High performance liquid chromatography (HPLC) generates a variety of spent solvents that are toxic and flammable. Federal and local regulations require that these chemicals be collected at the source, usually beneath the instrument, before they can be hauled away in bulk and safely disposed. Here’s some background on the chemicals involved, the requirements for short-term storage and some of the associated challenges.
HPLC solvents aren’t the sort of thing you’d want to touch or breathe. Acetonitrile, a common solvent, gets metabolized by the liver into hydrogen cyanide, notorious for its use in Nazi death camps. Ingestion of acetonitrile, should it occur, has its worst effect hours after exposure once the liver has had time to do its work. Acetonitrile poisonings in the US are rare, but this is just one of several dangerous HPLC solvents. Others are methanol and hexane known respectively for causing blindness and nerve damage. Columns are commonly cleaned with sodium hydroxide and other strong acids and bases. Many of the compounds used are also volatile and pose a fire risk, although mixture with water or other non-flammable fluids can lessen this danger.
The EPA specifies using “closed containers” to collect spent organic solvents under Title 40 CFR 261, Subpart D and under CFR 264.173. The EPA is a federal agency but local state and county workplace safety inspectors often enforce rules regarding waste solvents. Different regulators interpret the rules differently, and they enforce them with different levels of rigor, but there are some general precautions labs can take to avoid fines.
The regulations refer to closed containers, so what does that term mean? For practical purposes, a closed container is made of an inert material like high density polyethylene (HDPE) or polypropylene (PP). That is, it’s made from something that most HPLC solvents won’t dissolve. A closed container doesn’t permit volatile organic compounds (VOCs) to escape into the working environment. This requires that tubes carrying waste streams to the container connect securely, usually at the cap. The tubes exiting the HPLC system often come in different sizes so special caps containing manifolds with different sized ports facilitate these connections. Finally, as the container fills with waste chemicals, air must exit and that air often contains VOCs, so these fumes must exit through a charcoal filter that adsorbs the chemicals. To ensure that all escaping fumes go through the filter, any unused ports on the cap must be plugged. Charcoal filters saturate over time (and get noticeably heavier) so filters have to be replaced. Labs sometimes use color indicator strips that indicate when the filter has reached saturation.
Surprisingly, fear of regulatory inspections and not fear of breathing tainted air in the lab seems to drive the adoption of waste capture equipment. There is some logic to this point of view. Labs often have fume hoods that draw air through rooms so the concentrations of chemicals in the air are not generally high. It’s difficult to say, however, if chemical concentrations vary from one part of the lab to another or what effects low exposures to chemicals may have over time. Whether it’s to satisfy regulators or one’s own sense of safety, precautions about open waste containers are a good idea. While regulatory and common-sense safety requirements both dictate that labs should close up their waste solvent containers, a lot of labs don’t. A quick walk through many labs, particularly academic ones, reveals a motley array of open waste containers with differently sized tubes stuffed into their openings. To make the tubes stay in the openings people often wrap Parafilm™ around the whole bundle, adding to the chaotic appearance. This is not a look that makes inspectors feel relaxed.
Connecting Waste Lines
The use of Parafilm as an all-purpose tubing immobilizer doesn’t look great, but it does address a need. There can be a half dozen tubes coming from different parts of an HPLC system, each carrying its own waste stream. Chromatographers generally know all about lab equipment, but knowing how to connect jumbles of differently sized tubes isn’t usually a specialty. For example tubes can be “soft,” made from silicone or Tygon, or they can be “hard,” made from a fluoropolymer like PTFE or PFA. They all require different kinds of connections and different sized connectors. Just knowing what parts to buy, and where to buy them, can be a challenge all its own. There are ways to make these connections easier like using pre-set kits that come with commonly used connectors.
A final consideration on the topic of capturing and storing waste solvents is how to prevent containers from overflowing. In small labs with a few HPLC systems, it’s easy to monitor containers as they fill up and empty them before they overflow. But larger labs have dozens of systems running around the clock. If one system overflows it can create a flammable, toxic safety violation. The solution for this is using alarm systems that signal when containers fill up or that send a text message.
In sum, capturing waste HPLC solvents prior to disposal can improve the safety and overall look of the lab. It can also prevent lost time due to shut-downs caused by failed audits, spills or even fires. Sealing up containers and scrubbing fumes requires investment, but there are well-known and proven ways to do it.