Method Summaries

Orthophosphate

Orthophosphate is analyzed using the SEAL Analytical AQ2 Discrete Analyzer. An antimony-phospho-molybdate complex is formed when acidic molybdate and antimony potassium tartrate react in the presence of orthophosphate. Ascorbic acid reduction of this complex yields phosphomolybdenum blue; the phosphorus concentration is proportional to the color, measured photometrically at 880 nm.


References:


SEAL Analytical, AQ2 Method EPA-155-A Rev. 0

Methods for the Determination of Inorganic Substances in Environmental Samples, USEPA 600/R 93/100, August 1993: Method 365.1, Rev. 2.0.

Standard Methods for the Examination of Water and Wastewater, APHA/AWWA/WEF, method 4500-P-F (1999 forward).

Nitrate + nitrite

Nitrate + nitrite is analyzed using the SEAL Analytical AQ2 Discrete Analyzer. Nitrate is chemically reduced to nitrite with a cadmium coil. The nitrite (original nitrite plus nitrate from chemically-reduced nitrate) reacts with sulfanilamide and then couples with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a magenta azo dye. The color is measured photometrically at 520 nm.


References:


SEAL Analytical, AQ2 Method EPA-127-A Rev. 9


Methods for Determination of Inorganic Substances in Environmental Samples, USEPA 600/R 93/100, August 1993: Method 353.2, Revision 2.0

Standard Methods for the Examination of Water and Wastewater, APHA/AWWA/WEF, method 4500-NO3--F (2000).

Nitrite

Nitrite is analyzed using the SEAL Analytical AQ2 Discrete Analyzer. Nitrite reacts with sulfanilamide and then couples with N-(1-naphthyl)-ethylenediamine dihydrochloride (NEDD) to form a magenta azo dye. The color is measured photometrically at 520 nm.

References:

SEAL Analytical, AQ2 Method EPA-137-A Rev. 4

Methods for the Determination of Inorganic Substances in Environmental Samples, EPA 600/R93/100, August 1993; Method 353.2, Revision 2.0.

Standard Methods for the Examination of Water and Wastewater, APHA/AWWA/WEF method 4500-NO3--F (2000).

Ammonia

Ammonia is analyzed using the SEAL Analytical AQ2 Discrete Analyzer. Ammonia reacts with hypochlorite, previously liberated from dichloroisocyanurate, to form a chloramine. At an alkaline pH of 12.6, salicylate and the chloramine react to form indophenol blue dye. The color is proportional to the concentration of ammonia, and is measured photometrically at 660 nm.


References:

SEAL Analytical, AQ2 Method EPA-148-A Rev. 2

Methods for the Determination of Inorganic Substances in Environmental Samples, USEPA 600/R 93/100, August 1993: Method 350.1, Revision 2.0.

Standard Methods for the Examination of Water and Wastewater, APHA/AWWA/WEF method 4500-NH3-G (19th, 20th Ed.).

Total alkalinity (m-alkalinity)

Total alkalinity is analyzed using the SEAL Analytical AQ2 Discrete Analyzer. The sample is added to a buffered (pH 3.1) potassium hydrogen phthalate (KHP) solution. The KHP solution neutralizes alkaline species in the sample and adjusts to a slightly higher pH. Methyl orange has a red to yellow color change; the pH range of its color transition from 3.0 to 4.5 encompasses the equivalence point of a titration for total alkalinity (4.5). The alkalinity of a sample leads to a red color loss proportional to the total alkalinity of the sample. The color is measured photometrically at 520 nm.


References:

SEAL Analytical, AQ2 Method EPA-100-A Rev. 4


Methods for Chemical Analysis of Waters and Wastes, USEPA 600/4-79-020, 1983: Method 310.2.

Total organic carbon (TOC)

Standard analysis

Total organic carbon is analyzed using the Shimadzu TOC-LCPH analyzer with TNM-L. Prior to injection, samples are acidified to convert inorganic carbon to CO2, then sparged to remove the CO2. The remaining carbon is referred to as “non-purgeable organic carbon”, or NPOC. The sample is injected into a combustion tube that contains oxidation catalyst, and is combusted at 680°C to convert the organic carbon into CO2. Carbon-free carrier gas delivers the CO2 to a non-dispersive infrared (NDIR) gas analyzer, and the NDIR signal forms a peak that is measured.



High sensitivity analysis

High sensitivity TOC measurements are for samples under 3 mg-C/L. The standard catalyst is replaced with a high-sensitivity catalyst that has a higher surface area. The remainder of the method is the same as the standard NPOC method (above).

NOTE: If samples with higher amounts of TOC are submitted for high-sensitivity analysis, this can lead to carryover and cause issues with the catalyst. Please contact us with questions or you are unsure which TOC analysis is appropriate for your samples.



Reference:

Standard Methods for the Examination of Water and Wastewater, APHA/AWWA/WEF, method 5310-B (21st Ed).

Total nitrogen (TN)

Total nitrogen is analyzed using the Shimadzu TOC-LCPH analyzer with TNM-L. Samples are combusted at 720°C and TN decomposes to nitrogen monoxide. The carrier gas delivers the nitrogen monoxide to a chemiluminescence gas analyzer, where a peak that can be measured is generated.