Modified by Adrian Green for Arctic Streams analysis – December, 2003
This method is based onprevious methods used by Ian Washbourne and Suzanne Thomas, using acid persulfate digestion and analysis on a spectrophotometer. Because our water samples are pre-acidified with HCl in the field (0.1 ml of6N HCl/50 ml sample), I did not acidify them further. I used acidified DI water, acidified to the same approximate normality as the samples, to make the working standards. I also digested a standardcurve with each batch of samples, and ran a non-digested curve each time as well. Changes to Ian’s method are highlighted in bold.
Chemicals/reagents Amount / Composition.
Potassium persulfatesolution** < 5 ml (5.0 g / 100 ml, 0.18 M)
HCl(aq) ~ 2 ml (5.6 N )
A/ Ammonium heptamolybdate tetrahydrate solution* 12.5 ml (2.5 g in 25 ml H2O)
B/ Potassium antimonyl tartrate solution*2 ml (0.5 g in 20 ml H2O)
C/ Sulfuric acid solution 85 ml (250 ml made up to 1 L with H2O)
Acidified DI for working standards (0.012 N) 2.14 ml 5.6 N HCl in 1 L DI
Working reagent 1**100 ml (Add 50 ml of C to 50 ml of 10g / 50ml Ascorbic acid solution.)
Working reagent 2** ~ 50 ml (Add 35 ml of C to 12.5 ml of A, mix on the vortex and then add 2 ml of B. Re-mix)
* stable formonths in dark bottle
**make these fresh each time
-To each vial, sample (10 ml) was added and then concentrated HCl was added in order to acidify to pH 1, (1 drop, 5.6 N) (notnecessary for pre-acididfied samples). I only added acid to non-acidified standards and blanks - ACG. The tubes were then vortexed to mix.
-Potassium persulfate reagent (0.25 ml, 0.05g/ml) was then addedto each vial and vortexed to mix. Each tube was tightly capped with Teflon lined phenolic caps ready for autoclaving. A few of the tubes were marked with etching or pen in order to create a visual...