Mass Spectrometry at Pittcon 2024

For 75 years, Pittcon has promised attendees a dynamic, transnational conference and exposition on laboratory science, a venue for presenting the latest advances in analytical research and scientific instrumentation, and a platform for continuing education and science-enhancing opportunity (1). This past Pittcon was held in San Diego, California, the first time the conference has ventured west of the Mississippi River. LCGC took advantage of the opportunity to speak with key opinion leaders on the cutting edge of analytical science (both from academia and the private sector) to gauge the evolution of a variety of techniques and the opportunities this evolution will present. This article presents insights from three of these individuals on the forefront of mass spectrometry who presented their research at one of the many sessions organized at the 2024 conference.

Metal Ion Leaching from Stainless Steel and Hastelloy in Common Pharmaceutical Solvents and its Impact on Production and Analysis: An Interview with Jesse Bischof

Leaching occurs when metal ions make their way into the pharmaceutical production process and interact with the active ingredients within the medication. As small as parts-per-billion (ppb) variation of elements such as iron, chromium, nickel, and manganese can negatively impact the pharmaceutical production process. Suppliers of raw materials diligently attempt to control the amount of metal in their product so as not to negatively impact their formulations. However, once these materials are stored, distributed, and processed in stainless steel or hastelloy (a nickel alloy used for its high resistance to corrosion) components, leaching can still occur and cause problems. At the Pittcon session “Mass Spectrometry in Pharmaceuticals,” Jesse Bischof of SilcoTek presented metal ion leaching data measured using inductively coupled plasma-mass spectrometry (ICP-MS) and described a method to mitigate leaching in the form of a nano chemical vapor deposition (CVD) silicon-based coating. This coating is added to block metal ions from leaching into various pharmaceutically relevant solvents such as water, methanol, and acetonitrile, both in their pure forms as well as in mixtures. The results showed that, after the application of this coating to tubing, valves, filters, tanks, and any other metal processing equipment, metal ions in product can be reduced to sub-ppb levels of leaching, thus providing greater control over various pharmaceutical processes. Bischof discussed the CVD silicon coating approach with us shortly after his technical presentation.

Briefly discuss the impact of metal ion leaching on pharmaceutical production.

In pharmaceutical production, specifically biopharmaceutical production, metal concentrations need to be tightly controlled to optimize yields, to prevent product degradation, and to reduce irreversible protein aggregation, among many other issues. This problem is not limited to just pharmaceutical production either. Any process requiring microbes for their process would benefit from tight control over metal ion concentrations, including beer and wine fermentation, cheese and yogurt production, and chemicals that are manufactured via microbial fermentation such as citric acid from Aspergillus niger. Much of this is well known and documented in the literature, so many scientists take care to get metal concentrations in their cell culture media into the proper range, but metal ions leaching into the media can occur and dramatically impact those concentrations. Unfortunately, the leaching can be unpredictable and can lead to batch-to-batch product variation.

How do metal ions get introduced into the drug manufacturing process?

Stainless steel has been the alloy of choice for most pharmaceutical production facilities for over a century. It is used due to its resistance to harsh chemicals, and it can hold up to sterilization processes. It is used for tubing, valves, pumps, tanks, filtration, and more. The material often appears to be unaffected by exposure to various solvents as there are no obvious signs of rust or corrosion, but the leaching of metals at ppm levels and even lower levels are constantly occurring. This leaching often has no visual impact to steel surfaces, so it goes unnoticed. For highly corrosive situations, some manufacturers turn to Hastelloy as an alternative to stainless steel, but even that alloy is susceptible to ppb and ppm levels of leaching metal ions.

Please summarize the scenario covered at your recent talk that inspired your research.

There are many areas where metals are exposed to fluidic flow paths, but one of the first areas we targeted was in separation and purification processes, specifically column hardware for high performance liquid chromatography (HPLC) and prep separations. In an HPLC system, the column alone accounts for at least 75% of the metallic surface area. Many pharmaceutical molecules are prone to non-specific bonding to metal surfaces as well as metal ions that leach into the separation media causing sticking sites as well. We had an end user that was operating under high pH, high salt content, and relatively high temperatures for an oligonucleotide purification. They were trying to collect impurities for liquid chromatography–mass spectrometry (LC–MS) analysis on a semi-prep system. After about 6–8 injections on the column, the impurities that they were trying to collect were lost in the noise of the chromatogram and no longer able to be separated. They opened their column to find the frit and end cap covered in rust spots and the top of the separation media to be brownish orange, rather than white. While we worked to address their problem, it got us wondering: What conditions cause this metal ion leaching? There are some obvious answers such as acidic conditions or higher temperatures that can cause larger quantities of metal ions to solvate, but what about benign conditions? What would just water or acetonitrile or methanol do to stainless steel surfaces at room temperature?

In your session, you presented metal ion leaching data via ICP-MS. What was the benefit in using this technique as opposed to other atomic methods?

The detection limits of ICP-MS for these metal species were the main reason for choosing it. Some samples were only leaching at ppb levels of metals, which is well within the capabilities of ICP-MS. For other samples that are leaching at ppm levels of metal ions, ICP-optical emission spectrometry (OES) or atomic absorption spectroscopy (AAS) would be sufficient, or even favorable, as they have better quantitation in these concentrations.

Please discuss the steps you took to resolve any challenges you encountered and summarize your findings.

One of the largest challenges that we have run into with this testing is the huge variability of metal leaching from stainless steel and hastelloy materials, especially for sintered frits. Even within the same order from the same company, the leaching rates of these materials can vary drastically, let alone considering one company to another company’s product. I would imagine there are many separation scientists out there that wonder how or why the exact same column from a company can result in such drastically different responses, especially to metal sensitive analytes.

Could this possibly have to do with the different suppliers of the stainless-steel raw material that component manufacturers use?

We have certainly seen differences from different suppliers of stainless steel, but we have also seen differences from the same company purchasing the same stainless steel raw material from the same vendor. There seems to be lot to lot variation even with the entire supply chain being consistent.

How does the use of chemical vapor deposition (CVD) silicon-based coatings mitigate metal leaching for exposed metallic surfaces?

CVD coatings provide a uniform barrier across three-dimensional surfaces to block interactions between the solvents and the metal surfaces. This means that analytes are not exposed to metal surfaces and metal ions are not leaching into the solvent. One nice part about thermal CVD depositions is that the coating can penetrate small pores, such as those found in sintered metal frits.

What were your findings for the metal leaching test for CVD coated verses non-coated metals?

Depending on the solvent system and temperature, metal surfaces can leach anywhere from single digit ppb levels of metal up to near percent levels. The CVD coated metals showed near baseline (what was already present in the solvent before the test) amounts of metal ion leaching. For instance, pure water at 60 °C causes over 2 ppm of metals to leach from an uncoated stainless-steel sample. With those same conditions, a coated sample showed under 5 ppb when corrected to baseline concentrations.

What best practices that can you recommend for oligo recovery analysis using a coated column and frit system?

We’ve heard from end users that oligonucleotides sticking to metal surfaces can cause a lot of frustration, especially when trace analysis is the goal. The silica-like coating will allow for this analysis to be done without the negative effects from exposed metal surfaces. The coating is also durable and resistant to most chemicals that would be used in such an analysis. We have seen that for non-metal active materials, there is no difference between a coated system and an uncoated system. At the same time, we have received reports of the coating helping with compounds that were otherwise seen as non-metal active, and we have also seen an increase in column lifetimes.

Can you please summarize the feedback that you have received from others regarding this work, especially the individual who had the initial issue and brought it to your attention?

Thus far, the feedback regarding coated column hardware has been positive. The oligonucleotide scientist that was only getting 6–8 injections before their impurities were lost in the baseline noise reported that they were getting 100x lifetime improvements on his column. At that point, they stopped the experiment and were so satisfied with the results, they ended up sending us the rest of their flow path as well for coating: capillary tubing, pump heads, valves, and so forth.

Are there any next steps in this research?

The next step is to look at more mobile phase additives and take a deep dive into quantifying the metal leaching impact on stainless steel and hastelloy. We’ve seen some ion pairing additives like triethylammonium acetate that cause an increase in metal ion leaching and others such as triethylamine hexafluoroisopropanol that have a passivating effect and reduce the metal leaching. The plan is to look at some common HPLC additives like formic acid, acetic acid, perchlorate salts, phosphate buffers, ammonium acetate, as well as some common pharmaceutical ingredients like citric acid, guanidine HCl, and histidine. We want to know which of these additives could have the biggest impact to metal ion leaching and explore how our coatings could reduce this leaching to help both upstream and downstream pharmaceutical scientists.

ABOUT THE INTERVIEWEE

Jesse Bischof began his career teaching high school chemistry before returning to graduate school at Penn State where he earned his PhD in chemistry. Upon completion of his degree in 2016, Jesse began his role as a scientist in SilcoTek’s research and development department. Currently, Jesse’s research is focused on developing and optimizing bio-inert and anti-metal leaching coatings for medical, semiconductor, and analytical markets.

Non-Target Characterization and Simultaneous Quantitation for Reformulation of Complex Fragrance Samples with GC×GC–MS/FID: An Interview with Elizabeth Humston-Fulmer

The determination of the many chemical components that can make up a fragrance sample is important for multiple objectives, including reformulation, which typically involves determining the identification and relative amounts of components in a sample. As it is usually not practical to quantify and calibrate all the fragrance components using reference standards, workflows to achieve fragrance analysis use mass spectrometry (MS) for identification with a flame ionization detector (FID) for relative area percent quantification. At the Pittcon session “Mass Spectrometry in Pharmaceuticals,” Elizabeth Humston-Fulmer of LECO Corporation presented an improved workflow which uses two-dimensional gas chromatography (GC×GC) with dual time of flight (TOF)-MS/FID detection. Humston-Fulmer has found that this process yields reliable identification and area percent quantification using a single injection, rather than the traditional multiple injection requirements. Shortly after Pittcon, Humston-Fulmer discussed this analytical method with us.

From a separation standpoint, what are some of the challenges associated with fragrance analysis and formulation?

There are a few reasons why fragrance analyses and formulation tasks can be challenging. One of the reasons is that the samples tend to be complex; there are often hundreds of analytes in a fragrance mixture, which can make it hard to determine all the individual components. Another reason these tasks are challenging is because they are usually nontargeted, and we don’t know which analytes will be important when we start. You are also trying to learn what analytes are present and their relative amounts, so it is a lot of information to try to understand about a complex sample.

In your presentation, you demonstrated an improved workflow using GC×GC–TOF-MS-FID detection to yield reliable identification and area percent quantification in a single injection. What made you decide to choose this analytical technique?

We really like the approach of using GC×GC with dual MS and FID detection for these kinds of projects because we get a lot of information from a single injection. GC is a common tool for fragrance analyses because the analytes that contribute to the aroma profile tend to have volatilities that are a good match with GC. When the samples are complex, adding a second dimension of separation with GC×GC can be helpful because the sample is separated with two complementary stationary phases in the same analysis. If analytes are coeluted on one phase, they often separate on the other, so we end up with more of the individual analytes chromatographically separated. This improved separation sometimes reveals analytes that were coeluted to the point that they were hard to find in the 1D data, so we can usually learn new information about the samples this way. It’s also helpful to have both MS and FID data because we use the MS information to identify the nontarget analytes and the FID information for area percent determinations. Injecting once and splitting the effluent to both FID and MS saves us from having to make separate injections for each detector.

What were some of the specific hardware and data analysis methods used for this workflow to ensure reliable quantitative results?

The hardware and software for this system were both designed carefully to try to ensure that the peak areas would be reliable so they could be used for area percent calculations. The modulator and the splitter were two components of the instrument that received a lot of attention. The system uses a reverse fill/flush (RFF) flow modulator where the primary column effluent is collected in a sample loop, which is then flushed to the second column at the modulation period interval. This type of modulator can achieve total transfer, where everything that is on the first column is transferred to the second column, but there are a handful of parameters like flow, fill time, loop size, and so on that must be considered to make sure that happens. If the parameters are not set appropriately, the sample loop can be overfilled or underflushed, which can cause inconsistencies in the peak areas. This system has method checks and calculators built into the software to verify all these conditions and ensure that all the primary column effluent gets on to the second column and that everything will be reliable. In addition to that, the MS and FID splitter was designed with back-pressure regulation to ensure that there would be a consistent split ratio and consistent flow to both detectors, even when the GC temperature conditions change through the separation. All of this makes sure that the FID peak areas are reliable so you can use those for area percent to better understand your sample.

How does your work differ from previous approaches by yourself or others for fragrance analysis?

Most of the work we have done with fragrances in the past was either a nontarget qualitative analysis or a targeted quantitative analysis. We would use GC or GC×GC with MS to characterize the sample and try to learn what analytes were present, or we would analyze calibration standards for specific target analytes to get quantitative information. This new approach maintains the non-target qualitative information and adds some approximate quantitative information for these non-target compounds. FID area percent is more approximate than calibration standards, but it’s a common approach for describing relative amounts of the components within a sample, and we can reliably add that information to our nontarget characterization.

A lot of existing workflows for reformulation will also use MS for identifications and FID for area percent calculations. Sometimes this involves multiple injections to the different detectors or multiple injections to different GC columns with different stationary phases to try to address coelutions and to get both the identification information and the FID peak areas for relative quantitative analysis. This approach aims to achieve this without multiple injections.

Please summarize your findings of what was learned from this study.

We used this system to explore a variety of different fragrance and perfume samples in a non-targeted way. We looked at standards, essential oils, and perfumes. In each case, we were able to get good characterization information about the sample. We searched the MS data against spectral libraries to get the analyte identifications. We also used the GC information, both first dimension retention index (RI) and second dimension eluted position, to support and add confidence to these identifications. The MS peaks were then linked to their associated FID peaks, so we could use that for area percent determinations. This gave us good reformulation information on each of the samples.

We found several analyte pairs in these samples that coelute and appear as a single chromatographic peak in the 1D data that were chromatographically separated in the second dimension with GC×GC. If we hadn’t used GC×GC for our analysis, we would have overcounted the amount of one of the analytes and missed the other in each of these pairs.

We were also able to make some interesting comparisons between different samples. One of the comparisons was a name brand perfume to drug store imitations of that brand. We could see how the aroma compounds and diluents differed. For example, all the perfumes had analytes with “musk” and “floral” aroma descriptions, but there were differences in the specific compounds with those aroma notes.

Can you please summarize the feedback that you have received from others regarding this work?

This approach can both save time and improve the characterization of the sample.

Do you imagine these techniques to be adaptable to other applications in other industries?

We do see applicability for these tools for other samples that have similar challenges and goals. This project was characterizing fragrances and perfumes, but we have other projects in our laboratory where the same tools are being used for other types of samples. For example, we are also looking at alternative aviation fuels where the quantitative aspect is important for meeting blending specifications and the nontarget qualitative information can be used to screen for compounds that could cause fouling of engines or other performance problems.

What are the next steps for your research?

We are excited about the capabilities of this system and how we can get so much information from one injection. We have plans to explore additional fragrance samples and are also looking at analyzing other related samples.

ABOUT THE INTERVIEWEE

Liz Humston-Fulmer is an Application Chemist at LECO Corporation in Saint Joseph, MI. She received her BS in Chemistry from the University of Pittsburgh and her PhD in Analytical Chemistry from the University of Washington. She currently works with GC, GC×GC, TOF-MS, and FID on a variety of food, flavor, and fragrance applications.

Applications of Untargeted Chemical Analysis to Determine Psilocybin and Psilocin Content in Multiple Psilocybe cubensis Mushroom Strains Using LC–MS/MS: An Interview with Kevin Schug

Untargeted analysis is designed to capture as much information about samples (including, but not limited to, classes of molecules, such as volatiles, lipids, proteins, metals, and metabolites) as possible. Preparation of samples and methods of analysis are designed to profile a particular sample dimension and provide a reproducible fingerprint which can be used to compare and potentially differentiate different sample types using a variety of data treatment strategies. Differing chemical features between samples are then identified and used as markers for discrimination. Untargeted analysis often involves the use of techniques such as liquid chromatography coupled with high resolution mass spectrometry (LC–HRMS), so that complex mixtures can be resolved, and specific features of interest can be noted with the resulting information. At the 2024 Pittcon session “LCGC Lifetime Achievement and Emerging Leader in Chromatograph,” Kevin Schug discussed the efforts of he and his colleagues to use untargeted analysis in the study and differentiation of psilocybin mushroom strains; shortly after, we discussed these efforts with Schug in greater detail.

What made you decide to focus on psilocybin mushrooms in your research?

Our laboratory has been long interested in less traditional research areas. For example, we have spent a great deal of time researching the potential environmental impacts of unconventional oil and gas extraction since 2012. At that time, little was known about how this massive industrial process might affect the environment. Further, and still to this date, it is extremely difficult to obtain research funding from traditional sources to carry out such research.

The legalization of cannabis in the United States brought about another potential interest. However, the schedule 1 status of cannabis has made it difficult to perform cutting edge research using the wide variety of cultivars being produced. Cannabis is a plant rich in bioactive chemical components. Modern analytical methods are ideal to investigate the wide variety of cannabinoids, terpenes, and flavonoids; however, limited access had us initially working with hemp (low-THC) plants. While we did make some substantive contributions, the inability to obtain a rich set of varied cannabis plants, especially high-THC variants, without Drug Enforcement Administration (DEA) approval, still has limited what could be done in a state like Texas. It is important to note that not only does one need a DEA license to perform research, the supplier of plants for research must also be a DEA approved manufacturer, and few of these exist, even with the massive landscape of cannabis cultivation that exists today.

The potential to research psilocybin mushrooms came about due to our being connected with Sue Sisley at the Scottsdale Research Institute. A medical doctor, she was the first to receive DEA approval for the manufacture of psilocybin mushrooms. With that source available, we obtained our own DEA schedule 1 research license, with the intent to help develop the analytical research landscape around magic mushrooms. Compared to cannabis, it felt like we could step into the magic mushroom space and be at a place where cannabis research was 15 years ago. Very few research studies have been published on psilocybin mushrooms and many of these publications have been centered around forensics evaluations of mushrooms and biological metabolite analysis associated with illegal consumption. Sisley is interested in promulgating clinical studies to investigate the potential therapeutic benefit of psilocybin mushrooms, especially for palliative (end-of-life) care. Though some interesting clinical work has been reported on the therapeutic benefit of psilocybin, all that work has used synthetic psilocybin. Just as cannabis is known to have a variety of different bioactive compounds, which modulate the effect of its use on individuals—think, sativa vs. indica vs. hybrid strains—it is believed that psilocybin mushrooms delivered in their natural state could also provide benefit through experiences that were more natural, presumably modulated by the presence of other compounds besides just the psychedelic psilocybin and psilocin molecules.

With the analytical techniques we have in hand, we are well situated to characterize the different molecules in psilocybin mushrooms, and we can obtain a variety of different cultivars from our connection to the Scottsdale Research Institute. Moreover, the potential to contribute to meaningful clinical treatment of mental illnesses and end-of-life care for individuals is fulfilling. It is exciting to think that our work could sit at the forefront of a new paradigm in mental health treatments based on the use of psychedelic substances.

You utilized liquid chromatography-quadrupole time of flight mass spectrometry (LC–QTOF-MS) in your analysis. What made you choose this analysis technique?

Our initial work was to develop a potency test for psilocybin and psilocin in mushrooms using liquid chromatography–triple quadrupole-mass spectrometry. Such a method provides good sensitivity and specificity for targeted analysis, and a reliable potency method was needed to help advance strategies for formulation and dosing for subsequent clinical testing. However, to gain a better understanding of the full spectrum of potential bioactive components in psilocybin mushrooms, we would need to cast a wider net. Untargeted chemical analysis methods provide this net, and a key piece to obtaining reliable chemical information is high resolution mass spectrometry. Thus, liquid chromatography coupled with quadrupole time-of-flight mass spectrometry became the appropriate choice. We are just now scratching the surface to understand the molecular composition of psilocybin mushrooms. Much more work needs to be done to compare the potential variations in chemical content amongst different strains of psilocybin mushrooms, but it is exhilarating to be in a position now to start to do that.

How does your work differ from what has been previously done by yourself or others?

While some excellent baseline investigations have been published in the literature, much of that work has had a forensic focus. Foremost in our effort is to advance science to support the use of psilocybin mushrooms in a clinical context, as a potential therapy for mental disorders, such as PTSD, depression, and anxiety. The development of new, accurate, efficient, and reliable sample preparation and chromatographic methods are needed to support a paradigm shift in the use of a substance long viewed as an illegal drug (hence, the greater forensic context of prior studies), as opposed to recognizing them as potential medicines with rigorous quality control requirements. Reliable potency determinations are needed to formulate proper dosing of the therapeutic. Regulatory agencies require well-established and reproduced methods for quality control and product safety. Our potency study adds significantly to a growing consensus on how to best analyze psilocybin mushrooms. Our continued work into the untargeted analysis of psilocybin mushroom content is very new. There are many types of psilocybin mushroom strains that can be grown, but next to nothing has been reported in the scientific literature about how these strains could vary in their broader chemical content.

Please summarize your findings.

We have in hand and have published a reliable methodology for potency determinations of mushrooms. Moving on, our initial untargeted analytical work has shown clearly that the chemical profiles of psilocybin mushrooms differ greatly from that which you would find in standard mushrooms that people consume daily. That work is still preliminary. We initially utilized reversed phase separations; however, our studies have shown that we need to explore other modes of separations, such as HILIC, because many of the key compounds, which differentiate magic mushrooms from regular mushrooms, are not well retained in reversed phase separations. While reversed phase separations may be sufficient for characterizing and profiling the wider range of tryptamine alkaloids, which have similar structure to psilocybin and psilocin, we seek a more comprehensive understanding of the chemical content of psilocybin mushrooms. It will take us some time to get there.

Were there any limitations or challenges you encountered in your work?

A significant challenge in the analysis of psilocybin mushrooms is maintaining the stability of active components. Psilocybin will readily hydrolyze and degrade into psilocin in the presence of water and humidity. Thus, it was crucial to develop reliable sample milling and extraction techniques that would minimize degradation. Psilocin is also not particularly stable. When it degrades, it forms blue quinoid dimers–the blue color of extracts is a hallmark of psilocybin mushrooms, but once a significant blue color is observed, potency has been lost, because these quinoid dimers are presumably inactive. Moving forward to formulating reliable indications, which can be used for clinical testing, it will be essential to develop a process where reliable doses can be created, which are stable over enough time, such that we know what a patient is receiving during treatment.

What best practices that can you recommend in this type of analysis for both instrument parameters and data analysis?

Maintaining the stability of extracts means that one must work quickly and avoid exposure of the material to a significant amount of water. Acidification of extracts is important to improve stability. Also, proper milling of the samples prior to extraction is important to obtain a repeatable and homogeneous material for extraction. One of the aspects we are also studying using our untargeted methods is the stability of extracts. While this work is still in its infancy, we can use the sample analysis and data treatment techniques, which would be used to differentiate different mushroom strains, also to monitor how the chemical composition of extracts change over time. And they do change over time, which emphasizes the need to be careful and to work quickly, to obtain accurate profiles of the chemical constituents in the mushrooms that represent their natural state.

Can you please summarize the feedback that you have received from others regarding this work?

Feedback has been overwhelmingly positive. We have the feeling that we are doing some important work and venturing into the unknown using analytical measurements. While positive feedback from outside interests is nice, it is also nice to see the strong interest of students who want to work with us and pursue studies in this topic. It is an excellent topic for the development of solid analytical skills, since one must take close care to make reliable extractions, but also in chemical separations, measurement, and curating the data to make sure meaningful results are obtained.

What are the next steps in this research?

While we have been working on this topic for some months, it is still in its infancy. We need to work through our untargeted data sets and publish that work. Next steps might be to consider how we can create some extracts of psilocybin mushrooms that could be useful for study in the clinical setting. Of course, just exploring the rich variety of chemical components present in psilocybin mushrooms is interesting, but it will also be important to eventually understand how compounds other than psilocybin and psilocin might have some therapeutic benefit.

What other hallucinogen or psychedelic natural products might you analyze going forward?

Our DEA license is not limited to cannabis and psilocybin mushrooms. Eventually, we would like to be able to spend efforts investigating peyote cactus for its chemical content. Peyote cactus contains the psychedelic mescaline and there is anecdotal evidence that treatments using this natural product could be beneficial for treatment of addiction and pain. Thus, work in that area could contribute substantially to providing alternatives for opioid and opioid addiction treatments. In the end, we are interested in breaking new ground and performing non-traditional research. I am extremely interested in how we can expand the work that we have done in cannabis and psilocybin mushrooms to other psychedelic substances. We need to develop robust clinical collaborations soon to take the analytical research to the next step.

ABOUT THE INTERVIEWEE

Kevin A. Schug is with the Department of Chemistry & Biochemistry at the University of Texas at Arlington, in Arlington, Texas. Direct correspondence to: kschug@uta.edu

Reference

(1) Home - Pittcon Conference + Expo. https://pittcon.org/ (accessed 2024-05-03).