ANALYTICAL
METHOD
FOR
TURBIDITY
MEASUREMENT
METHOD
180.1
JUNE
2003
DRAFT
Draft
June
2003
1
Analytical
Method
for
Turbidity
Measurement
Method
180.1
1.
Scope
and
Application
1.1
This
method
is
applicable
to
drinking
water
samples
in
the
range
of
turbidity
from
0
to
40
nephelometric
units
(
NTU).
Higher
values
may
be
obtained
with
dilution
of
the
sample.
A
method
detection
limit
of
0.100
NTUs
is
recommended
for
this
procedure.

NOTE:
NTUs
are
considered
comparable
to
the
previously
reported
Formazin
Turbidity
Units
(
FTU).

1.2
This
method
covers
the
determination
of
turbidity
in
drinking,
ground,
surface,
and
saline
waters,
domestic
and
industrial
wastes.

2.
Summary
of
Method
2.1
The
method
is
based
upon
a
comparison
of
the
intensity
of
light
scattered
by
the
sample
under
defined
conditions
with
the
intensity
of
light
scattered
by
a
standard
reference
suspension.
The
higher
the
intensity
of
the
scattered
light,
the
higher
the
turbidity.
Readings,
in
NTUs,
are
made
in
a
nephelometer
designed
according
to
specifications
outlined
in
"
APPARATUS."
A
standard
suspension
of
Formazin,
prepared
under
closely
defined
conditions,
is
used
to
calibrate
the
instrument.

2.1.1
Formazin
polymer
is
used
as
the
turbidity
reference
suspension
for
water
because
it
is
more
reproducible
than
other
types
of
standards
previously
used
for
turbidity
standards.

2.1.2
A
commercially
available
polymer
primary
standard
is
also
approved
for
use
for
the
National
Interim
Primary
Drinking
Water
Regulations.
This
standard
is
identified
as
AMCO­
AEPA­
1,
available
from
Advanced
Polymer
Systems.

3.
Sample
Handling
and
Preservation
3.1
Collect
each
sample
in
a
soft
or
hard
plastic,
or
soft
or
hard
glass
container.
Immediately
refrigerate
or
ice
the
sample
to
4
º
C
and
analyze
within
48
hours.

4.
Conditions
Affecting
Turbidity
Reading
4.1
The
presence
of
floating
debris
and
coarse
sediments,
which
settle
out
rapidly,
will
give
low
readings.
Finely
divided
air
bubbles
will
affect
the
results
in
a
positive
manner.

4.2
The
presence
of
color,
that
is
the
color
of
water
which
is
due
to
dissolved
substances
which
absorb
light,
will
cause
turbidities
to
be
low,
although
this
effect
is
generally
not
significant.
Draft
June
2003
2
4.3
Light
absorbing
materials
such
as
activated
carbon
in
significant
concentrations
can
cause
low
readings.

5.
Apparatus
5.1
The
turbidimeter
shall
consist
of
a
nephelometer,
with
light
source
for
illuminating
the
sample,
and
one
or
more
photo­
electric
detectors
with
a
readout
device
to
indicate
the
intensity
of
light
scattered
at
right
angles
to
the
path
of
the
incident
light.
The
turbidimeter
should
be
designed
so
that
little
stray
light
reaches
the
detector
in
the
absence
of
turbidity
and
should
be
free
from
significant
drift
after
a
short
warm­
up
period.

5.2
Differences
in
physical
design
of
turbidimeters
will
cause
differences
in
measured
values
for
turbidity,
even
though
the
same
suspension
is
used
for
calibration.
To
minimize
such
differences,
the
following
design
criteria
should
be
observed:

5.2.1
Light
source:
Tungsten
lamp
operated
at
a
color
temperature
between
2200­
3000
°
K.

5.2.2
Distance
traversed
by
incident
light
and
scattered
light
within
the
sample
tube:
Total
not
to
exceed
10
cm.

5.2.3
Detector:
Centered
at
90
°
to
the
incident
light
path
and
not
to
exceed
±
30
°
from
90
°
.
The
detector,
and
filter
system
if
used,
shall
have
a
spectral
peak
response
between
400
nm
and
600
nm.

5.3
The
sensitivity
of
the
instrument
should
permit
detection
of
a
turbidity
difference
of
0.02
NTU
or
less
in
waters
having
turbidities
less
than
1
unit.
The
instrument
should
measure
from
0­
40
units
turbidity.
Several
ranges
may
be
necessary
to
obtain
both
adequate
coverage
and
sufficient
sensitivity
for
low
turbidities.

5.4
The
sample
tubes
to
be
used
with
the
available
instrument
must
be
of
clear,
colorless
optical
glass.
They
should
be
kept
scrupulously
clean,
both
inside
and
out,
and
discarded
when
they
become
scratched
or
etched.
They
must
not
be
handled
at
all
where
the
light
strikes
them,
but
should
be
provided
with
sufficient
extra
length,
or
with
a
protective
case,
so
that
they
may
be
handled.
Tubes
should
be
checked,
indexed
and
read
at
the
orientation
that
produces
the
lowest
background
blank
value.

6.
Reagents
6.1
Reagent
water,
turbidity­
free:
Pass
deionized
distilled
water
through
a
0.45:
pore
size
membrane
filter,
if
such
filtered
water
shows
a
lower
turbidity
than
unfiltered
distilled
water.

6.2
Stock
standard
suspension
(
Formazin):

6.2.1
Dissolve
1.00
g
hydrazine
sulfate,
(
NH2)
2.
H2SO4,
(
CASRN
10034­
93­
2)
in
reagent
water
and
dilute
to
100
mL
in
a
volumetric
flask.
CAUTION
­­
carcinogen.
Draft
June
2003
3
6.2.2
Dissolve
10.00
g
hexamethylenetetramine
(
CASRN
100­
97­
0)
in
reagent
water
and
dilute
to
100
mL
in
a
volumetric
flask.
In
a
100
mL
volumetric
flask,
mix
5.0
mL
of
each
solution
(
Sections
6.2.1
and
6.2.2).
Allow
to
stand
24
hours
at
25
±
3
°
C,
then
dilute
to
the
mark
with
reagent
water.

6.3
Primary
calibration
standards:
Mix
and
dilute
10.00
mL
of
stock
standard
suspension
(
Section
7.2)
to
100
mL
with
reagent
water.
The
turbidity
of
this
suspension
is
defined
as
40
NTU.
For
other
values,
mix
and
dilute
portions
of
this
suspension
as
required.

6.3.1
A
new
stock
standard
suspension
(
Section
6.2)
should
be
prepared
each
month.
Primary
calibration
standards
(
Section
6.3)
should
be
prepared
daily
by
dilution
of
the
stock
standard
suspension.

6.4
Formazin
in
commercially
prepared
primary
concentrated
stock
standard
suspension
(
SSS)
may
be
diluted
and
used
as
required.
Dilute
turbidity
standards
should
be
prepared
daily.

6.5
AMCO­
AEPA­
1
Styrene
Divinylbenzene
polymer
primary
standards
are
available
for
specific
instruments
and
require
no
preparation
or
dilution
prior
to
use.

6.6
Secondary
standards
may
be
acceptable
as
a
daily
calibration
check,
but
must
be
monitored
on
a
routine
basis
for
deterioration
and
replaced
as
required.

7.
Procedure
7.1
Turbidimeter
calibration:
The
manufacturer's
operating
instructions
should
be
followed.
Measure
standards
on
the
turbidimeter
covering
the
range
of
interest.
If
the
instrument
is
already
calibrated
in
standard
turbidity
units,
this
procedure
will
check
the
accuracy
of
the
calibration
scales.
At
least
one
standard
should
be
run
in
each
instrument
range
to
be
used.
Some
instruments
permit
adjustments
of
sensitivity
so
that
scale
values
will
correspond
to
turbidities.
Solid
standards,
such
as
those
made
of
lucite
blocks,
should
never
be
used
due
to
potential
calibration
changes
caused
by
surface
scratches.
If
a
pre­
calibrated
scale
is
not
supplied,
then
calibration
curves
should
be
prepared
for
each
range
of
the
instrument.

7.2
Turbidities
less
than
40
units:
If
possible,
allow
samples
to
come
to
room
temperature
before
analysis.
Shake
the
sample
to
thoroughly
disperse
the
solids.
Wait
until
air
bubbles
disappear.
Then
pour
the
sample
into
the
turbidimeter
tube.
Read
the
turbidity
directly
from
the
instrument
scale
or
from
the
appropriate
calibration
curve.

7.3
Turbidities
exceeding
40
units:
Dilute
the
sample
with
one
of
more
volumes
of
turbidity­
free
water
until
the
turbidity
falls
below
40
units.
The
turbidity
of
the
original
sample
is
then
computed
from
the
turbidity
of
the
diluted
sample
and
the
dilution
factor.
For
example,
if
5
volumes
of
turbidity­
free
water
were
added
to
1
volume
of
sample,
and
the
diluted
sample
showed
a
turbidity
of
30
units,
then
the
turbidity
of
the
original
sample
was
180
units.
Draft
June
2003
4
8.
Calculations
8.1
Nephelometric
turbidity
units
(
NTU)

=
A
x
(
B
+
C)
where:
A
=
NTU
found
in
diluted
sample
C
B
=
volume
of
dilution
water,
in
mL
C
=
sample
volume
taken
for
dilution,
in
mL
8.2
Report
results
as
follows:

NTU
Record
to
Nearest
0.0
­
1.0
0.05
1
­
10
0.1
10
­
40
1
40
­
100
5
100
­
400
10
400
­
1000
50
>
1000
100
9.
Precision
and
Accuracy
9.1
In
a
single
laboratory
(
EMSL­
Cincinnati),
using
surface
water
samples
at
levels
of
26,
41,
75,
and
180
NTU,
the
standard
deviations
were
±
0.60,
±
0.94,
±
1.2,
and
±
4.7
units,
respectively.

9.2
The
interlaboratory
precision
and
accuracy
data
in
Table
1
were
developed
using
a
reagent
water
matrix.
Values
are
in
NTU.

10.
Safety
10.1
The
toxicity
or
carcinogenicity
of
each
reagent
used
in
this
method
has
not
been
fully
established.
Each
chemical
should
be
regarded
as
a
potential
health
hazard
and
exposure
should
be
as
low
as
reasonably
achievable.

10.2
Each
laboratory
is
responsible
for
maintaining
a
current
awareness
file
of
OSHA
regulations
regarding
the
safe
handling
of
the
chemicals
specified
in
this
method.
A
reference
file
of
Material
Safety
Data
Sheets
(
MSDS)
should
be
made
available
to
all
personnel
involved
in
the
chemical
analysis.
The
preparation
of
a
formal
safety
plan
is
also
advisable.

10.3
Hydrazine
Sulfate
(
Section
6.2.1)
is
a
carcinogen.
It
is
highly
toxic
and
may
be
fatal
if
inhaled,
swallowed,
or
absorbed
through
the
skin.
Formazin
can
contain
residual
hydrazine
sulfate.
Proper
protection
should
be
employed.
Draft
June
2003
5
11.
Quality
Assurance
11.1
Each
laboratory
using
this
method
in
regulated
environmental
monitoring
is
required
to
operate
a
formal
quality
assurance/
control
program.
The
minimum
initial
requirements
of
this
program
consist
of
the
demonstration
of
the
laboratory's
capability
with
this
method.
On
a
continuing
basis,
the
laboratory
should
check
its
performance
(
accuracy
and
precision)
by
analyzing
reagent
blanks
and
check
standards,
fortified
blanks,
and/
or
fortified
samples,
preferably
at
a
minimum
frequency
of
10%
of
the
total
samples
analyzed
by
the
method.
The
laboratory
should
maintain
the
performance
records
that
define
the
quality
of
the
data
generated
with
the
method.

12.
Pollution
Prevention
12.1
Pollution
prevention
encompasses
any
technique
that
reduces
or
eliminates
the
quantity
or
toxicity
of
waste
at
the
point
of
generation.
Numerous
opportunities
for
pollution
prevention
exist
in
laboratory
operation.
The
EPA
has
established
a
preferred
hierarchy
of
environmental
management
techniques
that
places
pollution
prevention
as
the
management
option
of
first
choice.
Whenever
feasible,
laboratory
personnel
should
use
pollution
prevention
techniques
to
address
their
waste
generation.
When
wastes
cannot
be
feasibly
reduced
at
the
source,
the
Agency
recommends
recycling
as
the
next
best
option.

12.2
The
quantity
of
chemicals
purchased
should
be
based
on
expected
usage
during
its
shelf
life
and
disposal
cost
of
unused
material.
Actual
reagent
preparation
volumes
should
reflect
anticipated
usage
and
reagent
stability.

12.3
For
information
about
pollution
prevention
that
may
be
applicable
to
laboratories
and
research
institutions,
consult
"
Less
is
Better:
Laboratory
Chemical
Management
for
Waste
Reduction,"
available
from
the
American
Chemical
Society's
Department
of
Government
Regulations
and
Science
Policy,
1155
16th
Street
N.
W.,
Washington
D.
C.
20036,
(
202)
872­
4477.

13.
Waste
Management
13.1
The
U.
S.
Environmental
Protection
Agency
requires
that
laboratory
waste
management
practices
be
conducted
consistent
with
all
applicable
rules
and
regulations.
Excess
reagents,
samples
and
method
process
wastes
should
be
characterized
and
disposed
of
in
an
acceptable
manner.
The
Agency
urges
laboratories
to
protect
the
air,
water
and
land
by
minimizing
and
controlling
all
releases
from
hoods,
and
bench
operations,
complying
with
the
letter
and
spirit
of
any
waste
discharge
permit
and
regulations,
and
by
complying
with
all
solid
and
hazardous
waste
regulations,
particularly
the
hazardous
waste
identification
rules
and
land
disposal
restrictions.
For
further
information
on
waste
management
consult
the
"
Waste
Management
Manual
for
Laboratory
Personnel,"
available
from
the
American
Chemical
Society
at
the
address
listed
in
Section
12.3.
Draft
June
2003
6
Bibliography
1.
Annual
Book
of
ASTM
Standards,
Volume
11.01
Water
(
1),
Standard
D1889­
88A,
p.
359,
(
1993).

2.
Standard
Methods
for
the
Examination
of
Water
and
Wastewater,
18th
Edition,
pp.
2­
9,
Method
2130B,
(
1992).

3.
Standard
Methods
for
the
Certification
of
Laboratories
Analyzing
Drinking
Water:
Criteria
and
Procedures,
Quality
Assurance,
EPA/
570/
9­
90/
008,
April,
1990.

14.0
Tables,
Diagrams,
Flowcharts
and
Validation
Data
TABLE
1.
INTERLABORATORY
PRECISION
AND
ACCURACY
DATA
Number
of
Values
Reported
True
Value
(
T)
Mean
(
X)
Residual
for
X
Standard
Deviation
(
S)
Residual
for
S
373
0.450
0.4864
0.0027
0.1071
­
0.0078
374
0.600
0.6026
­
0.0244
0.1048
­
0.0211
289
0.65
0.6931
0.0183
0.1301
0.0005
482
0.910
0.9244
0.0013
0.2512
0.1024
484
0.910
0.9919
0.0688
0.1486
­
0.0002
489
1.00
0.9405
­
0.0686
0.1318
­
0.0236
640
1.36
1.3456
­
0.0074
0.1894
0.0075
487
3.40
3.2616
­
0.0401
0.3219
­
0.0103
288
4.8
4.5684
­
0.0706
0.3776
­
0.0577
714
5.60
5.6984
0.2952
0.4411
­
0.0531
641
5.95
5.6026
­
0.1350
0.4122
­
0.1078
REGRESSIONS:
X
=
0.955T
+
0.54,
S
=
0.074T
+
0.082
