In Defense of Methylene Chloride

If you’re familiar with methylene chloride (which I’m sure you are since it’s one of the most widely used laboratory solvents), you know that it’s developed a reputation for being one of the “bad boys” of the solvent world.  The bad press has certainly been earned.  It’s been attributed to over 60 deaths in the last 4 decades.  It’s also pretty aggressive – exposure to just a few ounces for a few minutes can be enough to cause severe damage or death.  And since it’s a colorless liquid, an innocent-looking spill could be a severely harmful hazard.

Though it’s a solvent with a bad reputation, I feel as though I need to come to its defense, because it’s a necessary solvent for a lot of laboratories doing sample preparation and extractions of volatile and semi-volatile organic compounds.  EPA Methods 8270 and 625.1 (just to name a couple of examples) require the use of methylene chloride during the extraction process.  This solvent is critical for accurately and reliably extracting the hundreds of compounds that are outlined in those methods.  Methods like 8270 and 625 are just 2 out of dozens and dozens of methods that are designed to guide labs in extracting compounds that are contaminating our air, soil and water.  So, if you ask me, methylene chloride is one of my heroes.  The key is to handle it with caution and respect.

Treat Methylene Chloride with Respect

Almost all laboratories use dangerous reagents and chemicals in their day-to-day or month-to-month operations.  Anyone who has used a blast shield when using perchloric acid or suffered skin burns from an aqua regia spill knows just how dangerous some of these chemicals can be.  But we can’t always avoid using them.  If we could, alternative laboratory procedures would have been developed a long time ago!  Since we find ourselves in contact with these chemicals from time to time, it’s important to respect them.  It’s also important not to fear them.  That may seem like a strange thing to say since the effects of these chemicals are kind of scary.  But fear can cause us to react physically (to become paralyzed or to shake violently).  Fear can cause us to do something quickly, without pausing to think through all the possible consequences.

Imagine yourself using hydrofluoric acid in the lab.  (For anyone who’s unfamiliar, it’s a great solvent for dissolving silica-based compounds, but it’s also a calcium-loving chemical that will eat through your bones if it comes into contact with your skin – not cool!)  Now imagine yourself working with that acid and you spill a small amount as you’re pouring it from the solvent bottle to a graduated cylinder.  If fear takes over, you’d see the acid splash onto your skin and you’d probably react by panicking, hyperventilating and crying.  If you’d been trained to treat the acid with the respect it deserves, you’d see the acid splash onto your skin and you’d probably react by grabbing the nearest tube of calcium gluconate, applying it generously to your skin, then make your way quickly to the nearest hospital.

Now let’s go back to methylene chloride and review what you need to know to handle it with the respect it deserves.

Know Your Exposure Routes         

If you’re using a chemical in the lab, the best way to learn its potential to harm you is through its safety data sheet (SDS).  Here’s an example SDS for methylene chloride.

It’s never a bad idea to skim through the SDS periodically to refresh your memory on how to handle the chemical properly and how to react if you become overexposed to it in some way.  But if this is your first time working with a particular chemical, you should definitely review the SDS and ask questions if there’s anything in it that doesn’t make sense or doesn’t seem clear to you.

Here are a few general tips to help make sure you handle methylene chloride with caution and react properly if an accident occurs:

Ingestion

Presumably, this is the least likely way for you to be exposed to methylene chloride, but accidents are unpredictable – hence why they’re called accidents.  If methylene chloride splashes anywhere near your face and mouth, make sure you wash your face really well with soap and water and rinse out your mouth.  Then drink lots and lots of water.  And when you think you’ve had enough water, drink some more.  Methylene chloride is one of the solvents that’s harmful if you try to throw it up.  It’s safer to let your body handle the solvent the way it would handle all the liquids you drink during a normal day – as long as there isn’t too much solvent for your body to handle.  That’s where the water comes into play.  Drinking a lot of water dilutes the amount of solvent that’s in your body and helps to flush it out of your system.

Absorption

We always work diligently to avoid spills in the laboratory, but accidents happen – flasks tip over, beakers crack and leak, splashes occur as you’re pouring from a large stock bottle to a small graduated cylinder.  If a spill or splash occurs and any part of you comes into contact with methylene chloride, wash it off immediately with soap and water.  If any of your clothing gets splashed, get it off your body as quickly as possible and wash it thoroughly before you put it back on.

Inhalation

This route of exposure is the most dangerous and the exposure route responsible for almost all the deaths that have been attributed to methylene chloride.  Methylene chloride has a noticeable smell, but if you work with organic solvents in the lab, you’re used to being around solvents with noticeable smells and you may not necessarily distinguish those coming specifically from methylene chloride.

Methylene chloride vapors act quickly and attack via 2 different mechanisms.  When we inhale methylene chloride vapors, our body converts it to formaldehyde and carbon monoxide to metabolize it.  The carbon monoxide displaces oxygen in our body and eventually causes us to suffocate.  It doesn’t take much carbon monoxide to develop before you’ll start to feel dizzy and eventually pass out.  Once you’re unconscious, suffocation and death isn’t far behind.  At the same time, the methylene chloride vapors can overwhelm your nervous system and cause sensory problems or cognitive impairment.

Given the inhalation hazard, methylene chloride should always be handled in well-ventilated locations, but if you become exposed to the vapors in some way (accidentally, of course!), find some fresh air fast.  Once you’re breathing the safe air you’re used to breathing, your body will slowly replace all that carbon monoxide with oxygen and get rid of the carbon monoxide that was building up.

Know the After-Effects

Knowing what to watch for after an exposure is just as important as knowing what to watch for at the time of exposure.  It’s not always easy to figure out how much methylene chloride you came into contact with during an accident.  How many milliliters of solvent splashed onto your arm?  How concentrated were the vapors in the air when you started feeling dizzy?

And even if you did know the answers to those questions, each person’s reaction to the solvent could be a little bit different.  So even if you’ve reacted to an accident exactly as you should have, it’s important to know what to watch for in the following days.  Did a rash develop on your skin the next day?  Did you develop a sudden headache or are you feeling more tired than usual?  Many SDS sheets have a section that includes notes for a physician to help them treat someone who has been exposed – methylene chloride is no different.  Make sure you’re familiar with the symptoms and effects that are described for physicians and watch for those in the days following an accident.

Know How to Be Safe

The key to working safely with methylene chloride – or any solvent, for that matter – is knowing how to be safe around it.  Knowing how to react to an accident is certainly part of that.  But knowing how to be around it, in general, is part of being safe.  How should it be stored?  How should it be transported?  How should it be disposed of?

When you’re actively working with it, how should it be handled?  Are there certain materials that should be avoided (should you avoid using plastic labware, for example)?  Are there solvents that will react violently with methylene chloride?  Will it react to moisture or oxygen in the air?  Will it react if it’s exposed to light?

It’s important to know this information before you even step foot into the lab.  The safety data sheet will help answer all these questions, so keep a copy handy, and proceed with caution – not with fear.

Feel free to share your “bad boy” solvent examples in the comments below!

Environmental Pollution – Are We All Doomed?

Have you ever stopped to enjoy a bright, vibrant sunset, only to have that really annoying friend interrupt your thoughts with a comment like “you know you’re just looking at all the pollution in the air, right?”

I used to wonder how someone could focus on pollution while looking at a stunning landscape, but it’s becoming a topic that more and more people are thinking about.

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The Hidden Dangers of Organic Solvents

“Our laboratory uses organic solvents every day.  Should we be concerned about solvent exposure?”

I hear this question fairly often and the short and simple answer is: YES.

But if this were a simple yes/no question, I wouldn’t have anything else to say, and this would be the shortest blog post that’s ever been written.

Continue reading The Hidden Dangers of Organic Solvents

7 Horrible Mistakes You’re Making with Solid Phase Extraction

Solid phase extraction (SPE) is a powerful sample preparation tool that makes it possible to extract semi-volatile organic compounds with varying physical and chemical properties.  When used properly, this tool will simultaneously extract hundreds of analytes from the most challenging sample matrices.  When used improperly – well, this tool can quickly become as effective as using a hammer to paint the walls in your house.

Continue reading 7 Horrible Mistakes You’re Making with Solid Phase Extraction

Why It’s Easier to Succeed With Wastewater Extractions Than You Might Think

There’s nothing more satisfying than successfully extracting a really challenging sample.  Solid phase extraction (SPE) is a powerful technique for extracting semi-volatile organic compounds and hexane-extractable materials (HEMs).  When the chemistry is tailored to meet the requirements of the application, literally hundreds of compounds can be extracted with a single pass of solution through an SPE disk.

Continue reading Why It’s Easier to Succeed With Wastewater Extractions Than You Might Think

Tips for Improving Your Oil & Grease Recoveries

On the surface, EPA Method 1664B seems pretty straightforward – use n-hexane to extract compounds (commonly referred to as “oil and grease”) from an acidified water sample.  Evaporate the hexane from the extract, weigh the residue that gets left behind, and report that weight in terms of a concentration (often as mg/L of HEM).  Yet many laboratories have found themselves looking at data which indicates that their spikes aren’t being recovered at levels that are compliant with the method.  Unfortunately, there are a few details in the method that can cause trouble, regardless of whether you are extracting your samples using liquid-liquid extraction (LLE) or solid phase extraction (SPE).  Keep reading for some tips to improve your analyte recoveries when doing oil and grease extractions.

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A Better Way to Do Dishes

“I’m so tired of doing dishes!”

Between the dishes I wash at home and those I wash in the lab, that phrase leaves my lips no fewer than 3 times a day.  If I were to add up the number of hours I’ve spent washing dishes over the past year, I’d….well…it’s too upsetting, so I try not to do that calculation.  Let’s just say I’d have had time to become a seasoned marathon runner and to backpack across both Europe and parts of Australia.

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Solid Phase Extraction of Drinking Water – How do I Dry My Extracts?

If you’re a laboratory that’s processing drinking water samples using solid phase extraction, you’ve inevitably gotten to the step in your procedure where you’ve eluted your analytes from your SPE media and you find yourself saying “How do I dry my extracts?”

What’s the best way to dry my extracts? 

This is a question we get quite frequently and it’s a reasonable question to ask.  Unfortunately, the answer is – it depends.  Solvent drying (not to be confused with solvent evaporation) is an important step in your extraction process when you’re using organic solvents to elute your target analytes.  Residual water in your solvent can cause issues if your target analytes extract back out of the solvent and into the water while you’re trying to evaporate or analyze your sample.  Water can also damage your chromatography system, so if you’re quantifying your extracts by GC/MS or LC/MS, you want your solvent extracts to be dry prior to analysis.

So, given the importance in solvent drying, I thought I’d share some of the commonly asked questions that come up under this topic.

Q: I’m processing my samples against EPA Method 525.3.  Does it matter how I dry my extracts?

A: If your lab is being audited against EPA Method 525.3, you need to dry your extracts per the recommended procedure – in this case, sodium sulfate.  Make sure you purchase the recommended grade of anhydrous sulfate and store it appropriately.

If your lab processes a large volume of samples, you may have sought out alternative approaches to solvent drying, such as phase separation membrane.  While sodium sulfate is readily available for purchase in bulk quantities and is pretty easy to learn how to use, it has some potential downsides to it.

  • It has to be dried and carefully stored, which is time-consuming and requires you to have adequate drying and storage equipment
  • It has to be disposed of as hazardous waste
  • It’s a chemical that dries your solvent by reacting with water to form a hydrated salt, which means it can retain some of your target compounds (particularly those that are highly water soluble)
  • It can contaminate your extract, particularly if it’s stored incorrectly or purchased at a lower grade than is recommended
  • It can be saturated. What that means is, if you didn’t calculate the mass of sodium sulfate you needed, given the volume of water you needed to remove, you could exceed the capacity of the salt and end up with a solvent that’s not completely dry

Phase separation membranes physically separate the water from your solvent, which eliminates all of the challenges you face with a chemical drying agent such as sodium sulfate.  Plus, it’s compact and easy to store, intuitive to use and easy to dispose of.

There are a handful of benefits to using a phase separation membrane over sodium sulfate – just make sure you check the method you’re following and adhere to the drying method outlined there (if there is one).  Check out the method summary in this app note for an example protocol that adheres to EPA Method 525.3 guidelines.

Q: Since EPA Method 525.3 specifies that I use sodium sulfate, can I put sodium sulfate on top of phase separation membrane to dry my extracts?

A: While clever, this is an idea that you would want to run past your auditor first.  Since the method specifies the use of sodium sulfate but does not specify the physical separation of water (using a phase separation membrane, for example), physical separation isn’t forbidden, but it’s also not specifically allowed.  Yep, this one is a gray area so have a conversation with your auditor before cleverly devising a drying setup that includes both chemical and physical solvent drying.

Q: I’m running samples against EPA Method 525.2.  Do the same rules apply to me?

A:  Yes.  As with Method 525.3, this method specifies the use of sodium sulfate.

Q: I’m not processing samples against an EPA Regulated Method and my protocol doesn’t specify a protocol for extract drying.  What should I do?

A: If your lab is not reporting results against a method that specifies an extract drying method, you should have the option to decide whether you want to dry your extracts using physical or chemical separation (double check your laboratory’s established protocols to make sure your SOP allows you this flexibility).

If this decision were up to me, I’d order myself a huge stack of DryDisk® Disks and wave goodbye to sodium sulfate forever!

Do you prefer physical drying over chemical drying?  If so, let us know in the comments and share this post to spread the word!

Better Water Testing for Safer Produce

“Do what you can, with what you have, where you are.”
-Theodore Roosevelt

As the seasons change, I’m reminded of this quote and its significance to the air, land and water that sustain us.  As the weather gets warmer and winter transitions into spring, I love listening to the sound of birds chirping in the morning and watching new flowers blossom.  I look forward to the coming weeks and months of picking strawberries, raspberries, cucumbers and a myriad of other fresh fruits and vegetables.  There’s nothing like the feel of the warm sun and a gentle breeze as you pluck a fresh apple from a tree and bite into it.

Continue reading Better Water Testing for Safer Produce

The Importance of Methanol in Oil & Grease Extractions

Have you ever been extracting samples for oil and grease compounds using solid phase extraction (SPE) and thought, “why do I have to use all these different solvents, when I’m just trying to get my compounds to retain on, and then elute from, an SPE disk?”

If you’ve been digging into the extraction method a bit, you’ve probably asked yourself “I wonder what the purpose of the methanol is” at least once or twice.  If you’re processing samples for oil and grease, your goal is to determine the concentration of compounds that can be extracted in n-hexane (also known as HEMs), so it’s logical to think that you’d load your sample onto your SPE disk, then pour some hexane through it to elute your target analytes.

For the most part, that logic is sound; however, there’s more to the chemistry than that.  I was trying to explain this chemistry to a colleague of mine recently and his eyes started glazing over about 3 minutes into my explanation.  I tested my explanation on a few other colleagues and got the same response so I started to give up hope that anyone was going to share my excitement for chemistry and what’s going on within the SPE disk.

Then I stumbled across this graphic and my hope was restored.  In this simple graphic, the overall extraction scheme is listed in the center and the addition of methanol and hexane are illustrated to the left and to the right, respectively.  What I really like about this graphic is that it allows me to walk through the extraction, step-by-step, and see the impact of each solvent.  Let’s walk through it and I’ll show you what I mean.

If you start at the top, the box labeled “1” shows you the state of your sample after it’s been passed through your SPE disk.  The bulk of your water matrix has passed through the disk and been directed to waste, while your target analytes remain trapped in the disk.  Some of your target analytes (the beige-colored circles) are present in solution with water molecules surrounding them.  Water molecules are polar and their net dipole moments cause them to be attracted to each other (the positive dipole moment of one water molecule is attracted to the negative dipole moment of another water molecule).  So, in their effort to cluster together, water molecules end up trapping a few compounds – compounds that you’d like to extract and quantify.  Unfortunately, passing your sample through the SPE disk does not remove these water molecules.

In an ideal world, you would add some hexane, elute all your compounds, then evaporate off the hexane and record your HEM weight.  Unfortunately, those pesky water molecules are going to prevent the hexane from reaching some of your compounds (don’t forget that hexane isn’t miscible in water).  So you would add hexane to elute the analytes that are free from water molecules and accessible by the hexane (follow the first arrow to the right in the graphic).  This will leave you with just the water-bound analytes (the box labeled “2).

Here is where methanol will come to your rescue.  Methanol is a polar solvent and is soluble in water.  Methanol isn’t as polar as water, but it’s still pretty polar.  When methanol passes through your disk, the attraction between methanol molecules and water molecules becomes stronger than the attraction between water molecules and other water molecules.  As water molecules seek out methanol molecules, the water molecule clusters break up and release the remaining target analytes you’re trying to extract (i.e. the box labeled “3).  One more pass of hexane elutes those target analytes into your collection flask and now you’ve collected all your analytes of interest.

Skeptical of the chemical journey I’ve just outlined?  Check out these data tables where the proof is in the numbers.  I wanted to see if I could prove out my theory in the lab, so I obtained 6 liters (yes, SIX liters) of a real-world influent sample and divided the sample into six, 1-liter replicates.  The six samples were extracted using an automated SPE extraction system.  All six of the SPE samples were processed using the exact same system and the same extraction conditions, with one exception – three were extracted using methanol at the appropriate steps and the remaining three were extracted without methanol.

Extraction with methanol

Sample IDStarting Weight (g)Final Weight (g)HEM Weight (mg)
Replicate #16.18316.213630.5
Replicate #26.20306.235932.9
Replicate #36.20156.235734.2
Avg. HEM Weight (mg)32.5

Extraction without methanol

Sample IDStarting Weight (g)Final Weight (g)HEM Weight (mg)
Replicate #16.24736.2656
18.3
Replicate #26.18016.204524.4
Replicate #36.25066.264313.7
Avg. HEM Weight (mg)18.8

 

Under the exact same conditions, the use of methanol produced an HEM weight of 32.5 mg.  Without methanol, the average weight of the hexane extractable material was 18.8 mg – a difference of 42% by weight!

Seems like methanol plays a pretty important role in oil and grease extractions.