The Dumas principle of N/protein analysis is carried out through the quantitative conversion of the analyte into well-defined gaseous species at heightened temperatures in an environment supplemented with oxygen.
Surplus oxygen from the combustion phase is usually bound on metals such as copper or tungsten, usually known as reducing metals, ahead of chromatographic separation of the combustion gases and lastly, the detection of N2 relating to overall protein content.
The process through which copper or tungsten slowly convert to their respective metal oxides over successive analyses leads to a shortage in oxygen binding, along with the inadequate conversion of NOx to N2. This, in turn, leads to flawed nitrogen and protein values.
In order to minimize such effects, the majority of producers of Dumas-type analyzers suggest a regular exchange of reducing metals as a tactic to lessen these effects. This is the key leading factor in determining the cost-per-analysis.
Elementar developed a pioneering method to recover metal oxide to an active metal species known as EAS REGAINER® technology, lengthening the lifespan of these vital reagents. Trial results demonstrate that this can allow manufacturers to cut their costs per analysis by up to half, as well as enjoying a lifespan of up to five times longer on their reducing metal.
The EAS REGAINER Technology
Combustion instruments conventionally use heated metals such as copper or tungsten to bind surplus oxygen and condense formed nitrogen oxides to N2. In this instance, the reduction metal suffers corrosion, usually turning it to inactive metal oxide following around 200 - 300 samples considering whole gas analysis.
Elementar’s exclusive EAS REGAINER technology offers a reduction metal lifespan of up to five times higher while lessening maintenance requirements by a factor of up to five. During continuous flow, the EAS REDUCTOR® reducing unit is renewed throughout each combustion phase by the economical EAS REGAINER, allowing for a lifespan of up to 2000 samples for the rapid N exceed, and over 1000 samples for the rapid MAX N exceed.
The exclusive EAS REGAINER, which reacts specifically with oxygen, is neither a toxic nor hazardous material. As a by-product, reducing gases are created, and these respond to the EAS REDUCTOR by restoring the metal-oxides created from the reaction of NOx to N2, back to active metals (Figure 1).
When this system is used alongside Elementar’s exclusive post-combustion technology, it can be guaranteed that a total combustion of even the trickiest of species will be executed.
The EAS REGAINER technology was developed in 2014 with the rapid N exceed. This unique analyzer makes use of affordable carbon dioxide as a carrier gas, leading to the obsoletion of the process in which CO2 formed by the combustion process is removed. A 3-step gas drying design assures that only nitrogen is detected by the thermal conductivity detector (Figure 1).
Figure 1. Functional principle of the rapid N exceed utilizing the EAS REGAINER technology.
The rapid MAX N exceed is enhanced for high levels of output, and a broad range of sample varieties and weights. It employs argon as a carrier gas to guarantee total digestion of even difficult species at greater sample weights. Carbon dioxide resulting from the combustion process is quantitatively adsorbed with the help of a gas-selective trap column.
The two-part process of a pair of gas-selective trap columns guarantees rapid analysis times as low as five minutes. As one column adsorbs the carbon dioxide, the other column is warmed to let go of the carbon dioxide of the earlier run through an inventive recycling channel (Figure 2). Dry carbon dioxide is exposed to the gas membrane drying.
Figure 2. Functional principle of the rapid MAX N exceed utilizing the EAS REGAINER technology.
The rapid N exceed was utilized for all studies discussed in this report.
As a trial to demonstrate the lasting performance and robustness of the EAS REGAINER technology, testers carried out a one-week continuous operation of the rapid N exceed, employing a low-cost carbon dioxide as the carrier gas. Over this period, 2,000 sample runs were performed with no need to change the EAS REDUCTOR, adding up to over 300 analyses each day.
A wide variety of sample mediums were selected to reflect a great assortment of protein applications within food and feed manufacturing: milk powder, cat food, starch, soybean flour, wheat flour, dry yeast, soil, reed, and chocolate.
Samples ranging from 100 - 300 mg weight were enfolded in tin foil and, without any preceding stages aimed at uniformity, such as milling or grinding, underwent a 10-fold determination in a rapid N exceed. The total nitrogen content was found to register between from 0.24 to 7.40%, equivalent to 1.5 - 46.3% crude protein, where an average protein factor of 6.25 is assumed.
A standard out-of-the-box calibration was used for all studies shown. At intervals of every 300 samples, accuracy tests with glutamic acid were carried out. At intervals of around every 500 runs, each sample medium was measured. Between these tests, unweighted peas were measured to maintain uninterrupted operation of the rapid N exceed. The findings of the study can be seen in Figure 3 and Table 1.
Figure 3. Repeatability for different sample matrices over 2000 consecutive runs using the rapid N exceed. Each data point is calculated according to the given international standard. The corresponding required repeatability is marked by a line.
Table 1. Nitrogen content [%] ± absolute standard deviation for the different sample matrices in the 10-fold determination on a rapid N exceed on five independent days.
Every sample demonstrates outstanding absolute standard deviations, as well as a high degree of reliability between the results on different days. The measurements surpass what is required to meet international standards such as ISO 16634-1, ISO 14891 and ISO 13878, as can be seen in Figure 3. It can, therefore, be confidently concluded that the use of CO2 as carrier gas does not affect the accuracy and sensitivity of the N/protein analysis.
Cost per Analysis
Taking into account suggested end-user prices, the price per analysis totals around 0.25€, counting all necessary reagents and gases. Uniting EAS REGAINER technology with inexpensive carbon dioxide as opposed to the usual helium carrier gas was a particularly strong cost saver. A comprehensive summary can be found in Table 2.
Table 2. Overview of reagent usage of the rapid N exceed for 2000 analyses.
All available data suggests that 0.25€ per sample is the best price available in Dumas N/protein analysis at this time.
Total oxygen and carbon dioxide usage during the complete experiment was about 345 l and 6300 l, respectively. This key figure shows that only 3.5% of a typical laboratory oxygen gas cylinder and approximately 1/3 of a typical laboratory carbon dioxide gas cylinder were used for the entire 2,000 analyses carried out for these experiments.
This information has been sourced, reviewed and adapted from materials provided by Elementar Analysensysteme GmbH.
For more information on this source, please visit Elementar Analysensysteme GmbH.