Tag Archives: detect

Rapid Pathogen Detection for the 21st Century: A Look at PathogenDx

By Aaron G. Biros
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In 1887, Julius Petri invented a couple of glass dishes, designed to grow bacteria in a reproducible, consistent environment. The Petri dish, as it came to be known, birthed the scientific practice of agar cultures, allowing scientists to study bacteria and viruses. The field of microbiology was able to flourish with this handy new tool. The Petri dish, along with advancements in our understanding of microbiology, later developed into the modern field of microbial testing, allowing scientists to understand and measure microbial colonies to detect harmful pathogens in our food and water, like E. coli and Salmonella, for example.

The global food supply chain moves much faster today than it did in the late 19th century. According to Milan Patel, CEO of PathogenDx, this calls for something a little quicker. “Traditional microbial testing is tedious and lengthy,” says Patel. “We need 21st century pathogen detection solutions.”

Milan Patel first joined the parent company of PathogenDx back in 2012, when they were more focused on clinical diagnostics. “The company was predominantly built on grant funding [a $12 million grant from the National Institute of Health] and focused on a niche market that was very specialized and small in terms of market size and opportunity,” says Patel. “I realized that the technology had a much greater opportunity in a larger market.”

Milan Patel, CEO of PathogenDx
Photo: Michael Chansley

He thought that other markets could benefit from that technology greatly, so the parent company licensed the technology and that is how PathogenDx was formed. Him and his team wanted to bring the product to market without having to obtain FDA regulatory approval, so they looked to the cannabis market. “What we realized was we were solving a ‘massive’ bottleneck issue where the microbial test was the ‘longest test’ out of all the tests required in that industry, taking 3-6 days,” says Patel. “We ultimately realized that this challenge was endemic in every market – food, agriculture, water, etc. – and that the world was using a 140-year-old solution in the form of petri dish testing for microbial organisms to address challenges of industries and markets demanding faster turnaround of results, better accuracy, and lower cost- and that is the technology PathogenDx has invented and developed.”

While originally a spinoff technology designed for clinical diagnostics, they deployed the technology in cannabis testing labs early on. The purpose was to simplify the process of testing in an easy approach, with an ultra-low cost and higher throughput. Their technology delivers microbial results in less than 6 hours compared to 24-36 hours for next best option.

The PathogenDx Microarray

Out of all the tests performed in a licensed cannabis testing laboratory, microbial tests are the longest, sometimes taking up to a few days. “Other tests in the laboratory can usually be done in 2-4 hours, so growers would never get their microbial testing results on time,” says Patel. “We developed this technology that gets results in 6 hours. The FDA has never seen something like this. It is a very disruptive technology.”

When it comes to microbial contamination, timing is everything. “By the time Petri dish results are in, the supply chain is already in motion and products are moving downstream to distributors and retailers,” Patel says. “With a 6-hour turnaround time, we can identify where exactly in the supply chain contaminant is occurring and spreading.”

The technology is easy to use for a lab technician, which allows for a standard process on one platform that is accurate, consistent and reproduceable. The technology can deliver results with essentially just 12 steps:

  1. Take 1 gram of cannabis flower or non-flower sample. Or take environmental swab
  2. Drop sample in solution. Swab should already be in solution
  3. Vortex
  4. Transfer 1ml of solution into 1.5ml tube

    A look at how the sample is added to the microarray
  5. Conduct two 3-minute centrifugation steps to separate leaf material, free-floating DNA and create a small pellet with live cells
  6. Conduct cell lysis by adding digestion buffer to sample on heat blocks for 1 hour
  7. Conduct Loci enhancement PCR of sample for 1 hour
  8. Conduct Labelling PCR which essentially attaches a fluorescent tag on the analyte DNA for 1 hour
  9. Pipette into the Multiplex microarray well where hybridization of sample to probes for 30 minutes
  10. Conduct wash cycle for 15 minutes
  11. Dry and image the slide in imager
  12. The imager will create a TIFF file where software will analyze and deliver results and a report

Their DetectX product can test for a number of pathogens in parallel in the same sample at the same time down to 1 colony forming unit (CFU) per gram. For bacteria, the bacterial kit can detect E. coli, E. coli/Shigella spp., Salmonella enterica, Listeria and Staph aureus, Stec 1 and Stec 2 E.coli. For yeast and mold, the fungal kit can test for Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger and Aspergillus terreus.

Their QuantX is the world’s first and only multiplex quantification microarray product that can quantify the microbial contamination load for key organisms such as total aerobic bacteria, total yeast & mold, bile tolerant gram negative, total coliform and total Enterobacteriaceae over a dynamic range from 100 CFU/mL up to 1,000,000 CFU/mL.

Not all of the PathogenDx technology is designed for just microbial testing of cannabis or food products. Their EnviroX technology is designed to help growers, processors or producers across any industry identify areas of microbial contamination, being used as a tool for quality assurance and hazard analysis. They conducted industry-wide surveys of the pathogens that are creating problems for cultivators and came up with a list of more than 50 bacterial and fungal pathogens that the EnviroX assay can test for to help growers identify contamination hotspots in their facilities.

Using the EnviroX assay, growers can swab surfaces like vents, fans, racks, workbenches and other potential areas of contamination where plants come in contact. This helps growers identify potential areas of contamination and remediate those locations. Patel says the tool could help growers employ more efficient standard operating procedures with sanitation and sterilization, reducing the facility’s incidence of pathogens winding up on crops, as well as reduction in use of pesticides and fungicides on the product.

Deploying this technology in the cannabis industry allowed Milan Patel and the PathogenDx team to bring something new to the world of microbial testing. Their products are now in more than 90 laboratories throughout the country. The success of this technology provides another shining example of how the cannabis market produces innovative and disruptive ideas that have a major impact on the world, far beyond cannabis itself.

Product Release: PathogenDx Announces New Products, Branding

By Aaron G. Biros
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According to a press release published earlier this week, PathogenDx, Inc., is expanding their product portfolio and doing some rebranding. The DNA-based pathogen detection testing provider, headquartered in Scottsdale, Arizona, produces microarray testing platforms for the cannabis, agriculture and food and beverage industries. Their rapid testing technology can reportedly identify and detect 50+ pathogens all in a single test, including common pathogens such as E. Coli, Salmonella and Aspergillus.

Here is a look at their new product suite, taken from the press release:

  • DetectX – Tests for the presence of pathogenic microbial organisms down to a single organism, at less than 0.1 CFU/gram for state regulated compliance. Test 96 or more samples a day for multiple state mandated microbial pathogens, with product safety certainty delivered in 6 hours, far more rapid than current industry standards of 72 hours or more.

  • QuantX – The world’s first quantification microarray test for Cannabis. This test measures the microbial load in a sample, while also providing discrimination of the organism content relative to testing standards. Regulatory agencies will now have the opportunity to improve microbial testing standards to ensure safety.

  • EnviroX – With a single swab, one can identify 50+ species and classes of microbes, with quick-turn results, by simply swabbing a grower/cultivation facility surfaces and vents. Submit, identify, and remediate. It’s that simple to mitigate risk to high-value crops.

  • PhytoX – Coming in Summer of 2019, PathogenDx will introduce the ultra-rapid, easy plant pathogen test to detect powdery mildew, gray mold, mites and other microbial bugs that can become destructive threats to one’s crop. Acquire results in 6 hours to intercept and redress infestation that can destroy one’s yield.

According to CEO and Co-Founder Milan Patel, they want their technology to set the standard for product safety testing. “We’re making the accurate testing of cannabis, food and agriculture faster, more definitive and less expensive with trackable results benefitting growers, producers, regulators and consumers worldwide,” says Patel. “Our new brand is inspired by our unique microplex array and is bright, fresh, memorable and expansive, enabling us to move from cannabis only to much larger global consumable markets where we can continue to offer new products and applications for the technology.”

This announcement comes as the company is positioning itself to expand far beyond just the cannabis testing arena, diving into the food and beverage and agriculture industries with a much stronger presence. As recently as late February, the company announced purchases of new real estate, expanding their production capacity, as well as announcing a few key hires, expanding their leadership team. 

Heavy Metals Testing: Methods, Strategies & Sampling

By Charles Deibel
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Editor’s Note: The following is based on research and studies performed in their Santa Cruz Lab, with contributions from Mikhail Gadomski, Lab Manager, Ryan Maus Technical Services Analyst, Laurie Post, Director of Food Safety & Compliance, and Charles Deibel, President Deibel Cannabis Labs.


Heavy metals are common environmental contaminants resulting from human industrial activities such as mining operations, industrial waste, automotive emissions, coal fired power plants and farm/house hold water run-off. They affect the water and soil, and become concentrated in plants, animals, pesticides and the sediments used to make fertilizers. They can also be present in low quality glass or plastic packaging materials that can leach into the final cannabis product upon contact. The inputs used by cultivators that can be contaminated with heavy metals include fertilizers, growing media, air, water and even the clone/plant itself.

The four heavy metals tested in the cannabis industry are lead, arsenic, mercury and cadmium. The California Bureau of Cannabis Control (BCC) mandates heavy metals testing for all three categories of cannabis products (inhalable cannabis, inhalable cannabis products and other cannabis and cannabis products) starting December 31, 2018. On an ongoing basis, we recommend cultivators test for the regulated heavy metals in R&D samples any time there are changes in a growing process including changes to growing media, cannabis strains, a water system or source, packaging materials and fertilizers or pesticides. Cultivators should test the soil, nutrient medium, water and any new clones or plants for heavy metals. Pre-qualifying a new packaging material supplier or a water source prior to use is a proactive approach that could bypass issues with finished product.

Testing Strategies

The best approach to heavy metal detection is the use of an instrument called an Inductively Coupled Plasma Mass Spectrometry (ICP-MS). There are many other instruments that can test for heavy metals, but in order to achieve the very low detection limits imposed by most states including California, the detector must be the ICP-MS. Prior to detection using ICP-MS, cannabis and cannabis related products go through a sample preparation stage consisting of some form of digestion to completely break down the complex matrix and extract the heavy metals for analysis. This two-step process is relatively fast and can be done in a single day, however, the instruments used to perform the digestion are usually the limiting step as the digesters run in a batch of 8-16 samples over a 2-hour period.

Only trace amounts of heavy metals are allowed by California’s BCC in cannabis and cannabis products. A highly sensitive detection system finds these trace amounts and also allows troubleshooting when a product is found to be out of specification.

For example, during the course of testing, we have seen lead levels exceed the BCC’s allowable limit of 0.5 ppm in resin from plastic vape cartridges. An investigation determined that the plastic used to make the vape cartridge was the source of the excessive lead levels. Even if a concentrate passes the limits at the time of sampling, the concern is that over time, the lead leached from the plastic into the resin, increasing the concentration of heavy metals to unsafe levels.

Getting a Representative Sample

The ability to detect trace levels of heavy metals is based on the sample size and how well the sample represents the entire batch. The current California recommended amount of sample is 1 gram of product per batch.  Batch sizes can vary but cannot be larger than 50 pounds of flower. There is no upper limit to the batch sizes for other inhalable cannabis products (Category II).

It is entirely likely that two different 1 gram samples of flower can have two different results for heavy metals because of how small a sample is collected compared to an entire batch. In addition, has the entire plant evenly collected and concentrated the heavy metals into every square inch of it’s leaves? No, probably not. In fact, preliminary research in leafy greens shows that heavy metals are not evenly distributed in a plant. Results from soil testing can also be inconsistent due to clumping or granularity. Heavy metals are not equally distributed within a lot of soil and the one small sample that is taken may not represent the entire batch. That is why it is imperative to take a “random” sample by collecting several smaller samples from different areas of the entire batch, combining them, and taking a 1 g sample from this composite for analysis.


References

California Cannabis CPA. 12/18/2018.  “What to Know About California’s Cannabis Testing Requirements”. https://www.californiacannabiscpa.com/blog/what-to-know-about-californias-cannabis-testing-requirements. Accessed January 10, 2019.

Citterio, S., A. Santagostino, P. Fumagalli, N. Prato, P. Ranalli and S. Sgorbati. 2003.  Heavy metal tolerance and accumulation of Cd, Cr and Ni by Cannabis sativa L.. Plant and Soil 256: 243–252.

Handwerk, B. 2015.  “Modern Marijuana Is Often Laced With Heavy Metals and Fungus.” Smithsonian.com. https://www.smithsonianmag.com/science-nature/modern-marijuana-more-potent-often-laced-heavy-metals-and-fungus-180954696/

Linger, P.  J. Mussig, H. Fischer, J. Kobert. 2002.  Industrial hemp (Cannabis sativa L.) growing on heavy metal contaminated soil: fibre quality and phytoremediation potential. Ind. Crops Prod. 11, 73–84.

McPartland, J. and K. J McKernan. 2017.  “Contaminants of Concern in Cannabis: Microbes, Heavy Metals and Pesticides”.  In: S. Chandra et al. (Eds.) Cannabis sativa L. – Botany and Biotechnology.  Springer International Publishing AG. P. 466-467.  https://www.researchgate.net/publication/318020615_Contaminants_of_Concern_in_Cannabis_Microbes_Heavy_Metals_and_Pesticides.  Accessed January 10, 2019.

Sidhu, G.P.S.  2016.  Heavy metal toxicity in soils: sources, remediation technologies and challenges.   Adv Plants AgricRes. 5(1):445‒446.

Top 10 Common Findings Detected During Cannabis Laboratory Assessments: A Guide to Assist with Accreditation

By Tracy Szerszen
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With the cannabis industry growing rapidly, laboratories are adapting to the new market demand for medical cannabis testing in accordance to ISO/IEC 17025. Third-party accreditation bodies, such as Perry Johnson Laboratory Accreditation, Inc. (PJLA), conduct these assessments to determine that laboratories are following relevant medical cannabis testing standard protocols in order to detect potency and contaminant levels in cannabis. Additionally, laboratories are required to implement and maintain a quality management system throughout their facility. Obtaining accreditation is a challenge for laboratories initially going through the process. There are many requirements outlined in the standard that laboratories must adhere to in order to obtain a final certificate of accreditation. Laboratories should evaluate the ISO 17025 standard thoroughly, receive adequate training, implement the standard within their facility and conduct an internal audit in order to prepare for a third-party assessment. Being prepared will ultimately reduce the number of findings detected during the on-site assessment. Listed below is research and evidence gathered by PJLA to determine the top ten findings by clause specifically in relation to cannabis testing laboratories.

PJLA chart
The top 10 findings by clause

4.2: Management System

  • Defined roles and responsibilities of management system and its quality policies, including a structured outline of supporting procedures, requirements of the policy statement and establishment of objectives.
  • Providing evidence of establishing the development, implementation and maintenance of the management system appropriate to the scope of activities and the continuous improvement of its effectiveness.
  • Ensuring the integrity of the management system during planned and implemented changes.
  • Communication from management of the importance of meeting customer, statutory and regulatory requirements

4.3: Document Control

  • Establishing and maintaining procedures to control all documents that form the management system.
  • The review of document approvals, issuance and changes.

4.6: Purchasing Services and Supplies

  • Policies and procedures for the selection and purchasing of services and supplies, inspection and verification of services and supplies
  • Review and approval of purchasing documents containing data describing the services and supplies ordered
  • Maintaining records for the evaluation of suppliers of critical consumables, supplies and services, which affect the quality of laboratory outputs.

4.13: Control of Records

  • Establishing and maintaining procedures for identification, collection, indexing, access, filing, storage and disposal of quality and technical records.
  • Providing procedures to protect and back-up records stored electronically and to prevent unauthorized access.

4.14: Internal Audits

  • Having a predetermined schedule and procedure for conducting internal audits of its activities and that addresses all elements that verify its compliance of its established management system and ISO/IEC 17025
  • Completing and recording corrective actions arising from internal audits in a timely manner, follow-up activities of implementation and verification of effectiveness of corrective actions taken.

5.2: Personnel

  • Laboratory management not ensuring the competence and qualifications of all personnel who operate specific equipment, perform tests, evaluate test results and sign test reports. Lack of personnel undergoing training and providing appropriate supervision
  • Providing a training program policies and procedures for an effective training program that is appropriate; identification and review of training needs and the program’s effectiveness to demonstrate competence.
  • Lack of maintaining records of training actions taken, current job descriptions for managerial, technical and key support personnel involved in testing

5.4: Test and Calibration Methods and Method Validation

  • Utilization of appropriate laboratory methods and procedures for all testing within the labs scope; including sampling, handling, transport, storage and preparation of items being tested, and where appropriate, a procedure for an estimation of the measurement of uncertainty and statistical techniques for analysis
  • Up-to-date instructions on the use and operation of all relevant equipment, and on the handling and preparation of items for testing
  • Introduction laboratory-developed and non-standard methods and developing procedures prior to implementation.
  • Validating non-standard methods in accordance with the standard
  • Not completing appropriate checks in a systematic manner for calculations and data transfers

5.6: Measurement Traceability

  • Ensuring that equipment used has the associated measurement uncertainty needed for traceability of measurements to SI units or certified reference materials and completing intermediate checks needed according to a defined procedure and schedules.
  • Not having procedures for safe handling, transport, storage and use of reference standards and materials that prevent contamination or deterioration of its integrity.

5.10: Reporting the Results

  • Test reports not meeting the standard requirements, statements of compliance with accounting for uncertainty, not providing evidence for measurement traceability, inaccurately amending reports.

SOP-3: Use of the Logo

  • Inappropriate use of PJLA’s logo on the laboratories test reports and/or website.
  • Using the incorrect logo for the testing laboratory or using the logo without prior approval from PJLA.
Terpene_KAS2
From The Lab

The Other Side of Cannabis: Terpenes

By Dr. Zacariah Hildenbrand, Allegra Leghissa, Dr. Kevin A. Schug
2 Comments
Terpene_KAS2

Have you ever wondered why all beers have that strong, characteristic smell? Or why you could tell the smell of cannabis apart from any other plant? The answer is simple – terpenes.

These 55,000 different molecules are responsible for a majority of the odors and fragrances around us, from a pine forest, to the air diffuser in your house 1–3. They all share the same precursor, isoprene, and because of that, they are all related and have similar molecular structures. Unfortunately, it is this uncanny similarity that makes their analysis so challenging; we still lack a complete list of which terpenes expected to be found in each given plant species 1,2.

Many different methods have been developed in an effort to provide a time-optimized and straightforward analysis. Gas chromatography (GC) is usually center stage due to the volatility of the terpenes. Therefore, there is significant concern with the type of GC detector used 2.

The flame ionization detector (FID) is a good quantitative detector for GC, but qualitatively it does not provide any information, except for retention time; the differentiation between terpene species is achieved solely by use of retention indices (RI), which are based on elution times from a particular GC stationary phase. The best part of the FID is its low cost, reliability, and relatively easy interface, which make it an effective tool for quality control (QC) but less so with respect to research and discovery 2.

The primary choice for a research setting is the mass spectrometer (MS) detector. It is more expensive and complicated than FID, but importantly, it provides both good quantitative capabilities, and it provides mass spectra for each species that elutes from the chromatograph. However, for terpene analysis, it may still not be the best detector choice. Since terpene class molecules share many structural and functional similarities, even their fragmentation and sub-sequential identification by MS may lead to inconsistent results, which need to be confirmed by use of RI. Still, MS is a better qualitative analysis tool than the FID, especially for distinguishing non-isobaric terpenes 2.

Recently, new technology based on vacuum ultraviolet spectroscopy (VUV) has been developed as a new GC detector. The VUV detector enables analysis of virtually all molecules; virtually all chemical compounds absorb light in the range in the 125-240 nm wavelength range probed by the detector, making it an essentially universal detector 4–11. Previously, spectroscopic absorption detectors for GC have lacked sufficient energy to measure absorption of most GC-amenable species. The VUV detector fills a niche, which is complementary to MS detection in terms of the qualitative information it provides.

Terpene_KAS2
Figure 1: A, Section of the chromatographic separation of a terpenes standard mix; B, highlight of the co-eluting terpenes, camphor and (-)-isopulegol; C, differences in the absorbance spectra of camphor and (-)-isopulegol.

With the VUV detector, each compound exhibits its own unique absorbance spectrum. Even isomers and isobars, which are prevalent in terpene mixtures and can be difficult to distinguish different species by their electron ionization mass spectra, can be well differentiated based on their VUV spectra 6,9,10.  Nevertheless, because analytes exhibit different spectra, it is not required to achieve a perfect chromatographic separation of the mixture components. Co-eluting peaks can be separated post-run through the use of library spectra and software inherent to the instrument 4,10. This ability is called “deconvolution”, and it is based on the fact that two co-eluting terpenes will give a peak with an absorbance spectrum equal to the sum of the two single absorbance spectra 4. Figure 1 shows the deconvolution process for two co-eluting terpenes, camphor and (-)-isopulegol. Due to their different absorbance spectra (Figure 1C), it is possible to fully separate the two peaks in post-run, obtaining sharp peaks for both analytes 6.

The deconvolution process has been shown to yield precise and accurate results. Thus, chromatographic resolution can be sacrificed in favor of spectroscopic resolution; this enables the development of methods with faster run times. With the ability to deconvolve unresolved peaks, a long temperature ramp to chromatographically separate all isomeric terpenes is not required 6. Additionally, the presence of coeluting components, which might normally go undetected with some GC detectors, can be easily judged based on comparison of the measured spectra with pure reference spectra contained in the VUV spectral library.

The other issue in terpenes analysis is the extraction process. Terpenes can be extracted with the use of solvents (e.g., methanol, ethanol, hexane, and cyclohexane, among others), but the process is usually time-consuming, costly and not so environmentally-friendly 2. The plant needs to be manually crushed and then aliquots of solvent are used to extract components from the plant, ideally at least 3 times and combined to achieve acceptable results. The problem is that some terpenes may respond better to a certain solvent, making their extraction easier and more optimized than for others 2. The choice of solvent can cause discrimination against the extraction some terpenes, which limits the comprehensiveness of analysis.

Headspace is another technique that can be used for the sample preparation of terpenes. Headspace sampling is based on heating the solid or liquid sample inside a sealed vial, and then analyzing the air above it after sufficient equilibration. In this way, only volatile analytes are extracted from the solid/liquid sample into the gas phase; this allows relatively interference-free sampling 12–14.

How do we know whether our extraction analysis methods are correct and comprehensive for a certain plant sample? Unfortunately, there is not a complete list of available molecules for each plant species, and even if two specimens may smell really similar to our nose, their terpenes profiles may be notably different. When working with a new plant material, it is difficult to predict the extraction efficiency for the vast array of terpenes that may be present. We can only perform it with different extraction and detection methods, and compare the results.

The route for a comprehensive and fast analysis of terpenes is therefore still long; however, their intoxicating aromas and inherent medicinal value has provided a growing impetus for researchers around the world. Considering the evolving importance of Cannabis and the growing body of evidence on the synergistic effects between terpenes and cannabinoids, it is likely that newly improved extraction and analysis methods will be developed, paving the way for a more complete list of terpene species that can be found in different cultivars. The use of new analytical technologies, such as the VUV detector for GC, should aid considerably in this endeavor.


References:

[1]          Breitmaier E., Terpenes: Flavors, Fragrances, Pharmaca, Pheromones. John Wiley & Sons 2006.

[2]          Leghissa A., Hildenbrand Z. L., Schug K. A., A Review of Methods for the Chemical Characterization of Cannabis Natural Products. J. Sep. Sci.2018, 41, 398–415 .

[3]          Benvenuto E., Misra B. B., Stehle F., Andre C. M., Hausman J.-F., Guerriero G., Cannabis sativa: The Plant of the Thousand and One Molecules. Front. Plant Sci2016, 719, DOI: 10.3389/fpls.2016.00019.

[4]          Schug K. A., Sawicki I., Carlton D. D., Fan H.,Mcnair H. M.,Nimmo J. P., Kroll P.,Smuts J.,Walsh P., Harrison D., Vacuum Ultraviolet Detector for Gas Chromatography. Anal. Chem.2014, 86, 8329–8335 .

[5]          Fan H.,Smuts J., Walsh P.,Harrison D., Schug K. A., Gas chromatography-vacuum ultraviolet spectroscopy for multiclass pesticide identification. J. Chromatogr. A2015, DOI: 10.1016/j.chroma.2015.02.035.

[6]          Qiu C.,Smuts J., Schug K. A., Analysis of terpenes and turpentines using gas chromatography with vacuum ultraviolet detection. J. Sep. Sci.2017, 40, 869–877 .

[7]          Leghissa A., Smuts J., Qiu C., Hildenbrand Z. L., Schug K. A., Detection of cannabinoids and cannabinoid metabolites using gas chromatography-vacuum ultraviolet spectroscopy. Sep. Sci. Plus2018, 1.

[8]          Bai L.,Smuts J., Walsh P., Fan H., Hildenbrand Z., Wong D., Wetz D., Schug K. A., Permanent gas analysis using gas chromatography with vacuum ultraviolet detection. J. Chromatogr. A2015,1388, 244–250 .

[9]          Skultety L., Frycak P., Qiu C.,Smuts J., Shear-Laude L., Lemr K., Mao J. X., Kroll P., Schug K. A., Szewczak A., Vaught C., Lurie I., Havlicek V., Resolution of isomeric new designer stimulants using gas chromatography – Vacuum ultraviolet spectroscopy and theoretical computations. Anal. Chim. Acta2017, 971, 55–67 .

[10]       Bai L., Smuts J., Walsh P., Qiu C., McNair H. M., Schug K. ., Pseudo-absolute quantitative analysis using gas chromatography–vacuum ultraviolet spectroscopy–a tutorial. Anal. Chim. Acta2017, 953, 10–22 .

[11]       Schenk J., Nagy G., Pohl N. L. B., Leghissa A., Smuts J., Schug K. A., Identification and deconvolution of carbohydrates with gas chromatography-vacuum ultraviolet spectroscopy. J. Chromatogr. A2017, 1513, 210–221 .

[12]       Van Opstaele F., De Causmaecker B., Aerts G., De Cooman L., Characterization of novel varietal floral hop aromas by headspace solid phase microextraction and gas chromatography-mass spectrometry/olfactometry. J. Agric. Food Chem.2012, 60, 12270−12281 .

[13]       Hamm S., Bleton J., Connan J., Tchapla A., A chemical investigation by headspace SPME and GC-MS of volatile and semi-volatile terpenes in various olibanum samples. Phytochemistry2005,66, 1499–1514 .

[14]       Aberl A., Coelhan M., Determination of volatile compounds in different hop Varieties by headspace-trap GC/MS-in comparison with conventional hop essential oil analysis. J. Agric. Food Chem.2012, 60, 2785−2792 .