AT526965A1 - Method for determining the quantity of a psychoactive substance in a sample - Google Patents

Abstract

A method is described for determining the quantity of a psychoactive substance in a sample (P) by means of diffuse reflection spectroscopy, in which reference spectra of reference samples with a known quantity of the substance are recorded in advance (1) and quantity classes are defined on the basis of the reference spectra (2), whereupon a near-infrared spectrum of the sample (P) is recorded and assigned to a quantity class by comparison with the reference spectra (6). In order to design a method of the type described at the outset in such a way that the quantity of a psychoactive substance, for example tetrahydrogen cannabinol (THC), in a sample can be determined by means of diffuse reflection spectroscopy in mobile use, in particular by law enforcement agencies, and in the process a preparation of the sample is avoided, it is proposed that for each quantity class a characteristic spectrum and a permissible deviation from this characteristic spectrum is determined from the reference spectra (3), after which a near-infrared spectrum of the sample (P) delimited by a film which is at least partially semi-transparent in the near-infrared range is recorded by means of a measuring head (14) of a near-infrared spectrometer (4), the measuring head (14) and the sample (P) being in contact with the film and facing each other with respect to it, after which the deviation of the recorded near-infrared spectrum of the sample (P) from the characteristic spectrum of each quantity class is determined (5) and a signal assigned to that quantity class is output whose characteristic Spectrum differs from the recorded near-infrared spectrum of the sample (P) by at most the permitted deviation (8).

Description

The invention relates to a method for determining the quantity of a psychoactive substance in a sample by means of diffuse reflection spectroscopy, in which reference spectra of reference samples with a known quantity of the substance are recorded in advance and quantity classes are defined on the basis of the reference spectra, whereupon a near-infrared spectrum of the sample is recorded and

is assigned to a quantity class by comparison with the reference spectra.

Methods are known from the state of the art in which the content of phytocannabinoids in a cannabis sample is analyzed (WO2021242964A1). The sample is dried to less than 10% moisture, homogenized, sieved, placed in a sample container on the measuring window of the spectroscope and rotated during the measurement to compensate for inhomogeneities in the surface texture. Since the sample is usually a plant sample that has a rough surface due to its substance, the analysis is carried out using diffuse reflection near-infrared spectroscopy and a near-infrared spectrum of the sample is recorded. First, reference spectra of samples with a known phytocannabinoid quantity are recorded using high-performance liquid chromatography (HPLC), the quantity of the psychoactive substance is determined using gas chromatography and a mathematical model is created on the basis of this data, which allows a statement to be made about the phytocannabinoid quantity in the measured sample when the measured near-infrared spectra are subsequently compared with the reference spectra.

However, the disadvantage of the current technology is that the sample has to be prepared in a complex manner

must be carried out, which means that the analysis can only be carried out in a laboratory

The invention is therefore based on the object of determining the quantity of a psychoactive substance, for example tetrahydrogen cannabinol (THC), in a sample by means of diffuse reflection spectroscopy in mobile use, in particular by law enforcement agencies, and thereby enabling the sample to be prepared

avoid.

The invention solves the problem by determining a characteristic spectrum and a permissible deviation from this characteristic spectrum for each quantity class from the reference spectra, after which a near-infrared spectrum of the sample delimited by a film that is at least partially semi-transparent in the near-infrared range is recorded by means of a measuring head of a near-infrared spectrometer, the measuring head and the sample being in contact with the film and facing each other with respect to it, after which the deviation of the recorded near-infrared spectrum of the sample from the characteristic spectrum of each quantity class is determined and a signal assigned to that quantity class is output whose characteristic spectrum differs from the recorded near-infrared spectrum of the sample by at most the permissible deviation. Since the samples to be analyzed, for example parts of cannabis plants, are usually handled and stored in small transparent plastic sample bags, the content or quantity of a psychoactive substance can be determined through the bag's foil without the sample having to be removed, manipulated or prepared. If this sample preparation is omitted, the actual determination of the quantity can be carried out using mobile near-infrared spectroscopes, particularly by law enforcement officers in the field. The disadvantage is that the bags usually used contain foils made of materials such as polyethylene or other plastics. These have similar absorption bands in the near-infrared wavelength range to the substances usually to be determined, such as THC. The foils

In order to enable quick and easy determination of the quantity, particularly for mobile applications, two quantity classes can be provided, one of which is defined by reference spectra of reference samples with a quantity above a threshold value and the other by reference spectra of reference samples with a quantity below a threshold value. In principle, it is possible to define any number of quantity classes, but by defining only two quantity classes, not only can the comparison of the measured near-infrared spectrum of the sample with the reference spectra be accelerated, but the reading of the measurement results can also be made easier, which means that official procedures can be carried out more quickly and easily, for example. This is an advantage, particularly for mobile applications, as it allows the signal output to be kept simple. For example, the threshold value can correspond to the legally permitted quantity of a psychoactive substance in a sample, with a red light being emitted as a signal if this threshold value is exceeded and a green light being emitted as a signal if the threshold value is not reached. Optionally, an additional signal, such as a flashing red light, can be emitted if the measured near-infrared spectrum of the sample cannot be assigned to a quantity class

could be.

In order to compensate for measurement differences between near-infrared spectrometers of different designs and/or the aging of the light source of the near-infrared spectrometer, it is suggested that a white reference be recorded to calibrate the near-infrared spectrometer before recording a reference spectrum.

As a result of these measures, variations in the intensity and

7729

The near-infrared light detected by the measuring head may not come entirely from the sample because the detector also picks up background noise and light reflected from other objects, for example. In order to inform the user without complicated calibration and display methods whether the signal quality of a recorded near-infrared spectrum of a sample is high enough to meaningfully determine the quantity of a psychoactive substance, it is therefore proposed to use the measuring head to create a specular reflection spectrum and then to use this and the recorded near-infrared spectrum of the sample to determine the signal portion of diffusely reflected light in the recording, with a warning signal being issued if this signal portion falls below a diffusivity limit. The idea behind this is that the sample reflects the near-infrared light diffusely, while other interfering objects in the beam path reflect it regularly, i.e. with specular reflection. If a specular reflection spectrum, i.e. the spectrum of a sample that only specularly reflects the near infrared light except for a small residual portion, is recorded, this specular reflection spectrum can then be subtracted from the measured near infrared spectrum of the sample in order to obtain the absolute or relative portion of the diffusely reflected near infrared light. The specular reflection spectrum can preferably be designed in such a way that it reflects the measurement conditions in actual use. Preferably, a special sample is made from a known highly specularly reflecting material, for example gold, for a specular reflection spectrum. In this way, in the

expected application area maximum expected proportion of mirror-reflected

be recorded.

In order to reduce the possibility of manipulating the sample before determining the quantity of the psychoactive substance, particularly in official procedures, it is proposed that the film be part of a sealable bag in which the sample is stored. Since samples are usually stored and handled in sealable bags, the quantity of the psychoactive substance in the sample can be determined without removing it from the bag. This makes manipulating the sample before measurement very difficult, since no direct physical external contact with the sample is possible.

The invention also relates to a device for carrying out the method with a computing unit and a near-infrared spectrometer having a measuring head, wherein a storage unit is provided for the quantity classes, the characteristic spectra and the permissible deviations from these, a sample support is arranged opposite the measuring head and the measuring head and the sample support are arranged between a measuring and a

The shift between the insertion and measuring position can be carried out in a particularly user-friendly way for mobile applications by providing two arms connected to a handle, with one arm holding the measuring head and the other arm holding the sample support. This allows the device to be easily carried by the person measuring with one hand, while the sample is positioned between the arms with the other hand. The arms enable simple and reproducible contact between the measuring head and the film or between the sample and the film and allow easy application of a

contact pressure. For this purpose, at least one arm can be moved around a joint,

so that the contact pressure can be applied more easily due to the leverage effect. In a preferred embodiment, the device can be operated one-handed via the handle after positioning the sample between the arms. Furthermore, a signal generator, such as one or more LEDs, can be attached to the handle in order to output the signal assigned to the respective quantity class.

In order to obtain reliable measurement results despite a compact design of the device, it is proposed that the sample support forms a second measuring head. As a result of these measures, two near-infrared spectra of the same sample can be recorded at two spatially separate locations during one measurement run. If the measuring heads are opposite each other with respect to the sample, this also enables easy determination at two different locations without having to take the size of the sample into account. The measurement results of the two measuring heads can then be compared, averaged or otherwise processed. As a result of these measures, two near-infrared spectrometers can be used, each with a

measuring head.

In mobile determination, the quality of the determination depends, particularly in particularly compact embodiments of the device, on whether the sample can be correctly placed in the measuring position. In order to be able to determine whether a meaningful recording can be carried out before the near-infrared spectrum of the sample is actually recorded, it is proposed that a color sensor directed towards the recording area for the sample be provided to verify the measuring position. The idea behind this is that the color in the recording area can be determined more easily and therefore more quickly than the near-infrared spectrum of a sample that may be located there. If such a relatively quick color determination is carried out before the actual, relatively long-lasting determination of the near-infrared spectrum, it can be determined before the near-infrared spectrum is determined whether a sample is in the recording area and that

The near-infrared spectrum of the sample can only be measured if the color determination has been positive. For example, if the THC content of a cannabis sample is to be determined, the recording of the near-infrared spectrum can only be initiated if the color of the cannabis sample, for example a green or brown tone, has been determined during the color determination. In a preferred embodiment, the color sensor can also be used to carry out a white reference before measuring the near-infrared spectrum. An RGB sensor, for example, can be used as a color sensor.

The relevant signal component for determining the quantity is the near-infrared light diffusely reflected from the sample. However, during operation the measuring head also detects specularly reflected light from other objects, whereby the signal component of diffusely reflected light cannot be read directly from the spectrum. To ensure that the proportion of diffusely reflected light is sufficient for a quantity determination, it is proposed that the measuring head is designed so that the proportion of diffusely reflected light in the recorded near-infrared spectrum is at least 20%, preferably at least 50%. To determine the proportion of diffusely reflected light, the near-infrared spectra of two calibration samples are determined using a given measuring arrangement. One of the two calibration samples is designed such that it predominantly reflects diffusely. A white reference sample can be used for this, for example. The second calibration sample is designed such that it predominantly reflects specularly. A gold mirror can be used for this, for example. The signal of the predominantly specularly reflecting sample can be subtracted from the signal of the predominantly diffusely reflecting sample and the relative proportion of the diffusely reflected signal can be determined. The proportion of the measured diffusely reflected light depends on the near infrared spectrometer used, in particular on the relative arrangement of the light sources and the sensor to each other. When determining the proportion of diffusely reflected infrared light is preferably high in relation to the specularly reflected infrared light, since the diffusely reflected infrared light contains information about the sample and the specularly reflected light comes from other interfering objects in the beam path. In conjunction with the

In the measurement according to the invention through a semi-transparent film to which the measuring head of the near-infrared spectrometer is applied, it has been shown that a correct assignment of a sample to a quantity class is possible if the relative proportion of diffusely reflected infrared light due to the configuration of the measuring head is at least 20%. In order to avoid the sample not being able to be assigned to a quantity class in the case of correspondingly narrow permitted deviations, it is proposed that the relative proportion of diffusely reflected infrared light due to the configuration of the measuring head is at least 50%.

The drawing shows the subject matter of the invention as an example.

show

Fig. 1 shows the schematic sequence of a method according to the invention,

Fig. 2 shows the absorption spectra of a sample, a sample bordered by a film that is at least partially semi-transparent in the near infrared range, and the film alone,

Fig. 3 is a partially broken away schematic perspective view of an apparatus for carrying out the method according to the invention,

Fig. 4 is a view corresponding to Fig. 3 of a device for carrying out the method according to the invention in a slightly opened position and

Fig. 5 a section along the line V — V of Fig. 4 with inserted sample in

Measuring position on a larger scale.

As can be seen from Fig. 1, in a method according to the invention for determining the quantity of a psychoactive substance in a sample P, reference spectra of reference samples are recorded in a first step 1. These reference samples contain a known quantity of the substance to be determined, wherein the quantity of the substance to be determined can be determined from the respective spectra. The reference spectra can also be recorded using diffuse reflection spectroscopy and/or other analysis methods, such as high performance liquid chromatography.

Due to the determinability of the quantity from the respective reference spectra, 2 quantity classes can therefore be defined in a further step. These quantity classes can, for example, be defined using the reference spectra of samples in a certain quantity range, such as "15-20 percent by weight" or "more than 10 percent by volume". The reference spectra are then subjected to one or more optional preprocessing steps, such as passing through one or more filters, and a characteristic spectrum is determined from the reference spectra of a quantity class in step 3. This can be done, for example, by calculating the average of the reference spectra of the quantity class. The permissible deviation from this characteristic spectrum is also determined in this step. This deviation can be set taking into account the individual reference spectra and external circumstances and can be different for each quantity class. The sample P to be determined is delimited by a film that is at least partially semi-transparent in the near infrared range, since commercially available plastic bags in which the substances are usually traded and stored are made of such films. The method according to the invention solves the problem that the absorption bands of many substances to be determined overlap with the absorption bands of a film that is at least partially semi-transparent in the near infrared range, making it impossible to determine the quantity directly. However, the measures according to the invention can reduce the influence of these interference factors to the extent that a meaningful determination is again possible. This situation can be further promoted by not defining too many quantity classes, but by setting a threshold value that only separates two quantity classes from one another. This threshold value can, for example, be the legally prescribed maximum permitted value of the substance. The two quantity classes are then defined using the reference spectra of the reference samples with a quantity above or below this threshold value. Since fewer quantity classes have to be checked and the permissible deviation

can be kept larger, the measurement can be simplified and accelerated

become.

Another way to reliably carry out the determination despite the disturbing influences of the film is to record at least one reference spectrum in the same way as the near-infrared spectrum of the sample P to be determined. This means that in order to record the near-infrared spectrum of the reference sample, the measuring head and the reference sample are in contact with a film that is at least partially semi-transparent in the near-infrared range and are opposite each other with respect to this. Preferably, the same reference sample can be recorded with and without a film and used to define a quantity class.

become.

In step 4, a near-infrared spectrum of a sample P is measured, the quantity of which is unknown and the sample P is delimited by a film that is at least partially semi-transparent in the near-infrared range. Such a film can, for example, be a polyethylene film from which the bags in which the samples are usually traded and stored are at least partially made. If the reference spectra were subjected to an optional pre-processing step, it is recommended that this pre-processing step is also applied to the measured near-infrared spectrum. In step 5, the deviation of the measured near-infrared spectrum of the sample P from the characteristic spectrum of each quantity class is determined and then it is determined whether a characteristic spectrum exists from which the measured near-infrared spectrum deviates by at most the permissible deviation of this spectrum. If such a characteristic spectrum is found, the measured near-infrared spectrum is assigned to the quantity class of this characteristic spectrum in step 6. If no such characteristic spectrum is found, the measured near-infrared spectrum is not assigned to a quantity class and this is output in an optional step 7.

Conversely, if a characteristic spectrum is found, in step 8

a signal is issued which is specific to the quantity class to which the

measured near-infrared spectrum.

In Fig. 2, the absorption spectrum 9 of a sample that was measured directly, i.e. not bordered by a film, is shown with a dash-dotted line, the absorption spectrum 10 of the same sample, but this time bordered by a film that is at least partially semi-transparent in the near infrared range, is shown with a solid line, and the absorption spectrum of this film 11, which is a polyethylene film, is shown with a dashed line. The wavelength in nanometers is plotted on the x-axis 12 and the absorption in arbitrary units is plotted on the y-axis 13. Fig. 2 clearly shows how the absorption spectrum of the sample 10 bordered by the film results from the superposition of the absorption spectra of the film 11 and the sample, and how strongly the absorption spectrum of the film 11 influences the resulting absorption spectrum 10.

Figs. 3, 4 and 5 show a device for carrying out the method according to the invention. This comprises a measuring head 14 of a near infrared spectrometer and a handle 15 in which the near infrared spectrometer, a storage unit and a computing unit are arranged. The quantity classes, the characteristic spectra and the permissible deviations from these are stored in the storage unit. The device also comprises a sample support 16. Measuring head 14 and sample support 16 are

can be moved between a measuring position and an insertion position.

In the measuring position, the sample P to be determined is placed in the insertion position on the sample support, as can be seen in Fig. 5. The sample P is bordered by a film that is at least partially semi-transparent in the near infrared range, which in the embodiment shown forms a bag B in which the sample P is stored. After being moved into the measuring position, the measuring head 14 and the sample P lie opposite one another with respect to this film, with both the measuring head

14 and sample P are pressed against the foil of bag B. In this

In the measuring position, the near-infrared spectrum of a sample P can now be recorded according to the invention and the deviation of the recorded near-infrared spectrum of the sample P from the characteristic spectrum of each quantity class is determined. In the example shown, the signal to be output in the method according to the invention is output via a light source 17 in the switch 18 which triggers the recording of the near-infrared spectrum of the sample P.

In order to enable mechanical displacement between the measuring and insertion positions so that the sample P can, on the one hand, be easily placed on the sample support 16 in the insertion position and, on the other hand, is locked in the measuring position so that the most reliable and reproducible images of the near-infrared spectrum are possible, the embodiment shown has two arms 19, 20 connected to the handle 15, which preferably apply an adjustable preload to the sample P in the measuring position. One arm 19 encompasses the measuring head 14 and the other arm 20 the sample support 16. As can be seen in Fig. 3, both arms 19, 20 are brought closer together in the measuring position. In addition, the sample support 16 can form a second measuring head 21, whereby measurement data from two different points on the sample P are obtained during one measuring process. Fig. 4 shows the insertion position in which the two arms 19, 20 are spaced apart from each other so that a sample B can be placed on the sample support 16.

In order to verify that the measuring position has been correctly reached before determining the near-infrared spectrum of the sample P, a color sensor (not shown) directed towards the receiving space 22 for the sample P may be present.

Claims (1)

(344898.0) IV Patent claims 1. Method for determining the quantity of a psychoactive substance in a sample (P) by means of diffuse reflection spectroscopy, in which reference spectra of reference samples with a known quantity of the substance are recorded in advance (1) and quantity classes are defined on the basis of the reference spectra (2), whereupon a near-infrared spectrum of the sample (P) is recorded and assigned to a quantity class by comparison with the reference spectra (6), characterized in that for each quantity class a characteristic spectrum and a permissible deviation from this characteristic spectrum are determined from the reference spectra (3), whereupon a near-infrared spectrum of the sample (P) delimited by a film which is at least partially semi-transparent in the near-infrared range is recorded by means of a measuring head (14) of a near-infrared spectrometer (4), the measuring head (14) and the sample (P) being in contact with the film and facing each other with respect to it, whereupon the deviation of the recorded near-infrared spectrum of the sample (P) from the characteristic spectrum of each A quantity class is determined (5) and a signal is output which is assigned to that quantity class and whose characteristic spectrum differs from the recorded near-infrared spectrum of the sample (P) by at most the permitted deviation (8). 2. Method according to claim 1, characterized in that two quantity classes are provided, of which one quantity class is based on reference spectra of reference samples with a quantity above and the other quantity class is based on reference spectra of reference samples with a quantity defined below a threshold. and are opposite each other with regard to this. 4. Method according to one of claims 1 to 3, characterized in that before recording a reference spectrum, a white reference for calibrating the Near-infrared spectrometer. 5. Method according to one of claims 1 to 4, characterized in that the film is part of a sealable bag (B) in which the sample (P) is stored. 6. Device for carrying out the method according to one of the preceding claims with a computing unit and a near-infrared spectrometer having a measuring head (14), characterized in that a storage unit is provided for the quantity classes, the characteristic spectra and the permissible deviations from these, a sample support (16) is arranged opposite the measuring head (14), and the measuring head (14) and the sample support (16) are displaceable relative to one another between a measuring position and an insertion position. 7. Device according to claim 6, characterized in that two arms (19, 20) connected to a handle (15) are provided, wherein one arm (19) comprises the measuring head (14) and the other arm (20) comprises the sample support (16). 8. Device according to claim 6 or 7, characterized in that the sample support (16) forms a second measuring head (21). intended to verify the measuring position. 10. Device according to one of claims 6 to 9, characterized in that the measuring head is designed such that the proportion of diffusely reflected light in the recorded near infrared spectrum is at least 20%, preferably at least 50%.