ANALYTICAL
METHOD
FOR
TURBIDITY
MEASUREMENT
GLI
METHOD
2
JUNE
2003
DRAFT
Draft
June
2003
1
Analytical
Method
for
Turbidity
Measurement
GLI
Method
2
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).

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.

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.

5.
Apparatus
5.1
The
turbidimeter
shall
consist
of
a
nephelometer
with
two
light
sources
for
illuminating
the
sample
and
two
detectors
with
a
readout
device
to
indicate
the
intensity
of
light
scattered
at
right
angles
to
the
path
of
the
incident
light.
The
turbidimeter
shall
accomplish
two
measurement
phases
every
0.5
seconds
(
see
Figure
1).

In
the
first
phase,
Light
Source
#
1
shall
pulse
a
beam
of
light
directly
into
Photodetector
#
2.
Simultaneously,
Photodetector
#
1
shall
measure
the
light
scattered
at
a
90
degree
angle.
Diffused
light
measured
by
Photodetector
#
2
shall
be
called
a
reference
signal
while
scattered
light
measured
by
Photodetector
#
1
shall
be
called
an
active
signal.
Draft
June
2003
2
In
the
second
phase,
Light
Source
#
2
shall
pulse
a
beam
of
light
directly
into
Photodetector
#
1.
Simultaneously,
Photodetector
#
2
shall
measure
the
light
scattered
at
a
90
degree
angle.
This
time,
the
diffused
light
measured
by
Photodetector
#
1
shall
be
called
a
reference
signal
and
scattered
light
measured
by
Photodetector
#
2
shall
be
called
an
active
signal.

The
two­
phase
measurement
shall
provide
four
independent
measurements
from
the
two
light
sources;
two
reference
signals
and
two
active
signals.
A
"
ratiometric"
algorithm
will
then
be
used
to
calculate
the
turbidity
value
from
these
four
measurements.

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

5.3
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.

5.4
Any
apparatus
may
be
used,
provided
that
it
complies
with
the
following
requirements:

5.4.1
The
wavelength
of
the
incident
radiation
shall
be
860
nm;

5.4.2
The
spectral
bandwidth
of
the
incident
radiation
shall
be
less
than
or
equal
to
60
nm;

5.4.3
There
shall
be
no
divergence
from
parallelism
of
the
incident
radiation
and
any
convergence
shall
not
exceed
1.5
degrees;
Draft
June
2003
3
5.4.4
There
shall
be
two
light
sources
and
two
detectors;

LIGHT
SOURCE
#
1
PHOTO
DETECTOR
#
1
LIGHT
SOURCE
#
2
PHOTO
DETECTOR
#
2
PHASE
1
PHASE
2
90
°
±
2.5
°
180
°
180
°
90
°
±
2.5
°
LIGHT
SOURCE
#
1
PHOTO
DETECTOR
#
1
LIGHT
SOURCE
#
2
PHOTO
DETECTOR
#
2
Figure
1
5.4.5
The
measuring
angle
between
the
optical
axis
of
the
incident
radiation
and
that
of
the
diffused
radiation
for
light
pulsed
through
the
sample
by
Light
Source
#
1
shall
be
90
±
2.5
degrees;

5.4.6
The
measuring
angle
between
the
optical
axis
of
the
incident
radiation
and
that
of
the
diffused
radiation
for
light
pulsed
through
the
sample
by
Light
Source
#
2
shall
be
90
±
2.5
degrees.

The
narrow
definition
of
the
light
source
makes
it
unnecessary
to
specify
sensitivity
of
the
photodetector.

6.
Reagents
6.1
Turbidity­
free
water:
Pass
distilled
water
through
a
membrane
filter
having
precision­
sized
holes
of
0.2
:
m;
the
usual
membrane
filter
used
for
bacterial
examinations
is
not
satisfactory
(
Sec.
3.1,
EPA­
approved
Standard
Method
214A,
16th
edition).

6.2
Stock
formazin
turbidity
suspension:

Solution
1:
Dissolve
1.00
g
hydrazine
sulfate,
(
NH2)
H2S04,
in
distilled
water
and
dilute
to
100
mL
in
a
volumetric
flask.

Solution
2:
Dissolve
10.00
g.
hexamethylenetetramine
in
distilled
water
and
dilute
to
100
mL
in
a
volumetric
flask.
In
a
100
mL
volumetric
flask,
mix
5.0
mL
Solution
1
with
5.0
mL
Solution
2.
Allow
to
stand
24
hours
at
24
degrees
C
±
2.5
degrees,
then
dilute
to
the
mark
and
mix.

6.3
Standard
formazin
turbidity
suspension:
Dilute
10.00
mL
stock
turbidity
suspension
to
100
mL
with
turbidity­
free
water.
The
turbidity
of
this
suspension
is
defined
as
40
units.
Dilute
portions
of
the
standard
turbidity
suspension
with
turbidity­
free
water
as
required.
Draft
June
2003
4
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.
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:
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.

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,
using
surface
waters
filtered
to
minimum
turbidity
with
0.04
micron
filters
and
dosed
with
formazin
to
levels
of
0.47,
0.91,
5.6,
9.8,
39.3,
82.7
and
99.4
NTU.
The
±
standard
deviations
were
0.007,
0.014,
0.
l,
0.22,
0.45,
0.7
and
0.83
units
respectively.
Draft
June
2003
5
9.2
Accuracy
of
the
Great
Lakes
Instruments
Turbidity
Method
The
range
of
the
mean
percent
recoveries
of
turbidity
from
10
fortified
drinking
water
samples,
each
analyzed
in
triplicate
by
the
Great
Lakes
Instruments
Turbidity
Method,
was
as
follows:

Turbidity
Added
to
Sample
Range
of
Percent
Recovery
4.5
98.1
­
112.2
9.5
96.8
­
111.1
34.5
93.7
­
114.3
PRECISION
OF
GREAT
LAKES
INSTRUMENTS'
TURBIDITY
METHOD
The
range
of
the
standard
deviations
and
percent
relative
standard
deviations
(
or
percent
coefficient
of
variations)
associated
with
the
triplicate
observations
of
the
total
theoretical
concentration
of
10
fortified
drinking
water
samples
by
the
Great
Lakes
Instruments
Turbidity
Method
were
as
follows:

Total
Theoretical
Turbidity
(
NTU)
Standard
Deviation
(
NTU)
Relative
Standard
Deviation
(%)

0.5
0.01
­
0.06
1.1
­
10.7
5.0
0.00
­
0.10
0.0
­
2.0
10.0
0.00
0.0
­
5.6
35.0
0.00
­
0.58
0.0
­
1.8
9.3
Accuracy
and
precision
should
be
checked
on
a
routine
basis
to
monitor
the
overall
performance
of
the
instrument.
A
series
of
reagent
blanks
and
check
standards
should
be
run
to
validate
the
quality
of
sample
data.
These
checks
should
occur
at
a
frequency
that
is
required
for
regulatory
compliance.

10.
Safety
10.1
Operators
handling
reagents
should
wear
safety
glasses,
rubber
gloves,
and
appropriate
protective
clothing.
Consult
the
Materials
Safety
Data
Sheets
for
additional
safety
information
before
working
with
reagents.

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
Solution
samples
should
be
used,
collected
and
disposed
of
in
accordance
with
all
Federal,
state
and
local
regulations.
Draft
June
2003
6
Worldwide
Headquarters
and
Sales:

GLI
International,
Inc.
9020
West
Dean
Road
Milwaukee,
Wisconsin
53224
U.
S.
A.
Represented
By:

In
the
interest
of
improving
and
updating
its
equipment,
GLI
reserves
the
right
to
alter
specifications
to
equipment
at
any
time.
A
company
Viridor
Instrumentation
Phone:
Fax:
E­
mail:
Web:
[
414]
355­
3601
[
414]
355­
8346
info@
gliint.
com
www.
gliint.
com
13.
Waste
Management
13.1
In
case
of
spill
or
release:
Dilute
with
water.
Dispose
of
in
accordance
with
all
Federal,
state,
and
local
regulations.

Bibliography
l.
Book
of
ASTM
Standards,
Part
31,
"
Water",
Standard
D1889­
71,
p.
223
(
1976).

2.
Methods
for
the
Examination
of
Water
and
Wastewater,
14th
Edition
p.
132.
Method
214A,
(
1975).

3.
Standard,
Ref.
No.
ISO
7027­
1984
(
E).

4.
Methods
for
the
Examination
of
Water
&
Wastewater,
16th
Edition
p.
135.
Method
214A.

5.
Standard
Methods
for
the
Certification
of
Laboratories
Analyzing
Drinking
Water:
Criteria
and
Procedures,
Quality
Assurance,
EPA/
570/
9­
90/
008,
April,
1990.
