Validation of a quantitative NMR method for suspected counterfeit products exemplified on determination of benzethonium chloride in grapefruit seed extracts

A general analytical platform and strategy in search for illegal drugs

“…Spectra were processed using TopSpin 2.1 software (Bruker Biospin Scandinavia AB, Stockholm, Sweden) using a 0.3 Hz exponential window function and zero-filling to 64k data points prior to Fourier transformation. For structure determination/confirmation, a set of five Bruker standard NMR experiments was used: 1 H, 13 C attached proton test, 2-dimensional gradient H,H-COSY, 2D gradient H,C-HSQC, and 2D gradient H,C-HMBC.qNMR measurements were performed using a repetition delay of 90 s to ensure complete relaxation, and 16 scans resulted in high signal-tonoise ratios. Locking, shimming, tuning/matching and acquisition were executed automatically using ICON-NMR software (Bruker Biospin Scandinavia AB, Stockholm, Sweden).…”

“…The platform consists of a combination of liquid chromatography coupled to mass spectrometry (LC-QTOF-MS) and NMR spectroscopy. The API is identified using LC-QTOF-MS and determination is made using quantitative NMR (qNMR) [13][14][15]. Most products consisting of tablets and capsules can be analyzed with LC-QTOF-MS after simple generic extraction with methanol.…”

A method for improved quantification of 1H NMR signals under low-resolution conditions for solids

“…Since qNMR is well established in liquid-state NMR [1,2] here we focus on quantification of solid-state NMR spectra. Under typical conditions the sensitivity of the NMR experiment is rather limited which does not make NMR a likely candidate for trace analysis where the analyte is below 1% in concentration.…”

“…Systematic studies in solid-state qNMR have highlighted different sources of errors, for example repetition delays (related to spin-lattice relaxation) [3,9], pulse-length effects [9], spectrometer stability issues [15], sample preparation, quantitative analysis with internal or external reference [2,3,14,15] and packing effects of the material in the MAS rotor [14,15], which lead to false intensities when excited by inhomogeneous radio-frequency fields. An exhaustive protocol for solid-state qNMR has recently been published [9].…”

“…As for other analytical methods also in qNMR many of the above mentioned problems can be circumvented by quantification relative to an internal reference [2,3], in contrast to quantification to an external reference, which critically depends on the stability of the spectrometer sensitivity constant. For this purpose the tobe-analyzed sample is mixed with a known reference sample of high purity (internal reference) where the mass ratio, reference mass m ref to analyzed sample mass m sample , is known.…”