Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 1140-1143  
J. Environ. Treat. Tech.  
ISSN: 2309-1185  
Journal web link: http://www.jett.dormaj.com  
Structural Information from Ratio Bands in the  
FTIR Spectra of Long Chain and Branched  
Alkanes in Petrodiesel Samples  
Flora Ferati 1*  
Department of Technology, University of Mitrovica “Isa Boletini” Ukshin Kovaqica, Mitrovica, 40000, Kosovo  
Received: 15/06/2020  
Accepted: 14/07/2020  
Published: 20/09/2020  
Abstract  
FTIR is a widely used equipment for determining the chemical structure of organic materials. Vibrational analysis was  
employed to characterize hydrocarbon structure from which depends their quality and environmental effect. The results showed  
that the FTIR spectrum of petrodiesel allowed structural information about degree of branched or aliphatic chain hydrocarbons.  
2 3  
The ratios of aliphatic carbons especially CH /CH (A2920/A2950) and A1376/(A1376+A1460) appeared to be suitable indicators for  
identifying type of alkanes present in petrodiesel samples.  
Keywords: FTIR, Petrodiesel, Hydrocarbon structure  
Introduction1  
others applied NIR-Spectroscopy (4, 15), or NMR (5, 16).  
Most of them use a lot of toxic chemicals also need a lot of  
time for sample preparation and cost analysis are very  
expensive.  
1
Most of air contaminants have origin from diesel  
petroleum which is urgent problem in most world countries  
and simplicity of determination of fuel quality is still  
challenge. Today all European countries have strong quality  
control of quality diesel fuel, but all these quality parameters  
do not involve petroleum hydrocarbons (PHCs) which can  
contain a lot of contaminants, or can initiate formation of  
other air contaminants which can be chemical product in  
engine combustion of diesel petroleum. Nakakita et al.  
reports about diesel fuel which contain branched and ring  
hydrocarbon compounds under engine combustion produced  
high level of PM precursors, such as benzene and toluene  
which are in high level produced from branched paraffins  
compare with n-paraffins where their formation are in low  
level (1, 13). Their funding’s suggest branched  
hydrocarbons to be in low level in diesel fuel because of  
possibility to increase PM emissions in air also particle  
matter of are in strong correlation with composition and  
physico-chemical parameters (1, 14). Anyway, high level of  
n-paraffins or long chain aliphatic hydrocarbons have lower  
impact in PM emissions compared with branched paraffins;  
but also has other negative effect which originates from their  
higher boiling point and under engine incomplete  
combustion some of them can be exhaust gases or can be  
condensed droplets from unburned fuel (2). From this point  
of view it is very important to know what type of  
hydrocarbons contain diesel fuel branched or long chain  
hydrocarbons. Cetane number and molecular composition of  
petrodiesel properties was done by gas chromatography (3),  
Other important parameter used in fuel quality is cetane  
number which depends from organic structure of molecules  
and can be in correlation with molecular structure of  
hydrocarbons but from cetane number is not possible to  
know more details about type of hydrocarbons. Most of  
methods used in cetane number determination are expensive  
and time consuming but using this cetane number is possible  
to know molecular structure of fuel hydrocarbons (6).  
Cetane Number has minimum legislative limit, but not the  
maximum, based on European Commission legislation.  
Cetane number, combustion level and PM emissions are in  
strong correlation between and as a conclusion high cetane  
number provide complete and faster combustions and lower  
PM emissions (7, 17). Our research group proposed FTIR-  
spectroscopy application which has a lot of benefits  
compared with other methods for the reason that it does not  
need any sample preparation, it does not use any hazardous  
chemicals, the cost analysis is cheaper and FTIR-  
Spectroscopy known as green but also as fast and sensitive  
method of analysis. FTIR spectroscopy was applied in order  
to estimate structural information of hydrocarbon molecules  
present in coal using single wavenumber and using ratio of  
frequencies from asymmetric stretching vibrations of  
2 3  
CH /CH ratio (8, 18). Cetane number is one fuel parameter  
which corresponds with ignition delay, but in general this  
depends on the type of hydrocarbons content in fuel. Similar  
application in coal sample characterization was reported  
Corresponding author: Flora Ferati, Department of Technology, University of Mitrovica “Isa Boletini” Ukshin Kovaqica,  
Mitrovica, 40000, Kosovo. E-mail: flora.ferati@umib.net.  
1
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Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 1140-1143  
about using same ratio of frequencies to find branched  
aliphatic degree and long chain side of hydrocarbons (9).  
They found correlation between intensity ratio and type of  
hydrocarbons (long or short chain and branched degree) as  
follows:  
For comparison between branched and long chain  
compounds was used two standard compounds one as a long  
chain aliphatic compounds was used hexadecane >99 %  
Sigma-Aldrich (below STD1) and isocetane as highly  
branched alkane reference compound 2.2.4.4.6.8.8-  
heptamethylnonane Sigma-Aldrich, 98 % (below STD2).  
The assignment of bands was done by comparison with  
literature spectral data and with reference compounds  
spectra included in the software spectral library. Height and  
area of each band were measured and calculated by the  
essential FTIR software. Cetane Number were determined  
according to the standard methods EN ISO 5165 method  
(11).  
Decrease or lower ratio- High level of branched degree  
or shorter aliphatic chain  
Increase or high ratio-Longer aliphatic chain of alkanes  
are present or less branched.  
Other authors’ reports about other ratio combinations  
that determine the branched degree of alkanes following  
1376/(A1376+A1460) apply in oils from reservoirs (10). The  
A
intensity of this ratio is in correlation with branched degree  
of hydrocarbons which means that high intensity of this ratio  
corresponds with the highest branched hydrocarbon  
structure. There are published reports about the use of the  
ratio of frequencies, but not directly about fuel analysis and  
their usage as indicators for type of hydrocarbons which still  
remain unclear. Novelty of this proposed method is the  
promotion of FTIR-Spectroscopy as an alternative method  
of cetane number determination and to give information  
about type of hydrocarbons. This FTIR offers opportunities  
to detect the type of hydrocarbons branched or long chain  
which is sufficient information for monitoring contaminants  
in air and their origin of contamination. The aim of this  
research is to optimize FTIR-Spectroscopy method by using  
those two types of ratio frequencies from two different IR  
region of methyl and methylene vibrations. Challenge is to  
determine exact type of hydrocarbons in petrodiesel samples  
present in different diesel fuels from 5 different brands of  
fuel companies around Kosovo in comparison with cetane  
number as a standard method.  
3 Results and Discussion  
Based on reported results (Table 2a) sample number 4  
has higher cetane and also based FTIR results has similarity  
in ratio 2925/2954 and conclusion is they are not different  
which means their chemical structure is very similar between  
standard long chain molecule and real analyzed sample.  
From this point of view higher cetane number are in  
correlation with long chain aliphatic molecules. All other  
analyzed petrodiesel samples are classified as different  
compared with standard long chain compound because  
relative difference is higher than 10 %. Same samples were  
analysed by FTIR Spectroscopy and all results were  
compared with branched aliphatic standard compound  
results presented in Table 2b, relative difference is lower  
than 10 % classified as Not Different chemical structure  
except in sample 4 where relative difference is higher than  
10% and it is classified as different chemical structure.  
Conclusion based on a standard compounds was confirmed  
from both compounds long and branched aliphatic  
compounds and based on this sample 1,2,3 and 5 contain  
branched aliphatic compounds and only sample 4 has long  
aliphatic chain molecules. In Figure 1 are shown scanned  
FTIR spectra of petrodiesel compounds and their  
characteristic band of methylene and methyl vibrations of  
hydrocarbon molecules and in Table 1 are presented group  
frequencies for crucial type of vibrations in petrodiesel  
samples. Ratio I was used to compare standard analyzed  
compounds and both reference compounds and sample 4 has  
similarity with STD1 or long chain aliphatic compounds and  
all other samples has similarity in intensity ratio with STD2  
or branched aliphatic reference compounds Figure 2.  
2
Experimental  
2
.1 Samples and applied Measurements  
Diesel fuel purchased from local and international  
brands in Kosova were used and analyzed by FTIR-  
Spectroscopy. An Irrafinity-1 Shimadzu FT-IR  
spectrophotometer equipped with a deuterated triglycine  
sulfate (DTGS) detector was used to acquire FT-IR spectra.  
Fuel sample were deposited between two CaF transparent  
2
-
windows. All spectra were recorded from 4000 to 1000 cm  
1
and processed using IR-Solution Software for Windows  
(
Shimadzu). After each operation, the CaF window was  
2
thoroughly cleaned up, washed with acetone and then dried.  
Table 1: Selected FTIR spectra peak frequencies in petrodiesel (12).  
-
1
Functional Group  
Region (cm )  
3010~3080  
2950~2975  
Intensity*  
Comments  
Str.  
asym.str.  
sym.str.  
asym.str.  
sym.str.  
Str.  
asym.def  
sym def.  
acissors vib.  
Ar‒H  
m
m-s  
m
m-s  
m
w
m
m-s  
m
‒
CH  
3
2
865~2885  
2915~2940  
840~2870  
2880~2890  
1440~1465  
‒
CH  
2
2
‒
CH  
‒
CH  
3
1
370~1390  
1440~1480  
‒
CH  
2
*w = weak; m = medium; s = strong; vs = very strong; v = variable; asym= asymmetric; str.= streching  
1
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Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 1140-1143  
Table 2: Comparison of peak height ratio 2924/2954 cm-1 data for the petrodiesel samples with standard long aliphatic chain  
-
1
hydrocarbon. (a), and comparison of peak height ratio 2924/2954 cm data for petrodiesel samples compared with standard  
branched aliphatic hydrocarbon (b). If the relative difference for a single peak height ratio is greater than the threshold of 10%, the  
peak height ratio is classified as ‘different’; vice versa, the peak height ratio is classified as ‘not different’  
a)  
Sample Ratio I Long Aliphatic  
chain standard compound  
Ratio I Real Cetane  
Mean Absolute  
Difference  
Relative  
Difference  
12.50  
13.91  
12.39  
Conclusion  
sample  
1.544  
1.522  
1.545  
1.7  
Number  
1
2
3
4
1.75  
1.75  
1.75  
1.75  
52  
1.65  
1.64  
1.65  
1.72  
0.2  
0.22  
0.2  
Different  
Different  
Different  
Not  
51.5  
53.6  
55  
0.05  
2.83  
Different  
Different  
5
1.75  
1.58  
53.8  
1.66  
0.17  
10.27  
b)  
Sample  
Ratio I for real  
sample  
Ratio II for  
Mean  
Absolute  
Difference  
Relative  
Diffference  
Conclussion  
Branched  
Aliphatic  
standard  
compounds  
1.5  
1
2
3
4
5
1.54  
1.52  
1.545  
1.7  
1.52  
1.51  
1.52  
1.6  
0.044  
0.022  
0.045  
0.201  
0.079  
2.89  
1.47  
3
12.56  
5.13  
Not Different  
Not Different  
Not Different  
Different  
1.5  
1.5  
1.5  
1.5  
1.58  
1.53  
Not different  
before and also correlation of this intensity ratio of  
frequencies analyzed for real samples reference compounds  
are in strong relation between Figure 3. More similarity has  
Sample 4 with STD1 and sample 1 is very close with STD 2  
but all other samples are between two standard compounds  
and this can be explained with their different components  
present in every sample with different alkane type.  
0.41  
0.4  
0.39  
0.38  
0.37  
Figure 1: FTIR-Spectra of petrodiesel sample  
0
0
.36  
.35  
1
.8  
.75  
.7  
.65  
.6  
.55  
.5  
.45  
.4  
.35  
0.34  
1
1
1
1
1
1
1
2
3
4
5
STD 1 STD 2  
Sample Number  
1
Figure 3: Ratio II comparison analyzed sample with both standard  
compounds  
1
Based on both Ratios sample 4 corresponds with longer  
aliphatic chain and all other samples contain more branched  
aliphatic compounds. Both ratios from FTIR Spectroscopy  
results can be in correlation with Cetane Number meausered  
for same samples.  
1
1
2
3
4
5
STD 1 STD 2  
Sample Number  
Figure 2: Ratio I comparison analyzed sample with both standard  
compounds  
4
Conclusions  
Based on our investigations most of brands in Kosovo  
use petrodiesel classified as branched molecular structure.  
This can be confirmed by both FTIR ratio confirming each  
During research we also used and other frequency  
combinations which is combination of two frequencies  
-1 -1  
377cm and 1458 cm . (Ratio II) used reported formula  
1
1
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Journal of Environmental Treatment Techniques  
2020, Volume 8, Issue 3, Pages: 1140-1143  
other, and they are also in complete agreement with cetane  
number. Petrodiesel in Kosovo petrol companies` brands  
contains branched alkanes which can be powerful sources  
for benzene and toluene precursor for PM formation. These  
are critical air pollutants in Kosovo and have high negative  
environmental and health impact. We strongly recommend  
analysis of air particles for their chemical structure and their  
contaminants origin. Branched molecular structures of  
petrodiesel converted in benzene and toluene during engine  
conditions which are precursor for formation of PM. Based  
on this, most of petrodiesels can be source of benzene and  
toluene emissions. Only one brand sample contains long  
aliphatic chain which can be unburned from engine  
conditions which can be source of emission for other exhaust  
gases. FTIR tool can be very suitable because this tool  
known as green method, cheaper, faster, easily operated and  
sensitive to monitor chemical structure of petrodiesel  
components, especially parameter ratio I. As such, we  
suggest to start optimizing the FTIR method and its  
validation with the purpose of its application in fuel analysis  
to monitor molecular structure of hydrocarbons.  
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66.  
A comparative study with gas  
8
1
1
1. Petroleum Products—Determination of the ignition quality of  
diesel fuels—Cetane engine method ISO-5165-1998.  
2. Fuller, E.L., Smyrl, N.R., Howell, R.L. and Daw, C.S.  
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1
1
4. Jianbing G, Guohong T, Chaochen C, Liyong H,  
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Ethical issue  
Authors are aware of, and comply with, best practice in  
publication ethics specifically with regard to authorship  
(2018) 62–68.  
1
5. Juan F, Francisco J, Irene M, Paloma Á. Cetane number  
prediction of waste cooking oil-derived biodiesel prior to  
transesterification reaction using near infrared spectroscopy.  
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6. Yu W, Yi C, Wei W, David F. D, Ronald K.H, A new method  
of estimating derived cetane number for hydrocarbon fuels.  
Fuel, Volume 241, 1 April 2019, Pages 319-326.  
7. Himansh K, Anil K, Pramod K, A novel approach to study the  
effect of cetane improver on performance, combustion and  
emission characteristics of a CI engine fuelled with E20 (diesel  
(avoidance of guest authorship), dual submission,  
manipulation of figures, competing interests and compliance  
with policies on research ethics. Authors adhere to  
publication requirements that submitted work is original and  
has not been published elsewhere in any language.  
1
1
Competing interests  
The authors declare that there is no conflict of interest  
that would prejudice the impartiality of this scientific work.  
–
bioethanol) blend. Sustainable Chemistry and Pharmacy  
Volume 14, December 2019, 100185.  
1
8. Qiuxiang Y, Yabo L, Xing T , Junwen G, Rucheng W, Yujuan  
Zh, Ming S, Xiaoxun M. Separation of petroleum ether  
extracted residue of low temperature coal tar by  
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Authors’ contribution  
Author of this study have a complete contribution for  
data collection, data analyses and manuscript writing  
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