Experiment 2: Samples

Potassium Hydrogen Pthalate (KHP)

Concentration Range: 0.5, 1, 2, 3, 4, 5, 10 mg/L C

Salicylic Acid: [TOC] = 5 mg/L as C

Filtered Water: 0.45 um Whatman GF-C glass filter
Unfiltered Water
Glutamic Acid (HOOCCH₂CH₂CCHCOO- NH₃+) - [TOC] = 2 mg/L as C

Standards were prepared by diluting a 100 ppm as carbon (ppm C or mg C/L) stock solution of potassium acid phthalate (KAP) with bidistilled water to make seven standards of 0.5, 1, 2, 3, 4, 5, and 10 ppm C.

Samples of 2 ppm C glutamic acid, 5 ppm C salicylic acid, tap water, Histosol soil extract (17.5% TOC) and natural water from the Prado wetlands were prepared. The glutamic acid and salicylic acid solutions were made by dissolving 9.8 mg and 16.4 mg of respective material in bidistilled water to make a 200 ppm C solution of glutamic acid and a 500 ppm C solution of salicylic acid. These stock solutions were diluted with bidistilled water to make the 2 ppm C and 5 ppm C samples listed above.

The pH of each standard and sample was measured using a pH meter. The absorbance at 254 nm, 365 nm, 465 nm and 665 nm (A₂₅₄, A₃₆₅, A₄₆₅, and A₆₆₅) of all samples and standards plus a blank were read on a Cary 1-E UV-Visible Dual -Beam Scanning Spectrophotometer in a 1 cm quartz cell. The samples, the blank and the 4 ppm C KAP standard were also scanned from 250 nm to 700 nm.

The pH of each standard, sample and the blank was lowered by adding enough nitric acid to get pH 2. The absorbances at 254 nm, 365 nm, 465 nm and 665 nm of all preparations were again measured using the Cary spectrophotometer. As before the acidified samples, blank and the 4 ppm C KAP standard were scanned from 200 nm to 700 nm.

Sample Description

Prado Wetlands Santa Ana River
Histosol Soil Extract, 17.5% TOC