APPENDIX B. DETERMINATION OF
TURBIDITY BY
NEPHELOMETRY
METHOD 180.1
DETERMINATION OF TURBIDITY BY NEPHELOMETRY
Edited by James W. O'Dell
Inorganic Chemistry Branch
Chemistry Research Division
Revision 2.0
August 1993
ENVIRONMENTAL MONITORING SYSTEMS LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
180.1-1
April 1999 B-1 EPA Guidance Manual
Turbidity Provisions
APPENDIX B. DETERMINATION OF TURBIDITY
1.0 SCOPE AND APPLICATION
1.1 This method covers the determination of turbidity in drinking, ground,
surface, and saline waters, domestic and industrial wastes.
1.2 The applicable range is 0 to 40 nephelometric turbidity units (NTU).
Higher values may be obtained with dilution of the sample.
2.0 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 scattered
light, the higher the turbidity. Readings, in NTUs, are made in a
nephelometer designed according to specifications given in sections 6.1 and
6.2. A primary standard suspension is used to calibrate the instrument. A
secondary standard suspension is used as a daily calibration check and is
monitored periodically for deterioration using one of the primary standards.
2.1.1 Formazin polymer is used as a primary turbidity suspension for
water because it is more reproducible than other types of standards
previously used for turbidity analysis.
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.
3.0 DEFINITIONS
3.1 CALIBRATION BLANK (CB) - - A volume of reagent water fortified
with the same matrix as the calibration standards, but without the analytes,
internal standards, or surrogates analytes.
3.2 INSTRUMENT PERFORMANCE CHECK SOLUTION (IPC) - - A
solution of one or more method analytes, surrogates, internal standards, or
other test substances used to evaluate the performance of the instrument
system with respect to a defined set of criteria.
3.3 LABORATORY REAGENT BLANK (LRB) - - An aliquot of reagent
water or other blank matrices that are treated exactly as a sample including
exposure to all glassware, equipment, solvents, reagents, internal standards,
and surrogates that are used with other samples. The LRB is used to
EPA Guidance Manual B-2 April 1999
Turbidity Provisions
APPENDIX B. DETERMINATION OF TURBIDITY
determine if method analytes or other interferences are present in the
laboratory environment, the reagents, or the apparatus.
3.4 LINEAR CALIBRATION RANGE (LCR) - - The concentration range
over which the instrument response is linear.
3.5 MATERIAL SAFETY DATA SHEET (MSDS) - - Written information
provided by vendors concerning a chemical=s toxicity, health hazards,
physical properties, fire, and reactivity data including storage, spill, and
handling precautions.
3.6 PRIMARY CALIBRATION STANDARD (PCAL) - - A suspension
prepared from the primary dilution stock standard suspension. The PCAL
suspensions are used to calibrate the instrument response with respect to
analyte concentration.
3.7 QUALITY CONTROL SAMPLE (QCS) - - A solution of the method
analyte of known concentrations that is used to fortify an aliquot of LRB
matrix. The QCS is obtained from a source external to the laboratory, and
is used to check laboratory performance.
3.8 SECONDARY CALIBRATION STANDARDS (SCAL) - - Commercially
prepared, stabilized sealed liquid or gel turbidity standards calibrated
against properly prepared and diluted formazin or styrene divinylbenzene
polymers.
3.9 STOCK STANDARD SUSPENSION (SSS) - - A concentrated suspension
containing the analyte prepared in the laboratory using assayed reference
materials or purchased from a reputable commercial source. Stock
standard suspension is used to prepare calibration suspensions and other
needed suspensions.
4.0 INTERFERENCES
4.1 The presence of floating debris and coarse sediments which settle out
rapidly will give low readings. Finely divided air bubbles can cause high
readings.
4.2 The presence of true color, that is the color of water which is due to
dissolved substances that absorb light, will cause turbidities to be low,
although this effect is generally not significant with drinking waters.
4.3 Light absorbing materials such as activated carbon in significant
concentrations can cause low readings.
April 1999 B-3 EPA Guidance Manual
Turbidity Provisions
APPENDIX B. DETERMINATION OF TURBIDITY
5.0 SAFETY
5.1 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 lows as reasonably achievable.
5.2 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.
5.3 Hydrazine Sulfate (7.2.1) 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.
6.0 EQUIPMENT AND SUPPLIES
6.1 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.
6.2 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:
6.2.1 Light source: Tungsten lamp operated at a color temperature
between 2200-3000EK.
6.2.2 Distance traversed by incident light and scattered light within the
sample tube: Total not to exceed 10 cm.
6.2.3 Detector: Centered at 90E to the incident light path and not to
exceed + 30E from 90E. The detector, and filter system if used,
shall have a spectral peak response between 400 and 600 nm.
6.3 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 to 40 units turbidity. Several
ranges may be necessary to obtain both adequate coverage and sufficient
sensitivity for low turbidities.
EPA Guidance Manual B-4 April 1999
Turbidity Provisions
APPENDIX B. DETERMINATION OF TURBIDITY
6.4 The sample tubes to be used with the available instrument must be of clear,
colorless glass or plastic. They should be kept scrupulously clean, both
inside and out, and discarded when they become scratched or etched. A
light coating of silicon oil may be used to mask minor imperfections in
glass tubes. 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.
6.5 Balance - - Analytical, capable of accurately weighing to the nearest 0.0001
g.
6.6 Glassware - - Class A volumetric flasks and pipettes as required.
7.0 REAGENTS AND STANDARDS
7.1 Reagent water, turbidity-free: Pass deionized distilled water through a
0.45F pore size membrane filter, if such filtered water shows a lower
turbidity than unfiltered distilled water.
7.2 Stock standard suspension (Formazin):
7.2.1 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
7.2.2 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 (7.2.1 + 7.2.2).
Allow to stand 24 hours at 25 + 3EC, then dilute to the mark with
reagent water.
7.3 Primary calibration standards: Mix and dilute 10.00 mL of stock standard
suspension (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.
7.3.1 A new stock standard suspension (7.2) should be prepared each
month. Primary calibration standards (7.3) should be prepared
daily by dilution of the stock standard suspension.
7.4 Formazin in commercially prepared primary concentrated stock standard
suspension (SSS) may be diluted and used as required. Dilute turbidity
standards should be prepared daily.
April 1999 B-5 EPA Guidance Manual
Turbidity Provisions
APPENDIX B. DETERMINATION OF TURBIDITY
7.5 AMCO-AEPA-1 Styrene Divinylbenzene polymer primary standards are
available for specific instruments and require no preparation or dilution
prior to use.
7.6 Secondary standards may be acceptable as a daily calibration check, but
must be monitored on a routine basis for deterioration and replaced as
required.
8.0 SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1 Samples should be collected in plastic or glass bottles. All bottles must be
thoroughly cleaned and rinsed with turbidity free water. Volume collected
should be sufficient to insure a representative sample, allow for replicate
analysis (if required), and minimize waste disposal.
8.2 No chemical preservation is required. Cool sample to 4EC.
8.3 Samples should be analyzed as soon as possible after collection. If storage
is required, samples maintained at 4EC may be held for up to 48 h.
9.0 QUALITY CONTROL
9.1 Each laboratory using this method is required to operate a formal quality
control (QC) program. The minimum requirements of this program consist
of an initial demonstration of laboratory capability and analysis of
laboratory reagent blanks and other solutions as a continuing check on
performance. The laboratory is required to maintain performance records
that define the quality of data generated.
9.2 INITIAL DEMONSTRATION OF PERFORMANCE.
9.2.1 The initial demonstration of performance is used to characterize
instrument performance (determined of LCRs and analysis of QCS).
9.2.2 Linear Calibration Range (LCR) - - The LCR must be determined
initially and verified every 6 months or whenever a significant
change in instrument response is observed or expected. The initial
demonstration of linearity must use sufficient standards to insure
that the resulting curve is linear. The verification of linearity must
use a minimum of a blank and three standards. If any verification
data exceeds the initial values by + 10%, linearity must be
reestablished. If any portion of the range is shown to be nonlinear,
EPA Guidance Manual B-6 April 1999
Turbidity Provisions
APPENDIX B. DETERMINATION OF TURBIDITY
sufficient standards must be used to clearly define the nonlinear
portion.
9.2.3 Quality Control Sample (QCS) - - When beginning the use of this
method, on a quarterly basis or as required to meet data-quality
needs, verify the calibration standards and acceptable instrument
performance with the preparation and analysis of a QCS. If the
determined concentrations are not within + 10% of the stated
values, performance of the determinative step of the method is
unacceptable. The source of the problem must be identified and
corrected before continuing with on-going analyses.
9.3 ASSESSING LABORATORY PERFORMANCE
9.3.1 Laboratory Reagent Blank (LRB) - - The laboratory must analyze
at least one LRB with each batch of samples. Data produced are
used to assess contamination from the laboratory environment.
9.3.2 Instrument Performance Check Solution (IPC) - - For all
determinations, the laboratory must analyze the IPC (a midrange
check standard) and a calibration blank immediately following daily
calibration, after every tenth sample (or more frequently, if
required) and at the end of the sample run. Analysis of the IPC
solution and calibration blank immediately following calibration
must verify that the instrument is within + 10% of calibration.
Subsequent analyses of the IPC solution must verify the calibration
is still within + 10%. If the calibration cannot be verified within the
specified limits, reanalyze the IPC solution. If the second analysis
of the IPC solution confirms calibration to be outside the limits,
sample analysis must be discontinued, the cause determined and/or
in the case of drift the instrument recalibrated. All samples
following the last acceptable IPC solution must be reanalyzed. The
analysis data of the calibration blank and IPC solution must be kept
on file with the sample analyses data. NOTE: Secondary
calibration standards (SS) may also be used as the IPC.
9.3.3 Where additional reference materials such as Performance
Evaluation samples are available, they should be analyzed to
provide additional performance data. The analysis of reference
samples is a valuable tool for demonstrating the ability to perform
the method acceptably.
10.0 CALIBRATION AND STANDARDIZATION
April 1999 B-7 EPA Guidance Manual
Turbidity Provisions
APPENDIX B. DETERMINATION OF TURBIDITY
10.1 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, calibration
curves should be prepared for each range of the instrument.
11.0 PROCEDURE
11.1 Turbidities less than 40 units: If possible, allow samples to come to room
temperature before analysis. Mix 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.
11.2 Turbidities exceeding 40 units: Dilute the sample with one or 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.
11.2.1 Some turbidimeters are equipped with several separate scales. The
higher scales are to be used only as indicators of required dilution
volumes to reduce readings to less than 40 NTU.
NOTE 1: Comparative work performed in the Environmental
Monitoring Systems Laboratory B Cincinnati (EMSL-
Cincinnati) indicates a progressive error on sample
turbidities in excess of 40 units.
12.0 DATA ANALYSIS AND CALCULATIONS
12.1 Multiply sample readings by appropriate dilution to obtain final reading.
12.2 Report results as follows:
EPA Guidance Manual B-8 April 1999
Turbidity Provisions
APPENDIX B. DETERMINATION OF TURBIDITY
NTU Record to Nearest
0.0 ?1.0 0.05
1 ?10 0.1
10 ?40 1
40 ?100 5
100 ?400 10
400 ?1,000 50
> 1,000 100
13.0 METHOD PERFORMANCE
13.1 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.
13.2 The interlaboratory precision and accuracy data in Table 1 were developed
using a reagent water matrix. Values are in NTU.
14.0 POLLUTION PREVENTION
14.1 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.
14.2 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.
14.3 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, DC 20036, (202) 872-4477.
15.0 WASTE MANAGEMENT
April 1999 B-9 EPA Guidance Manual
Turbidity Provisions
APPENDIX B. DETERMINATION OF TURBIDITY
15.1 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 Sect. 14.3.
16.0 REFERENCES
1. American Society for Testing and Materials (ASTM). 1993. Annual Book
of ASTM Standards, Volume 11.01. Water (1), Standard D1889-88A, p.
359. West Conshohocken, PA,
2. Standard Methods. 1992. Standard Methods for the Examination of
Water and Wastewater. Eighteenth Edition, pp. 2-9, Method 2130B.
APHA, AWWA, and WEF. Port City Press, Baltimore, MD.
17.0 TABLES, DIAGRAMS, FLOWCHARTS AND VALIDATION DATA
Table 1. Interlaboratory Precision And Accuracy Data
Number of Standard
Values True Value Mean Residual for Deviation Residual for
Reported (T) (X) X (S) 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
EPA Guidance Manual B-10 April 1999
Turbidity Provisions
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