Larry Soderblom
12/02/2006, 09:09 PM
I posted this on the Salifert discussion but I thought I'd post it here as well:
I have been working with a new Sr test kit (expiration date 9/2011). This is the one that tests for Ca (w/Sr-1, Sr-2, Sr-3) and then, in the same vial, continues on to test for Sr (w/Sr-4, Sr-5, Sr-3). It's a tough kit to use but testing for Sr in the presence of lots of Ca & Mg is tough to do in any case, so I've read. I think I am getting the hang of it but have a couple of questions about color change. I had been adding drops of Sr-3 until the solution becomes as blue as it will get---with little or no purple or pink cast. I concluded that I must have been adding too much Sr-3, particularly in the last part as I was getting Sr in the range of 0-4 ppm. From one of Randy Holmes-Farley's articles on water parameters I read that Instant Ocean made-up water has a Sr of ~15 ppm. I made up a new batch of this salt water and adjusted the Ca so as to be ~450ppm (the initial Instant Ocean water was ~350ppm). I got consistent results for Sr from the Salifert Sr test kit if I stopped adding reagent Sr-3 as soon as the color changed from bright pink to dull purplish blue. This change seems to happen rapidly (within a drop). If I kept adding Sr-3 until the color was full blue I got a very low and unrealistic Sr concentration. So I think the final color can have some purplish tone and does not have to be full blue. Does this make sense? :)
I have been working with a new Sr test kit (expiration date 9/2011). This is the one that tests for Ca (w/Sr-1, Sr-2, Sr-3) and then, in the same vial, continues on to test for Sr (w/Sr-4, Sr-5, Sr-3). It's a tough kit to use but testing for Sr in the presence of lots of Ca & Mg is tough to do in any case, so I've read. I think I am getting the hang of it but have a couple of questions about color change. I had been adding drops of Sr-3 until the solution becomes as blue as it will get---with little or no purple or pink cast. I concluded that I must have been adding too much Sr-3, particularly in the last part as I was getting Sr in the range of 0-4 ppm. From one of Randy Holmes-Farley's articles on water parameters I read that Instant Ocean made-up water has a Sr of ~15 ppm. I made up a new batch of this salt water and adjusted the Ca so as to be ~450ppm (the initial Instant Ocean water was ~350ppm). I got consistent results for Sr from the Salifert Sr test kit if I stopped adding reagent Sr-3 as soon as the color changed from bright pink to dull purplish blue. This change seems to happen rapidly (within a drop). If I kept adding Sr-3 until the color was full blue I got a very low and unrealistic Sr concentration. So I think the final color can have some purplish tone and does not have to be full blue. Does this make sense? :)