Ortho-phosphate 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 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 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).

Ammonium 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 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.

Silica (SiO2) is analyzed using the SEAL AQ2 Discrete Analyzer. When combined with ammonium molybdate under acidic conditions, molybdate-reactive silica forms a yellow molybdo-silicic acid complex, which is then reduced with 4-amino-3-hyrdoxy-1-naphthalenesulfonic acid and forms a silico-molybdenum blue complex. The color is measured photometrically at 660 nm.

References:

SEAL Analytical, AQ2 Method EPA-122-A Rev. 9

Methods for Chemical Analysis of Waters and Wastes, USEPA 600/4-79-020, 1983: Method 370.1.

Standard Methods for the Examination of Water and Wastewater, APHA/AWWA/WEF, method 4500 SiO2– D (2000 forward)

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 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.

Inorganic carbon is analyzed using the Shimadzu TOC-LCPH analyzer with TNM-L. The inorganic carbon measured in this method includes carbonates and dissolved carbon dioxide. Samples are acidified to convert carbonates to CO2. This CO2, plus dissolved CO2 in the sample, are sparged with carbon-free carrier gas to volatize the CO2 and deliver the CO2 to a non-dispersive infrared (NDIR) gas analyzer. The NDIR signal forms a peak that is measured.

The AQUA Lab extracts chlorophyll a pigments concentrated on filters using an ethanol extraction, and then measures chlorophyll a on a Turner 10-AU fluorometer. We use the Welschmeyer method, which uses specific filters that read chlorophyll a in the presence of chlorophyll b and pheophytins. Sample acidification is not necessary with this method.

Related references:

Arar EJ and GB Collins.  1997.  In vitro determination of chlorophyll a and phaeophytin a in marine and freshwater algae by fluorescence.  Cincinnati, Ohio: U.S. Environmental Protection Agency, method 445.0

Nusch EA. 1980. Comparison of different methods for chlorophyll and phaeopigment determination. Arch. Hydrobiol. Beih. Ergebn. Limnol. 14:14-36

Welschmeyer NA.  1994.  Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and phaeopigments.  Limnol. Oceanogr. 39: 1985 – 1992.

Total phosphorus is measured by first converting organic and inorganic-bound phosphorus compounds to soluble phosphorus through digestion. The AQUA Lab uses an alkaline persulfate digestion, which becomes acidic during autoclaving to facilitate the conversion of bound phosphorus compounds to soluble phosphorus.

After digestion, 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 with a spectrophotometer at 880 nm.

Related references:

Ameel, J.J., R.P. Axler, C.J. Owen. 1993. Persulfate digestion for determination of total nitrogen and phosphorus in low nutrient water.  American Environmental Laboratory. 5: 2-11.

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).

Valderrama, J.C., 1981. The Simultaneous Analysis of Total Nitrogen and Total Phosphorus in Natural Waters: Marine Chemistry, v. 21, p. 109–122.