Sample Processing

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Although the majority of water samples collected from stream and reservoir sites look "clean", a certain amount of sample preparation must be done on the samples before lab analyses are started.

Sample Preparation for Metal Analysis

Water samples arrive in 1-Liter plastic bottles. For metals analysis, a portion of each sample is removed and placed into a new, 250-mL HDPE[1] plastic bottle with screw top lid. To this smaller aliquot, we add a solution of nitric acid (HNO3) in order to reduce the pH of the sample to < 2. This helps to keep metal cations (M+) dissolved and prevent them from forming insoluble hydroxide precipitates until they can be analyzed.[2]

When ready to analyze, a small portion of the acidified sample (~15 mL) is filtered through a 0.45-μm syringe filter disk into a sample test tube and capped. Filtration is necessary to remove any suspended solids or biologics present that may harm the instrument used for analysis.

Sample Preparation for TDS and Salts Analyses

When ready to analyze a sample for dissolved anionic salt constituents (e.g., chloride, nitrate, etc.) by ion chromatography, a small portion of the non-acidified sample (~15 mL) is filtered through a 0.45-μm syringe filter disk into a sample test tube and capped. Filtration is necessary to remove any suspended solids or biologics present that may harm the instrument used for analysis.

When ready to analyze a sample for total dissolved solids (TDS), a larger portion (~110 mL) of the non-acidified sample is filtered through a 0.45-μm syringe filter disk. Then, 100 mL of this filtered sample is placed into a porcelain drying crucible to carry out the remainder of the analysis. For TDS, we filter samples to remove any suspended solids that would add mass to the final calculation and provide an error.

Sample Preparation for Organics Analysis

See Analysis of Organics.

Notes

  1. ^ High density polyethylene.
  2. ^ Once acidified, these samples can be stored up to 6 months.