Benchtop nuclear magnetic resonance spectroscopy in forensic chemistry

Abstract

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique well known for its ability to elucidate structures and analyse mixtures and its quantitative nature. However, the cost and maintenance of high field NMR instruments prevent its widespread use by forensic chemists. The introduction of benchtop NMR spectrometers to the market operating at 40-80 MHz have a small footprint, are easy to use and cost much less than high field instruments, which makes them well suited to meet the needs of forensic chemists. These modern low field spectrometers are often capable of running multiple nuclei including 1 H, 13 C, 19 F and 31 P; 2D NMR experiments and advanced experiments such as solvent suppression and diffusion-ordered spectroscopy (DOSY) are possible. This has resulted in a number of publications in the area of forensic chemistry using benchtop NMR spectroscopy in the last 5 years that was previously missing from the literature. This mini review summarises this research including examples of benchtop NMR being used to identify and quantify compounds relevant to forensics and some advanced methods that may be used to overcome some of the limitations of these instruments for forensic analysis. Further validation and automation are likely required for widespread uptake of benchtop NMR in industry; however, it has been demonstrated as a useful complement to other analytical techniques commonplace of forensic laboratories.

A CASE (Computer-Assisted Structure Elucidation) for Bench-Top NMR Systems in the Undergraduate Laboratory for De Novo Structure Determination: How Well Can We Do?

“…Magnetic field strengths of less than 1.8 T (80 MHz) may encounter difficulties in de novo structure determination for some large molecular weight compounds. Nevertheless, their potential applications in the undergraduate lab, ranging from reaction monitoring to mixture quantification, advocate and encourage their incorporation to the chemistry curriculum. ,,− For the 1.8 T (80 MHz) magnetic field strength, instructors can expect to study a much wider breadth of organic compounds with varying molecular weights. Based on previous studies, compounds with a high degree of symmetry can provide additional benefits due to the reduction in the number of resonances, which leads to better spectral resolution .…”

Forensic seized drug analysis: Current challenges and emerging analytical solutions

“…In recent years, the miniaturization of NMR systems and replacement of superconducting magnets with permanent magnets has led to the creation of low‐field systems that are benchtop sized and do not require cryogens. These systems operate in the range of 40–100 MHz and can be used in a range of forensic applications to provide structural information on unknowns (Draper & McCarney, 2021). Castaing‐Cordier et al propose a workflow that includes benchtop NMR in combination with DART‐MS and integrated databases for the structural elucidation of unknown NPS (Castaing‐Cordier et al, 2021, 2022).…”

Slice through the water—Exploring the fundamental challenge of water suppression for benchtop NMR systems

“…2 In fact, most benchtop NMR systems can be comfortably situated on a lab bench, increasing accessibility for many users. 2,4 Benchtop NMR systems use a permanent magnet, removing the need for cryogens, which significantly reduces their maintenance costs compared to high-field NMR systems. [1][2][3] Therefore, benchtop NMR systems have attracted significant attention from many laboratories that want to use NMR spectroscopy but cannot support a high-field NMR system.…”

“…[1][2][3] Therefore, benchtop NMR systems have attracted significant attention from many laboratories that want to use NMR spectroscopy but cannot support a high-field NMR system. 2,[4][5][6][7] For instance, benchtop NMR is being increasingly applied in research related to adulteration of food, mobility of ions in batteries, and profiling of biofluids for disease diagnosis. 6,8,9 Many benchtop NMR systems can perform a wide array of advanced experiments commonly employed in high-field NMR instruments, albeit with a reduction in sensitivity and spectral dispersion.…”