The movement toward renewable energy sources has led to an increased production and use of biofuels, specifically biodiesel. Biodiesel provides an attractive alternative to traditional petroleum-based diesel fuel. The Environmental Protection Agency (EPA) estimates that over 2 billion gallons of biodiesel were utilized in 2015.1 Biodiesel is produced by the trans-esterification of vegetable oils or animal fats. These oils and fats, which contain triglycerides, are reacted with methanol and an acid or base catalyst to produce biodiesel, also known as fatty acid methyl esters, or FAME, as shown in Figure 1. The resulting biodiesel is often blended with petroleum-based diesel at a variety of concentration levels. The most common biodiesel blend in the United States is referred to as B20 (20% biodiesel, 80% petroleum diesel). B20 is a popular biodiesel mixture because it represents a good balance of fuel cost, emission levels, cold-weather performance, and engine compatibility. Concentrated biodiesel blends, such as B80 or B100 (80% or 100% biodiesel), are less commonly used because, while they are compatible with most modern diesel engines, they cannot be used in many older vehicles. High level biodiesel blends also have lower energy content per gallon, perform poorly in cold weather, and carry a premium price. The non-uniform performance of biodiesel mixtures creates the need for accurately determining biodiesel concentration in fuel blends.