• 16 •
800-356-1688 •
2005vol. 1
NewReferenceMixes forDeterminationof
ChlorinatedDisinfectionByproducts,
ChlorinatedSolvents,orHalogenated
Pesticides inDrinkingWater
by John Lidgett, Analytical ReferenceMaterialsTechnical Specialist
•Complete set of high concentration referencematerials for US EPAMethod 551.1.
•Target pesticides/herbicides at equal concentration, for GC/MS analysis.
•Chloral hydrate andmetribuzin offered as separate solutions, for assured stability.
Chlorine has been used
to disinfect drinking
water formany years.
Chlorinating agents,
however, can form
harmful and potentially
carcinogenic byprod-
uctswith organic com-
pounds inwater, and
this potential led toUS
Environmental
Protection Agency regulation in 1979.
1
Extensive
research has been done on the origination of
disinfection byproducts (DBPs), and on prevent-
ing their formation. DBPs can form by reaction
of chlorinewith naturally present organic com-
pounds inwater, such as humic acid or fulvic
acid - organic compounds found inwater as a
result of decomposition of plant matter.
Disinfection byproducts include 3 groups of
compounds: trihalomethanes (THMs), haloace-
tonitriles, and amixed group that includes chlo-
ral hydrate, chloropicrin, and chloropropanones.
Many other DBPs, including haloacetic acids,
haloacetaldehydes, cyanogen halides, aldehy-
des, ketoacids, chlorite, bromate, and other
organic and inorganic compounds also have
been identified in chlorinated or ozonated drink-
ingwater.
2
Several US EPAmethods regulate themonitor-
ing of drinkingwater, includingmethods 502.2,
524.1, 551.1, and 552.2. In addition toTHMs,
Method 551.1 is followed formonitoring chlori-
nated solvents and halogenated pesticides/her-
bicides. EPAMethod 551 requires liquid-liquid
extractionwithmethyl-
tert
-butyl ether (MTBE)
as a primary extraction solvent and analysis by
GC, using electron capture detection (ECD).The
latest version of Method 551, Method 551.1,
allows pentane to be used as the extraction sol-
vent if chloral hydrate is not being analyzed.
Qualitative confirmation of the target com-
pounds is required by GC/MS analysis or by GC
on two dissimilar columns.The listed primary
analytical column is a bondedmethyl polysilox-
ane stationary phase Restek column, Rtx
®
-1
(30m, 0.25mm ID, 1.0µm film, cat.# 10153); the
listed confirmation column is a bonded 6%
cyanopropylphenyl / 94% dimethyl polysiloxane
stationary phase Restek column, Rtx
®
-1301
(30m, 0.25mm ID, 1.0µm film, cat.# 16053).
Restek chemists have formulated three new cal-
ibrationmixes, Disinfection Byproducts &
Chlorinated SolventsMix (cat.# 30615),
Disinfection ByproductsMix (cat.# 30616), and
Method 551.1 Pesticide/HerbicideMix (cat.#
32438), to include all but twoMethod 551.1 tar-
get compounds, based on enhanced stability and
the testing requirements of our customers.We
prepare the three new solutions in acetone,
becausemethanol causes degradation of most
haloacetonitriles, and acetone should be used
for primary dilution in preparingworking solu-
tions. Bromochloroacetonitrile, a target com-
poundwe include in two of our newmixes
(DisinfectionByproducts&Chlorinated Solvents
Mix, DisinfectionByproductsMix) is not available
commercially at purity higher than 89%.
Dichloroacetonitrile and dibromoacetonitrile are
both target compounds in the calibrationmixes
and impurities in bromochloroacetonitrile, at 0.5
to 2.2%. After careful review, we determined that
Method 551.1 allows a 4% concentration error
and, based on this information, we have included
bromochloroacetonitrile in both referencemate-
rials after compensating for the impurities.
Because chloral hydrate is unstable, due to
hydrogen-bond interactionswith halide ions, we
offer it as a separate solution. After several
months of stability studies, using various sol-
vents, we determined that chloral hydrate
should be offered in acetonitrile, andwe seal
the referencematerial in light-resistant ampuls
as defined in theUnited States Pharmacopoeia
(USP).When using chloral hydrate all working
solutions and glassware should be free of alka-
line substances and the referencematerial
should be stored away from heat, because heat-
ing chloral hydratewith alkali produces chloro-
form. Note that chloral hydrate is a hypnotic
depressant included in Schedule IV of the
Controlled Substance Act.We have the required
license and exception approval to offer chloral
hydrate as a referencematerial.
For stability, we also offer another compound in
this interest group, metribuzin, as a separate
mix (cat.# 32436). In earlier studieswe deter-
mined that metribuzin could react with certain
pesticides/herbicides at high concentration.
We offer an internal standard, bromofluoroben-
zene, and a surrogate standard, decafluoro-
biphenyl, in acetone, permethod recommenda-
tions.Themethod recommends the use of a lab-
oratory performance check (LPC) solution in
MTBE, the extraction solvent.The check solution
is amix of method analytes used to evaluate the
performance of the instrument.The parameters
evaluated are instrument sensitivity, chromato-
graphic performance, column performance, and
analyte breakdown. Special caremust be taken
when analyzing endrin, a component in our new
pesticide/herbicidemix, because it can break
down to aldo and keto derivatives on contact
with activemetal sites in the injection port.The
analyzed value of each compound in the check
solution should be 95% to 105% of its expected
value. For analysts using pentane as the extrac-
tion solvent, we offer the laboratory perform-
ance check solution in pentane. Analysis of the
LPC solution is especially difficult because of the
substantial range in concentration (0.2 to 83
µg/mL) of the components. Because of the high
sensitivity and narrow range of linear detection
of the ECD, and the possibility of coelution of
solvent impuritieswith some of the target com-
pounds, we use high purityMTBE and pentane in
preparing the LPC solutions.
Our complete set of referencematerials for
determiningMethod 551.1 target compounds is
listed on page 17. If you are analyzing for disin-
fection byproducts, chlorinated solvents, or
chlorinated pesticides/herbicides, we highly
recommend these carefully prepared standards.
We also offer Rtx
®
-1 and Rtx
®
-1301 capillary
columns, which are ideal for the analysis, and
are listed inMethod 551.1.
References
1.
US Environmental Protection Agency National Interim
Primary DrinkingWater Regulations: Control of
Trihalomethanes inDrinkingWater, Final Rule
Fed. Reg. 44
(231): 68624 (1979).
2. Yue Feng Xie,
Disinfection By-Product Analysis inDrinking
Water
American Laboratory, Nov. 2000, p. 50.
new
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