Aliphatic Compounds

Aliphatic hydrocarbons, a diverse suite of compounds, are an important lipid fraction which is either natural (i. e., from photosynthesis by marine biota inhabiting the surface waters or by terrestrial vascular plants) or anthropogenic (i. e., of petroleum origin from land runoff, and/or industrial inputs). Aliphatic hydrocarbons have been studied and characterized from various environmental multimedia [1,53-56,99-109].

Aliphatic hydrocarbons of petroleum origin (Fig. 1) (also coal) in the environment are usually composed of:

1. Homologous long chain n-alkane series ranging from <C15 to >C38 with no carbon number predominance [1,53-55,73,109-114]

2. Unresolved complex mixture (UCM) ofbranched and cyclic hydrocarbons [1, 53-56,68,70,113,115-119]

Diasteranes

XI. ap-Diasteranes

Fig. 1. Chemical structures of some aliphatic hydrocarbon molecular markers as cited in the text

XI. ap-Diasteranes

Fig. 1. Chemical structures of some aliphatic hydrocarbon molecular markers as cited in the text

3. Isoprenoid hydrocarbons such as norpristane (2,6,10-trimethylpentade-cane), pristane (2,6,10,14-tetramethylpentadecane), and phytane (2,6,10,14-tetramethylhexadecane) (Structures I-III, Fig. 1) [1,53-56,68,70,120-123]

4. Tricyclic terpanes (Structure IV, Fig. 1), usually ranging from C19H34 to C30H56,and in some cases to C45H86 [68,124-126]

5. Tetracyclic terpanes such as 17,21- and 8,14-seco-hopanes (Structures V-VI, Fig. 1) [125-127]

6. Pentacyclic triterpanes, such as the 17a(H),21^(H)-hopane series (Structures VII-VIII, Fig. 1), consisting of 17a(H)-22,29,30-trisnorhopane (Tm),

17a(H),21^(H)-29-norhopane, and the extended 17a(H),21^(H)-hopanes (>C31) with subordinate amounts of the 17^(H),21a(H)-hopane series and 18a(H)-22,29,30-trisnorneohopane (Ts), [1,53-55,114] 7. Steranes and diasteranes with the 5a(H),14a(H),17a(H)-configuration (IX), 5a(H),14^(H),17^(H)-configuration (X), and the 13a(H),17^(H)-diastera-nes (Structure XI, Fig. 1) (e.g., [1,53-55,101,103,105-107,117]).

Typical GC-MS traces of aliphatic hydrocarbon patterns representative of different environmental samples are shown in Fig. 2. The aliphatic hydrocarbons of petroleum contaminated sediment and water are present from C16 to C38 with no carbon number predominance and a Cmax at C21 and C30 or C32 (Figs. 2 a, b). The source of these hydrocarbons as well as the UCM can be confirmed to be due to petroleum input by the presence of the biomarkers discussed below. Crude oil has a high concentration of alkanes compared to UCM (Fig. 2 c) and typically a smooth decreasing concentration from low carbon numbers to high [63, 66, 111]. The alkanes <C20 are initially lost by evaporation and subsequent biodegradation (see Chap. 5) removes additional amounts of the same compounds, leaving an enhancement of the isoprenoids (cf., Figs. 2 a, b) [53-55,111,116]. In contrast, an example of primarily natural background alkanes from higher plant waxes is shown in Fig. 2 d. This is a terrigenous component brought into marine environments by river washout and atmospheric fallout and is sedimented with minerals. Such «-alkanes have a strong odd carbon number predominance and a Cmax at C27,C29,or C31 [56].A minor component from petroleum is also present as UCM and «-alkanes from C20 to C26.An example of hydrothermal petroleum is shown in Fig. 2e, where the «-alkanes range from C13 to C25 with significant amounts of isoprenoids. There have been numerous compositions reported for petroleums formed from the hydrothermal alteration of immature organic matter in sediment covered marine rift areas as for example in the Gulf of California and the northeastern Pacific Ocean [128-130]. Runoff from roads, especially in urban areas, contains significant amounts of petroleum residues. These consist of lubrication oils, particles from vehicle emissions and fuel residues [1]. An example is shown in Fig. 2f, where the dominant components are «-alkanes ranging from C22 to C38, with a Cmax at C29 and no carbon number predominance. In other cases, the washout contains mainly a UCM with minor alkanes.

Characteristic examples of biomarker distributions typical for petroleum consisting of tricyclic terpanes (key ion m/z 191), hopanes (key ion m/z 191), and steranes/diasteranes (key ions 217, 218, 259) are shown in Fig. 3. The tertacyclic terpanes are not major components in the m/z 191 plots, because their key ion is at m/z 123. The tricyclic terpanes range from C21 to C29,with a Cmax at C23 and no C22 and C27. The mature hopanes range from C27 to C35,with the 17a(H),21^(H) configuration and the homologs >C31 are resolved into the C-22S and R diastereomers [68,73,68,114]. The steranes range from C27 to C29 and are generally less concentrated than the hopanes. The mature sterane series have the 5a(H),14a(H),17a(H)- and 5a(H),14^(H),17^(H)-configurations with all homologs also resolved into the respective C-21 S and R diastereomers (Figs. 3b, c). The diastereomers also range from C27 to C29 and in part coelute with the steranes (Fig. 3 b). A summary of the identifications of the various aliphatic hydrocarbons just discussed is given in Table 1.

Moisture And Hydrocarbon Scrubbers
Fig. 2a-c. GC-MS traces (m/z 99 key ion) of various aliphatic hydrocarbon fractions from different environmental matrices: a sediment - Red Sea; b water - Red Sea; c Kuwait crude oil spill
Guaymas Basin Oil
Fig. 2d-f (continued) d sediment, terrestrial source - Mediterranean Sea; e hydrothermal petroleum - Guaymas basin, Gulf of California; f road surface runoff water
Bad Source Power Cable
Fig. 3a-c. GC-MS key ion traces representing the: a m/z 191 tricyclanes and a/hopane series; b m/z 217 aaa-steranes and diasteranes; c m/z 218 a////-steranes (Red Sea sediment)

Table 1. Typical hydrocarbon identifications and chemical compositions (representative structures are shown in Fig. 1)

Compound Name Composition MW

n-Alkanes n-Hexadecane C16H34 226

n-Heptadecane C17H36 2 40

n-Octadecane C18H38 2 54

n-Nonadecane C19H40 268

n-Eicosane C20H42 282

n-Heneicosane C21H44 2 96

n-Docosane C22H46 310

n-Tricosane C23H48 3 24

n-Tetracosane C24H50 338

n-Pentacosane C25H52 352

n-Hexacosane C26H54 3 66

n-Heptacosane C27H56 3 80

n-Octacosane C28H58 3 94

n-Nonacosane C29H60 408

n-Triacontane C30H62 422

n-Hentriacontane C31H64 4 3 6

n-Dotriacontane C32H66 4 50

n-Tritriacontane C33H68 4 64

n-Tetratriacontane C34H70 478

n-Pentatriacontane C35H72 492

n-Hexatriacontane C36H74 5 06

n-Heptatriacontane C37H76 5 20

n-Octatriacontane C38H78 534 Isoprenoids

2,6,10-Trimethylpentadecane (norpristane) C18H38 2 54

2,6,10,14-Tetramethylpentadecane (pristane) C19H40 268

2,6,10,14-Tetramethylhexadecane (phytane) C20H42 282

Unresolved complex mixture of C12-C27 branched and cyclic hydrocarbons

Tricyclic Terpanes

C19-Tricyclic C19H34 2 62

C20-Tricyclic C20H36 2 76

C21-Tricyclic C21H38 2 90

C23-Tricyclic C23H42 318

C24-Tricyclic C24H44 332

C25-Tricyclic C25H46 3 46

C26-Tricyclic C26H48 3 60

C28-Tricyclic C28H52 388

C29-Tricyclic C29H54 4 02

Tetracyclic terpanes

C24-Tetracyclic (17,21-seco-hopane) C24H42 330

C28-Tetracyclic (18,14-seco-hopane) C28H50 386

C29-Tetracyclic (18,14-seco-hopane) C29H52 400

Table 1 (continued)

Compound name Composition MW

Pentacyclic triterpanes

18a(H)-22,29,30-Trisnorneohopane (Ts)

C27H46

370

17a(H)-22,29,30-Trisnorhopane (Tm)

C27H46

370

17a(H),21ß(H)-29-Norhopane

C29H50

398

17a(H),21ß(H)-Hopane

C30H52

412

17a(H),21ß(H)-Homohopane (22S)

C31H54

426

17a(H),21ß(H)-Homohopane (22R)

C31H54

426

17a(H),21ß(H)-Bishomohopane (22S)

C32H56

440

17a(H),21ß(H)-Bishomohopane (22R)

C32H56

440

17a (H),21ß(H)-Trishomohopane (22S)

C33H58

454

17a (H),21ß (H)-Trishomohopane (22R)

C33H58

454

17a (h),21 ß (H)-Tetrakishomohopane (22S)

C34H60

468

17a (h),21 ß (H)-Tetrakishomohopane (22R)

C34H60

468

17a (h),21 ß (H)-Pentakishomohopane (22S)

C35H62

482

17a (h),21 ß (H)-Pentakishomohopane (22R)

C35H62

482

Diasteranes

13 a (H),17ß (H)-Diacholestane (20S)

C27H48

372

13a(H),17ß(H)-Diacholestane (20R)

C27H48

372

Steranes

5a(H),14a(H),17a(H)-Cholestane (20S)

C27H48

372

5a(H),14ß(H),17ß(H)-Cholestane (20R)

C27H48

372

5a(H),14ß(H),17ß(H)-Cholestane (20S)

C27H48

372

5a(H),14a(H),17a(H)-Cholestane (20R)

C27H48

372

5a(H),14a(H),17a(H)-Ergostane (20S)

C28H50

386

5a(H),14ß(H),17ß(H)-Ergostane (20R)

C28H50

386

5a(H),14ß(H),17ß(H)-Ergostane (20S)

C28H50

386

5a(H),14a(H),17a(H)-Ergostane (20R)

C28H50

386

5a(H),14a(H),17a(H)-Sitostane (20S)

C29H52

400

5a(H),14ß(H),17ß(H)-Sitostane (20R)

C29H52

400

5a(H),14ß(H),17ß(H)-Sitostane (20S)

C29H52

400

5a(H),14a(H),17a(H)-Sitostane (20R)

C29H52

400

Continue reading here: Polycyclic Aromatic Compounds

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