Thermo-Scientific: AQ4500: Turbidity of Water by LED Nephelometry
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Official Method Name
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Determination of Turbidity by LED Nephelometry |
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Current Revision
| Revision 1.0, May 2009 |
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Media
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WATER |
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Instrumentation
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Nephelometer |
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Method Subcategory
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Physical |
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Method Source
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Citation
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Determination of Turbidity by LED Nephelometry, Thermo Scientific Orion Method AQ4500, Rev. 1, May 8, 2009 |
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Brief Method Summary
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The method is based upon a comparison of the intensity of light scattered by the sample at 900 to the beam path, with the intensity of light scattered by a standard reference suspension. The higher the intensity of scattered light, the higher the turbidity. The transmitted beam is used as a reference beam to correct for small amounts of color, if present in the sample. 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 a primary standard. |
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Scope and Application
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The present method is based on the use of Thermo Scientific Orion AQUAfast LED Turbidimeter Model AQ4500, Primary Formazin Stock Solution Cat. No. AQ45FZ, and the associated calibration kit of secondary standards, Cat. No. AQ45ST, or suitable equivalents. This method covers the determination of turbidity in drinking, ground, surface, and saline waters, domestic and industrial wastes.Each laboratory that uses this method must demonstrate the ability to generate acceptable results using the quality control procedure in section 9.2. |
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Applicable Concentration Range
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0.06 to > 1,000 NTU |
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Interferences
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The presence of floating debris and coarse sediments which settle out rapidly will give low readings. Finely divided air bubbles can cause high readings. 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. Also, this interference is minimized by the use of a ratiometric optical design which compares the transmitted and scattered signals. Light absorbing materials such as activated carbon in significant concentrations can cause low readings. |
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Quality Control Requirements
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The minimum requirements of this program are initial demonstration of laboratory capability, and the periodic analysis of laboratory reagent blanks, fortified blanks, fortified samples, duplicates and other laboratory solutions as a continuing performance check. |
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Sample Handling
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Samples should be collected in plastic or glass bottles. All bottles must be thoroughly cleaned and rinsed with turbidity free water. The volume collected should be sufficient to insure a representative sample, allow for replicate analyses (if required), but minimize waste disposal. No chemical preservation is required. Cool sample to 4 degrees C. |
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Maximum Holding Time
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Samples 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. |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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