Christy Abbas (00:03):

Hello, everyone and welcome to our webinar today entitled Understanding Oil and Grease Analysis, and the webinar will be presented by Katie Challis. I'm Christy Abbas, and I will be your moderator today. I'd like to go over a few housekeeping details before we get started. This is [00:00:30] an image of the console screen that you're looking at, and we've got the slides there in the middle that Katie will go through.

 

(00:39):

We've got Katie's bio there off to the right. We also have a survey, and we would love your feedback. We always appreciate that. And off to the left-hand side, we've got a Q&A panel where you can put your questions for Katie during the webinar. And then we've got the resources section [00:01:00] there also on the left, and you can go there to gain access to some of our additional resources.

 

(01:12):

So our topic today is understanding oil and grease analysis. It's fairly easy to say oil and grease and have a good idea of what is meant, but it is quite difficult to come up with a good scientific definition and even harder to design a selective test. [00:01:30] This webinar will cover defining oil and grease, our product offerings and their purpose, and a step-by-step overview for performing hexane extractable materials, HEM, gravimetric analysis in water matrices.

 

(01:48):

The presentation will also focus on common issues associated with oil and grease analysis and troubleshooting tips and tricks. The goal of this webinar is to provide you with a deeper understanding of oil [00:02:00] and grease to help improve your results. Your speaker today is Katie Challis, and Katie is our research chemist two here at ERA and she's been with us for three years.

 

(02:13):

She graduated in 2020 with a PhD in environmental biogeochemistry from the Colorado School of Mines. She's been working in laboratories for the past 14 years, so you're in good hands with Katie. And with that, I'd like to thank Katie and turn [00:02:30] it over to her.

 

Katie Challis (02:38):

Good morning again and thank you for being here. Here's an outline of what I'm going to talk about today. First, we're going to touch on what oil and grease is. Then we're going to discuss the products available for analysis via oil and grease from ERA, quick overview of the methods that are available for oil and grease, and then a step-by-step liquid-liquid and step-by-step [00:03:00] solid-phase partition overview. Those are the two most common methods used for HEM extraction and I think will be helpful for you all.

 

(03:09):

And finally, we're going to close out with some troubleshooting tips so you can be more confident to understand how well you are doing your analysis. What makes up oil and grease? The main definition of it is that it's made up of mineral hydrocarbons like the fuel and oil you put in your car and biological lipids, which could be the cooking oil that you cook [00:03:30] with or the breakdown of cell matter in water. Broken down pieces that could be considered a biological lipid. Why do we care?

 

(03:41):

Well, if you're a wastewater treatment plant operator, you may care because it can cause interference with your water treatment. And of course, it is an environmental pollutant. If we have oil slicks forming on rivers and oceans and lakes, that can be very detrimental to the fish and other life that [00:04:00] live in our aqueous water systems. Finally, a thing that you need to understand about oil and grease is that it's a method-defined analyte.

 

(04:09):

That means that although oil and grease is made up of mineral hydrocarbons and biological lipids, if we go and do this HEM extraction, we're actually going to be getting a little bit more stuff than just the things we're looking at. So what we've done is set the EPA method [00:04:30] 1664 as the standard and all other methods must have the same kind of result as that method. So if you change anything in a method, you have to prove that you're still going to be getting the same results.

 

(04:47):

Now I want to cover some important definitions for oil and grease. So hexane extractable material will extract everything on this list out of water. That would be soaps, [00:05:00] non-volatile hydrocarbons, animal fats, waxes and greases, and also some other things like sulfonated molecules that I didn't list here. So that is again why we have this method-defined analyte. We're going to get some stuff out of the water that are not just oil and grease. Another part of oil and grease is the non-polar materials, which you get when you do the silica gel treated hexane extractable [00:05:30] materials method.

 

(05:31):

I'm not going to be covering that method in detail today, but I just want you to know that that would be what would separate molecules like the hexadecane, which is a non-polar molecule, and the steric acid, which is a polar molecule, from each other. In that method, you would be measuring molecules more like the hexadecane. Also, total petroleum hydrocarbon is a term that is still used in the oil and grease area. It is very similar to the non-polar materials, [00:06:00] but it is specific to hydrocarbons of petroleum origin.

 

(06:04):

However, it is analyzed the same way as the non-polar material method analysis. Here are the products Waters ERA offers for oil and grease for HEM extraction. The first is our whole volume oil and grease, which comes in a ready-to-use already pH-adjusted bottle that you can just analyze. The next is our oil and [00:06:30] grease concentrate, which is one you have to dilute up yourself prior to analysis, but that is nice if you want to do a smaller volume than one liter.

 

(06:40):

And finally, we have our HEM/SGT-HEM sample. This product is not considered a NELAC product due to the way it is made. Therefore, if you need to run a NELAC product, please order an oil and grease or oil and grease concentrate so that doesn't cause issues [00:07:00] when you're reporting it to the state. We do have some TPH and oil and grease in soil products available. They just are outside the scope of this presentation, so I did not put them up here, but we do have them available if you want to look in our catalog.

 

(07:18):

I always like to cover the results from last year's DMR-QA study so you can understand what the norm is for this analysis. So for 2023 DMR-QA 43, we had [00:07:30] around 150 participate in oil and grease across our oil and grease whole volume and oil and grease concentrate samples, which are available for DMR-QA. Around 12 or 13% of people failed, which is a little bit higher than normal, but not absurd, but most people passed well. So what I want you to know is that if you by chance fail this year, you're not alone.

 

(07:55):

It's happened to other people, but it's pretty unlikely that that is going to happen. [00:08:00] Now I want to cover how we determine if somebody has passed or failed their oil and grease analysis. We use the TNI Institute's Field of Proficiency Tables to evaluate all of our samples and to give us our manufacturing range. Our manufacturing range for oil and grease is 20 to 200 milligrams per liter. Any sample you ever buy from us will be within that range.

 

(08:26):

Therefore, if you get a value that is less than 11 milligrams [00:08:30] per liter or more than 240 milligrams per liter, I recommend not reporting that value as something has likely gone wrong in the analysis because you should not be getting a value outside of that range. The FOPT tables, besides giving us the made to value, also give us an equation for calculating expected recovery and acceptance limits. If you look, I've calculated some here in this table. And if you look at the top line, you can see that the expected recovery for [00:09:00] 20 milligrams per liter would be 18.4 milligrams per liter.

 

(09:04):

Another way to think of that would be that would be the average value that would be reported to us from customers. If you report a value between 10.5 and 29.5, you will pass the test. You can look across this table and see that the higher the value, usually the larger the acceptance criteria is, which gives you a little bit of wiggle room in your analysis. [00:09:30] Okay, here's a summary of the oil and grease methods available to run and one that's not supposed to be run any longer.

 

(09:39):

So we have the liquid partition gravimetric method, which is what we still do here at ERA, and then we'll jump down to the solid phase partition gravimetric method. That is the solid phase extraction that I know a fair number of our customers use. There's also the partition infrared method and the Soxhlet extraction method. [00:10:00] And finally, I did want to mention the total petroleum hydrocarbon method, which was withdrawn by the EPA a few years back due to the dangers of the Freon that was used as the solvent and extraction.

 

(10:13):

So if you are still using Freon, please switch to hexane just for your health and the safety of the environment. And finally, back up to the second one is the silica gel treated hydrocarbon method, which I'm not going to cover. That is about nonpolar [00:10:30] materials and silica gel extraction or TPH. Again, we do have samples for that, but I'm not talking about it today. Let's get into how to analyze oil and grease and the step-by-steps of the two methods I wanted to talk about. First, you want to make sure you've prepared everything properly.

 

(10:50):

It is surprising how many analyses are impacted by how well you've cleaned your glassware, unfortunately. Anyway, you do want to wash your glassware with soap [00:11:00] and detergent and then rinse with tap water so that that soap doesn't become one of the things you analyze in your oil and grease. Then you want to either bake it off at 200 to 250 degrees C in an oven for an hour or rinse it with hexane. You also need to confirm that your balance calibration or your daily balance checks are done.

 

(11:22):

The weighing steps of this analysis are very important and if they're done improperly can have a big impact on your results. [00:11:30] So it's always best to use a calibrated scale. There's sodium sulfate that you need to have ready before you go about your analysis. You need to make sure it is dry by putting it in an oven at 200 to 250 degrees C for 24 hours prior to use. Once you've done that, you can store it tightly capped, but I would probably do a bunch of this and just keep it around tightly capped until I want to use it because 24 hours is a long time.

 

(11:59):

I also [00:12:00] recommend you prepare or purchase a QC sample so you can evaluate yourself how well you perform your analysis at the end of your analysis. We have those available for purchase, but also you may make your own using the stearic acid hexadecane standard that is described in detail in the standard methods book or the EPA Methods 1664. And this preparation is something you do more directly before you [00:12:30] begin your analysis steps. You need to mark or weigh all the sample bottles so that you can figure out your total sample volume at the end of your analysis.

 

(12:40):

Your choice on what you do, but either put a mark with a Sharpie or something on the bottle so you can see the level of the water in the bottle and later determine what the original volume was or weigh it and write it down so you can just weigh that same empty bottle at the end and determine the total mass, [00:13:00] which can be converted to volume of your sample. Also, you need to pre-weigh your evaporation flask or evaporation container for your hexane or slash sample collection throughout this.

 

(13:14):

If you don't have your pre-weight, you're not going to get any results, so you better write that down as well. Then confirm the pH of your sample is less than two prior to extraction. If you don't do this, this can cause emulsions or other annoying things to happen in your analysis. [00:13:30] Finally, for the liquid-liquid partition method, you want to prepare funnels that have your dried sodium sulfate in it so that as you collect your hexane, it'll dry the water out of it, which is the net. All right, now that you're fully prepared, it's time to perform the first method.

 

(13:53):

Well, one of your methods. Here I'm covering the liquid-liquid partition method. First thing you need to do is transfer [00:14:00] your water sample to your separatory funnel that you've probably set up on a stand and make sure you get as much water in there as you can. Then add your 30 mils hexane sample to your sample bottle cap and shake so that you can get any oil and grease that might be on the sides of the bottle into the hexane and into your sample again. Then transfer your hexane from the sample bottle into your separatory funnel.

 

(14:27):

Cap it and shake your separatory funnel [00:14:30] for two minutes. Once you have been shaking your separatory funnel for two minutes, you will have quite a bit of pressure built up in there. So I recommend tipping it upside down a little bit with the lid on and releasing the valve a little bit to release all of the pressure. Recommend doing that in the hood, honestly, so you don't just accidentally spray the whole area with hexane. And then allow the layers to separate. According to the EPA method, [00:15:00] it's recommended 10 minutes.

 

(15:01):

In the standard methods, there is no time for allowing the layers to separate. So that is something that you can play with a little. Once you have waited the appropriate or sufficient amount of time for the layers to be fully separated, you drain the lower aqueous layer back into your sample bottle. I would allow a little bit of your hexane to go through into the sample bottle at least for your first two times. Then drain your solvent layer through the sodium [00:15:30] sulfate and collect it in your pre-weighed flask, and repeat two more times all of these steps.

 

(15:38):

Once you've done it three times, you will want to rinse your sodium sulfate with a little bit of clean hexane to make sure there's no oil grease that got stuck in there and with your pre-weighed flask. And on that one, maybe let a few drops of water go through the sodium sulfate, which is your drying material, but make sure you don't [00:16:00] get sodium sulfate in your sample.

 

(16:02):

So it's a tough little balance there. Now that you have collected your hexane and oil and grease together in your pre-weighed flask or container, you need to evaporate off the hexane so that you can weigh just your oil and grease and get that value. Both standard methods and the EPA method recommend you use a distillation apparatus to collect the hexane after you evaporate it. [00:16:30] You can see the schematic here on the right-hand side of my slide. This is from the standard methods book we have in house.

 

(16:37):

You would heat your sample bottle that has your oil and grease and hexane in it and water bath around 80 degrees C, and then collect hexane in an ice water cooled flask at the base of this apparatus. You would also pull a little vacuum at the end of it to make sure you got all the hexane off and into [00:17:00] your new bottle. And then you would take that flask and set it in a desiccator for at least 30 minutes. I want to be clear that this is wonderful for the environment, but I'm sure everybody doesn't do it.

 

(17:14):

We don't even do it. We simply allow the hexane to evaporate off in a hood, and then we place it in the oven, a vented oven, a hood vented oven for 45 minutes at 70 degrees C, which is another option available to you [00:17:30] as well. Then you set it in the desiccator to cool. Finally, once it's cool, you weigh your container. Then place the flask back in the desiccator for another 30 minutes, and then you reweigh your container. This is just to confirm that you have fully evaporated the hexane from your sample.

 

(17:48):

So what you're looking for is a weight loss of less than 0.5 milligrams between the two weighings. This will help prove that, hey, I'm not measuring anything extra or any extra hexane [00:18:00] in my analysis and inflating my value. All right, oil and grease calculations. Once you've performed the method, you've got your weight of residue and the volume of your sample, it's a very simple calculation. You divide your weight of residue in milligrams over your volume of solution in liters, and you have your final milligrams per liter of oil in grease in your sample.

 

(18:25):

A few more details on that. You got your milligrams of oil and grease [00:18:30] residue by subtracting the weight of the flask at the beginning, the empty flask, from the weight of the flask and the residue after you collected and evaporated the hexane from that flask. The volume of the sample you're going to want expressed in liters. But if you weighed the bottle at the beginning, you can weigh the empty bottle at the end of your analysis.

 

(18:55):

And when you assume that the density is one, that means one gram [00:19:00] equals one milliliter of water and you can convert to volume that way, or you could refill your sample bottle with water to the original line that you marked at the beginning and then transfer it to a large graduated cylinder and figure out the total volume of water that you analyzed that way. All right, next I want to cover the solid phase partition gravimetric method.

 

(19:22):

It is very similar to the liquid-liquid extraction method, except we have another component in it where you [00:19:30] take the water through an SPE disk or solid phase extraction disk where it collects the oil and grease, and then you run hexane through that disk to get the oil and grease off of that disk and into the hexane. One of the nice things about this method is it can be fully automated. Pictured here is a Horizon oil and grease extractor, which I know many of our customers have, and that would be very nice if you were running tons and tons of oil and grease analysis.

 

(19:59):

You can [00:20:00] also get setups from companies that allow you to have the double stations that you need for your water and hexane extractions. The step-by-steps are: first, you condition your solid phase extraction disk following the instructions from your manufacturer. Then you slowly filter your water sample through the SPE disk. This is done at 100 mils per minute or that's what's recommended. So if you are using one liter sample, that would be a 10 [00:20:30] minute filtering step.

 

(20:32):

Finally, you want to continue to hold vacuum on the disk to get the water sucked out of the disk so that it doesn't cause interference later in the analysis. Next, you're going to move your filter over to the hexane place if you're doing this manually and not via automation where you can collect your hexane into a pre-weighed bottle. You're going to rinse your sample bottle with hexane to [00:21:00] get all the oil and grease off the sides as we talked about before. And then you're going to add your hexane onto the filter and suction it slightly.

 

(21:07):

And once that hexane is just a little permeated into the disk, you're going to let it sit for two minutes to collect the oil and grease off that disc. Then you're going to vacuum that sample into your pre-weighed flask, again collecting the hexane. Then you need to repeat your hexane steps two more times to get all of the oil and grease out of the bottle and into [00:21:30] your final sample. Then you can follow the evaporation steps I outlined earlier.

 

(21:36):

So now that you know the basic methods that are used for analyzing oil and grease, I want to talk about a few things about the other methods. So the silica gel treated hydrocarbon method is just a continuation of your liquid-liquid partition gravimetric or solid-phase partition gravimetric method. You can do it after where you separate out [00:22:00] those non-polar materials from the polar materials. So that is something you can do. It's another step you can do or you don't have to.

 

(22:09):

The partition infrared method is very similar to the liquid-liquid partition gravimetric method, except for you do use a Freon type extraction material instead of hexane, a solvent, I'm sorry, that's the word. And then you bring it to a known volume and you analyze it on an infrared spec. [00:22:30] If you do this method, it is good for low-level methods and you can report it to us. So that is not a problem. You can definitely report that method to us. You just want to enter it on the IR line instead of the gravimetric line for reporting.

 

(22:46):

The Soxhlet extraction method is kind of just a fancy separation glassware apparatus, which I'm not overly familiar with, but you can use it if you have one already. And then [00:23:00] once again, the total petroleum hydrocarbons is very similar to the silica gel treated hydrocarbon extraction, but that was a specific method that has now been withdrawn due to concerns about the use of Freon in it. All of these can be used and reported to us if you want to. I just covered the most common ones.

 

(23:22):

The silica gel treated hydrocarbons is best used for TPH samples that you can purchase from us and are not part of [00:23:30] DMR-QA. All right, finally, troubleshooting recommendations. The part you're all looking forward to. I always recommend that you run a QC either purchased or made. As I've mentioned before, this gives you a really solid understanding of how well the analysis worked that day. Here at ERA, we actually run a QC at the beginning and end of our analysis to make sure that our sample analysis was solid throughout our time [00:24:00] doing it.

 

(24:02):

I also always recommend running a lab blank or field blank, whatever is relevant to you guys. This will help you understand if there might be some contamination in the bottles you used or other sorts of issues that might be unforeseen otherwise. If you get high recoveries, you're going to want to check if there's any solid residue from taking the sample through sodium sulfate.

 

(24:24):

I forgot to mention that sodium sulfate can be used when you're doing the solid phase extraction [00:24:30] and some analyses as well to help clean the water out of the sample. But if there's water in the sample when you put it through the sodium sulfate, you might dissolve up some sodium sulfate and get it into your sample, causing abnormally high recoveries or unexpected high recoveries. It's usually visible as a white salt once you have fully evaporated the hexane.

 

(24:52):

And if that is something you see in your sample, you can rescue that sample by re-dissolving it up in hexane, add a little heat and hexane, [00:25:00] but the sodium sulfate won't go back into the hexane, and then transferring it fully to another pre-weighed flask and re-weighing it, evaporating and weighing it. Also, you want to make sure there's no water that just gets left in your hexane. If you do see a little bit of water in your hexane in your final bottle, you can try separating it with a glass pipette.

 

(25:21):

Just be very careful not to lose sample or just take the water up and put it back in again. That would be pointless. [00:25:30] If you're running a concentrate from us, please double-check that you did the dilutions properly. It is unfortunate how many issues happened because people did the dilutions improperly from the instructions we sent them. Finally, you can always look at the purity of your hexane if you've gone through everything else and see if maybe you need to increase the purity of that because that has sometimes caused high recoveries in our experience.

 

(25:58):

If you get low recoveries [00:26:00] and you're doing the liquid-liquid extraction, I would like you to make sure you are breaking up emulsions. That is not something that should be happening with a PT sample, so I didn't cover it today, but it is something that can happen in the more natural samples. That would just be a third layer between your hexane and water layer in your liquid-liquid extraction. There are good details on how to break it up in either standard methods or EPA 1664.

 

(26:28):

If I haven't mentioned yet, EPA [00:26:30] 1664 can be found for free on the internet. I literally just searched EPA 1664 and downloaded it. Also, did you do all three extractions? Did you include the bottle rinses? Did you let the separation happen for long enough? These would all be places I would look at increasing or double checking how well I did if I was getting low recoveries. All right, here is my reference slide. [00:27:00] I've referenced standard methods and Method 1664 from the EPA for this presentation.

 

(27:07):

Hopefully you have access to those. The EPA one is available online, I just mentioned. And if you have to dig into that, it's got lots of details. You can also reach out to me if you ever have any questions.