Polymers are an integral part of our everyday lives. With a global production of a about 300 million tonnes per year it is obvious that is very important to understand and being able to control the synthesis process of polymers. Benchtop NMR offers the possibility to follow such synthetic processes online in real time as demonstrated by Nicholas Warrens group from the University in Leeds. In their recent publication in in the journal “Polymer Chemistry” (DOI: 10.1039/C9PY00982E) they follow the conversion of different polymerization reactions in batch and in flow reactors. They investigated the polymerisation of acrylamide and methacrylate monomers in homogenous medium, as well in dispersion. Thanks to the build-in lock system of the Spinsolve spectrometers, deuterated solvents were not required for their study and the presaturation water suppression method allows them to get detailed kinetic information under different conditions.
The method can be extended to a wider range of polymers, as for example polyesters. The plot below shows how benchtop NMR can be used to quantify the monomer content inside a polymer solution. The inset in the graph shows that the monomer content determined by NMR is in excellent agreement with the gravimetrically determined content.
1D 1H spectra recorded on the Spinsolve 80 with different ratios of ε-caprolactone (εCL) and poly(ε-caprolactone) (PCL). The integrals of marked areas were used for quantification. The inset shows the content of ε-caprolactone as a function of the gravimetrically determined εCL content.
In Vietnam, for the observation of animals in the jungle of the national park of Cat Tien (and in other parts of the country and in Asia), the rangers give the tourists leech socks and a repellent cream for land leeches to put on the socks. Land leeches are terrestrial blood-sucking worm-like parasites. Reading the cream container, I noticed that it contains diethyl phthalate (DEP). Out of curiosity, I dissolved some of the cream in CDCl3 and acquired a NMR spectrum with the Spinsolve 80 MHz benchtop NMR spectrometer.
The 1D 1H spectrum confirms that the cream is mainly composed of diethyl phthalate (Fig. 1, a). A zoom of the spectrum (Fig. 1, b) shows the presence of some additional compounds overlapping with the 13C satellite peaks of DEP (0.55% of the main peaks). To simplify the identification of the additional compounds present in the cream I acquired a 1D 1H spectrum using the carbon decoupling protocol available in the Spinsolve software (Fig. 1, c). This method removes the satellites from the spectra making it possible to detect compounds dissolved at concentration smaller than 1% with respect to DEP.
Typical excipients used in such creams are fatty acid mixtures from butter and/or oils, glycerol/glycine, alcohol (multiplet ~ 3.5 ppm, CH2-OH) and PEG based compounds (peak ~ 3.6 ppm) and even perfume(s).
In our case, the fatty acid peaks are easily recognized. The terminal methyl of fatty acids is observed in region F around 0.8 ppm, the aliphatic chain in region E and probably under the CH3 of DEP, and the olefinic protons of saturated fatty acids around 5.2 ppm in the region A. As no signal is observed around 2.8 ppm, the saturated fatty acids present in the cream are mono unsaturated. The singlet at 2.47 ppm (singlet C) could be a residual solvent like DMSO or 1,3-dioxan, common solvents contaminating cosmetic cream. To check this hypothesis, ~ 2 µL of solvent was added. If the cream contains the solvent, the integral of peak C would increase, but in our case new peaks were observed (data not show). Region B correspond to a CH3 group next to a (mono or di) substituted aliphatic. The area D could be a triplet with a J coupling of 7 Hz. These peaks probably belong to a perfume, where the additional peaks of the perfume molecule overlap with peaks of DEP.
This week our team is at the excellent Magnetic Moments in Central Europe conference in Prague. Our applications team are there with a working Spinsolve and would be delighted to show you the Spinsolve NMR spectrometer in action. If you are attending please come by our booth to say hi and see the best benchtop NMR for yourself.
There are two naturally occurring NMR active nuclei of Boron, 11B (80.1%) and 10B (19.9%). Both nuclei are quadrupolar with spin of greater than ½. 11B has a spin of 3/2 and 10B is spin 3. In terms of sensitivity, 11B is the better nucleus to use as it has a higher natural abundance, a higher gyromagnetic ration, and a lower quadrupole moment. A Spinsolve benchtop NMR spectrometer with a proton frequency of 60 MHz can be configured to measure the 11B NMR signal which has a frequency of 19.2 MHz.
The 11B NMR spectrum of a 0.23 M solution Sodium tertraphenylborate in MeOH-d4 is shown below. The first spectrum shows the excellent sensitivity of Spinsolve using just 8 scans to acquire a spectrum in only 16 seconds.
SMASH is Celebrating its 20th Anniversary in 2019!
Magritek is participating in the SMASH 2019 on 22-25 September 2019 in Porto-Portugal. You’ll get a chance to meet us, learn about our company and we’ll get you acquainted with Spinsolve – high-performance benchtop NMR spectrometer that offers impressive sensitivity and resolution, it is robust and easy to use. We are looking forward to seeing you at this conference !!!
The best-selling Magritek 80 MHz Spinsolve benchtop NMR is also available with the X-channel set to 31-Phosphorus. 31P NMR spectroscopy is routinely used by chemists to determine structure and measure impurities. When looking for impurities it is important to know the lower limit of detection (LOD). The LOD is the lowest concentration of a molecule that can be distinguished from the absence of that molecule.
In NMR it is the sensitivity that determines the LOD for a particular substance, and the higher magnetic field of an 80 MHz magnet brings a number of advantages including increased sensitivity. We thought it would be interesting to determine the LOD for tetramethylphosphonium chloride with different acquisition times. We defined the LOD as an NMR peak with signal height that was 3 times the noise level, i.e. an SNR of 3.
We are very excited to announce the launching of our new Spinsolve Autosampler. It enables up 20 separate samples to be measured in any order and can be fitted to all Spinsolve models. We have been developing this for some time, and already have quite a number of units with some of our reference customers who tell us they are delighted with its operation, functionality and high quality construction.
The Autosampler is particularly useful for customers who often have a series of samples to run on their benchtop NMR and want to save the hassle of having to keep coming back to exchange samples. Another benefit is the ability to increase utilization by setting up a queue of experiments to run on their Spinsolve overnight.
After 1H, 13C is easily the next most important nuclide in the NMR periodic table; 13C measurements can provide a wealth of valuable structural info. Unfortunately, with a receptivity that is around 5,500 smaller than that of 1H, 13C is a much less sensitive nuclide. This lower sensitivity demands the maximum performance from the NMR spectrometer to keep the measurement times and sample concentration within practical limits. Since 13C NMR has the reputation to be challenging even for high field spectrometers, people tend to think that only overnight experiments can be performed on bench top systems. In the first example below we want to show you that even at frequencies like 43, 60 or 80 MHz high quality 13C spectra can be acquired in a single scan. If your goal is to teach the principles of 13C NMR to students, it is worth knowing that good 13C NMR spectra can be acquired on concentrated organic liquid samples in just under a minute. Moreover students can collect a whole set of powerful multidimensional heteronuclear experiments in well under an hour. The spectrum below of neat propylbenzoate could serve as a useful example for teaching 13C NMR in an educational environment.
Figure1: 1D 13C NMR spectra of neat Propylbenzoate acquired with a single scan (blue), 4 scans (green) and 16 (red) scans totalling 5, 20 and 80 seconds of acquisition time respectively.
As the concentration of the sample decreases the experiment will take more time depending on the concentration and 13C sensitivity of your instrument. As described in the previous post, the effect of lower sensitivity can cause the experiment time to increase dramatically because of the square root relationship with the number of scans. Because 13C sensitivity is such a critical parameter we want to provide some standards that can be used as reference to understand and evaluate 13C measurements when considering a benchtop NMR instrument.
Malvern, PA, USA, 4th December 2018: Magritek announces that it has been awarded a major contract by the US Drug Enforcement Administration (DEA) for two Spinsolve 80 Carbon benchtop NMR spectrometers. The purchase was made through a competitive award process and will allow DEA laboratories in Virginia and California to utilize the latest benchtop NMR technology to assist in forensic analysis applications.
Speaking about this prestigious award, Magritek Inc’s CEO, Dr Hector Robert, says
“We are very excited to be awarded this contract by the DEA. The selection of the 80 MHz Spinsolve instrument with 1H, 19F and 13C nuclei provides a versatile system suited to the analysis of many substances studied in forensic science. The systems are supplied with autosamplers which enable the measurement of multiple samples with an automated and efficient workflow.”