Another way to avoid DTPA is to add the ascorbate (or ascorbic acid) just before using. But doing so constrains you to one-shot processing and thus no replenishment.
Mark
The easiest thing to do is simply avoid ascorbates when scratch-mixing developers so that exotic sequestering agents aren’t needed.
Another way to avoid DTPA
I don't want to avoid DTPA-Na5 because I have it as 40% solution. I just mixed a bottle of Xtol and tomorrow I will make first test.
I was thinking.. what if I would double DTPA quantity? Ron Mowrey's C41 formula asks for 8.43 g of this solution which translates into 3.37 g of dry product (3.3 times more than Xtol) and CD4 is far less temperamental than ascorbate being also protected by the HAS
First, I re-read your spreadsheet and now understand how you computed the weight of NaOH.
Regarding DTPA: The patent might have too little. Here are two comparisons from my notes:
(1) The MSDS for DDX states that 1-5% of the concentrate is DTPA-5Na. Based on its specific gravity, that is at least 13 g. It's diluted 1+4, which is 2.6 g/L in working solution. At least, and probably higher.(2) Fuji Patent 6878510 specifies 2 g/L of DTPA-5Na, twice Kodak's XTOL patent.These two data suggest that your 3.37 g/L is closer to what Kodak ships than 1 g/L.
If I were cloning Xtol as you are, I'd boost DTPA-5Na to Mowrey's 3.37 g and raise the pH to 8.2 by adding NaOH or s. carbonate.
Mark
Incidentally a decade or more ago (I can’t remember exactly when but I did discuss it with Dick Dickerson at the time) the metaborate was substituted with borax in commercially packaged XTOL.
Speaking with my Patent Engineer hat on, don't take any example like this given in a patent as gospel. It's just what it says it is: an example of a B&W film developer. Which may or may not be Xtol. More likely than not, it only bears a passing resemblance to the actual formula Kodak used.BTW, the XTOL patent specifies 1 g of DTPA*5Na for its "Dry Formulation", so that weight is for the dry powder and not a solution.
For your reference, here is a screenshot of the formula in the patent:
@Craig, I get what you're saying, but given that the XTOL-derivatives that align closely with the patented formula appear to work identically to 'real' XTOL as manufactured, what's the practical implication of your words?
C41 patent formulas are fairly close to the real deal
However note in the XTOL patent it is suggested the chelating agent(s) can be present in amounts up to 0.02 mol/l.
Regarding DTPA-Na5:
The MSDS for the 5-liter packets of XTOL say that DTPA is 1-5% of the packet's weight. That works out to 0.5 to 2.5 g/L.
This tells me that you have extensive knowledge of developers.
Can you recommend a quantity of DTPA-5Na?
Also, would boosting pH by adding s. carbonate increase buffering? I don't think so, but my knowledge of chemistry is poor, so I have no confidence in my analysis. @Alain Deloc wishes to clone XTOL, and that would mean not altering its buffering.
target pH of 8.2
4g/l DTPA or 5g/l DTPA-Na5 maybe?
Kodak patent recommends a pH between 8.0 and 8.5, so any value in between is basically ok.
I'm not sure I follow the buffering/pH question. I definitely would not move from the target pH of 8.2 so I would not use sodium carbonate.
Adding carbonate will shift pH up
Well, yes, as long as the final pH after adjustment is 8.2 - or you'd have to revise the development times for the pH you end up at.
I can see what @Alain Deloc might have been hinting at (Alain, correct me if I'm wrong). Adding carbonate will shift pH up, but if you then adjust with e.g. acetic acid, you end up with a buffer of a higher molarity. The buffering action is effectively stronger/more robust. But pH adjustment is needed to set the buffer at the desired pH.
I must laugh at the XTOL patent. In the "summary of the invention" near the beginning, it says "borate as the sole buffer", yet the formula includes both sulfite and metabisulfite, which form a second buffer (the first is s. metaborate or borax). As @Craig posted, patents can contain shenanigans.
In patent language, the "Summary of the invention" is just the claims paraphrased. So perhaps they had to claim only one buffer, as two might have been unpatentable.
Kodak patent recommends a pH between 8.0 and 8.5, so any value in between is basically ok.
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