# تحديد النتريت والنترات في مياه الشرب



## نزيه محمد1985 (10 مارس 2010)

اريد طرق عن كيفية تحديد النتريت و النترات في مياه الشرب


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## M.eltaief (6 أغسطس 2011)

*Determination of Nitrate NO3-*​ ​​ This method enclosed in water and wastewater standard test method book by world health organization, and American Public Health Association.​​ Determination of nitrate (NO3-) is difficult because of relatively complex procedures required, the high probability that interfering constituents will present, and the limited concentration ranges of the technique.​​ Principle:​​ This method is screening techniques for determining approximate NO3- concentration. An ultraviolet (UV) technique that measures the absorbance of NO3- at 220 nm is suitable for uncontaminated waters (low in organic matter). Because dissolved organic matter may absorb at 220 nm and NO3- does not absorb at 275 nm, a second measurement made at 275 nm may be used to correct the NO3- value. The extent of this empirical correction is related to the nature and concentration of organic matter and may vary from one water to another. Consequently, this method is not recommended for waters requiring a significant correction for organic matter absorbance although it may be useful in monitoring NO3- levels within a water body in which the nature of the dissolved organic matter remains constant.​​ ​​ *Interference: *​​ 

Filtration of the sample is intended to remove possible interference from suspended particles.
Acidification with _1N_ HCl is designed to prevent interference from Hydroxide or Carbonate concentrations up to 1000 mg CaCO3/L. chloride has no effect on the determination.
Dissolved organic matter, surfactants, NO2, and Cr6+ interfere
Inorganic substances can be compensated for independent analysis of their concentrations and preparation of individual correction curves.
 ​ *Apparatus: *​​ ​​ 

*Spectrophotometer*, for use at 220 nm and 275 nm with matched silica cells of 1-cm or longer.
For sample filtration use membrane filter (0.45- μm pore diameter membrane filter and appropriate filter assembly), or acid wash filter paper sufficiently for fine precipitates.
Nessler Tubes, 50-mL, short form
 ​ *Reagents:*​ ​ 

Use distilled or deionized water of highest purity to prepare all solutions and dilutions.
Stock nitrate solution: dry potassium nitrate (KNO3), in an oven at 105 ◦C for 24 h. Dissolve 0.7218 g in water and dilute to 1000 mL. Preserve with 2 mL chloroform/L; this solution is stable for at least 6 months (1.0 mL = 100 μg NO3- - N).
Standard nitrate solution: Dilute 50.0 mL stock nitrate solution to 500 mL with water; 1.0 mL = 10.0 μg NO3- - N).
1_N_ HCl. 
 ​ *Procedure:*​ Start NO3- determination promptly after sampling. If storages is necessary, preserve samples with 40 mg HgCl2/L and store at 4 C or freeze at – 20 C.​ 

*Sample Treatment:* to 50 mL clear sample, filtered if necessary , add I mL HCl solution and mix well
*Preparation of standard curve:* Prepare NO3- calibration standards in the range 0 to 7 mg NO3- - N/L (0 to 350 μg NO3- - N/50 mL) by added the following volumes of standard nitrate solution: 0, 1.0, 2.0, 4.0, 7.0, and 35.0 mL to the Nessler tube and treated in same manner as samples, then diluted to 50 mL by deionized water. 
*Spectrophotometric measurement:* Read absorbance against distilled or deionized water and set at zero absorbance. Use a wavelength of 220 nm to obtain NO3- reading and a wavelength of 275 nm to determine interference due to dissolved organic matter.
 ​ *Calculation:*​ 


*Correction for dissolved organic matter:* subtract two times the absorbance reading at 275 nm from the reading at 220 nm to obtain absorbance due to NO3-. Convert this absorbance value to NO3- - N from standard curve. *NOTE: If correction value is more than 10% of the reading at 220 nm, do not use this method*.

 ​ ​ *mg NO3- - N/L = net μg NO3- - N ( in 50 mL final volume) ∕ mL sample*​


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