Review of Oil and Grease Analytical Procedures

1. REVIEW OF Oil and
Grease ANALYTICAL
PROCEDURES
PRESENTED BY:
AGNES A. MARALIT
LAB. SUPERVISOR
ESL

2.  In the determination of oil and grease, an absolute quantity of a specific
substance is not measured. Rather, groups of substances with similar
physical characteristics are determined quantitatively on the basis of their
common solubility in an organic extracting solvent.
 ‘‘Oil and grease’’ is defined as any material recovered as a substance
soluble in the solvent. It includes other material extracted by the solvent
from an acidified sample (such as sulfur compounds, certain organic dyes,
and chlorophyll) and not volatilized during the test.
 Certain constituents measured by the oil and grease analysis may
influence wastewater treatment systems. If present in excessive amounts,
they may interfere with aerobic and anaerobic biological processes and lead
to decreased wastewater treatment efficiency. When discharged in
wastewater or treated effluents, they may cause surface films and shoreline
deposits leading to environmental degradation.
 A knowledge of the quantity of oil and grease present is helpful in proper
design and operation of wastewater treatment systems and also may call
attention to certain treatment difficulties. In the absence of specially
modified industrial products, oil and grease is composed primarily of fatty
matter from animal and vegetable sources and from hydrocarbons of
petroleum origin.
5520 OIL AND GREASE

3. PRINCIPLE
 Dissolved or emulsified oil and grease is extracted from water by
intimate contact with an extracting solvent.
 Some extractables, especially unsaturated fats and fatty acids,
oxidize readily; hence, special precautions regarding temperature
and solvent vapor displacement are included to minimize this effect.
 Organic solvents shaken with some samples may form an emulsion
that is very difficult to break.
 This method includes a means for handling such emulsions.
Recovery of solvents is discussed.
 Solvent recovery can reduce both vapor emissions to the
atmosphere and costs.
5520 B. Liquid-liquid, Partition Gravimetric
Method

4. INTERFERENCES
 Some extractables, especially unsaturated fats and fatty acids,
oxidize readily; hence, special precautions regarding temperature
and solvent vapor displacement are included to minimize this effect
 Organic solvents shaken with some samples may form an emulsion
that is very difficult to break
 Solvent recovery can reduce both vapor emissions to the
atmosphere and cost
5520 B. Liquid-liquid, Partition Gravimetric
Method

5. SAMPLING AND HANDLING OF SAMPLES
 1-L glass bottled samples are brought to the lab that was sealed
with foil and a cap with 5mL of 1+1 HCl to bring pH t0 2.
 Samples should be @ 4◦C stored in a chiller for not more than 7
days prior to date received.
 Bring samples to room temp before analysis.
5520 B. Liquid-liquid, Partition Gravimetric
Method

6. APPARATUS/ MATERIALS
 Centrifuge
 Centrifuge tubes, 100-mL, glass
 Water bath, capable of maintaining 85°C
 Distilling adapter with drip tip
 Waste receptacle, for used solvent
5520 B. Liquid-liquid, Partition Gravimetric
Method

7. REAGENTS
 Hydrochloric or sulfuric acid, 1:1
 Methyl-tert-butyl ether (MTBE), boiling point 55°C to 56°C
 Sodium sulfate, Na2SO4, anhydrous crystal
 Solvent mixture, 80% n-hexane/20% MTBE, v/v.
5520 B. Liquid-liquid, Partition Gravimetric
Method

8. Desiccator
E-flask with sample
Weighing of QC

9. Water bath, capable of maintaining 70°C

10. Separatory funnel, 2-L, with TFE*#(117) stopcock
Distilling flask, 125-mL
Liquid funnel, glass
Filter paper, 11-cm diam.†#(118)

12. Sample Analysis
Mark the
glass
bottle to
determine
volume
and
transfer
the liquid
sample in
a 2 L
separatory
funnel
Rinse the
sample
bottle with
30mL of
petroleum
ether then
transfer
solvent
washing
to the
separatory
funnel
Shake
vigorously
for 2 mins
then let
the layer
separate.
Drain the
aqueous
layer to
the sample
bottle and
transfer
organic
layer to
the flask
Repeat
extraction
twice for
each
sample
then
transfer
the flask to
the stem
bath at
70◦C
If emulsion occurs, add small amount of 2-propanol then shake
until organic layer is visible
5520 B. Liquid-liquid, Partition Gravimetric
Method

13. PROCEDURE
1. Preparation of 125mL Erlenmeyer flask (constantly weighed)
2. 10.0g anhy. Na2SO4 for every sample (oven-dried @ 200◦C for
24hr)
3. 1.00xxg of Soybean oil added with 5mL 2-propanol and 5ml 1+1
HCl (QC sample)
5520 B. Liquid-liquid, Partition Gravimetric
Method

14. CALCULATION
mg oil & grease/L = Wf - Wi x 1000
Vs
Where:
Wf = total weight of flask and residue, minus the weight of flask, mg
Vs = initial sample volume, L
5520 B. Liquid-liquid, Partition Gravimetric
Method

15. METHOD VERIFICATION:
MEASUREMENT UNCERTAINTY:
5520 B. Liquid-liquid, Partition Gravimetric
Method

16. REFERENCE:
 American Public Health Association, American Water Works Association and Water
Environment Federation. 2012: Standard Methods for the Examination of Water and
Wastewater. 22nd ed.: American Public Health Association 800 I Street, NW
Washington, DC 20001-3710; p.2-64.
5520 B. Liquid-liquid, Partition Gravimetric
Method