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2005 vol. 1

New Reference Mixes for Determination of

Chlorinated Disinfection Byproducts,

Chlorinated Solvents, or Halogenated

Pesticides in DrinkingWater

by John Lidgett, Analytical Reference Materials Technical Specialist

•Complete set of high concentration reference materials for US EPA Method 551.1.

• Target pesticides/herbicides at equal concentration, for GC/MS analysis.

•Chloral hydrate and metribuzin offered as separate solutions, for assured stability.

Chlorine has been used

to disinfect drinking

water for many years.

Chlorinating agents,

however, can form

harmful and potentially

carcinogenic byprod-

ucts with organic com-

pounds in water, and

this potential led to US

Environmental

Protection Agency regulation in 1979.

Extensive

research has been done on the origination of

disinfection byproducts (DBPs), and on prevent-

ing their formation. DBPs can form by reaction

of chlorine with naturally present organic com-

pounds in water, such as humic acid or fulvic

acid - organic compounds found in water as a

result of decomposition of plant matter.

Disinfection byproducts include 3 groups of

compounds: trihalomethanes (THMs), haloace-

tonitriles, and a mixed 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-

ing water.

Several US EPA methods regulate the monitor-

ing of drinking water, including methods 502.2,

524.1, 551.1, and 552.2. In addition to THMs,

Method 551.1 is followed for monitoring chlori-

nated solvents and halogenated pesticides/her-

bicides. EPA Method 551 requires liquid-liquid

extraction with methyl-

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 bonded methyl 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-

ibration mixes, Disinfection Byproducts &

Chlorinated Solvents Mix (cat.# 30615),

Disinfection Byproducts Mix (cat.# 30616), and

Method 551.1 Pesticide/Herbicide Mix (cat.#

32438), to include all but two Method 551.1 tar-

get compounds, based on enhanced stability and

the testing requirements of our customers. We

prepare the three new solutions in acetone,

because methanol causes degradation of most

haloacetonitriles, and acetone should be used

for primary dilution in preparing working solu-

tions. Bromochloroacetonitrile, a target com-

pound we include in two of our new mixes

(Disinfection Byproducts & Chlorinated Solvents

Mix, Disinfection Byproducts Mix) is not available

commercially at purity higher than 89%.

Dichloroacetonitrile and dibromoacetonitrile are

both target compounds in the calibration mixes

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 reference mate-

rials after compensating for the impurities.

Because chloral hydrate is unstable, due to

hydrogen-bond interactions with 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, and we seal

the reference material in light-resistant ampuls

as defined in the United States Pharmacopoeia

(USP). When using chloral hydrate all working

solutions and glassware should be free of alka-

line substances and the reference material

should be stored away from heat, because heat-

ing chloral hydrate with 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 reference material.

For stability, we also offer another compound in

this interest group, metribuzin, as a separate

mix (cat.# 32436). In earlier studies we 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, per method recommenda-

tions. The method recommends the use of a lab-

oratory performance check (LPC) solution in

MTBE, the extraction solvent. The check solution

is a mix 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 care must be taken

when analyzing endrin, a component in our new

pesticide/herbicide mix, because it can break

down to aldo and keto derivatives on contact

with active metal 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 impurities with some of the target com-

pounds, we use high purity MTBE and pentane in

preparing the LPC solutions.

Our complete set of reference materials for

determining Method 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 in Method 551.1.

References

US Environmental Protection Agency National Interim

Primary Drinking Water Regulations: Control of

Trihalomethanes in Drinking Water, Final Rule

Fed. Reg. 44

(231): 68624 (1979).

2. Yue Feng Xie,

Disinfection By-Product Analysis in Drinking

Water

American Laboratory, Nov. 2000, p. 50.

new