The Large Lakes Observatory at the University of Minnesota Duluth operates a Seal Analytical AQ400 discrete analyzer that can be used for a broad range of analytical chemical procedures.
At present, the analytical services we offer are given below.
SEAL AQ400 Method
Equivalent EPA/Standard Methods
Range, Detection Limit
Internal sales (any U of M account)
USEPA 350.1 Rev 2.0
Range = 0.02-2.0 mg N/L,
MDL = 0.004 mgN/L
USEPA 353.2 Rev 2.0
Range = 0.012-2.0 mg N/L
MDL = 0.003 mg N/L
o-Phosphate (SRP) (155A)3
USEPA 365.1 Rev 2.0
Range = 0.003-0.3 mg P/L
MDL = 0.0006 mg P/L
Total Phosphorus (TDP, TP, PP) (119A)4
USEPA 365.1 Rev 2.0
Range = 0.01-1.0 mg P/L
MDL = 0.003mg P/L
USEPA 370.1 Rev 2.0
Range = 0.1-10.0 mg Silica/L
MDL = 0.018mg Silica/L
SM 4500-SO42- E
Range = 5.0-40 mg SO4/L
MDL = 0.09 mg SO4/L
Spectrophotometric Determination of Sulfide, HMSO.
Range = 0.03-1.0 mg S2-/L
MDL = 0.004 mg S2-/L
1Ammonia: Hypochlorite-phenol method equivalent to EPA 350.1 version 2 (1993) and Standard Methods 4500-NH3 G (19th and 20th). Freshwater only (not for brackish or saline water). Interferences include dissolved calcium and magnesium, sample turbidity and color.
2Nitrate/Nitrite: Cadmium column reduction to nitrite with reaction with phosphoric acid, sulfanilamide and N-(1-naphthylethylenediamine) dihydrochloride. Equivalent to EPA 353.2, version 2 and Standard Methods 4500-NO3 F (18th, 19th, and 20th). Interferences include chlorine, sodium thiosulfate, highly alkaline or overly acidified samples, iron, copper, other metals, oil and grease.
3Phosphate, Ortho: Acidic molybdate/antimony with ascorbic acid reduction (phosphomolybdenum blue). Equivalent to EPA 365.1, version 2 (1993) and Standard Methods 4500-P F (18th, 19th, and 20th). Interferences include bariuim, lead, silver, silica, nitrite, sulfide, arsenate, hexavalent chromium, and arsenic.
4Phosphorus, Total: Acidic molybdate/antimony with ascorbic acid reduction (Manual persulfate digestion required). Equivalent to EPA 365.1, version 2 (1993) and Standard Methods 4500-P B, F (18th, 19th, and 20th). Interferences include high iron, copper, and silica; nitrite, sulfide, arsenate, and hexavalent chromium.
5Silica (Reactive Silica): Acidic molydate with ANSA reduction (silico-molybdenum blue). Equivalent to Standard Methods 4500-SiO2 D (20th). Interferences include phosphorus and tannins, iron and sulfides.
6Sulfate: Barium chloride turbidimetric method with use of gelatin as suspension agent. Equivalent to ASTM D516-11. Interferences include high iron, copper, and silica; suspended materials, polyphosphates and phosphonates, very high chloride, aluminum, polymers, and large quantities of organic matter.
7Sulfide: Potassium dichromate converts DPD (N,N-Diethyl-p-phenylenediamine) to the free radical which reacts rapidly with sulfide to produce a blue color (Ethylene Blue) which can be measured photometrically at 660nm. Interferences include thiosulfates, sulfites and iodides, and zinc as zinc acetate.
Preservation: Samples should be preserved by freezing or with the addition of sulfuric acid.
To inquire about any services listed on this page, please contact Sandra Brovold ([email protected]). Turnaround times are variable. We will give you our best estimate at the time of the order.