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California Ringtest: How Accurate is Potency Testing of Cannabis?
RING TEST: A standard procedure in the analytical testing industry for external quality-control assurance, in which identical samples are sent to a variety of testing facilities in order to compare results. Want to know the potency of your medicine? How much, if any CBD, does it contain? Has it been sprayed with dangerous pesticides? Is it infested by molds or bac-teria? The only way to answer these questions for sure is to have it tested by an analytical lab. Many labs now offer testing services for the medical cannabis industry. How accurate are the results they provide? Our investigation was launched in the winter of 2010/11. An identical set of samples was submitted to 10 labs. The labs were asked to measure THC, CBD, and CBN, the three major cannabinoids for which testing is generally available. To encourage participation, the identity of the labs was kept confidential; in this report they are identified by numbers only (Lab 1, 2 etc.). In most cases, lab results were consistent to within 20% of each other. To some degree, the differences in results might be explained by natural variations in the consistency of the cannabis samples used; to some degree, by differences in lab procedures. In certain cases, there were glaring discrepancies suggesting laboratory error. Three of the 10 labs performed poorly on half the tests. Particularly in the case of liquid alcohol extracts, test results were troublingly inconsistent. Nevertheless, the general results showed good agreement between most lab results involving herbal samples. Lab performance can be expected to improve in the future as the industry responds with improved standards. SAMPLES Labs were asked to examine six different samples: four herbal cannabis samples (AD), and two liquid (ethanol) extracts (F-G). The cannabis samples were taken from herbal material homogenized in a blender to minimize variations in potency. Samples were stored in a cool, dark room in tightly closed containers until sent to the labs. All testing was blinded: labs did not receive any information about the samples that could have skewed their analytical results. Samples A, C, and D: replicates These samples were exactly identical, and intended to check the reproducibility of participating labs, including their extraction protocol, sample preparation, and analytical methodology. Samples consisted of roughly one-gram packets of a THC-rich cannabis mixture that had been ho-mogenized in a kitchen blender, followed by manual stirring. Sample B: high CBD This sample consisted of one gram of a similarly prepared mixture of CBD-rich herbal cannabis. The sample was intended to check for labs' capability of identifying and quantifying CBD. Samples F and G: extracts Samples F and G were alcohol tinctures of about one milliliter each. Both were prepared from a single CBD-rich herbal mixture. Material in Sample F was decarboxylated by heating in a closed glass jar at 100°C for 90 minutes before soaking in alcohol. Sample G was prepared from the same material, but unheated. Samples were extracted in 99% pure ethanol for 12 minutes and filtered in cheese-cloth, then a coffee filter. These samples were intended to evaluate only the testing methodology of the participating labs, by removing the need for extraction and sample preparation. METHODOLOGIES Different kinds of lab equipment were used to test the samples. Five labs employed gas chromatography (GC), in which the sample is first vaporized under heat. The resulting gases were subsequently analyzed either by means of a flame ionization detector (GC-FID, used by four labs), or a mass spectrometer (GC-MS, used by one). Four labs used a technology known as high-pressure liquid chromatography (HPLC), in which the sample is analyzed by forcing it at high pressure through long columns to separate its components. GC and HPLC are by far the leading technologies for cannabis testing. One lab used a third method, Thin Layer Chromatography (TLC), which is commonly used for qualitative analysis (fingerprinting/profiling) of cannabis samples. As a tool for quantification (potency testing) it tends to be less accurate, because the results are scored inexactly by visually judging the size or density of a spot. Fresh herbal cannabis does not contain significant amounts of free THC. Instead, the plant produces its biological precursor, THC-acid (THCA), which lacks THC's activity and is not psychoactive. The same is true for most