• Repeat the elution with 5 mL of n-pentane/DCM (40:60 v:v) to collect the
second fraction (aromatic hydrocarbons).
• Finally, repeat the elution with 5 mL of methanol to collect the third
fraction (NSO components).
• Add an appropriate amount of surrogate standard to each fraction.
• Reduce the individual fractions to an appropriate analysis volume.
Further handling:
Measure all individual extracts separately by GC/MS or LC/MS
For special requirements or specific research questions some specialized procedure exist. As an example, the separation of nonbranched n-alkanes from branched
isoprenoic aliphatics is required e.g. for successful compound specific stable isotope
analyses, for increasing the sensitivity for isoprenoid analyses or for a successful
analysis of n-alkanes in highly biodegraded oils. This separation is most frequently
performed either with molecular sieve (5 Å) or with urea (so-called carbamide
method or urea adduction). In both cases, n-alkanes are isolated by inclusion into
pores or crystals with a diameter of 5 Å along with only iso- and anteiso-alkanes of
long series. Because of their size, the molecules of other alkane fraction compounds
(branched and cyclic alkanes) are not able to produce inclusion compounds neither
with carbamide nor with these molecular sieves and remain separated in the extract.
The result is visualized in Fig. 7.2.
Standard Operation Procedure SOP 5—Urea Adduction
• Evaporate the aliphatic fraction derived from the fractionation procedure to
dryness.
• Redissolve the aliphatic fraction with a mixture of n-hexane and acetone
(2:1 v:v)
• Add dropwise this solution to a saturated methanolic solution of urea.
• Separate the precipitate containing the urea adducts.
• Extract the nonadducts from the urea solution by n-hexane.
• Repeat the urea adduction with the nonadduct extract three times.
• Isolate the nonadducts in the residual n-hexane extract.
• Deliberate the adducts from the precipitated urea by dissolving it in water
and subsequent extraction with n-hexane.
Further handling:
Measure both adducts and nonadducts separately by GC/MS
140
7 Principal Analytical Procedures in Organic Geochemistry
second fraction (aromatic hydrocarbons).
• Finally, repeat the elution with 5 mL of methanol to collect the third
fraction (NSO components).
• Add an appropriate amount of surrogate standard to each fraction.
• Reduce the individual fractions to an appropriate analysis volume.
Further handling:
Measure all individual extracts separately by GC/MS or LC/MS
For special requirements or specific research questions some specialized procedure exist. As an example, the separation of nonbranched n-alkanes from branched
isoprenoic aliphatics is required e.g. for successful compound specific stable isotope
analyses, for increasing the sensitivity for isoprenoid analyses or for a successful
analysis of n-alkanes in highly biodegraded oils. This separation is most frequently
performed either with molecular sieve (5 Å) or with urea (so-called carbamide
method or urea adduction). In both cases, n-alkanes are isolated by inclusion into
pores or crystals with a diameter of 5 Å along with only iso- and anteiso-alkanes of
long series. Because of their size, the molecules of other alkane fraction compounds
(branched and cyclic alkanes) are not able to produce inclusion compounds neither
with carbamide nor with these molecular sieves and remain separated in the extract.
The result is visualized in Fig. 7.2.
Standard Operation Procedure SOP 5—Urea Adduction
• Evaporate the aliphatic fraction derived from the fractionation procedure to
dryness.
• Redissolve the aliphatic fraction with a mixture of n-hexane and acetone
(2:1 v:v)
• Add dropwise this solution to a saturated methanolic solution of urea.
• Separate the precipitate containing the urea adducts.
• Extract the nonadducts from the urea solution by n-hexane.
• Repeat the urea adduction with the nonadduct extract three times.
• Isolate the nonadducts in the residual n-hexane extract.
• Deliberate the adducts from the precipitated urea by dissolving it in water
and subsequent extraction with n-hexane.
Further handling:
Measure both adducts and nonadducts separately by GC/MS
140
7 Principal Analytical Procedures in Organic Geochemistry