# Leck Mitchell, Ph.D., PE

Instrumentation for Control and Monitoring

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



## MITCHELL ATP SUBMISSION FOR CHANGES IN

METHOD 180.1 USING LED

DETERMINATION OF TURBID ITY BY NEPHELOMETRY

Mitchell Method M5331

Alternate Test Procedures

Leck Mitchell, Ph.D., P.E. Patricia Lacy Mitchell, Ph.D.

Revision 1.0

July 31, 20082 

### MITCHELL ATP SUBMISSION FOR CHANGES IN

METHOD 180.1 USING LED

DETERMINATION OF TURBIDITY BY NEPHELOMETRY

Mitchell Method M5331

A lternate Test Procedures

1.0 SCOPE AND APPLICATION

1.1 This method covers the determination of turb idity in drinking, ground, surface, and saline waters, domestic and industrial wastes and an y colorless water with turbidity, less than 40

NTU.

1.2 This method introduces a solid state monochroma tic LED light source which falls within the accepted range for EPA 180.1 and meet s all quality control and performance characteristics.

1.3 The applicable range is 0 to 40 nephelometric turbidity units (NTU). Higher values may be obtained with dilution of the sample.

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

2.0 SUMMARY OF MATERIAL

2.1 The method is based upon a comparis on of the intensity of light scattered by the sample

under defined conditions with th e intensity of light scattered by a standard reference suspension. The higher the intensity of scattered light, the higher the turbidity. Readings in the 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 is used as a calibration check and is monitored periodically for deterioration using one of the primary standards.

2.1.1 Formazin polymer is used as a pr imary turbidity suspension for Water.

2.1.2 A commercially available polymer primary sta ndard is also approved for use in the National Interim Primary Drinking Water Regul ations. This standard is identified as AMCO Clear. It is stable over longer peri ods of time than Formazin and is available from GFS Chemical Company.

2.1.3 Stabilized Formazin, identified as Stab Ca l, is an approved derivative of the Formazin standard and is stable in storage for two years.3 3.0 DEFFINITIONS

3.1 CALIBRATION BLANK (CB) – A volume of reagen t water fortified with the same matrix as the calibration standards, but without the an alytes, 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 a liquot of reagent water or other blank matrices that are treated exactly as a sample in cluding exposure to all glassware, equipment, solvents, reagents, internal standards, and surr ogates that are used with other samples. The LRB is used to 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) – Wr itten 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. The PCAL suspen sions 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 used to fortify an aliquot of LBR 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, or ot her apparatus or mechanism calibrated against properly prepared and diluted Formazin or st yrene divinylbenzene po lymers (AMCO Clear).

3.9 STOCK STANDARD SUSPENSION (SSS) – A con centrated suspension containing the analytic 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 sedim ents 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, a lthough this effect is generally not significant with drinking waters.4 4.3 Light absorbing materials such as activated carbon in signifi cant concentrations can cause low readings.

5.0 SAFETY

5.1 The toxicity or carcinogenicity of each reag ent used in this method has not been fully established. Each chemical should be rega rded 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 safe handling of the chemicals spec ified 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 highly toxic and may be fatal if inhaled, swallowed, or absorbed through the skin. Formazin can contain residua l 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 reach es 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 turbidimeter s 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 LED light source: Monochromatic source operated at nominal wavelength of 525 ± 15nm. The source shall be used as a directly received reference for the scattered nephelometric signal. The beam shall not diverge and shall not converge over ± 1 1/2 degrees. Alternate light sources may be acceptable if they fall within the proscribed wavelength specifications and meet all quality control and performance characteristics. In addition, the Mitchell d esigns allow a variation of 50% in light intensity of the source without variation in turbidity response.

6.2.2 Distance traversed by incident light and scattered light not to exceed 10 cm.

6.2.3 Detector/ Light Receiver: Centered at 90o ± 1 1⁄2 degrees to the incident light path; the light cone not to exceed ± 30 degrees from 90 degrees. The receiver, if used, may be coupled to a photo detector using an optical path. The photo detector must have a spectral output that encompasses a complete sp ectral response of the light source. A Mitchell/Mersch light trap shall be incorporated for on-line use.

6.2.4 Instrument shall have incorporated a Mitchell/Mersch bubble trap for on-line use and Mitchell/Mersch anti-fog windows. Sensor shall be horizontal with vertical5 windows. Both windows shall be immersed in the measurement fluid for on-line use. Instrument shall be capable of being pressurized to 30 psig.

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

6.2.6 Turbidimeter example meeting these specifications is the Mitchell (M5331).

6.3 The sensitivity of the instrument should permit detection of a turbidity difference of .01 NTU or less, in waters having turbidities less than 1 unit. The instrument should measure from 0 to 40 NTU turbidity. Several ranges may be n ecessary to obtain both ad equate coverage and sufficient sensitivity for low turbidities.

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 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 th ey may be easily handled. Tubes should be checked, indexed and read at the orientati on 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.

7.2 Stock standard suspension (Formazin)

7.2.1 Dissolve 1.00 g hydrazine sulfate (CASRN 10034-93-2) in reagent water and dilute to 100 mL in a volumetric flask. (toxic)

7.2.2 Dissolve 10.00 g hexamethylenetet ramine (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 st and 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. Primary calibration standards (7.3) should be prepared daily by dilution of the stock standard suspension.6 7.4 Formazin in commercially prepared, certifi ed, primary concentrated stock standard suspension (SSS) may be diluted and used as requi red. Dilute turbidity standards should be prepared daily.

7.5 AMCO Clear, styrene diviny lbenzene polymer, primary standa rds are available for specific instruments and require no preparation or dilu tion prior to use. This is an approved EPA

standard.

7.6 Stabilized Formazin, (StablCal) turbidity standa rds, 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 basis 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. Volume collected should be sufficient to insure a represen tative sample, allow for replicate analysis (if required), and minimize waste disposal.

8.2 No chemical preservation is required for samples. Cool sample to 4 ° 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 ° C may be held for up to 48

hours.

8.4 Online instrumentation does not require sample cooling, preservation or storage.

9.0 QUALITY CONTROL

9.1 Each laboratory using this method is requi red to operate a formal quality control (QC) program. The minimum requirements of this pr ogram consist of an initial demonstration of laboratory capability and analysis of laborato ry 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 performan ce 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 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,

sufficient standards must be used to clearly define the nonlinear portion.7 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 performan ce with the preparation and analysis of a QCS. If the determined concentrations ar e 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 So lution (IPC) – For all determinations, the laboratory must analyze the IPC (A midra nge check standard) and a calibration blank immediately following daily calibration, afte r 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 calibra tion must verify that the instrument is within ± 10 % of calibration. Subsequent an alyses of the IPC solution must verify the

calibration is within ± 10 %. If the calibrati on 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 so lution, must 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 materi als such as Performance Testing samples are available, they should be analyzed to provide additional performance data. The analysis of reference samples is a valuab le tool for demonstrating the ability to perform the method acceptably.

10.0 CALIBRATION AND STANDARDIZATION

10.1 Turbidity Calibration: The manufacturer’s operating instructions should be followed. Measure standards on the turbidimeter covering th e 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 sens itivity so that scale values will correspond to turbidities. Solid standards, if used must be protected from surface scratches which may potentially cause calibration changes. If a pre-calibrated scale is not supplied, calibration curves should be prepared for each range of th e instrument. Calibration must be performed under identical optical conditions as the operati onal conditions. The unit may incorporate an optional Mitchell/Mersch self-check system for verification of operation.8 11.0 PROCEDURE

11.1 For on-line use, all instrument parameters shoul d be checked to insure constant sample flow

in the instrument. This will insure bubble interferences are minimized. Refer to the manufacturer’s instrument manual for the set up of measureme nt parameters and flow rates.

11.2 Turbidities less than 40 NTU: For instruments other than on-line, if possible, allow samples to come to room temperature before analysis . Mix the sample to thoroughly disperse the solids. Wait unit 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.

11.3 Turbidities exceeding 40 NTU: Dilute the samp le with one or more turbidity-free water until the turbidity falls below 40 NTUs. The turbidit y of the original sample is then computed from the turbidity of the diluted sample and the dilution factor.

11.3.1 Some turbidimeters are equipped with several separate scales. The higher scales are to be used only as indicators of required dilution volumes to re duce readings to less

than 40 NTU.

12.0 DATA ANALYSIS AND CALCULATIONS

12.1 Multiply sample readings by appropri ate dilution to obtain final reading.

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 foll owing readings for precision and accuracy were

established for M53319 True Value Sample Instrumentation Av erage Standard Deviation

0 .015 .0012

.1 .100 .0006

.3 .294 .0007

.5 .506 .0007

5 5.014 .008

10 9.975 .005

20 19.993 .088

40 39.966 .149

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 feasibl e, laboratory personnel should use pollution prevention techniques to address their waste generation. When wastes cannot be feasibly reduced at the source, the Agency recomme nds 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. Actu al reagent preparation volumes should reflect anticipated usage and reagent stability.

15.0 WASTE MANAGEMENT

The U.S. Environmental Protection Agency requir es that laboratory waste management practices be

conducted consistent with all a pplicable rules and regulations. Excess reagents, samples and method process wastes should be characterized a nd 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, complyin g 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 rul es and land disposal restrictions. For further information on waste management consult th e “Waste Management Manual for Laboratory Personnel”, available from the American Chemical Society.

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, a nd WEF. Port City Press, Baltimore, MD.

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