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The Analysis of Total Petroleum Hydrocarbons
Hazel Davidson
Technical Marketing Manager Derwentside Environmental Testing Services
Derwentside Environmental Testing Services
DETS is an independent testing laboratory with over 100 staff. We offer analytical testing on a variety of matrices including :
Soils, water, gases, waste, asbestos and fuels
We offer:
A personal service and designated point of contact
Accreditation to ISO 17025 for most determinands and sampling
Accreditation to MCERTs for soils and waters
Flexible testing protocols
Technical support and training for clients
DETS – dependable data, dependable delivery
DETS – dependable data, dependable delivery
Petroleum Hydrocarbons
Composition of TPH
Common refinery products
Behaviour of TPH in soil
Sampling precautions
VPH/EPH methods
Example chromatograms
TPH forensics
Characteristics of Petroleum Hydrocarbons
Thousands of compounds derived from crude oil
Varying in appearance from pale yellow condensates to black tars, with SG of <1 (0.7 – 0.95)
Toxicity, mobility and environmental persistance of compounds is highly variable
Crude oil: predominantly C + H, plus N, S + O
Properties of Petroleum Products (1)
Generally with increasing molecular size (usually recorded as ‘carbon number’) there is:
increase in boiling and melting points
lower vapour pressure
increase in density
decrease in water solubility
stronger adhesion to soils and therefore
less mobility in subsurface conditions
Oil Fraction C Range Boiling Pt. Sol. in H2O Density % Arom.
Gasoline C4-C10 25-215OC Moderate 0.74 10 - 25
Kerosene C10-C15 160-400OC Moderate/ 0.81 <15
& Jet Fuel Low
Diesel Fuel & C12-C28 160-400OC Low 0.86 15 - 20
Light Fuel Oils
Heavy Fuel Oils C19-C35 315-540OC V. low 0.88 15 - 35
Motor Oils & C20-C44 425-540OC V. low 0.90 < 15
Lube Oils
Bitumen > C 35 > 500oC Insol. 1.0 30 - 50
Properties of Petroleum Products (2)
Behaviour in Soil
B. Pt Density (g/cm3) Solubility (mg/l) oC in water Benzene 80 0.87 1800 Toluene 111 0.87 520 Pentane 36 0.62 40 MTBE 55 0.74 26,000 Octane 126 0.70 < 1 Eicosane nC20 343 solid < 1 Triacontane nC35 450 solid < 1
Behaviour in Soil
Hydrocarbons will break down or be removed by: Sorption Degradation – microbial or chemical Dispersion Volatilisation Advective flow – carried along by groundwater Diffusive flow – movement along a concentration gradient The environment (soil matrix, moisture content, pH, TOM, particle size, etc.) will significantly affect the rate of the above
Behaviour in Soil
Sampling for VPH
Soils Suitable for GRO, chlorinated solvents, TML/TEL
It is good practice to take duplicates for each of the above analyses
Also supply a tub of soil for moisture content
No headspace
Waters Volatile organic compounds as above, including
VFAs and dissolved gases
It is good practice to take duplicates, as above
Minimise aeration and agitation when sampling
No headspace, check by inverting vial
60 g glass jar
40 ml vial with PTFE septum
Sampling for EPH
Extractable organics – e.g. EPH, oils, grease, PAHs
Waters - 1 x 500 ml or 1 litre coloured glass bottle,
either no preservative or acid (H2SO4 or HCl)
Soils – 1 x 250 g glass jar
ALL ORGANIC SAMPLES SHOULD BE STORED IN GLASS VESSELS
AT 5oC
Analysis - Hydrocarbon Groups
PIANO - parafins - isoalkanes - aromatics - naphthenes - olefines
Methods of Analysis
Infra red (IR) – limited use
Gas Chromatography – Flame Ionisation Detector (GC- FID)
GCMS – MTBE, PAHs and biomarkers
TPH - Gas Chromatography
VPH by headspace
EPH by extract analysis
Modified US EPA methods
Detection limits:
Soil : 5 mg/kg
Water : 0.01 mg/l
Volatile Petroleum Hydrocarbons (VPH)
Also known as petrol range organics (PRO) or gasoline range organics (GRO)
Carbon range C5- C10, typically up to 400 compounds
Includes n- and iso-alkanes, e.g. pentane, dimethylpentane, octane; and naphthenes (cycloparaffins)
Includes mono-aromatics, e.g. benzene, toluene, ethyl benzene, and xylenes
Can include methyl tertiary butyl ether (MTBE), but GCMS gives greater certainty of identification
VPH - GCFID
Headspace method Column DB – 1 MS length 10 m, diameter 0.1mm Rapid turnaround Minimal sample handling Inexpensive Detection to 10 ppb Total volatiles (C5- C12) + BTEX + banding
BTEX by GC-FID
Benzene ring
Unleaded Petrol
Extractable Petroleum Hydrocarbons (EPH)
Requires solvent extraction Carbon range C10- C40 with speciation Column DB HP – 1MS length 15 m, diameter 0.25mm Includes aliphatics, aromatics and hetero-compounds Includes internal standards Identification of diesel, kerosene, lube oil, plus
degree of weathering Detection limit :
Soils 5 mg/kg Waters 0.01 mg/l
Over 10 years in progress Round robin trials Samples provided by Shell As received soil is preferable Comparison of solvents Analysis by GCFID, not IR Standard in draft format (80% done)
SCA TPH Working Group
Solvent Extraction
HEXANE/ACETONE DCM/METHANOL
DCM/PENTANE
CYCLOHEXANE
FREON 112
Image by ALcontrol
Laboratories
Solvent comparison
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Hexane / Acetone DCM / Methanol DCM / Pentane Cyclohexane Freon 112
Mineral O il
Aromatics
NSO
Solvent Ratio Polarity Total Extract Mineral Oil Aromatics NSO
Hexane / Acetone 1/1 0.5 15823 1549 5553 8721
DCM / Methanol 10/1 0.48 8625 1613 2923 4089
DCM / Pentane 3/1 0.3 2440 1420 749 271
Cyclohexane - 0.26 1739 617 796 328
Freon 112 - 0.24 1137 261 485 391
Extraction of Waters
Liquid/liquid extraction
Stir bar liquid/liquid
Solid Phase Extraction (SPE)
DNAPLs and LNAPLs
Issues to consider:
Solubility in water – generally low
Dissolved, colloidal, or product layer?
To filter or not to filter?
Identification – Known Sample
– Retention Time
Quantification – Calibration Standards
Banding – Retention Time
Quality – QC
– Blanks
– Duplicates
– Calibration Checks
– Proficiency Testing
Gas Chromatography
Chromatograms
Bio Fuel Sample with possible
PAHs Kerosene
Fuel Oil Diesel & Lube oil Diesel
Polar hydrocarbons
Oxygenated fuels
Non-Petroleum compounds
Biogenic material
Plant oils and waxes
Coal material
Fats
Possible Interferences in
TPH analysis
Cleaned up EPH and Mineral Oil
ISO Definition of mineral oil (drinking water):
Compounds in the range C10- C40 which are not
retained by a silica column, using a non-polar
solvent. Chemically, this consists of aliphatics (n-
alkanes, iso-alkanes and cyclo-alkanes) only.
A ‘cleaned up’ EPH requires a moderately polar
solvent for elution – only the polar NSO compounds
will be retained on the column
Speciation
Breakdown of TPH into narrow carbon band ranges (CWG)
Includes VPH and EPH
Includes aliphatics & aromatics
Used in risk assessment packages such as RBCA
Separation
NON-POLAR
SOLVENT
POLAR
SOLVENT
NSO’S (VERY
POLAR)
A A A
B B B
have more
affinity for solid
phase over
solvent
have more
affinity for
phase A over
solvent
have more
affinity for
solvent than
both phase A
and B
has no affinity for
either solid phase
and will elute with
solvent
has more affinity for
solvent and will
elute with solvent
VERY POLAR
SOLVENT
P.A.H’S (POLAR) MINERAL OIL
(NON-POLAR)
Image by ALcontrol Laboratories
Combined Aliphatic and Aromatic Standard
Aromatic Fraction
Aliphatic Fraction
TPH Screen by Rapid GC (C6 – C 40)
• Advantages
Rapid analysis
VPH & EPH in one run
Lower costs
• Disadvantages
Incomplete resolution of all peaks
Higher detection limits
Suitable for soils only
TPH – Forensics analysis
Four main questions: What is it? What was the source? When did it happen? Who was responsible?
Ageing = weathering + biodegradation
Ageing of petroleum products
Most Affected
C10-C20 n-alkanes
Alkylated aromatics
2 and 3 ring aromatics
Least Affected
C20+ alkanes
Cyclo naphthenes
C4-C6 ring aromatics
Most affected
C35-C10 alkanes
Least affected
Iso-prenoids
Pristane
Phytane
C6-C2 ring aromatics
Diesel – fresh and degraded
Most commonly used ratios:
nC17/Pristane
nC18/Phytane
Pristane/Phytane
Ageing of petroleum products
Images by ALcontrol Laboratories
GCFID Methods Advantages
Covers the full TPH range
Good sensitivity (10 ug/l for components)
Carbon chain speciation
Provides a fingerprint
Identify individual analytes i.e. BTEX
Identifies different products
Identifies degree of weathering
Good recovery efficiency
Disadvantages
Slower, and slightly more expensive
TPH Method Summary
VPH by headspace GC-FID – for gasoline
range organics (C5 – C10)
EPH by GC-FID for diesel and lube oil range
organics (C10 – C40)
Cleaned up EPH to remove polars
Speciated TPHCWG for aliphatic and aromatic
banding (C5 – C44)
TPH screen for VPH and EPH combined (C6 –
C40)
The Analysis of Total Petroleum
Hydrocarbons
Thank you
www.dets.co.uk