New perspective for the in-field analysis of cannabis samples using handheld near-infrared spectroscopy: A case study focusing on the determination of Δ9-tetrahydrocannabinol

Abstract

The aim of the present study was to explore the feasibility of applying near-infrared (NIR) spectroscopy for the quantitative analysis of 9 -tetrahydrocannabinol (THC) in cannabis products using handheld devices. A preliminary study was conducted on different physical forms (entire, ground and sieved) of cannabis inflorescences in order to evaluate the impact of sample homogeneity on THC content predictions. Since entire cannabis inflorescences represent the most common types of samples found in both the pharmaceutical and illicit markets, they have been considered priority analytical targets. Two handheld NIR spectrophotometers (a low-cost device and a mid-cost device) were used to perform the analyses and their predictive performance was compared. Six partial least square (PLS) models based on reference data obtained by UHPLC-UV were built. The importance of the technical features of the spectrophotometer for quantitative applications was highlighted. The mid-cost system outperformed the low-cost system in terms of predictive performance, especially when analyzing entire cannabis inflorescences. In contrast, for the more homogeneous forms, the results were comparable.The mid-cost system was selected as the best-suited spectrophotometer for this application. The number of cannabis inflorescence samples was augmented with new real samples, and a chemometric model based on machine learning ensemble algorithms was developed to predict the concentration of THC in those samples. Good predictive performance was obtained with a root mean squared error of prediction of 1.75 % (w/w). The Bland-Altman method was then used to compare the NIR predictions to the quantitative results obtained by UHPLC-UV and to evaluate the degree of accordance between the two analytical techniques. Each result fell within the established limits of agreement, demonstrating the feasibility of this chemometric model for analytical purposes.Finally, resin samples were investigated by both NIR devices. Two PLS models were built by using a sample set of 45 samples. When the analytical performances were compared, the mid-cost spectrophotometer significantly outperformed the low-cost device for prediction accuracy and reproducibility.

Analytical Techniques for Phytocannabinoid Profiling of Cannabis and Cannabis-Based Products—A Comprehensive Review

“…Binary mobile phase system consisted of H 2 O/MeOH (10:90, v/v ) [ 186 ], H 2 O/MeOH (17/83, v/v ) [ 187 ] and H 2 O + 0.1% formic acid/MeOH + 0.1%; formic acid is most commonly used for phytocannabinoid profiling [ 11 , 63 , 65 , 147 , 185 , 188 ]. Other binary systems that provide good peak shape and improved resolution are also used, such as H 2 O + 0.1% formic acid/MeCN + 0.1% formic acid [ 40 , 55 , 64 , 80 , 109 , 134 , 144 , 182 , 183 , 185 , 188 , 189 ], H 2 O + 0.1% TFA/MeOH + 0.1% TFA [ 68 ], MeCN/H 2 O (75:25, + 0.05% formic acid, v/v )/isopropanol:MeCN (80:20 + 0.05% formic acid, v/v ) [ 183 , 184 ], 5% MeCN + 0.1% formic acid/MeCN + 5% H 2 O + 0.1% formic acid [ 78 ], H 2 O + 0.1% formic acid/MeCN [ 27 , 63 , 185 ], 5% MeCN + 0.1% formic acid/80% MeCN + 0.1% formic acid [ 69 ] and MeCN/H 2 O + 0.85% phosphoric acid [ 42 ].…”

“…Only one methods use direct injection [ 184 ], bypassing the column. Most of the published methods employ columns with normal phase C 18 stationary phase (Ascentis Express C 18 [ 40 , 178 ], Luna C 18 [ 69 , 177 ], Kinetex C 18 [ 11 , 19 , 71 ], Luna Omega Polar C 18 [ 58 , 114 , 118 , 139 ], Luna Omega PS C 18 [ 27 ], XTerra MS C 18 [ 83 ], Acquity UPLC BEH C 18 [ 181 ], Acquity BEH Shield RP18 [ 144 ], MacMod ACE5 C 18 -AR [ 190 ], ACE 3 C 18 -PFP [ 187 ], ACE Excel 3 C 18 [ 111 ], Poroshell 120 SB-C 18 [ 182 ], Poroshell 120 EC-C 18 [ 188 , 189 ] or 120 SB-C 18 [ 34 , 35 , 36 , 38 ], Shim-pack XR-ODSII RP C 18 [ 149 ], Nucleodur ® C 18 Gravity [ 185 ], Zorbax Eclipse Plus C 18 [ 92 , 183 ], Zorbax Eclipse XDBC 18 [ 186 ], Zorbax SB-C 18 [ 133 ], Atlantis T3 C 18 [ 42 ], with [ 11 , 19 , 34 , 35 , 36 , 38 , 83 , …”

“…For DAD, a narrower range is selected (i.e., 200–400 nm [ 83 ], 190–500 nm [ 182 ]). Single wavelength can be selected for evaluation of multiple phytocannabinoids in hemp seed oils [ 179 ], in plant material (230 nm) [ 68 ], 214 nm [ 188 , 189 ] or 220 nm in plant material and resins [ 69 , 165 ] or cannabis extracts [ 27 ], in commercial veterinary supplements (225 nm) [ 192 ] or for quantification of Δ 9 -THC, Δ 9 -THCA, CBN and CBD (210 nm) [ 191 ] or Δ 9 -THC and Δ 9 -THCA in plant material (211 nm and 220 nm) [ 185 ]. For wide range methods, such as cannabis-based medical extracts [ 182 ], cannabis-infused cholcolate [ 65 ] and 17 phytocannabinoids in cannabis inflorescences and oils [ 100 ], 228 nm has been shown to be the most suitable.…”

“…Most commonly used MS analyzers include simple Q spectrometers [ 181 ], QQQ analyzers [ 11 , 58 , 68 , 97 , 114 , 147 , 193 , 194 ], IT analyzers [ 28 , 43 , 72 , 185 ], QTRAP [ 67 , 159 , 191 , 195 ] or high resolution-accurate mass MS (HRAM-MS) analysers, such as Q-TOF [ 83 , 88 , 139 , 189 ] and Q-Exactive TM Orbitrap [ 19 , 63 , 65 , 66 ].…”

“…Phytocannabinoid profiling is most commonly performed using ESI, rarely using variations such as dual source [ 78 ] or heated ESI source [ 19 , 63 ]. Acquisitions are performed in positive (+) [ 88 , 147 , 189 , 191 , 193 , 194 ], negative (−) [ 134 ] or both (+) and (−) modes [ 27 , 40 , 55 , 62 , 63 , 64 , 92 , 144 , 178 , 181 ]. In fact, all major phytocannabinoids are detected in both ionization modes, except for THCV [ 78 ].…”