Pulsed Nuclear Magnetic Resonance Spectrometer Research Articles

Improvement of industrial processes in Colombia. Case study: Cocoa pressing process in a chocolate factory

This work explored an industrial-scale cocoa liquor pressing process used to obtain two standard fat-reduced cocoa powders with 12% and 16% wt. fat, respectively. A novel methodology was developed to sample and characterize fat content in cocoa cakes as released from the press before the powdering. Cocoa liquors with ~ 53% wt. fat, and with solids containing maximum ~1% wt. of particle below mesh 200 were pressed at 90 °C, and up to 550 bar following a specific time-pressure profile. Fat content in samples was measured with a pulsed nuclear magnetic resonance spectrometer. Experiments enabled to evaluate the variability of fat content of products from different batches, in different cakes from a batch, and within the cakes, verifying large average deviations (~ 5% wt.). By using a Kernel canonical correlation analysis with a Kriging interpolation approach, it was possible to map the fat content profile within the cakes, enabling to identify suitable sampling areas in the cakes for consistent and more accurate measurements of fat content in the product. Finally, the developed methodology was used to characterize different pressing batches at the industrial facility, and to correlate the required processing time for a specific fat content in the liquor.

Nuclear Magnetic Resonance and X-ray Reflectometry of Co/Cu Superlattices

The state of interfaces in Co/Cu superlattices with various thicknesses of non-magnetic Cu layers (tcu) has been studied by the methods of nuclear magnetic resonance (NMR) and X-ray reflectometry. The samples glass/Fe(5 nm)/[Co(1.5 nm)/Cu(tcu)]10/Cr(3 nm) were fabricated by the method of magnetron sputtering on glass substrates under constant current in the ULVAC MPS-4000-C6 device. The 59Co NMR spectra were taken in a local magnetic field in the frequency range of 90–240 MHz at 4.2 K in the pulsed NMR spectrometer. The spin echo signal was formed by a sequence of two coherent radio-frequency pulses (τp)x − tdel − (τp)y − tdel – echo forming an alternate magnetic field with the round component amplitude H1 of about 10 Oe in a resonance coil. It has been shown both by NMR and X-ray reflectometry that the structure of interfaces deteriorates with an increase of the Cu layers thickness, and similar dependences of the parameters characterizing structural imperfection of interfaces were obtained by these two methods.

Study of regularities of distributing powdered dietetic additives in coarse dispersed foodstuffs

An important intervention in the composition of food products is enrichment of food with micronutrients. In this regard, the authors investigated how the additive with the corresponding trace element will be distributed in the food product, and in this case, in minced meat, in order to meet the human needs for microelements.Micronutrient deficiencies have a significant impact on the nutritional status and health of the population in well developed and developing countries. These deficiencies cause a delay in the growth of children, various diseases, mortality, brain damage, reduced cognitive capacity and the ability of people of all ages. The global scale of micronutrient deficiencies in dietary intakes, in particular the lack of trace elements, has led to the development of powdered dietary supplements containing essential elements that enrich the coarse-type food products to increase their nutritional value. The dietary supplement should provide the daily requirement of trace elements in the human body; therefore, it should be added to the product in a normalized amount and evenly distributed in the product.Two nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) analysis were performed to determine the distribution of the additive in food products. The analysis was carried out in two stages respectively: study of molecules mobility by measuring the spin-spin relaxation time (Т2) and spin-lattice relaxation (Т1) on a pulsed NMR spectrometer; establishment of a connection between the exponent of the amplitude of the sample A0 and its mass. Based on the data obtained, as a result of the measurement, a curve is constructed for the dependence of the amplitude of the echo signal from the value (time interval between the probing pulses). The spin label used in this work is one of the first variants of a paramagnetic probe-an easily accessible transition metal ion Mn2+. According to the constructed graphs and tomograms from the results of the studies, it is possible to study the characteristics of this dietary supplement and the expediency of its use.

Single bead detection with an NMR microcapillary probe

We have developed a nuclear magnetic resonance (NMR) microcapillary probe for the detection of single magnetic microbeads. The geometry of the probe has been optimized so that the signal from the background water has a similar magnitude compared to the signal from the dephased water nearby a single magnetic bead within the probe detector coil. In addition, the RF field of the coil must be uniform within the effective range of the magnetic bead. Three different RF probes were tested in a 7T (300MHz) pulsed NMR spectrometer with sample volumes ranging from 5nL down to 1nL. The 1nL probe had a single-shot signal-to-noise ratio (SNR) for pure water of 27 and a volume resolution that exhibits a 600-fold improvement over a conventional (5mm tube) NMR probe with a sample volume of 18μL. This allowed for the detection of a 1μm magnetite/polystyrene bead (m=2×10−14Am2) with an estimated experimental SNR of 30. Simulations of the NMR spectra for the different coil geometries and positions of the bead within the coil were developed that include the B0 shift near a single bead, the inhomogeneity of the coils, the local coil sensitivity, the skin effect of the coil conductor, and quantitated estimates of the proximity effect between coil windings.

Novel in situ NMR Measurement System for Evaluating Molecular Mobility during Drawing from Highly Entangled Polyethylene Melts

AbstractA novel in situ measurement system for evaluating molecular mobility during uniaxial drawing of polymeric materials was established by introducing drawing and stress‐detecting devices into a 1H pulse nuclear magnetic resonance spectrometer. In this study, we analyze the changes in molecular motion of amorphous chains during melt‐drawing of ultra‐high molecular weight polyethylenes (UHMW‐PEs) with different molecular weight distributions. In the initial stage of drawing, a three‐component resolution was possible for the relaxation decay curve, which includes “rigid”, “intermediate”, and “mobile” amorphous components. The quality and quantity changes in these components demonstrated that this intermediate amorphous component could be regarded as the index of the change in molecular entanglement characteristics during the orientation of PE chains.magnified image

Paul Christian Lauterbur

Paul Christian Lauterbur

A transmit-receive section of a pulsed nuclear magnetic resonance spectrometer

A transmit-receive section used in a prototype of the human-body drug detector, which can be applied in pulsed nuclear magnetic and quadrupole resonance spectrometers for investigations of solid samples, is described. The working frequency of the section is 11.3 MHz, the sample volume is ∼140 cm3, and the maximal amplitude of the high-frequency pulse in the circuit is 2000 V. A section recovery time of ∼2 μs was obtained due to the use of simple active high- and low-level dampers and quickly recovered preamplifier.

In situ monitoring of solid fat content by means of pulsed nuclear magnetic resonance spectrometry and ultrasonics

AbstractAn ultrasonic technique was developed to study the crystallization process of edible fats on‐line. A chirp wave was used instead of the conventional pulser signal, thus achieving a higher signal‐to‐noise ratio. This enabled measurements to be made in concentrated systems [≈20% solid fat content (SFC)] through a 8.11‐cm thick sample without significant signal loss. Fat samples were crystallized at 20, 25, and 30°C at a constant agitation rate of 400 rpm for 90 min. The crystallization process was followed by ultrasonic spectroscopy and a low‐resolution pulsed nuclear magnetic resonance spectrometer. Specific relationships were found between ultrasonic parameters [integrated response, time of flight (TF), and full width half maximum] and SFC. TF, which is an indirect measurement of the ultrasonic velocity (v), was highly correlated to SFC (r2>0.9) in a linear fashion (v=2.601 SFC+1433.0).

PALM OIL CRYSTALLIZATION: EFFECTS OF COOLING TIME AND OIL CONTENT

ABSTRACT Isothermal crystallization behavior of fluid shortening formulation from blends of palm oil and palm olein was investigated. The oil blends filled in nuclear magnetic resonance (NMR) tubes to a height of 2.5 cm were melted at 70C for 30 min crystallization time. A set of 11 tubes for each temperature was placed at selected crystallizing time and the solid fat content (SFC) measured in a Bruker pulse NMR spectrometer. Crystal distribution of the same blend was observed under polarized microscope at the same time interval. A correlation was developed between SFC and crystal distribution. The crystallization curves demonstrated two distinct steps corresponding to two crystallization stages as a result of the occurrence of mixed crystallization. Crystallization was selective to the high melting triacylglycerols (TAG) at all temperatures as shown by shorter induction periods in blends with more than 41.8% palmitic acid. High melting TAG crystallized first and acted as nuclei for recrystallization of the low melting TAG. However, the low melting TAG at the same time could also solubilize the formed crystals. The average SFC as a function of time was 50% lower than the SFC profile. Slow crystallization temperature was able to promote large crystal formation that influences SFC of palm‐based shortenings. Blends of 40–60% palm oil showed promising formulations of stable fluid palm‐based shortening.

1H and39K Nuclear Magnetic Resonance Relaxation Study in a KHSO4Single Crystal

¹H and³⁹K Nuclear Magnetic Resonance Relaxation Study in a KHSO₄Single Crystal

Cr 3+ (I) and Cr3+(II) centers in alexandrite single crystal

Nuclear magnetic resonance spectra of the Be9 and Al27 nuclei as well as electron paramagnetic resonance spectra of Cr3+ ion in an alexandrite single crystal (BeAl2O4:Cr) have been investigated by employing a pulse nuclear magnetic resonance spectrometer and an X-band electron paramagnetic resonance spectrometer, respectively. Be has two magnetically inequivalent sites. While Al(I) at inversion symmetry has four magnetically inequivalent Al sites, Al(II) at mirror symmetry has two. The Cr3+(I) center has four magnetically inequivalent sites, whereas the Cr3+(II) center has two. All resonance sets of nuclear magnetic resonance for Be9 and Al27 nuclei and electron paramagnetic resonance for Cr3+ ion are analyzed in terms of crystal symmetry, ionic size, and charge state. It is concluded that the Cr3+(I) and Cr3+(II) ions substitute for Al3+(I) at inversion symmetry and Al3+(II) at mirror symmetry, respectively, intact of Be2+ sites.

Teaching the Fundamentals of Pulsed NMR Spectroscopy in an Undergraduate Physical Chemistry Laboratory

Pulsed nuclear magnetic resonance (NMR) spectroscopy has become the premiere technique for chemists and biochemists studying the conformational, structural, and dynamic properties of a wide variety of molecular and biological systems. The theories and physical concepts associated with pulsed NMR spectroscopy are difficult for undergraduate students to comprehend and often require a thorough understanding of spin physics. Additionally, undergraduates in a laboratory course often consider a pulsed NMR spectrometer to be a "black box" and do not really understand how it operates. To address these issues, we developed an undergraduate physical chemistry laboratory experiment that utilizes a commercially available bench-top pulsed NMR spectrometer. In this experiment, the students assemble the components of an NMR spectrometer, program a variety of pulse sequences, and collect T1 and T2 relaxation data.

Direct measurement of thermal fat crystal properties for milk‐fat fractionation

AbstractThe temperature dependency of the solid‐fat content of a fat is important for predicting the consistency of the final product and for process control. Two direct analytical methods for determining the solid‐fat content and the melting characteristics of milk‐fat fractions have been developed. The fractions are analyzed during crystallization, and the results give reproducible information about the thermal behavior of the fractions and the actual crystal amount in the suspensions. The results are obtained within minutes, and no separation of the fractions before the measurement is necessary. New ways of reducing process time are proposed. It is possible to adapt crystallization time to seasonal variations of the initial milk fat and to the required properties of the final product. Partially crystallized milk fat was directly measured in a calorimeter and a pulsed nuclear magnetic resonance spectrometer. The data showed good correlations and even more accurate results than the conventional methods. The calorimetric method makes it possible to detect polymorphic changes and co‐crystallization in the crystals so that the influence of processing parameters, such as energy input, on crystallization behavior can be investigated.

A Computer Interface for Data Acquisition from a Pulsed Nuclear Magnetic Resonance Spectrometer

ABSTRACT A interface is described for rapid data acquisition from a pulsed nuclear magnetic resonance (NMR) spectrometer. The system is built using an IBM compatible PC/XT and a commercial data acquisition card. The computerization has been accomplished without making any changes in the commercial spectrometer. The data acquisition program is written in Basic using the driver routines supplied along with the data acquisition card. The data analysis is carried out using a non-linear, least square curve fitting procedure.

In vivo19f spin relaxation in index finger bones

19F free induction decay (FID) signals have been observed from the index fingers of four male and two female adult volunteers using a 27-MHz pulsed nuclear magnetic resonance spectrometer equipped with a split ring resonator probe. The value of the in vivo spin-lattice relaxation time T1 of the fluoride ions naturally accumulated in bone mineral has been determined to be 2.0 +/- 0.3 s. The shape of the observed FID signals in the inhomogeneous external magnetic field indicates that the F distribution is not uniform along the length of the finger. The fluoride ion content of the index finger (within a 65-mm length from its distal end) was measured with a sensitivity of +/- 0.5 mg F within a 30-min observation time.

A pulsed, broadband NMR spectrometer

A pulsed nuclear magnetic resonance spectrometer suitable for measurements in solids is described. The spectrometer is phase coherent, and the pulse timing is synchronous with the operating frequency of the spectrometer. The apparatus uses a versatile pulse programmer and a gated broadband rf power amplifier which delivers 1.6 kW at 60 MHz with a 3-db bandwidth of 5 to 90 MHz. With the exception of the probe, the spectrometer does not contain any tuned elements. This permits short (0.5 μsec) recovery times between the end of the rf pulse and the start of the signal. The spectrometer relies heavily upon the use of commercially available modules. A detailed description of the spectrometer construction and a discussion of typical operating characteristics are presented.

A low-cost solid state pulsed NMR transmitter

A simple transmitter required in a pulsed nuclear magnetic resonance spectrometer is described. The transmitter operates at 12.4 MHz with a radio frequency pulse output of 35 W, sufficient for the measurement of relaxation times in biological samples. Good long- and short-term stability, high reliability owing to the use of all solid state devices (transistors and integrated circuits), simplicity of circuitry, and low cost (about $100) are some of the salient features of the transmitter. The constructional and operational details of various electronic circuits of the pulsed transmitter are discussed.

Auto-increment circuit for a digital pulse programmer

A circuit is described which will automatically advance the time spacings between groups of pulses of a digital pulse programmer controlling a pulse nuclear magnetic resonance spectrometer. The automatically incremented spacings of the pulse groups is particularly useful in spin-lattice relaxation time measurements in either a single-passage analog recording of transient signal information or multiple-passage digital (signal-averaging) recordings. Circuitry for operation in these two modes is presented. This auto-increment circuitry has been used in conjunction with the digital pulse programmer described by Conway and Cotts (preceding paper).

Polyamines-sickling red blood cell interaction

Abstract The binding of polyamine as a function of concentration to normal and sickling rcc'. blood cells is analyzed by Langmuir type binding isotherms, based on the Gouy-Chapman model for an electrical double Iayer, where the zeta potential is a function of only the normal distance coordinate. For normal erythrocytes, the apparent exotropic binding constants are found to be 103, 110, and 130 dl/g at normal distance coordinates of 4, 5, and 6 A, iezpectively. The esotropic binding constant is determined to be 420 dl/g at a distance of 7 A. For sickling red blood cells, the apparent exotropic binding constants are 3.3, 3.8, 4.6, and 6-7 dl/g at a distance of 4 to 7 A. The esotropic binding constant at a distance of 8 A is found to be 12-9 dl/g. The apparent binding affinity of polyamines to the normal red blood cell. therefore, is approximately 30 times greater than to the sickling erythrocyte. The Praxis pulse nuclear magnetic resonance spectrometer is used to determine the spin-lattice relaxation time ( T 1 ) for water in the presence of normal and sickling red blood cells. The spin-lattice relaxation time is found to be 540 ms for normal erythrocytes and 445 ms for sickling red blood cells in the oxy state. Differences in the spin-spin relaxation time ( T 2 ) for the two types of erythrocyte are negligible, being within the range of normal experimental error.

Simple, Spin-Echo Spectrometer

In an attempt to make pulsed nuclear magnetic resonance (NMR) widely available for teaching purposes, the design and construction of a simple and inexpensive pulsed NMR spectrometer are described in considerable detail. This spectrometer requires only one twelve-volt power supply. A complete procedure for tuning the spectrometer to resonance is also presented.