Tag Archives: pesticides

By Amy Ankrum

Government regulations keep millions of Americans safe every year by controlling what companies can put in their products and the standards those products must meet to be sold to consumers.

Enter the strange case of legal cannabis: In order for cannabis to be legally distributed by licensed medical professionals and businesses, it must be tested. But unlike other consumable goods, cannabis is not regulated by the FDA. Without an overarching federal policy requiring cannabis testing laboratory accreditation, the testing and laboratory requirements differ greatly across state lines.For medical cannabis specifically, accredited testing facilities are especially important.

To be federally regulated, cannabis would first have to be federally legalized. It turns out that states and businesses alike are not willing to wait for a federal mandate. Many states have begun to adopt standards for cannabis testing and some, such as Ohio, have even announced mandatory ISO/IEC 17025 accreditation for all cannabis testing laboratories. As the industry evolves, increased compliance expectations are certain to evolve in tandem.

Some cannabis labs have even taken the initiative to seek ISO/IEC 17025 accreditation of their own volition. Seth Wong, President of TEQ Analytics Laboratories, shared in a press release:

“By achieving ISO/IEC 17025 accreditation, TEQ Analytical Labs believes that we can address the concerns throughout the cannabis industry regarding insufficient and unreliable scientific analysis by providing our clients with State required tests that are accredited by an international standard.”

Other laboratories, such as DB Labs in Las Vegas and EVIO Labs in Florida are also leading the accreditation charge in their respective states, ahead of any state mandates.

There are key reasons why accreditation in cannabis testing labs is important. First and foremost, cannabis is a consumable product. Like fruits and vegetables, cannabis is prone to pesticides, fungi and contaminants. The result of putting a potentially hazardous material on the market without proper and documented testing could lead to a public health crisis. An accredited testing lab, however, will ensure that the cannabis products they test are free from harmful contaminants.

By utilizing role-based trainings, labs can trust employees are receiving proper onboarding.

For medical cannabis specifically, accredited testing facilities are especially important. Because many consumers of medical cannabis are immuno-compromised (such as in the case of chemotherapy patients), ensuring that products are free from any and all contaminants is critical. Further, in order to accurately determine both short- and long-term effects of prescribed cannabis consumption, accredited and compliant laboratories are necessary.

Accreditation standards like ISO/IEC 17025 also provide confidence that testing is performed properly and to an internationally accepted standard. Rather than returning a “pass/fail” rating on products, the Cannabis Safety Institute reports that an ISO/IEC 17025 laboratory is required to produce numerical accuracy percentages in testing for “at a minimum, cannabinoids, pesticides, microbiology, residual solvents, and water activity.” Reliable data sets that can be reviewed by both accreditors and the public foster trust between producers and consumers.

Finally, ISO/IEC 17025 accreditation demonstrates that a laboratory is properly staffed and trained. The Cannabis Safety Institute’s “Standards for Cannabis Testing Laboratories” explains that conducting proper analytical chemistry on cannabinoids (the chemical compounds extracted from cannabis that alter the brain’s neurotransmitter release) requires personnel who have met specific academic and training credentials. A system to monitor, manage and demonstrate proficiency is necessary to achieve and maintain accreditation. With electronic systems in place, this management and documentation minimizes risk and also minimizes administrative time tracking and maintaining training records.

Following the proper steps of a standardized process is key to improving and growing the cannabis industry in coming yearsFor cannabis testing labs, utilizing a comprehensive software solution to achieve and maintain compliance to standards such as ISO/IEC 17025 is key. Absent of a software solution, the necessary compliance requirements can become a significant burden to the organization. Paper tracking systems and complex spreadsheets open up organizations to the likelihood of errors and ultimately risk.

Because ISO/IEC 17025 has clearly defined expectations for training, a software solution also streamlines the training process while simultaneously documenting proficiency. By utilizing role-based trainings, organizations can be confident employees are receiving proper onboarding and in-service training. Additionally, the effectiveness of training can be proven with reports, which results in smoother audits and assessments.

Following the proper steps of a standardized process is key to improving and growing the cannabis industry in coming years- which means utilizing technology tools such as electronic workflows to ensure proper process controls. Beyond adding critical visibility, workflows also create efficiencies that can eliminate the need to increase staffing as companies expand and grow.

For an industry that is changing at a rapid pace, ensuring traceability, efficient processes and visibility across organizations is paramount. Using a system that enables automation, process control, document management and documented training procedures is a step in the right direction. With the proper software tools in place, cannabis testing labs can achieve compliance goals, demonstrate reliable and relevant results and most importantly ensure consumer safety.

February 15, 2018

The Grass Isn’t Always Greener: Removal of Purple Pigmentation from Cannabis

By Danielle Mackowsky

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Cannabis strains used (clockwise from top left): Agent Orange, Tahoe OG, Blue Skunk, Grand Daddy and Grape Drink

Cannabis-testing laboratories have the challenge of removing a variety of unwanted matrix components from plant material prior to running extracts on their LC-MS/MS or GC-MS. The complexity of the cannabis plant presents additional analytical challenges that do not need to be accounted for in other agricultural products. Up to a third of the overall mass of cannabis seed, half of usable flower and nearly all extracts can be contributed to essential oils such as terpenes, flavonoids and actual cannabinoid content¹. The biodiversity of this plant is exhibited in the over 2,000 unique strains that have been identified, each with their own pigmentation, cannabinoid profile and overall suggested medicinal use². While novel methods have been developed for the removal of chlorophyll, few, if any, sample preparation methods have been devoted to removal of other colored pigments from cannabis.

Cannabis samples following QuEChERS extraction

Sample Preparation

Cannabis samples from four strains of plant (Purple Drink, Tahoe OG, Grand Daddy and Agent Orange) were hydrated using deionized water. Following the addition of 10 mL acetonitrile, samples were homogenized using a SPEX Geno/Grinder and stainless steel grinding balls. QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) non-buffered extraction salts were then added and samples were shaken. Following centrifugation, an aliquot of the supernatant was transferred to various blends of dispersive SPE (dSPE) salts packed into centrifugation tubes. All dSPE tubes were vortexed prior to being centrifuged. Resulting supernatant was transferred to clear auto sampler vials for visual analysis. Recoveries of 48 pesticides and four mycotoxins were determined for the two dSPE blends that provided the most pigmentation removal.

Seven dSPE blends were evaluated for their ability to remove both chlorophyll and purple pigmentation from cannabis plant material:

150 mg MgSO₄, 50 mg PSA, 50 mg C18, 50 mg Chlorofiltr®
150 mg MgSO₄, 50 mg C18, 50 mg Chlorofiltr®
150 mg MgSO₄, 50 mg PSA
150 mg MgSO₄, 25 mg C18
150 mg MgSO₄, 50 mg PSA, 50 mg C18
150 mg MgSO₄, 25 mg PSA, 7.5 mg GCB
150 mg MgSO₄, 50 mg PSA, 50 mg C18, 50 mg GCB

Based on the coloration of the resulting extracts, blends A, F and G were determined to be the most effective in removing both chlorophyll (all cannabis strains) and purple pigments (Purple Drink and Grand Daddy). Previous research regarding the ability of large quantities of GCB to retain planar pesticides allowed for the exclusion of blend G from further analyte quantitation³. The recoveries of the 48 selected pesticides and four mycotoxins for blends A and F were determined.

Grand Daddy following various dSPE cleanups

Summary

A blend of MgSO₄, C18, PSA and Chlorofiltr® allowed for the most sample clean up, without loss of pesticides and mycotoxins, for all cannabis samples tested. Average recovery of the 47 pesticides and five mycotoxins using the selected dSPE blend was 75.6% were as the average recovery when including GCB instead of Chlorofiltr® was 67.6%. Regardless of the sample’s original pigmentation, this blend successfully removed both chlorophyll and purple hues from all strains tested. The other six dSPE blends evaluated were unable to provide the sample clean up needed or had previously demonstrated to be detrimental to the recovery of pesticides routinely analyzed in cannabis.

References

(1) Recommended methods for the identification and analysis of cannabis and cannabis products, United Nations Office of Drugs and Crime (2009)

(2) W. Ross, Newsweek, (2016)

(3) Koesukwiwat, Urairat, et al. “High Throughput Analysis of 150 Pesticides in Fruits and Vegetables Using QuEChERS and Low-Pressure Gas Chromatography Time-of-Flight Mass Spectrometry.” Journal of Chromatography A, vol. 1217, no. 43, 2010, pp. 6692–6703., doi:10.1016/j.chroma.2010.05.012.

February 7, 2018

EVIO Labs: The First Accredited Cannabis Lab in Florida

By Lauren Masko

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EVIO Labs recently became the first cannabis laboratory in Florida to obtain ISO 17025 accreditation. Perry Johnson Laboratory Accreditation, Inc. (PJLA), an organization that provides third-party assessments to ISO/IEC 17025, accredited EVIO Labs. The assessment process that lead to ISO 17025 accreditation for EVIO Labs included a thorough review of their quality management system, their capability to perform potency and contaminant testing for cannabis products.

Tracy Szerszen, president and operations manager at PJLA, encourages this international standard for laboratories to provide confidence to end-users that the test results they receive are reliable. She says laboratories that achieve this accreditation are showing they have the proper tools, equipment and staff to provide accurate testing. “It is a very critical component of the industry, and becoming accredited provides the assurance that laboratories are performing to the highest standard,” says Szerszen. “EVIO Labs has taken the right step in their commitment towards meeting this standard and providing clean and safe cannabis for the patients of Florida.”

EVIO Labs provides cannabis testing for cannabinoid and terpene profiles, microbiological and pesticides contamination, residual solvent, heavy metals, mycotoxins, water activity and moisture content. Chris Martinez, co-founder and president of EVIO Labs Florida explains that the Florida Department of Health mandates that an independent third-party laboratory tests medical cannabis to ensure that these products are safe for human consumption. Martinez says their first priority is the safety of their patients, and ensuring that EVIO Labs provides clean and safe cannabis for Florida.

Chris Martinez, co-founder and president of EVIO Labs Florida

Martinez launched their laboratory with some help from Shimadzu last year. “Our Broward lab is powered by Shimadzu with over $1.2M in the latest testing equipment utilizing LCMS technology with the world’s fastest polarity switching time of 5 m/sec and scan speeds of 30,000 u/sec with UF Qarray sensitivity 90 times that of previously available technologies,” says Martinez. According to Martinez, their licensing agreement with EVIO Labs (OTC:SGBYD) marked a first for the publicly traded company with exclusivity in the Florida market. The agreement includes proprietary testing methodologies, operating procedures, training and support.

Every certificate of analysis is reviewed by a lab director with over 20 years of experience operating in FDA regulated labs. Martinez says that EVIO has some of the most advanced technology in the industry, which provides them the opportunity to quickly provide results, frequently as fast as a 24-hour period. Martinez and his team are currently building a 3,300 square-foot laboratory in Gainesville, which is expected to be running by March of this year.

October 2, 2017

PA Approves First Two Cannabis Labs

By Aaron G. Biros

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According to a PennLive article, Pennsylvania’s Department of Health approved the first two cannabis laboratories for their medical cannabis program. ACT Laboratories of Pennsylvania LLC and Keystone State Testing LLC are the companies that were approved to perform analytical testing for safety and quality in cannabis products.

Both laboratories expect to be operational before the end of 2017, according to the PennLive article. Those labs are required to test for CBD and THC content, pesticides, moisture content, residual solvents and microbiological contaminants.

The temporary lab testing regulations are somewhat comprehensive, detailing lab reporting, licensing, sampling protocols and ownership stipulations, among other rules. ACT and Keystone, the labs that were approved by the Department of Health, have their approval for two years and can renew their license after.

While the state still expects the program to be fully implemented by 2018, Health Secretary and Physician General Dr. Rachel Levine said last week they are hoping to launch the program sometime next year, according to a press release. December 2017 will mark a full year since the state opened applications for licensing businesses.

January 2018 has long been the goal for the full implementation of the program. “We have made significant progress in getting this program off the ground since Governor Wolf signed the Medical Marijuana Act into law last year,” says Dr. Levine. “These proposed regulations for patients and caregivers to participate are one of the final pieces we need to have in place to launch the program sometime next year.”

September 26, 2017

Nevada Cannabis Lab License Suspended

By Aaron G. Biros

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Last month, G3 Labs LLC, a Las Vegas-based cannabis-testing lab, had their license suspended for an unknown regulatory compliance issue. According to Stephanie Klapstein, spokeswoman for the Nevada Department of Taxation, the reason why their license was suspended is confidential. “We can’t disclose the details of the suspension, including anything about penalties,” says Klapstein.

When asked about the license suspension, Klapstein told us it was a compliance issue, but could not go into detail. “I can confirm that we did suspend G3’s license for compliance issues,” says Klapstein. “We are working with them to bring them back into compliance. In the meantime, they cannot operate.” Klapstein told the Las Vegas Review-Journal that the Nevada Department of Agriculture tested cannabis samples from the lab to determine if there was a need for a recall. She also confirmed with us that the compliance issue does not necessitate any product recalls.

According to the Las Vegas Review-Journal, this is the first time a cannabis business license is suspended in the state since the beginning of adult-use sales back in July of this year. Nevada’s cannabis regulations require independent lab testing of products before they reach shelves. That required testing includes checking for potency, microbials, pesticides, residual solvents, moisture content, growth regulators, Mycotoxins and foreign matter.

When we reached out to G3 Labs, they did not immediately respond to a request for comment.

Dr. Chao-Hsiung Tung, lab director at G3 Labs, told the Las Vegas Review-Journal that they couldn’t comment, based on advice from their legal counsel. “G3 Labs is actively sorting out the issues with the Department,” Dr. Tung told the Review-Journal in an email.

September 21, 2017

EVIO Labs Expands To Florida

By Aaron G. Biros

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Currently, there are no lab testing regulations for Florida’s medical cannabis market. Chris Martinez, co-founder and chief operating officer of EVIO Labs Florida, a veteran-owned business, is looking to change that.

Chris Martinez, co-founder and president of EVIO Labs Florida

When Martinez co-founded EVIO Labs Florida, he saw the need for a dedicated cannabis lab to ensure safety and quality of medicine for patients in the state. Partnering with EVIO Labs to accomplish this goal, Martinez secured a 5,500 sq. ft. facility in Broward County to test for potency, pesticides, microbial contaminants, terpenes, residual solvents and heavy metals. Their lab, a first of its kind in the industry, qualifies as a true pharmaceutical-grade clean room. This week, Martinez also secured their 2^nd laboratory location in the City of Gainsville, where they will test for potency, microbials, terpenes and residual solvents. And he isn’t doing it on the cheap. “Our Broward lab is powered by Shimadzu with over $1.2M in the latest testing equipment utilizing LCMS technology with the world’s fastest polarity switching time of 5 m/sec and scan speeds of 30,000 u/sec with UF Qarray sensitivity 90 times that of previously available technologies,” says Martinez.

Martinez, an entrepreneur at heart, started the lab with a team of experts to become the first completely cannabis-focused laboratory in Florida. Jorge Segredo, their head chemist and quality assurance director, has over 18 years of experience in the development of nutraceutical and pharmaceutical products under ISO and FDA accreditation. Segredo has helped launch three independent FDA-accredited laboratories and has extensive knowledge of HPLC, GCMS, LCMS, ICPMS technologies and development/validation of testing methods and procedures. Cynthia Brewer, their director of operations, was an active participant in the 2017 state legislative session and has been an advocate for medical cannabis, working with legislators on a suitable framework to increase patient access to cannabis.

The EVIO team is using instruments from Shimadzu

EVIO is one of the nation’s leaders in cannabis testing, research science and advisory services. It is an evolving network of laboratories with nine EVIO cannabis laboratories operating in five different states: Oregon, Colorado, Massachusetts, Florida and California. “After speaking with industry chemists around the country for months, the EVIO name was constantly brought up in conversation,” says Martinez. “When we spoke with the EVIO Team it was an easy decision for us to partner.” He says Lori Glauser, chief operating officer of EVIO, and William Waldrop, chief executive officer of EVIO, are truly visionaries in the cannabis industry.

According to Martinez, their licensing agreement with EVIO Labs (OTC:SGBYD) marked a first for the publicly traded company with exclusivity in the Florida market. The agreement includes proprietary testing methodologies, operating procedures, training and support.

In addition to testing cannabis for safety and quality, they are launching a technology platform called MJ Buddy, essentially a software tool that takes efficacy feedback from patients and uses testing and genetic data they gather from EVIO Labs across the country. “This will provide real data to the cannabis industry as to the medical benefits for thousands of patients in relation to the genotype and cannabinoid profiles of their medicine,” says Martinez.

Of the states that have legalized some form of cannabis, a large number of them have some lab testing regulations on the book, with some more comprehensive than others. Martinez says he hopes the Florida Department of Health, Office of Medical Marijuana Use follows some of the more thorough state programs, such as Oregon. His team has compiled a set of documents for regulators with recommendations for regulating the lab testing industry.

Without any regulations on paper, it is up to businesses to produce safe and quality medicine, without any oversight. EVIO Labs Florida follows FDA Good Laboratory Practices, has an ISO 17025:2005 accreditation pending, and is working on TNI 2016 accreditation.

When discussing what he wants to see happen with Florida’s regulatory framework, Martinez says the rules need to be specific to Florida. For example, due to the climate being so humid, microbial contaminant testing for things like yeast and mold will be particularly imperative. Because processing methods like butane and alcohol extraction are legal, he emphasizes the need for comprehensive residual solvents testing. “The most important regulation would be to have the laboratories select the samples at the MMTC facility and have the state randomly verify laboratory results to ensure accurate unbiased testing,” says Martinez.

In addition to that, he hopes their pesticide thresholds will be realistic and based on actual science. “We believe the public should receive carcinogenic data for products that are inhaled,” says Martinez. “Chemicals may be introduced into the processing of cannabis to vape liquid that may cause harm. This is important information for public health and communication of the risk related to exposure to such materials.” Martinez says EVIO Labs Florida was founded on the belief that through technology and science we can increase safety and patient outcomes.

September 21, 2017

Colorado Approves Emerald Scientific Proficiency Tests for Regulatory Compliance in Cannabis Testing

By Aaron G. Biros

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Emerald Scientific recently announced their proficiency-testing program, The Emerald Test, has been approved by Colorado as a third party provider for proficiency testing in licensed cannabis laboratories. The Emerald Test, held twice annually, is an inter-laboratory comparison and proficiency test (ILC-PT), allowing data to be collected pertaining to the performance of laboratories on a national scale. Proficiency testing is designed to measure how accurately laboratories perform and is a critical tool for quality assurance.

Colorado requires labs to participate in a proficiency-testing program in order to be certified to conduct required testing on cannabis and cannabis products for safety and quality. According to the press release, Colorado’s Marijuana Enforcement Division, under the Department of Revenue, conducted an evaluation process to determine which applicants could meet the performance standards for regulatory compliance concerning proficiency testing. The contract was awarded to Emerald Scientific following this evaluation process.

According to Ken Groggel, director of the Proficiency Testing Program at Emerald Scientific, a number of states have recognized the need for independent proficiency testing as a required piece of regulatory compliance. “The Emerald Test Inter-Laboratory Comparison/PT is state approved in Washington & Colorado for cannabis testing laboratory licensure,” says Groggel. “States with cannabis or hemp production, as well as labs in other countries are now actively participating in the Emerald Test as a tool for quality improvement, efficiency upgrades and product safety.” He says the Colorado Marijuana Enforcement Division has contracted with Emerald Scientific to provide third party PT programs for microbial contaminants, residual solvents and pesticides.

Beginning in 2014, The Emerald Test has been offered twice a year and, in 2017, over 50 labs participated from 14 states and 2 countries. “Laboratories that have enrolled more than once have seen significant improvement in their results, an indicator of improved performance for industry customers,” says Groggel.

Proficiency testing is important for ensuring quality, safety and product content accuracy. “This should be the priority whether you are a grower, manufacturer, testing laboratory, regulatory entity, medical patient or adult use consumer,” says Groggel. It also helps labs meet regulatory requirements and achieve ISO 17025 accreditation. “Independent proficiency testing helps determine if the lab is able to deliver the services marketed to its customers,” says Groggel. “Regulatory agencies can use this information when licensing, monitoring & enforcing good science for public safety.”

As new states legalize cannabis and develop consumer protection regulations, proficiency testing programs can help labs demonstrate their commitment to responsible and accurate testing. “When PT results show the cannabis testing lab is capable it is up to the government to ensure accountability for performance on behalf of all its citizens,” says Groggel. Labs can enroll starting on September 25^th in the Fall 2017 Emerald Test ILC/PT.

May 10, 2017

California Releases Draft Lab Testing Regulations

By Aaron G. Biros

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Last Friday, the Bureau of Marijuana Control, the regulatory body overseeing California’s cannabis industry, released a set of proposed regulations for the lab testing market. The regulations are somewhat comprehensive, covering sampling, licensing, pesticide testing, microbiological contaminants, residual solvents, water activity and much more.

Formerly named the Bureau of Medical Cannabis Regulation under the state’s Department of Consumer Affairs, the Bureau of Marijuana Control is tasked with overseeing the development, implementation and enforcement of the regulations for the state’s cannabis industry. In their statement of reasons for the lab testing regulations, the bureau says they are designed with public health and safety at top of mind. At first glance, much of these laboratory rules seem loosely modeled off of Colorado and Oregon’s already implemented testing regulations.

The regulations lay out requirements for testing cannabis products prior to bringing them to market. That includes testing for residual solvents and processing chemicals, microbiological contaminants, mycotoxins, foreign materials, heavy metals, pesticides, homogeneity as well as potency in quantifying cannabinoids.

The microbiological impurities section lays out some testing requirements designed to prevent food-borne illness. Labs are required to test for E. coli, Salmonella and multiple species of the pathogenic Aspergillus. If a lab detects any of those contaminants, that batch of cannabis or cannabis products would then fail the test and could not be sold to consumers. A lab must report all of that information on a certificate of analysis, according to the text of the regulations.

The proposed regulations stipulate requirements for sampling, including requiring labs to develop sampling plans with standard operating procedures (SOPs) and requiring a lab-approved sampler to follow chain-of-custody protocols. The rules also propose requiring SOPs for analytical methodology. That includes some method development parameters like the list of analytes and applicable matrices. It also says all testing methods need to be validated and labs need to incorporate guidelines from the FDA’s Bacterial Analytical Manual, the U.S. Pharmacopeia and AOAC’s Official Methods of Analysis for Contaminant Testing, or other scientifically valid testing methodology.

Labs will be required to be ISO 17025-accredited in order to perform routine cannabis testing. Laboratories also need to participate in proficiency testing (PT) program “provided by an ISO 17043 accredited proficiency-test provider.” If a laboratory fails to participate in the PT program or fails to pass to receive a passing grade, that lab may be subject to disciplinary action against the lab’s license. Labs need to have corrective action plans in place if they fail to get a passing grade for any portion of the PT program.

October 31, 2016

Pennsylvania Temporary Rules for Growers & Processors Released

By Aaron G. Biros

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Last week, Pennsylvania Department of Health Secretary Dr. Karen Murphy announced the formation of temporary regulations for cannabis growers and processors in the state, according to a press release. Those temporary rules were published on Saturday, October 29. Secretary Murphy asked for public comment on developing regulations for dispensaries as well.

The PA Department of Health published the new set of temporary regulations this past Saturday, outlining “the financial, legal and operational requirements needed by an individual to be considered for a grower/processor permit, as well as where the facilities can be located.” The regulations also discuss tracking systems, equipment maintenance, safety issues, disposal of cannabis, tax reporting, pesticides, recalls and insurance requirements. “One of our biggest accomplishments to date is the development of temporary regulations for marijuana growers and processors,” says Secretary Murphy. “We received nearly 1,000 comments from members of the community, the industry and our legislative partners.”

The general provisions published on Saturday outline the details of the application process, fees, inspections, reporting, advertising and issues surrounding locations and zoning. The temporary regulations for growers and processors delve into the minutia of regulatory compliance for a variety of issues: including security, storage, maintenance, transportation, tracking, disposal, recall, pesticides and packaging and safety requirements. A list of pesticides permitted for use can also be found at the bottom of the rules.

PA Department of Health Secretary Dr. Karen Murphy

The document discusses the regulations for performing voluntary and mandatory recalls in great detail. It requires thorough documentation and standard operating procedures for the disposal of contaminated products, cooperation with the Department of Health and appropriate communications with those affected by the recall.

The department has yet to release temporary regulations for laboratories and dispensaries, but hopes to do so before the end of the year. “I am encouraging the public – and specifically the dispensary community – to review the temporary regulations and provide us with their feedback,” says Secretary Murphy. “The final temporary regulations for dispensaries will be published in the Pennsylvania Bulletin by the end of the year.”

Since Governor Tom Wolf signed the medical cannabis program bill into law in April 2016, the state has made considerable progress to develop the program, including setting up a physician workgroup, public surveys for developing temporary rules and a request for information for electronic tracking IT solutions. The PA Department of Health expects to implement the program fully in the next 18 to 24 months.

June 1, 2016

The Practical Chemist

Calibration Part II – Evaluating Your Curves

By Amanda Rigdon

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Despite the title, this article is not about weight loss – it is about generating valid analytical data for quantitative analyses. In the last installment of The Practical Chemist, I introduced instrument calibration and covered a few ways we can calibrate our instruments. Just because we have run several standards across a range of concentrations and plotted a curve using the resulting data, it does not mean our curve accurately represents our instrument’s response across that concentration range. In order to be able to claim that our calibration curve accurately represents our instrument response, we have to take a look at a couple of quality indicators for our curve data:

correlation coefficient (r) or coefficient of determination (r²)
back-calculated accuracy (reported as % error)

The r or r² values that accompany our calibration curve are measurements of how closely our curve matches the data we have generated. The closer the values are to 1.00, the more accurately our curve represents our detector response. Generally, r values ≥0.995 and r² values ≥ 0.990 are considered ‘good’. Figure 1 shows a few representative curves, their associated data, and r² values (concentration and response units are arbitrary).

Figure 1: Representative Curves and r2 values

Let’s take a closer look at these curves:

Curve A: This represents a case where the curve perfectly matches the instrument data, meaning our calculated unknown values will be accurate across the entire calibration range.

Curve B: The r² value is good and visually the curve matches most of the data points pretty well. However, if we look at our two highest calibration points, we can see that they do not match the trend for the rest of the data; the response values should be closer to 1250 and 2500. The fact that they are much lower than they should be could indicate that we are starting to overload our detector at higher calibration levels; we are putting more mass of analyte into the detector than it can reliably detect. This is a common problem when dealing with concentrated samples, so it can occur especially for potency analyses.

Curve C: We can see that although our r² value is still okay, we are not detecting analytes as we should at the low end of our curve. In fact, at our lowest calibration level, the instrument is not detecting anything at all (0 response at the lowest point). This is a common problem with residual solvent and pesticide analyses where detection levels for some compounds like benzene are very low.

Curve D: It is a perfect example of our curve not representing our instrument response at all. A curve like this indicates a possible problem with the instrument or sample preparation.

So even if our curve looks good, we could be generating inaccurate results for some samples. This brings us to another measure of curve fitness: back-calculated accuracy (expressed as % error). This is an easy way to determine how accurate your results will be without performing a single additional run.

Back-calculated accuracy simply plugs the area values we obtained from our calibrators back into the calibration curve to see how well our curve will calculate these values in relation to the known value. We can do this by reprocessing our calibrators as unknowns or by hand. As an example, let’s back-calculate the concentration of our 500 level calibrator from Curve B. The formula for that curve is: y = 3.543x + 52.805. If we plug 1800 in for y and solve for x, we end up with a calculated concentration of 493. To calculate the error of our calculated value versus the true value, we can use the equation: % Error = [(calculated value – true value)/true value] * 100. This gives us a % error of -1.4%. Acceptable % error values are usually ±15 – 20% depending on analysis type. Let’s see what the % error values are for the curves shown in Figure 1.

Table 1: % Error for Back-Calculated Values for Curves A – D

Our % error values have told us what our r² values could not. We knew Curve D was unacceptable, but now we can see that Curves B and C will yield inaccurate results for all but the highest levels of analyte – even though the results were skewed at opposite ends of the curves.

There are many more details regarding generating calibration curves and measuring their quality that I did not have room to mention here. Hopefully, these two articles have given you some tools to use in your lab to quickly and easily improve the quality of your data. If you would like to learn more about this topic or have any questions, please don’t hesitate to contact me at amanda.rigdon@restek.com.