Hi Mark, I no longer have any standards for photograde chemicals. At one time I did, and once or twice posted some data as examples. One I can still find is for potassium carbonate - not your chemical - but probably similar specs. This was from ANSI PH4.229-1987: Iron (Fe): 0.001% (m/m) max. So my guess is that the sulfite spec was the same, meaning that probably your supplier (Spectrum) meets a photograde spec for iron in sulfite. Probably. (Assuming carbonate and sulfite had the same spec for iron, and that the standard hasn't changed, and that I didn't mistype the original post.)
Originally Posted by albada
Regarding water, in general, my standard photo reference has always been a 1965 paper, Water Quality Criteria, by Lloyd West of Kodak. (The 1997 edition of IS&T's Handbook of Photographic Science and Engineering still used this paper as a reference.) Per West, in 1965 the US Drinking Water Standard was 0.3 ppm iron. He notes, "that level of iron can be expected to gradually produce stains and deposits on equipment and possibly photographic products." In a separate table of "Practical Limits for Common Impurities for Water," he lists 0.1 ppm for each of copper, iron, and manganese.
West only has a couple of paragraphs on iron, also saying "Iron is usually present in well water...especially in acid waters of pH less than 7. Sulfates of iron and aluminum are common sources of acidity of well waters."
Part of what West did was a survey of processing labs, and specs on their water. Today, you can likely find all of those water analyses on-line, searching for the city name and "water analysis," or "water quality report."
Hope this helps a bit.