Quantifying QuEChERS Qualms: Emulsion Layers

OMG ew ! Ugly sample alert! Your sample has the biggest emulsion layer you have ever seen! What to do?

You were hoping it would look like this…

Preventing emulsion formation during sample preparation is important when working with a tricky matrix. An emulsion layer is the combination of tiny droplets of immiscible solvents dispersed in one another. Emulsions layers most commonly occur due to excess fats in your sample. It’s no secret that emulsion layers can interfere with accurate measurements and analysis, so it’s essential to take steps to prevent their formation. You can check out Nancy’s ultimate guide for selecting your ideal QuEChERS products HERE. Excess fats can not only lead to poor analyte recoveries, but it can also increase your need for instrument maintenance. The first step in optimizing your results is understanding your matrix. Is it aqueous? <20% water? Fatty? Sugary? Highly pigmented? Does your matrix have excess surfactant? Each of these traits are complemented with different chemistries. We cannot change the matrices we work with, but we can change our sample prep habits. Here are my tips & tricks on how to prevent emulsion layers in your sample prep:

1. Choosing the right solvents:
   Lipids are insoluble in polar solvents like water, but highly soluble in weakly polar organic solvents like acetone. Incorporating some amount of a weakly polar or nonpolar solvent into the QuEChERS extraction (or QuEChERS dSPE) can encourage correct partitioning, however there is a catch. Using nonpolar solvents like hexane with QuEChERS can lead to some nonpolar pesticide residues dissolving with the fats, and therefore can skew analyte recovery. Careful adjustments to your solvent ratios must be kept in mind for this tip.
2. Mixing techniques:
   Handle your samples carefully to avoid introducing air bubbles, which can promote emulsion formation. Use gentle techniques when transferring and mixing samples. Aggressive mixing can increase the risk of emulsion formation. Using gentle mixing methods over longer periods of time or vortexing to minimize shear forces.
3. Cryogrinding:
   Cyrogrinding can take a messy, hard to work with matrix and turn it into an easy-to-manage powder. With the simple addition of dry ice to your food processor, the homogenization of your matrix will improve, which can lead to less randomized emulsion layers in your samples due to even distribution of your lipid or wax aspects. Check out this link HERE to enjoy an all-expense paid trip to Landon’s Cryogrinding Tips! 
4. Diluting sample size volume:
   “Dilution is the solution.” Diluting down your sample concentration can help decrease the chances for an emulsion layer by decreasing the matrix effects. Too much fat or wax can overload the sample; try a 2:1 or 5:1 dilution to start. This trick also has some extra bonuses when considering time, material costs and waste costs all being saved with this technique. 
5. Physical breakage:
   If your matrix consistently gives you an unwanted emulsion layer, this tip is for you. Metal beads are an option to physically break the emulsion layer. Ceramic homogenizers are another great alternative. 
6. Temperature control:
   Controlling the temperature of your sample can help prevent emulsion formation. Changing the temperature can change the solubility of components and promote phase separation. Both heating (for your oily samples) and freezing (for your fatty samples) can be leveraged. Freezing your matrix for 2 hours or overnight can also help precipitate out fats. Know thy sample!
7. Monitor pH and Ionic Strength:
   Sometimes, adjusting the pH or ionic strength of the sample can help prevent emulsions, especially when working with biological samples. AOAC salts or acetate buffers are convenient options for this. When working with samples in the petrol industry, your emulsion could be due to surfactants or soaps; reducing the pH to around 2 with HCl could be your ticket – this will alter the charge of your surfactant so that it no longer acts as an emulsifying agent.  
8. Minimize contaminants:
   Best practice is to ensure that your samples and equipment are clean and free of contaminants that could interfere and act as emulsion stabilizers. Perhaps using the same pipette bulb for several months or even years is not the best way to save your company money. Ensuring your glassware is clean and dry, your hood wiped down and ready are all great ways to start off your sample prep on the right foot!

Remember the effectiveness of these strategies can vary depending on the specific nature of your samples and the emulsion-forming components. Is it fatty? Waxy? Soapy? It is essential to consider the properties of your samples and adjust your methods accordingly to prevent emulsion formation during sample preparation. If you are unsure of what sample prep techniques are right for you, reach out to the expertise from our Technical Support Team! Thanks for tuning in!