Have you ever wondered why solution flow rates are so important when performing sample preparation with solid phase extraction (SPE)? If you have, read on – I have the answer for you!
Throughout my college career, the phrase “like dissolves like” was referred to quite frequently. This phrase was particularly relevant when we did solubility experiments and for good reason – it’s 100% true! Solvents tend to dissolve solutes with physical and chemical properties that are similar to theirs. Other factors such as temperature, pressure and pH can affect the solubility of solutes as well, but let’s just keep it simple for the purposes of this discussion and keep it focused on physical and chemical properties. Given this simplistic definition of solubility, the opposite stands true as well – solutes don’t tend to dissolve into solvents with differing physical and chemical properties. These solvents and solutes want to stay as far from each other as is possible.
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.
Since its release in 1995, EPA method 525.2 has been one of the most widely used methods for quantifying semi-volatile compounds in drinking water. Chances are, if you work for or own a drinking water lab, you probably analyze for compounds in this method – at the very least, you’re probably at least familiar with the method. This is a widely accepted method for quantifying semi-volatile organic compounds; however, there are some glaring issues with the method that the EPA has recognized and addressed. These changes have been collected and implemented in a new revision – Method 525.3 – which was published in 2012. Method 525.2 is still more frequently used by laboratories processing drinking water samples; however, I would argue that Method 525.3 is more scientifically sound. In this 2-part blog series, I will address multiple aspects of Method 525.2 that have been modified to improve the collection, preservation, and processing of drinking water samples. In this first part, I will focus on the improvements that have been made with respect to the sample preservation process.
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.
Have you ever opened a jar of olives and noticed the shimmering liquid floating on the surface? Believe it or not, that liquid is actually residual oil that is given off by the olives themselves. Since the oil is less dense than the aqueous solution that the olives are stored in (olive brine), it floats to the top of the jar. This may not seem like a big concern to the typical olive consumer, however, olive manufacturers believe that too much oil in a jar is something that negatively affects the final product. For this reason, olive companies are putting effort and resource into finding a way to quantify the amount of oil in their final product.
Since oceans cover roughly two thirds of the Earth, and since oceans can demonstrate signs of ecosystem health and climate change, the U.S. EPA has watched the ocean for changes in their physical property for many years. From sea level height to ocean temperature to coastal flooding occurrences to surface temperature, the EPA has closely monitored changes in these properties as an indicator of climate change.
Just a reminder of last week’s post:
The United States has been using pesticides for decades to protect crops and livestock from disease, mold, insect damage and many other types of pesky organisms. According to the United States Geological Survey (USGS), roughly 540 million pounds of pesticides were used in 1964. How many pounds of pesticides were being used across the nation by 1993?
Answer: 1.1 billion
Technically, the term “pesticide” is a somewhat generic term to describe a substance that controls pests. Based on that definition, pesticides include herbicides, fungicides, insecticides and many more chemical solutions. Given the increase in the U.S. population between 1964 and 1993, and the growth in the number of viruses, fungi, bacteria and other organisms that could endanger the health of our crops and livestock, it’s not surprising that our use of pesticides rose significantly over that period of time.
Join us next week to Expand Your Horizon!
It’s that time of year again – avoiding the Thanksgiving “Fatberg”
Thanksgiving is that special time of year that we gather together with family and friends to give thanks and experience traditions that are carried on through generations. Our Thanksgiving meal consists of: roasted turkey, mashed potatoes, stuffing, gravy and homemade cranberry sauce. We also serve the not-so-customary stuffed artichokes – a family favorite, passed down from my Italian grandparents. Continue reading Surefire Ways to Avoid Fat Gain During the Holidays
For the past few years, news reporters have used words like “developing” and “emerging” and “crisis” to describe perfluorinated compounds. When you see adjectives like this, you can’t help but think “how did we not know about these PFC things before now?”
The truth is, these compounds have been produced for decades – some, for over half a century – and their chemical and physical properties are well-known. The strength of the carbon-fluorine bond in these compounds makes them heat-, water- and stain-resistant. Continue reading Extracting Perfluorinated Compounds from Drinking Water – Why is it so Challenging?