ENVIRONMENTAL LABORATORY 27


hopanes detected in a sediment sample collected sample from Somes River is showed in the Figure 3.


Hopanes are molecular markers used currently for estimation of the mineral maturity [2,5]. In low maturity materials the group of hopanes are dominated by stereochemistry 17β(H),21β(H) and configuration R at C22. As the maturity level increases increases17α(H), 21β(H) stereochemistry predominates and 22S configuration for the C31 and higher homologues [5,8].


The chromatogram obtained to m/z=191 can be used directly for estimation of the maturity minerals by comparition of the two compounds at C27: 18β(H)22,29,30-trisnorhopane and 17β(H)22,29,30-trisnorneohopane (the peaks 1 and 2 respectively).


Figure 3. Detection of Hopanes in a river sediment (m/z 191 in the time range 40-51.2 min). 3.4. Polyaromatic Hydrocarbons (PAHs).


An abundant class of compounds detected in the river sediment samples are Polyaromatic Hydrocarbons (PAHs). This type of compound presents a mass spectra of the molecular ion as base peak and therefore can be shown by selective chromatograms (Figure 4). The molecular ion is also used as the diagnostic ion for all PAHs in early papers [2].


Figure 4. Polyaromatic Hydrocarbons (PAHs) detected by ion chromatograms at m/z 178, 202, 228, 252, 276 and 300 respectively in the range time of 18-70 min.


3.2. Acyclic isoprenoid


The acyclic isoprenoid compounds have a large number of methyl branching points in their structure leading to the production of information rich spectral content enabling, in most cases, the branching points in the molecules to be determined. They are presented with the fragment m/z 183 containing 13 carbon atoms. The profiles of acyclic isoprenoids based on drawing the signal to m/z 183 is shown in Figure 2.


This group of compounds includes pristane (C19) and phytane (C20) often used as an indicator of depositional environments [5,8]. The idea is based on the premise that pristine is formed from phytol by oxidation and decarboxylation reactions and on other hand phytane is formed by hydrogenation and dehydration of phytol. The type of reaction is mainly dependant on the


oxidisation and reducing-type environments. The samples derived from terrestrial sources have higher concentration of the long chain isoprenoids than samples derived from marine sources [8].


3.3. Pentacyclic triterpanes (Hopanes)


Hopanes is a class of compounds that has a great impact on petroleum geochemistry. They are very resistant to biodegradation and can serve therefore as conserved internal standards for assessing the biodegradation of more degradable compounds [13]. They have carbon atom numbers ranging from 27 to 35. The hopans are detected by drawing the profile using the ion m/z 191. Additional detailed information can also be made for based on the detected molecular ions. In addition to providing maturity information, hopanes are also useful as source indicators. The


The presence of polycyclic aromatic hydrocarbons (PAHs) in sediment samples reflects the anthropogenic impact on sediment organic matter [2,7]. The input of PAHs into the environment are due to anthropogenic activities such as combustion of fossil fuel as well as natural processes (forest fires). The PAHs source can be of petrogenic, pyrogenic or biogenic origin [2,7]. Combustion of fossil fuels and plant materials leads to pyrogenic PAHs with four to eight parental rings. The pyrogenic markers include fluoranthene, benzofluoranthenes, benzoanthracenes, benzo[e]pyrene, benzo[a]pyrene and benzo[ghi]perylene, with low abundances of alkylated surrogates. The petrogenic sources (ancient plant material) are characterised by alkylated structures. The values of characteristic source parameters [2] defined as Fluorantene/ (Fluorantene + Pyrene) and Benz[a]antracene/(Benz[a] antracene + Chrysene) for investigated samples have the average values 0.47 and 0.40 respectively. These values show a pyrogenic origin of the detected PAHs.


3.5. Sulphonated Polyaromatic Hydrocarbons (SPAHs). Benzothiophenes


Benzothiophenes is another important group of pollutants used very often as biomarkers by the source information. The organosulfur compounds can be formed by the reaction of aromatic hydrocarbons with elemental sulphur [14]. They are, as are PAHs, very persistent chemicals [15]. Because of their environmental impact they are included in the list of priority pollutants. This group of compounds can be seen by ion chromatograms at molecular ion (Figure 5).


3.6. Linear Alkylbenzens (LABs).


A very important group of pollutants found in the sediment river samples is the Linear Alkylbenzens (LABs). This group of compounds was the subject of investigation in many early papers [7,16,17]. They can by seen by drawing the ion chromatogram at m/z 91. This class of compounds originate from alkyl sulphonic surfactants (present in a lot of detergents) by biodegradation. They comprise isomers of LABs with a number of carbons from 10 to 13 (Figure 6). The investigation of linear alkyl benzenes is performed in order to study the impact of sewage water on aquatic sediments.


3.7. Trialkylamines and 2M-Ketones


Trialkylamines are cationic surfactants that originate from detergents, methyl-ketones are photo-oxidation products of TAMs produced in sedimental conditions.


The detection of these families of compounds is very important in knowing the impact of sewage water on the sediment organic matter composition [18,19].


Based on chromatogram at m/z 58 two families of organic compounds can consecutively be detected: methyl-ketones and trialkylamines (TAMs) as can be seen in the Figure 7. The general structure of TAMs used as cationic surfactants is (CH3


)2 Figure 5. Benzothiophenes presented by ion chromatograms at m/z 184, 198, 212, 226 and 240 respectively in the range time of 18-45 min. WWW.ENVIROTECH-ONLINE.COM IET JANUARY / FEBRUARY 2021 N-Cn H2n+1


(n=12, 14, 16, 18). The ion to m/z 58 originating from methyl- ketones is produced by a rearrangement process, leading to


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