Methods of  Rainwater Analysis

Rain water samples collected on The Evergreen State College campus were analyzed for pH, alkalinity and for common ions using a variety of analytical techniques. Immediately upon sample collection, the volume and pH was measured. pH was determined using a variety of commercial pH meters. Alkalinity was measured by titration with standardized HCl to a pH of 4.5. 

Anion Analysis

Modified from EPA Method #300.0 The Determination of Inorganic Anions In Water By Ion Chromatography. Samples were pre-filtered (0.45micron) and analyzed the day of collection.  Quantitative analysis of chloride (Cl^-), Nitrite (NO₂^-), nitrate (NO₃^-), phosphate (PO₃^-) and sulfate (SO₄^2-) was performed using a Dionex Ion Chromatograph with a AS4A-SC 4mm ion exchange column.  Samples were filtered again (0.2 micron) at the time of analysis.  A three-point calibration curve, created within 24 hours of the sample analysis, was used to determine analyte concentrations. 

Cation Analysis

Samples were filtered (0.45 micron), acidified with ultra-pure HCl, and stored at 4^oCelcius prior to analysis. Analysis for calcium (Ca²⁺⁾, magnesium ( Mg²⁺⁾, potassium (K⁺) and sodium (Na⁺)  was performed using a Perking Elmer 305B Atomic Absorption Spectrophotometer.   Quantitative results were obtained using blanks and a three standard linear calibration curve.  Samples and blanks were treated with an excess of lanthanum chloride (releasing agent) and cesium chloride (ionization suppressor).