Analysis of Oils Part 3: Oil and Water Do Mix

In our last analysis of oils post we discussed the results of the VHG™ R&D team’s research into boron drop-out in working level standards, and initial indications that humidity played a role. When considering the impact of water in the atmosphere affecting the stability of an oil standard, you might pause and think that oil and water do not mix, but that is not entirely true. Many oil products, including multi-element metallo-organic mixes, lose some their hydrophobic qualities by virtue of the additives that are present.

An example of oil taking on and shedding water is outlined in Table 1 below. It shows that the 75wt base oil maintained low water content, changing little and preserving hydrophobic qualities (remaining <50 µg/g H2O), while the original water content in the 15-40w diesel engine oil changed value depending on the exposure conditions. Exposure to high humidity conditions added water to the 15-40w diesel oil, while warm, arid conditions removed water content. The implication? The open sample was chemically impacted by the atmospheric headspace above it. In addition, additive components in the oil increased reactivity between the oil and the atmosphere interface above it.

So what does this mean? Oil exposed to warm, humid atmospheric conditions can take up water, which can induce chemical reactions that may impact boron recovery. Additionally, once oil has taken up water it begins to separate into phases with the metallo-organic components possibly following suit, resulting in a drop-out or stratifying of the metal content. Working level standards prepared and left open to the environment have the opportunity to reduce boron recovery as a result of environmental factors.

Based on this information, VHG developed this study to determine the impact of environmental conditions on open auto-sampler tubes containing typical, solvent-diluted metallo-organic blends. The goal was to mimic typical laboratory situations, which often have loaded auto-sampler racks of prepared samples sitting out for extended periods of time. As most laboratories expose prepared samples for just one day, but some labs may use the same samples over multiple days, we evaluated our samples at one day and six days to provide more holistic data.

As you can see in Figure 1 and Figure 2 below, even one full day exposed to humid conditions dramatically impacts boron recovery, but the choice of diluent also has an impact on boron’s stability. In our next post we will examine this further, and explore VHG’s efforts to develop a humidity-inert boron material.

Click here to download our full Analysis of Oils: Understanding Chemical Stability & ICP Matrix Effects technical paper, which delves into this topic in more depth and provides full breakdowns of our stability testing.