Safety Practices Using Organic
Solvents in Flame Atomic Absorption
Spectroscopy
Author
Trevor McKenzie
Application Note
Atomic Absorption
Introduction
Atomic absorption spectroscopy has found broad acceptance in the analysis of
petroleum products and the determination of metals after organic solvent extraction. These analytical methods have been carried out in reasonable safety over
many years, but there is no doubt that the combination of an open flame and flammable solvents is potentially very dangerous. Chemists working with this combination are characteristically aware of the potential hazards, and the majority is
extremely safety-conscious. But, humans are fallible; even the most careful analyst
can sometimes be lulled into a false sense of security; even the most thoughtful
chemist can be forgetful; and even the most disciplined worker may suffer a lapse of
safety awareness.
With the increasing work burden now being placed on analytical laboratories, it
seems opportune to remind analysts of the constant need for safe working practices
when using flammable solvents in the presence of a naked flame. We hope that the
following notes will help to promote safety awareness in laboratories, and remind
analysts of factors that can so easily be overlooked in any analytical program
involving flammable solvents.
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6. Never aspirate chlorinated hydrocarbons such as chloroform or carbon tetrachloride since they will readily
decompose in the flame to produce phosgene-an
extremely hazardous compound.
7. Gasoline, carbon-disulfide and tetrahydrofuran (THF)
must not be aspirated directly as these have very low
flash points and can create an extreme fire hazard.
8. Use small waste vessels; empty them frequently; ensure
that your waste vessel is at a safe distance from the
instrument. Locate your waste vessel in an open, ventilated position where you can see it. Never locate the
vessel in a confined space. Use Buna N tubing for the
drain tube, and always secure the tube to the liquid trap
outlet with a hose clamp.
9. A vent tube of solvent resistant material must be connected to the vapor vent on the liquid trap and led to a
location where organic solvent vapors can be safely discharged. Secure the tubing to the trap vent with a hose
clamp.
10. When your analytical program has been completed:
a. Turn the flame off exactly as described in your
spectrophotometer operation manual.
b. Remove all samples from the vicinity of the instrument.
c. Allow the burner to cool.
d. Use protective gloves and remove the burner from the
spray chamber.
e. Detach the liquid trap from the spray chamber and
pour the organic solvent into an organic waste
container. Ensure that the liquid trap is emptied.
1. All relevant safety regulations governing the use of flammable solvents must be strictly followed.
2. When initially selecting an organic solvent, choose a solvent having the highest flash point possible consistent
with your analytical requirements. Note that recent methods have been developed for the determination of metals
in oils and gasoline, which do not require conventional
flammable solvents [6]. The sample is emulsified using
Emulsogen LBH, or Emulsifier MS 112 (Hoechst) and the
resultant gel can be quickly dispersed in water. The procedure allows aqueous standards to be used, and the
emulsions are reported to remain stable for several
months.
3. Never use a solvent having a specific gravity lower than
0.75, otherwise the liquid seal can be breached. This can
cause a flashback and create an explosion or fire hazard.
4. Never leave uncovered containers of flammable solvent
standing near the burner. When aspirating such solvents
always use a narrow-necked vessel or a container and
feed the capillary tubing through a 2 mm diameter hole in
the cover. Always use the smallest volume of solvent
consistent with your analytical requirements, ensuring
the sample vessel is sealed when the sample is not being
aspirated.
5. Never prepare organic samples and standards in or near
the atomic absorption spectrophotometer or any other
ignition source. Samples should be prepared in another
room or on another laboratory bench completely separated from the atomic absorption spectrophotometer. On
completion of the sample preparation the organic
reagents must be returned to a storage area away from
the vicinity of the atomic absorption spectrophotometer.
It is advisable to carry out organic sample preparations in
a fume cupboard.
Table 1. Organic Solvents Widely Used in Flame Atomic Absorption: (The Flash Point is the Lowest Temperature at Which the Liquid Gives Sufficient Vapor to
Form an Ignitable Mixture with Air and Produce a Flame when an Ignition Source is Brought Near the Surface of the Liquid)
Solvent Flash point (ºC) Boiling point (ºC) Specific gravity
4-methyl-pentan-2-one (MIBK) 22 118 0.79
2-methyl, propan-1-ol 23 108 0.78
m-xylene 29 139 0.80
cyclohexanone 34 155 0.948
kerosene 39–74 175–325 0.78
iso-amylalcohol 43 132 0.81
3-heptanone (ethylbutylketone) 46 148 0.818
Shellsol T 50 186–214 0.75
2, 6-dimethyl,heptan-4-one (DIBK) 60 166 0.806
cyclohexanol 68 161 0.96
tetrahydronaphthalene (Tetralin) 71 207 0.97
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f. Clean the liquid trap, spray chamber and nebulizer
bung thoroughly with alcohol so that all traces of the
original organic residues are removed.
g. Re-assemble the spray chamber, liquid trap and nebu-
lizer bung exactly as described in your
spectrophotometer operation manual.
h. If you are proposing to leave the instrument unused,
fill the liquid trap with water. NEVER leave hazardous
solutions standing in the liquid trap. If you are proposing to carry out another analytical program, fill the
liquid trap with the same solvent being used for your
samples.
i. Empty the waste vessel and ensure that all organic
residues are removed.
11. Ensure that nitric or perchloric acid residues are not
mixed with organic residues.
12. Always keep the burner slot clear of carbon or other
solids. Progressive burner blockage can increase the
static pressure in the liquid trap to the point at which the
liquid seal is breached.
13. Do not attempt to clean the burner while the flame is
burning.
14. Never leave a flame unattended.
Notes
It is thoroughly bad practice to attempt to alternate directly
between analyses using organic solvents and aqueous solutions. Always follow procedure number 10 so that the complete spray chamber system will be ready for use with another
organic solvent program or an aqueous solution program.
Some organic solvents such as MIBK and xylene may distort
the spray chamber and associated polypropylene components. In laboratories where such solvents are continually
used, an additional, complete spray chamber should be made
available. The two complete spray chamber assemblies can
then be used alternately on the shortest practicable working
cycle. While one assembly is being employed, the other can
be stripped down and left in a fume cupboard for the duration
of its off-duty cycle. The drying out process should effectively
remove any temporary distortion caused by the absorption of
solvent.
All other safety requirements noted in your operation
manual must be observed.
References
1. J. A. Riddick, E. E. Toops, Organic Solvents, Interscience,
New York, 1955.
2. L. Scheflan, M. B. Jacobs, Handbook of Solvents, Van
Nostrand, New York, 1953.
3. C. Marsden, S. Mann, Solvents Guide, Interscience, New
York 1963.
4. R. C. West (ed), Handbook of Chemistry and Physics,
C.R.C. Press Cleveland, Ohio
5. Fundamentals of Industrial Hygiene, National Safety
Council, 444 North Michigan Ave, IL, U.S.A.
6. Z. Fresenius, Anal. Chem., 294, 416 (1979)
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© Agilent Technologies, Inc., 1980
Printed in the USA
November 1, 2010
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