinting nor dehydrating the seeds is necessary in the present method. Even with the CPMG sequence, use of individual echoes is not recommended, as the T₂ variations give rise to erroneous values.     

In-situ volume fraction determination in multi-component mixtures using pulsed nuclear magnetic resonance

A simple method of determining in-sitn volume fractions in multiphase or multi-component systems using pulsed nuclear magnetic resonance is proposed and discussed from both the theoretical and experimental point of view. A 180° - τ -90° pulse sequence was employed. Different mixtures were examined both analytically and experimentally and the results compared.     

Rapid and nondestructive determination of seed oil by pulsed nuclear magnetic resonance technique

The pulsed NMR technique for rapid and nondestructive determination of oil in oilseeds has been developed. The effects of spin-lattice relaxation time, spin-spin relaxation time, seed moisture, angular position of the seeds, sample tube thickness, and sample height upon the magnitude and reproducibility of the NMR signal were studied. Based upon these studies, various parameters for seed oil analysis have been fixed. The oil content of Brassica, peanut, and sunflower seeds was determined. The reproducibility of the measurement is ± 1 %. The technique was tested by measuring the oil content of the same seeds by the cold percolation method (CCl₄ extraction). It was further tested by determining the oil content of 60 Brassica seed samples independently at three laboratories. The results of these tests are given.     

Experimental characterization of emulsion formation and coalescence by nuclear magnetic resonance restricted diffusion techniques

Nuclear magnetic resonance (NMR) is explored as a technique for noninvasively monitoring emulsion droplet formation and destabilization. The method makes use of the fact that the diffusion of oil molecules within oil-in-water emulsion droplets results in attenuation of a coherent magnetic signal that emanates from those molecules. If oil diffusion is limited by the size of the droplet, the shape of a plot of attenuation over time is directly affected by the droplet radius. We use this approach to determine noninvasively the effect of surfactant type, surfactant concentration, pH, and ionic strength on droplet sizes within a 40 wt% octane and water emulsion, stabilized by Tween 20 or β-lactoglobulin (β-Lg). We find that addition of the low-molecular-weight Tween 20 forms finer emulsion droplets than does addition of the protein, and that the Tween 20 emulsion is sensitive to surfactant concentration below a threshold “saturation” concentration. The droplet sizes in β-Lg-containing emulsions increase as pH increases above the isoelectric point and as ionic strength increases. The fact that the NMR technique does not mistake clusters of droplets for single large droplets makes the analysis of these effects unambiguous. We further extend the use of NMR diffusion techniques to monitor the effect of surfactant type, surfactant concentration, and convection on the rate of droplet coalescence. The ability of NMR methods to distinguish between large single droplets and droplet clusters makes it well-suited to monitor coalescence processes independently from flocculation.     

Seed oil determination by pulsed nuclear magnetic resonance without weighing and drying seeds

Pulsed nuclear magnetic resonance (NMR), which takes about 10 sec per analysis, has been used for rapid nondestructive determination of oil in oilseeds without weighing and oven drying the seeds. This has been done by measuring the free induction decay (FID) signal of solid and liquid in oilseeds. The oil values determined by this method for mustard, sunflower, and soybean seeds have been compared with the values determined by measuring the oil signal alone in the intact seeds, which takes about 2 min per analysis. Correlation for mustard is 0.988, for sunflower 0.945, and for soybean 0.931. The reasons for better agreement for mustard and the way of improving it for sunflower and soybean have been discussed.     

Determination of the solid fat content of commercial fats by pulsed nuclear magnetic resonance

A method and instrumentation for measuring the solid fat content is reported that is both accurate and precise. It involves using transient nuclear magnetic resonance (NMR) measurements for determining the percentage of solids in commercial shortenings and hydrogenated oils at selected temperatures. The incorporation of a tempering step at 26.7 C for all samples before measurement has improved the precision of the solids content actually measured (±0.2% solids) which approximates that of dilatometry. Duplicate measurements are not required to obtain this precision. The instrument is equipped with six 10-mm sample holders in combination with a precise variable temperature accessory system which eliminates the temperature difference between the sample and sample holder. This improved and exact temperature conditioning of samples provides better sample stability and easier handling for routine conditions of analysis. A single temperature result can be made in less than 1 hr and typical 5 temperature results obtained in 2.5 hr. Our work also indicates that tempering does influence results, the net effect being to decrease the amount of solids at temperatures less than the tempering temperature. In comparing the pulsed NMR measured solids with these measured by dilatometry, differences between methods of measurement are minimized when samples have had the same tempering and temperature history. This method provides flexibility, speed, and increased sample throughput of up to 60 samples/day. The self-contained equipment requires only 9 sq ft of space and is ready for measurements within 45 min after start-up.     

Simultaneous determination of moisture and oil content in oilseeds by pulsed nuclear magnetic resonance

Pulsed nuclear magnetic resonance technique using Carr-Purcell-Meiboom-Gill (CPMG) sequence has been used for simultaneous determination of moisture and oil content in rapeseed-mustard. This method involves sampling the free induction decay (FID) following 90° pulse in the CPMG sequence and resolving the trace of the amplitude of the CPMG echo signals into exponentially decaying liquid components of oilseeds. The data show that water in oilseeds generally exists in 2 phases and the relatively slow decaying component disappears around moisture content of 7% and below. The moisture and oil content have been determined by the method for 34 samples of 5 different varieties of seeds at varying moisture levels (∼3% to 22%). The measured moisture and oil content have been compared with the values obtained by the oven drying method and earlier known FID method of pulsed nuclear magnetic resonance (NMR) respectively, and the agreement is fairly good for rapid estimation with standard deviation of 0.70% for oil content and 0.99% for moisture content. This is a rapid and nondestructive method for determination of both moisture and oil content without weighing and drying the seeds and also seems suitable for other matrix samples.     

Estimation of solid-liquid ratios in bulk fats and emulsions by pulsed nuclear magnetic resonance

Several pulsed nuclear magnetic resonance (NMR) methods were evaluated to estimate the solid fat content of fats and oil-in-water emulsions. The methods were checked with samples of paraffin oil or triolein containing known quantities of crystalline tristearate. A method based on the signal of solid fat (with use of a correction factor, the “f-factor”) was rejected in this work for general use. Correct results were obtained with methods that used only the signal of the liquid phase. With emulsions, disturbances could arise due to the surfactant present and to possible solubilization of water in the oil phase, presumably by monoglycerides. Without these disturbances, solid fat content in emulsions could be estimated as in bulk fats, after correction of the liquid phase signal for the contribution of protons from the aqueous phase. The signal from fat crystals inside emulsion droplets differed from that of crystals of the same fat in bulk, which may have been due to difference in crystal size but not to difference in crystal modification. Measurements on natural cream showed that disturbances were also possible in this type of emulsion.     

The effect of hydrogen content on estimation of seed oil by pulsed nuclear magnetic resonance

In the nondestructive estimation of seed oil by pulsed nuclear magnetic resonance (NMR), an assumption generally is made that the hydrogen content of the oil in the seed sample under investigation is the same as that of the oil standard or that of the oil in the standard seed samples. The hydrogen content is defined as the number of hydrogen atoms per unit mass of oil. The validity of this assumption has been investigated by; (i) calculating the Hydrogen contents of various oils on the basis, of their reported fatty acid composition, and (ii) experimentally determining the hydrogen contents of cotton and mustard oils obtained from different varieties of seeds. The FID method was used to monitor the NMR signal intensities. Both calculated and experimental values show that that hydrogen contents can be different not only for different oils but also for the same oil extracted from different varieties of the seeds. This variation in hydrogen contents is shown to introduce an error in the oil content values as estimated by NMR methods. The magnitude of this error increases with oil content, and also with the difference in the hydrogen contents.     

Simultaneous determination of oil and water contents in different oilseeds by pulsed nuclear magnetic resonance

Routine analysis of oil and water contents in different oilseeds with the Bruker Minispec pulsed nuclear magnetic resonance (NMR) analyzer (Bruker Analytische Mestechnik, Rheinstetten, Germany) is rapid (16 s measurements), precise, accurate and nondestructive. In 1991, subcommittee SC2 (oil seeds) of the Technical Committee Number 34 [organized by the International Standards Organization (ISO), Geneva, Switzerland] organized an international collaborative study for pulsed NMR analysis of oil content in whole rapessed. An additional study was performed in 1993 to extend the method to sunflower, linseed and soy seeds. The Draft International Standard ISO DIS/10565 (Draft International Standards, International Standards Organization, Geneva, 1993) describes the procedure of the pulsed NMR method for determination of oil content in rapeseed and presents the interlaboratory comparison results based on the calculations described in the Normative ISO 5725 (Draft International Standards, International Standards Organization, Geneva, 1993). The standard was approved in 1992 and will be published in 1993. The interlaboratory collaborative studies showed that the analyses of oil and moisture by pulsed NMR were either comparable or more repeatable than measurements done by the traditional methods. No statistical differences between determinations by the traditional and pulsed NMR methods were found. Simultaneous determination of percent moisture and percent oil content in whole seeds is possible with pulsed NMR by the spin-echo method. In addition, multiple components of the oil can be detected and quantitated by T2 analysis from the Carr-Purcell-Meiboom-Gill pulse sequence. The instrument is easy to calibrate with whole oilseeds, and the calibration can be checked periodically with the same seeds because the measurement is nondestructive. Pulsed NMR provides a rapid alternative to the long, laborious, traditional methods of analysis and offers substantial long-term savings of both time and money. Minimal operator training is required once the technique has been established for routine use. Presented at the 84th AOCS Annual Meeting & Expo, April 27, 1993, Anaheim, California.     

Oxidative stability and nuclear magnetic resonance analyses of linoleic acid encapsulated in cyclodextrins

The effects of α- and β-cyclodextrin (CD) on the oxidative stability of linoleic acid (LA) at 35°C were studied by measuring headspace oxygen depletion in airtight 35-mL serum bottles. LA was encapsulated in α-CD or β-CD in an aqueous solution during homogenization at 8000 rpm for 1 min and then dried under vacuum for 60 h at room temperature. Headspace oxygen was measured by thermal conductivity gas chromatography. The rate of oxygen depletion for the control, which contained LA only, was 93.8 μmole/L·h. The rates of oxygen depletion for LA, encapsulated at a 1:1 mole ratio (mole CD/moles LA) in α-CD and β-CD, were 13.8 and 111 μmoles/L·h, respectively. When LA was encapsulated in α-CD and β-CD at a 2:1 mole ratio (moles CD/moles LA), the rates of oxygen depletion were 0.573 and 53.9 μmoles/L·h, respectively. Although α-CD protected LA from reaction with oxygen at both ratios, the rate of oxygen depletion by LA encapsulated in β-CD at a 1:1 mole ratio was not statistically different from the control. β-CD protected LA from reaction with oxygen at a 2:1 mole ratio. ¹H nuclear magnetic resonance spectra of the complexes formed from 1:1 mole ratios of LA and CD indicated that LA was encapsulated in α-CD or β-CD. Presented at the 87th Annual AOCS Meeting, April 28–May 1, 1996, Indianapolis, Indiana.     

Microstructure study of styrene/n-butyl acrylate emulsion copolymers by 13C nuclear magnetic resonance spectroscopy

A detailed study of the sequence distribution in styrene (S)/n-butyl acrylate (A) emulsion copolymers using ¹³C nuclear magnetic resonance spectroscopy is reported. From the interpretation of the spectra of the homopolymers and copolymers, assignment of the carbonyl (A) and quaternary (S) carbon atom resonances has been made. This provides a quantitative estimation of the compositional triad distributions in the copolymers. The results were found to be in relatively good agreement with calculated triad fractions deduced from a simulation program taking into account the actual reactivity ratios and type of emulsion process.     

Two-dimensional nuclear magnetic resonance of resins

A group of resins was synthesised from a series of phenols and aldehydes, and their structures comprehensively deduced from two-dimensional nuclear magnetic resonance spectroscopy (2-D NMR). Correlation spectroscopy, in particular carbon-proton heteronuclear chemical shift correlation spectroscopy, was shown to be especially incisive in assigning structural features to the NMR signals. The method has permitted fuller structural characterisation of these materials than was heretofore possible, and has identified, inter alia, methylene and methyleneoxy bridges unequivocally: complex substitution patterns in the phenol-derived aromatic rings have also been elucidated. It is demonstrably possible to apply the same techniques to similar complex resin structures, and to utilise these structural insights to determine the mechanistic processes involved in their syntheses.     

定量核磁共振法研究进展

核磁共振法广泛应用于有机化合物的定性分析,但是它在化合物纯度定值、含量测定中也具有很重要的作用,分为一维谱(1H、13C、14N、15N、19F、31PNMR)、二维谱(J-分辨、1H-1H、1H-13C、DOSY)、液相色谱-核磁共振联用法(LC-NMR)、固体NMR等NMR类型。其中,1H谱最常用,其他一维谱对不同化合物各有其优势。二维核磁共振法对于在一维谱图中信号严重重叠的复杂样品的定量分析非常重要。LC-NMR联用技术将高效的分离手段与NMR联用,可以获得复杂样品的信息。介绍了各类定量核磁共振法在各领域的研究进展。     

Protein determination by nuclear magnetic resonance

Protein may be determined using a pulsed nuclear magnetic reso-nance (NMR) spectrometer in conjunction with a relaxation reagent. These reagents exhibit characteristic nuclear relaxation rates, controlled by a paramagnetic ingredient such as copper, and these rates are altered if substances are added which can bind the copper. The method is fast and simple. Sample and reagent are mixed, brought to a standard temperature and transferred to the spectrom-eter for measurement. Sample throughput can be high since the time for the spectrometer reading is on the order of 30 sec. Compositions and methods of use are given for 2 copper-based reagents together with the results on a number of materials. The alkaline copper reagent gives a very similar response to different types of protein and it appears suitable for meat, fish and for other protein materials low in carbohydrates. It shows a response to carbohydrate which depends strongly on type. The acid copper reagent is intended for measurements of vegetable or seed protein and similar applications where carbohydrate is present. This reagent does not respond to carbohydrates tested; the response to protein depends on the type of protein.     

Assay of cyclopropenoid lipids by nuclear magnetic resonance

Nuclear magnetic resonance (NMR) method for the quantitative analysis of cyclopropenoid fatty acids (CPFA) in lipids is described. Good accuracy is obtained at CPFA concentrations of 1% to 100%. At a CPFA concentration of 10%, NMR is accurate to 0.5%. The position of absorption of the two ring methylene hydrogens is solvent dependent.     

Solid state nuclear magnetic resonance studies of nanocarbons

In the present article we review Nuclear Magnetic Resonance studies of different kinds of nanocarbons, such as nanodiamonds, nanographites, pure and doped fullerenes, giant carbon fullerenes and carbon nanotubes.     

A comparison of different pulse sequences in the nondestructive estimation of seed oil by pulsed nuclear magnetic resonance technique

Three basic pulse sequences,viz., Free Induction Decay (FID), Spin Echo (SE) and Carr-Purcell-Meiboom-Gill (CPMG), available in the pulsed nuclear magnetic resonance technique have been used to estimate the relative oil content in single as well as bulk samples of oil-bearing seeds. Conclusive evidence has been presented to show that the CPMG sequence is vastly superior to the other two as far as the effects of seed orientation and moisture content are concerned.