# Leck Mitchell, Ph.D., PE

656 Independence Valley Dr.; Grand Junction, CO 81507 Ph: 970-244-8661; Fax: 970-244-8856; Leckmitchell@Bresnan.net



## MITCHELL ATP SUBMISSION FOR CHANGES IN

METHOD 180.1 USING LASER

DETERMINATION OF TURBID ITY BY NEPHELOMETRY

Mitchell Method M5271

Alternate Test Procedures

Leck Mitchell, Ph.D., PE Patricia Lacy Mitchell, Ph.D.

Revision 1.0



## July 31, 20082 

### ATP SUBMISSION FOR CHANGES IN METHOD 180.1 USING LASER

DETERMINATION OF TURBIDITY BY NEPHELOMETRY

Mitchell Method M5271



## Alternate Test Procedures

1.0 SCOPE AND APPLICATION:

1.1 This method covers the determ ination of turbidity in finished, drinking, filtered effluent; distribution; ultra-pure micro-processe s, and colorless water with a turbidity of

less than 40 NTU.

1.2 This method introduces a solid state monochromatic laser li ght source which falls slightly outside the accepted range for EPA 180.1 but m eets all other quality control and performance characteristics of 180.1.

1.3 The applicable range is 0 to 40 NTU.

1.4 This method can be used for compliance monitoring and reporting under the Safe Drinking Water Act (SDWA).

2.0 SUMMARY OF METHOD:

2.1 The method is based upon a comparison of the intensity of light scattered by the sample under define d conditions, with the intensit y of light scattered by a standard reference suspension. The higher the intensity of scattered light, the the higher the turbidity. Readings in NTUs are made using a laser nephelometer designed according to specifications given in section 6.1 and 6.2. Primary standard suspensions are used to calibrate the instrument. A secondary standard is monitored periodica lly for deterioration using one of the primary standards.

2.1.1 Formazin polymer is used as a primary turbidity suspension for

Water.

2.1.2 AMCO Clear is available from GFS Chemical and is approved by USEPA as a polymer pr imary standard. It is stable over longer periods of time than

Formazin.

2.1.3 Stabilized Formazin, identified as StablCal , is an approved derivative of the Formazin standard and is stable in storage for two years.



### 3.0 DEFFINITIONS

3.1 CALIBRATION BLANK ( CB) – A volume of reagent water fortified with

the same matrix as the calibration standards, but without the analytes,3 

### internal standards, or surrogate analytes.

3.2 INSTRUMENT PE RFORMANCE CHECK SOLUTI ON (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 ali quot of reagent water

or other blank ma trices that are treated exactly as a sample including exposure to all glassw are, equipment, solvents, reag ents, internal standards, and surrogates that are used with other samples. The LRB is used to

determine if met hod 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 toxi city, health hazards, physical properties, fire, and reactivity data incl uding storage, spill, and handling precautions.

3.6 PRIMARY CALIBRATI ON STANDARD (PCAL) – A suspension prepared from the primary dilu tion stock standard suspensi on. The PCAL suspensions

are used to calibra te the instrument response with respect to analyte

concentration.

3.7 QUALITY CONTROL SAMPLE (QCS) - A solution of the method analyte of

known concentrations th at is used to fortify an al iquot of LBR matrix. The QCS is obtained from a source eternal to the laborato ry, and is used to check laboratory performance.

3.8 SECONDARY CALI BRATION STANDARDS (SCA L) – commercially prepared, stabilized seal ed liquid or gel turbidity sta ndards, or other apparatus

or mechanism calibra ted against properly prepared and diluted Formazin or styrene divinylbenzene polymers.

3.9 STOCK STANDARD SUSPE NSION (SSS) – A concentrated suspension containing the analy tic solution prepared in th e laboratory using assayed

reference materials or purchased from a reputable commercial source. Stock standard suspension is used to prepare calibration su spensions or other needed suspensions.

4.0 INTERFERENCES:

4.1 The presence of floating debris and coarse sediment s that settle out rapidly will4 give low readings. Finely divided air bubbles can cause high readings.

4.2 The presence of true color, that is the color of wa ter that is due to dissolved

substances that absorb light, will cause turbidities to be low, although this effect is generally not significant with drinking water.

4.3 Light-absorbing materials such as activated carbon in significant concentrations can cause low readings.

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 low as reasonably achievable.

5.2 Each laboratory is responsible for maintaining a current awareness file of OSHA regulations regarding the saf e handling of the chemicals specified in this

method. A reference file of Material Safety Data Sheets (MSDS) should be

made available to a ll personnel involved in the chemical analysis. The preparation of a formal safety plan is also advisable.

5.3 Hydrazine sulfate (7.2.1) 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 a 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 physi cal design of turbidimeters will cause differences in

measured values fo r turbidity, even though the sam e suspension is used for

calibration. To minimize such differences, the following design criteria should

be observed:

6.2.1 Laser light source: M onochromatic source operated at a nominal wavelength of 650 ±30nm. The light source shall be used as a directly

received reference for the scattered nephelometric signal. Alternative light sources may be incorporated as long as they fall within the proscribed wavelengths and me et all quality control performance characteristics. In addition, the Mitc hell designs allow a variation in light source without variation in turbidity response.

6.2.2 There shall be no divergence from parallelism as the incident radiation and any convergence shall not exceed ±1 1⁄2 degrees.5 6.2.3 Distance traversed by incident light and scattered light not to exceed 10 cm.

6.2.4 Detector/Light Receiver: Centered at 90o ± 1 1⁄2 degrees to the incident light path and the light cone not to exceed ± 30 degrees from 90degrees. The receiver, if used, may be coupled to a photo detector using an optical path.

6.2.4.1 The photo detector must have a spectral response that encompasses complete spectral output of the light source. A Mitchell/Mersch light trap shall be incorporated.

6.2.5 An optical device may be used to carry light from the light source to the sample or to carry scattered light from the sample to the photo detector.

6.2.6 Instrument shall have incorporated a Mitchell/Mersch bubble trap for

on line use and Mitchell/Mersch anti-fog wi ndows. Sensor shall be

horizontal with vertical windows. Both windows shall be immersed

in the measurement fluid for on-line use. Instrument shall be capable of being pressurized to 30 psig.

6.2.7 Turbidimeter example which meets these specifications is the Mitchell (M5271).

6.3 The sensitivity of the instrument should permit detection of a turbidity difference of .001 NTU or less in waters having turbidities less than 1 NTU units. The instrument should measure from 0 to 40 NTU turbidity

units.

6.4 The sample tubes for laboratory, bench top or portable units 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 etch ed. 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 0.0001g.

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 0.45 micron pore-size membrane filter, if such filtered water shows a lower turbidity

than unfiltered distilled water.6 7.2 Stock standard suspension (stabilized Formazin)

7.2.1 Dissolve 1.00g hydrazine sulfate (CASRN 10034-93-2) in reagent

water and dilute to 100 mL in a volumetric flask.

7.2.2 Dissolve 10.00g 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 ± 3 degree C, 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. Prim ary calibration standards (7.3) should be prepared daily by dilution of the stock standard suspension.

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

7.5 AMCO Clear- Styrene Divinylbenzene polymer primary certified, turbidity standards are available for specific instruments and require no preparation or dilution prior to use.

7.6 Stabilized Formazin, turbidity standards, certified, primary, polymer suspensions have long-term storage stability.

7.7 Secondary standards may be acceptable as a calibration check, but must

be monitored on a routine b asis for deterioration and replaced as required.

8.0 SAMPLE COLLECTION, PRESERVATION AND STORAGE

8.1 Samples for bench top and portable laboratory units should be collected in plastic or glass bottles. All bottles must be thoroughly cleaned and rinsed with turbidity free water. Volu me 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 for samples. Cool sample to 4 degrees C.

8.3 Samples for bench top and portable laboratory units should be analyzed as soon as possible after collection. If storage is required, samples maintained at 4 degrees C may be held for up to 48 hours.

8.4 Online instrumentation does not require sample cooling, preservation or

storage.7 9.0 QUALITY CONTROL

9.1 Each laboratory using this met hod is required to opera te a formal quality control (QC) program. The mi nimum 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 demonstr ation 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 whenever a significant change in instrument response is observed or expected. The initial demonstration of linearity

must use sufficien t standards to insure that th e 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, 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 w ithin ± 10 % of calibration. Subsequent analyses of the IPC solution must verify the calibration is within ± 10 %. If the calibration cannot be verified within the specified limits, reanalyze the IPC solution. If the second analysis of the IPC solution confirms8 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 refe rence materials such as Performance Testing 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

10.1 Turbidity Calibrati on: 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 pr ocedure 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 sensitivit y so that scale values will correspond to turbidities. Solid standards, if used, must be protected from

surface scrat ches which may cause potential calibration changes. If a pre-

calibrated scal e is not supplied, calibration curves should be prepared for each range of the instrument. Calibration must be performed under

identical optical conditions as operationa l conditions. The unit may optionally incorporate a Mitchell/Mersch self-check system for verification of operation.

11.0 PROCEDURE:

11.1 For on-line use, all instru ment parameters should be set to insure constant sample

flow is fed to the in strument. This will insure bubbl e interferences are minimized. Refer to the manufacturer’s instrument manual for the set up of measurement parameters and flow rates.

11.2 Turbidities less than 40 NTU: In instruments other than on-line, allow samples to

come to room temp erature before analysis. Mix th e sample to thoroughly disperse

the solids. Wa it until air bubbles disappear, and then pour the sample into the

turbidimeter tube. Read the turbidity directly from the instrument scale or from the appropriate calibration curve.

12.0 DATA ANALYSIS AND CALCULATIONS:

12.1 Multiply sample readings by appropriate dilution to obtain final reading.9 12.2 Report Results as follows:

NTU Record to Nearest

0.0 – 1.0 .01

1 – 10 0.1

10 – 40 1.

40 – 100 5.

100 – 400 10. 400 – 1,000 50.

≥ 1,000 100.

13.0 METHOD PERFORMANCE:

In an intra laboratory test facility the following readings for precision and accuracy were

established for M5271:

Tr ue Value Sample Instrumentation Average Standard Deviation

______________________________________________________________________

0 .015 .0012

.1 .097 .0004

.3 .297 .001

.5 .506 .0012

5 5.044 .005

10 10.022 .009

20 20.048 .054

40 39.971 .482

14.0 POLLUTION PREVENTION:

14.1 Pollution prevention encompasses any technique that reduces or eliminates the quantity or toxicity of waste as the point of generation. Numerous opportunities for pollution prevention exists in laboratory operation. The EPA has established a preferred hierar chy 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 chemi cals purchased should be based on expected usage during its shelf life and dispo sal cost of unused material. Actual reagent preparation volumes should reflect anticipated usage and reagent stability.

15.0 WASTE MANAGEMENT:

15.1 The U.S. Environmental Protection Agency requires that laboratory waste

management pr actices be conducted consistent w ith all applicable rules and regulations. Excess reagents, samples and method process wastes should be10 characterized and disposed of in an acceptable manner. The Agency urges laboratories to protect air, water, and land by minimizing and controlling all

releases from hoods and bench operations; complying with the letter and spirit of any waste disch arge permit and regulations; and by complying with all solid hazardous waste regulations, particularly the hazardous waste identification rules and land disposal restrictions.

16.0 REFERENCES:

16.1 Annual Book of ASTM Standards , Volume 11.01 Water (1), Standard D1889-88A, p. 359, (1993).

16.2 Standard Methods for the Examination of Water and Wastewater , 18 th Edition, pp.2-9, Method 2130B (1992). APHA, A WWA, and WEF. Port City Press, Baltimore, MD.

16.3 McKee, Gerald F., (1985); Turbidity Standard , EPA Record.