Drug Discovery, Pharmaceuticals & Cannabis Testing
Investigating the oxidation stability of cannabis products with RapidOxy 100
Dr Carolin Edinger, Product Management, Anton Paar GmbH
Hemp products, above all CBD (Cannabidiol), have become widely used ingredients in many industries. Whether cannabinoids are used for an anti-infl ammatory effect in skin care products or as a natural way to help with anxiety, or sleep disorders in pharmaceuticals, their chemical structure similar to messengers of the human body is key. However, in many cases autoxidation can be the root cause for chemical changes affecting not only quality, but most of all the effi ciency of contained cannabinoids independent from product type. To exclude a decrease or worse a loss of effi cacy during the shelf life of the product means to guarantee the corresponding oxidation stability. Keeping this in mind, during product development or reformulation, it is absolutely crucial not only to draw up the respective methods for the required oxidation stability but also prove their effectiveness. For the latter, Anton Paar’s RapidOxy 100 is a highly effective tool.
RapidOxy 100 artifi cially accelerates the oxidation process by using increased temperature and an excess of pure oxygen. The whole measuring process is fully automatic, limiting error sources to a minimum. One of the major benefi ts is its applicability with all kinds of products because you can measure fl uid, semi-solid, and solid samples without any prior sample preparation. It lets you investigate the oxidative behaviour of the product as a whole while additionally saving you a lot of time. Information about the whole product is better than knowing just the oxidation stability of a single ingredient that might be infl uenced chemically by other molecules within the entire matrix of the product.
The induction period of a sample refl ects the time for its oxygen uptake and can even give information on the amount and rate of it. The principle is straightforward: Samples with a shorter induction period are usually less stable towards oxidation than samples with a longer induction period.
Since even solid samples can be measured without prior sample preparation, you can investigate the oxidation stability of complex products.
The major advantages of this method are the signifi cantly reduced measurement time and high precision, both allowing quick and direct measurements of the oxidation stability during product development and reformulation [3, 4, 5, 6].
Figure 1: RapidOxy 100.
Due to the defi ned oxygen volume in the closed test chamber, you can calculate the oxygen consumption. Moreover, for the majority of products you can observe Arrhenius behaviour regarding the applied temperature, which lets you determine the activation energy of a specifi c oxidation process and in case of fats and oils additionally allows you to estimate the shelf life. With the OxyLogger 100 PC software, all of these valuable investigation options are available [1, 2, 3, 4].
The Rapid Small-Scale Oxidation Test (RSSOT)
During a RapidOxy 100 measurement the sample is exposed to an excess of pure oxygen (up to 700 kPa) and elevated temperature (up to 180°C). Typical conditions of the method are temperatures between 80°C and 140°C and an initial oxygen pressure of 700 kPa to initiate a rapid oxidation process. The oxygen uptake of the sample during the measurement is monitored by recording the pressure until a predefi ned pressure drop or a specifi c time. The elapsed time until the pressure drop or the extent of the pressure drop within a specifi c time is directly related to the total oxygen consumption and therefore to the oxidation stability of the sample.
A standard measurement determines the induction period (IP) which is defi ned as the time elapsed between starting the heating procedure of the sample vessel and a pressure drop of 10% from the maximum pressure (= Breakpoint), measured in minutes (see Figure 2). The pressure drop from maximum pressure is directly related to the oxygen uptake of the sample.
Investigating the oxidation stability of oil containing cannabinoids
Oxidation stability of different cannabinoids
This section demonstrates the benefi ts of the Rapid Small-Scale Oxidation Test when it comes to determining the oxidation stability of formulations containing cannabinoids.
In the described study an MCT (Medium Chain Glyceride) oil which is commonly used for cosmetics and pharmaceuticals served as the carrier oil. To determine the oxidation stability order of MCT oil with different cannabinoids with the RSSOT, the following samples were investigated:
MCT oil, pure
Sample C1: 20 mg/mL CBD and 10 mg/mL THC extract Sample C3: 20 mg/mL CBD extract Sample C5: 20 mg/mL THC extract
The oxidation stability order of the different cannabinoids could be screened using the parameters described below:
Temperature: 100°C Initial fi lling pressure: 700 kPa Stop criterion: pmax – 5% Sample volume: 5 mL
A high precision of test results was demonstrated for all samples (see Table 1) and a clear trend of stabilities could be determined from the measured induction periods (see Figure 3).
Table 1: Repeatability of test results. MCT oil
IP in minutes Repeatability
3676.90 3709.97
0.9
Sample C1 Sample C3 Sample C5
572.21 574.95
0.5
266.53 266.26
0.1
1366.45 1376.02
0.7 Figure 2: Determination of the induction period (IP).
As expected, the MCT oil has a very high oxidation stability which is refl ected in a comparably long IP. Whereas sample C3 and its contained CBD extract is by far the least stable formulation, the combination of CBD and THC extract in sample C1 leads to a stability and IP in between samples C1 and C5. The measured IP values demonstrate the effectiveness of the measuring principle.
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