Standard Methods: 4500-Cl H: Chlorine by Syringaldazine
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Official Method Name
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4500-Cl H. Syringaldazine (FACTS) Method |
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Current Revision
| Standard Methods Online |
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Media
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WATER |
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Instrumentation
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Spectroscopy (Colorimetry; Photometry) |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Brief Method Summary
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The free (available) chlorine test, syringaldazine (FACTS) measures free chlorine over the range of 0.1 to 10 mg/L. A saturated solution of syringaldazine (3,5-dimethoxy-4-hydroxybenzaldazine) in 2-propanol is used. Syringaldazine is oxidized by free chlorine on a 1:1 molar basis to produce a colored product with an absorption maximum of 530 nm. The color product is only slightly soluble in water; therefore, at chlorine concentrations greater than 1 mg/L, the final reaction mixture must contain 2-propanol to prevent product precipitation and color fading. |
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Scope and Application
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The syringaldazine (FACTS) test was developed specifically for determining free chlorine in water. It is unaffected by significant concentrations of monochloramine, dichloramine, nitrate, nitrite, and oxidized forms of manganese. |
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Applicable Concentration Range
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0.1 to 10 mg/L |
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Interferences
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Interferences common to other methods for determining free chlorine do not affect the FACTS procedure. Monochloramine concentrations up to 18 mg/L, dichloramine concentrations up to 10 mg/L, and manganese concentrations (oxidized forms) up to 1 mg/L do not interfere. Trichloramine at levels above 0.6 mg/L produces an apparent free chlorine reaction. Very high concentrations of monochloramine (> or = 35 mg/L) and oxidized manganese (> or = 2.6 mg/L) produce a color with syringaldazine slowly. Ferric iron can react with syringaldazine; however, concentrations up to 10 mg/L do not interfere. Nitrite ( < or = 250 mg/L), nitrate (< or = 100 mg/L), sulfate (< or = 1000 mg/L), and chloride (< or = 1000 mg/L) do not interfere. Waters with high hardness (> or = 500 mg/L) will produce a cloudy solution that can be compensated for by using a blank. Oxygen does not interfere. Other strong oxidizing agents, such as iodine, bromine, and ozone, will produce a color. |
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Quality Control Requirements
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See Section 4020 Quality Assurance/Quality Control. |
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Sample Handling
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Chlorine in aqueous solution is not stable, and the chlorine content of samples or solutions, particularly weak solutions, will decrease rapidly. Exposure to sunlight or other strong light or agitation will accelerate the reduction of chlorine. Therefore, start chlorine determinations immediately after sampling, avoiding excessive light and agitation. Do not store samples to be analyzed for chlorine. |
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Maximum Holding Time
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0.25 hour (See Section 1060) |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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