This seventh in a blog series on robustness and its role in enhancing lab optimization processes focuses on organic elemental analyzers (OEA). The series takes a critical look at the term robustness and describes how it relates to a portfolio of analytical instruments (hardware and software) in quantifiable terms and benefits. The working definition for robustness (described in Part 1 of the series) includes three aspects: measurement, instrument, and process.
What is dynamic combustion?
The following describes an example of measurement robustness for OEA based on dynamic combustion (modified Dumas method) that does not require sample digestion or the use of toxic chemicals. The method operates according to the dynamic flash combustion of the sample. Powdered samples are weighed in tin containers while liquid samples are weighed in tin containers and adsorbed containing an inert Chromosorb® sorbent. Both samples are introduced into the combustion reactor with oxygen, determined by the Thermo Scientific™ OxyTune™ Function. The Thermo Scientific OxyTune Function automatically evaluates the oxygen required for combustion according to the weight and nature of the sample. After combustion, the produced gases are conveyed by a helium (or argon) flow to a second reactor filled with copper, then swept through CO2 and H2O traps and onto a gas chromatography (GC) column equipped with thermal conductivity detection. GC provides separation and higher sensitivity advantages over purge and trap techniques. Figure 1 provides a diagram of the process with an oil analysis application example.
Oil plays a critical role in the operation of machinery and equipment by reducing friction between surfaces, reducing heat when the surfaces move, and extending the life of wear surfaces, such as cutting tools used in drilling and milling operations. The property of reducing friction and wear is known as lubricity.
However, lubricity alone is not enough to provide protection for extended periods of time. To achieve this level of wear performance, nitrogen containing additives are added to the oil. Why nitrogen? Because N containing compounds increases its detergency, meaning the dispersant additive keeps wear metal and debris in suspension preventing them from damaging expensive machinery and equipment.
What is their value?
The modified Dumas method provides advantages in time, automation, and repeatability in the determination of total nitrogen content in lubricants.
Table 1 shows results from a study that compares N% reproducibility of lubricant obtained by ASTM D5291 with the Thermo Scientific Flash 2000 Elemental Analyzer using both helium and argon carrier gas (This analysis can be performed as well with the newly launched Thermo Scientific FlashSmart Elemental Analyzer). All data were obtained with excellent repeatability and no observable matrix effect when changing lubricant samples.
[caption id="attachment_18227" align="alignnone" width="977"] Table 1. Nitrogen reproducibility of ASTM lubricants with helium and argon carrier gas. Click to enlarge.[/caption]