Application Note · compEAct N

Determination of Trace Nitrogen Contents inDifferent Types of Fuels and Fuel Blends
According to ASTM D4629 resp. DIN 51444

Challenge
Fast and easy analysis of widely
varying nitrogen contents indifferent types of diesel fuelaccording to industry standards.

Solution
Reliable results, independent ofTN concentration or digestion
characteristics, in very short timeusing compEAct N and the LS 2
liquids sampler.

Introduction
Diesel is a mixture of various hydrocarbons that is produced during thefractionated distillation of crude oil. Its boiling interval is in the range of 150
to 390° C. Diesel is used mainly as fuel for automobiles. It can contain traces oforganically bound chlorine, sulfur and nitrogen originating either from natural
sources or from additives. During combustion of the fuel, these compounds form
environmental pollutants. As these pollutants are hazardous to the human healthand the environment, their content (N, S, Cl) should be kept as small as possible.
To ensure the product quality and adhere to legal limit values a permanent quality
control is essential.

The compEAct N is an analysis system which was specifically optimized for thefast and trouble-free determination of nitrogen contents in a wide concentration
range. Combining catalyst-free high-temperature combustion and highly sensitive
HiPerSens® detection it allows the detection of nitrogen at concentrations ranging
from 15 µg/l up to 10,000 mg/l with one and the same device.

2Determination of Trace Nitrogen Contents in Fuels and Fuel Blends according to ASTM D4629 / DIN 51444

Materials and Methods
Samples and Reagents■■
Different fuel samples■■
Isooctane (C8H18), Suprasolv®, GR for gas chromatography (Merck Art.-No.: 1.15440.1000)■■
Pyridine (C5H5N), GR for analysis (Merck Art.-No.: 1.09728.0100)■■
Calibration standard kit Nitrogen (0–25 mg/l) (Analytik Jena, Art.-No.: 402-889.069)
Sample Preparation
The samples are light volatile, have a low viscosity, and contain TN in the ultra-trace level. That is why a pretreatment step
was redundant. The samples were analyzed directly.
Calibration
Prior to the actual determination, the system was calibrated using nitrogen standard solutions based on pyridine (N) in
isooctane in the range of 0 to 2000 µg/kg. Figure 1 and 2 depict typical calibration curves and performance parameters.

Fig.1: Calibration range 1 – ultra-trace

Fig.2: Wide-range calibration curve of the HiPerSens detector

The calibration was checked with different concentrated standards.
Instrumentation
The measurements were performed using a compEAct N, equipped with HiPerSens CLD detection for the determinationof nitrogen. Sample introduction was carried out fully automatically by means of the LS 2 liquids sampler to ensure a highsample throughput.
The analyses have been run in vertical operation mode. The samples were dosed directly into the evaporation zone of thequartz glass combustion tube. This process took place fully automatically by means of the LS 2 high-throughput liquids
autosampler. The catalyst-free, bi-phasic combustion process is carried out at temperatures of up to 1050 °C. In the firstprocess phase, evaporation of volatile sample components in an inert gas stream takes place, followed by the combustion of
the formed gaseous products in an oxygen-rich atmosphere. In the second phase the heavier, nonvolatile sample components
and formed pyrolysis products are quantitatively oxidized in pure oxygen. Thereby the quartz pyrolyzer ensures a uniform
evaporation, modulates the combustion process, and prevents incomplete combustion. This establishes the best conditions
for a reproducible and fast ultra-trace analysis. The implemented Auto-Protection System guarantees highest operationalsafety (particle and aerosol trap) and a complete transfer of the formed NOx into the chemoluminescence detector after asufficient drying of the reaction gases. The compEAct N enables a detection limit of as low as 15 µg/l N.

Determination of Trace Nitrogen Contents in Fuels and Fuel Blends according to ASTM D4629 / DIN 51444

Method Parameters
The standard method ASTM D4629 from the ASTM method module was used for all analyses. The following tablesummarizes the parameter settings for the combustion process.
Table 1: Process parameters compEAct
Parameter

Specification

Furnace temperature

1050 °C

Second combustion

60 s

Ar flow (first phase)

150 ml/min

O2 main flow

200 ml/min

O2 flow (second phase)

150 ml/min

Draw up

2 µL/sInjection

0.5 µL/sEvaluation Parameters
Standard method settings were applied. The parameter settings are summarized in the following table.
Table 2: Detection parameters CLDParameter

Specification NSMax. integration time

300 sStart (N)

1 cts

Stop (N)

1 cts

Results and Discussion
The examined samples are a representative spectrum from the field of fuel production. The results given in Table 3 areaverages of three replicate analyses of samples and test standards. For all samples and standards an injection volume of 40 µlwas used. Figures 3–6 show typical measuring curves for selected samples as well as for one standard.
Table 3: Results of the total nitrogen determination in different fuels
Measurement

TNSD

Diesel (automotive, DK)

0.87 ppm± 0.02 ppm

UL-Diesel (UL-DK)

7.77 ppm± 0.04 ppm

Bio Diesel (2nd generation, B-t-L)

0.22 ppm< 0.01 ppm

Diesel + 7 % FAME

2.53 ppm± 0.04 ppm

Diesel (Marine Gasoil)

28.7 ppm± 0.71 ppm

Regular Gasoline (OK)

2.24 ppm± 0.12 ppm

Light Gasoline

0.14 ppm< 0.01 ppm

Jet Fuel A

9.17 ppm± 0.04 ppm

Kerosene3.65 ppm< 0.01 ppm

TN Standard (c = 0.07ppm)

0.07 ppm< 0.01 ppm

TN Standard (c = 0.72ppm)

0.72 ppm± 0.03 ppm

TN Standard (c = 36 ppm)

36.2 ppm± 0.09 ppm

3

4

Determination of Trace Nitrogen Contents in Fuels and Fuel Blends according to ASTM D4629 / DIN 51444

Fig. 3: TN analysis curve for sample “Kerosene”

Fig. 4: TN analysis curve for sample “Light Gasoline”

Fig. 5: TN analysis curve for sample “Marine Gasoil”

Fig. 6: TN analysis curve for standard “0.72 ppm N”

Due to the optimal process conditions a threefold determination is generally sufficient to reach results within 3 % RSD. Thisis remarkably affecting the sample processing time and thereby generates a higher sample throughput. The analysis resultsreceived and their reproducibility depict the high quality of the sample combustion. The proper performance of the analysis
system was confirmed by analyzing standard materials with known N contents (see Table 3).
Conclusion
The compEAct N is extremely well suited for the measurement of widely varying nitrogen contents in versatile fuel samples(e.g., diesel, gasoline, kerosene, bio diesel). The detector, with its unique HiPerSens® technology, achieves a measuring rangeof up to 10,000 mg/l starting at a limit of detection as low as 15 µg/l of nitrogen.
The optimal sample digestion and the efficient Auto-Protection system enable excellent reproducibility, independent of TNconcentration or digestion characteristics and composition of the analyzed fuel (e.g., FAME, color additives etc.). A highsample throughput is easily achieved by using the LS 2 liquids sampler.
The sample volume can be reduced to 10 to 20 µl to save further analysis time. Thanks to compEAct’s sensitivity, thisis sufficient to gain reliable results in very short time. For analysis of gaseous fuels and LPG, the analysis system can beextended by adding the suited sampling system.

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