Pyrocat-HD sol. A - keeping airtight, just a thought

[eumenius]

Hello friends,

I just want to share my idea how to keep the Pyrocat-HD first solution for long without a serious deterioration by air oxygen. I've got some plastic single-use injection syringes (5 ml for my 500 ml tank, and 20 ml for Combiplan-T), and filled each syringe with a precise dose of pyrocatechin-containing solution needed for one tank volume of working developer - almost without air bubbles, capping each syringe with its shielded needle. I am quite sure that it would keep really long this way - in the dark, and maybe in a fridge. Mixing it is also very easy now - you just press the piston, and the pre-measured volume goes in your mixing beaker. The syringes are of course recyclable, and both versions (fully plastic and with silicone rubber piston) are equally good - the rubber does not deteriorate from contact with pyro solution.

Is it better that making an inert atmosphere in a bottle every time? On my opinion, yes - and much more hygienic

Cheers from Moscow,
Zhenya

 

[gainer]

Most of the air that gets into developers that we mix is in the water from the start. There is nothing wrong with your idea, but I would suggest working on a way to mix the developer without entraining air in the process. Of course, you could mix the stock in propylene glycol and then use the individual syringes for storage.

 

[w35773]

I wonder about oxygen migration across the plastic syringe wall. Am I crazy?

 

[gainer]

I wonder about oxygen migration across the plastic syringe wall. Am I crazy?

I thought that was a prerequisite for posting here

 

[eumenius]

Yes, I completely agree with you - but I am mixing my developers, both stocks and working solutions, with ultrasound bath-degassed distilled water, because I have the whole setup in my lab (I'm a virologist, after all ). So it looks to me that the full elimination of any air overhead in storage of Pyrocat would much improve its keeping capabilities

Most of the air that gets into developers that we mix is in the water from the start. There is nothing wrong with your idea, but I would suggest working on a way to mix the developer without entraining air in the process. Of course, you could mix the stock in propylene glycol and then use the individual syringes for storage.

 

[eumenius]

Oh Russell,

I think you are missing the point - the air would migrate through the needle's natural opening, ruining all the pyrocatechine inside May I ask you to calculate the speed of developer's half-oxidation if I supply you with oxygen diffusion rate and needle gauge and length? )))))

I wonder about oxygen migration across the plastic syringe wall. Am I crazy?

 

[pkrentz]

Needels

If I remember right from my nursing days, all syringes had caps on the needels that were pretty tight. Pat:

 

[eumenius]

But of course - how else are they going to keep the needle sterile, eh?

If I remember right from my nursing days, all syringes had caps on the needels that were pretty tight. Pat:

 

[noseoil]

Zhenya, the only problem I've had with pyrocat came from age after about a year. It just went flat when I was developing. The next batch I got came mixed with glycol and has a much better shelf life (per Pat's suggestion above). Not sure about the extra keeping qualities, but in the quantity I get, it will be used up well before age is a consideration (mine or the solution's). If you have access to a supply of glycol, next time give it a try and you will have a long lasting shelf life. I do like your idea for a supply of pre-measured developer. Sounds like a good idea. I keep two different syringes (labeled "A" & "B") for measuring. More important now at my age is to have the reading glasses handy for seeing the lines on the cylinder! Best, tim

 

[gainer]

Do we have a veterinarian in our midst? I am thinking of a quite large syringe without a needle to hold the main supply, hanging with the plunger up, with a smaller syringe of the sort avaliable at many drugstores for oral dosing, also without a needle, closing off the larger syringe. As liquid is drawn off into the smaller syringe, the plunger of the large one moves down, keeping air out. The whole system must be pivoted so that it can be inverted when the small syringe is removed until it is replaced. I have had experiences with collapsible storage of other types, and the only other one I can think of that was reasonably good is the wine bag type.
With regard to glycol, either propylene or ethylene will do if access by children or retarded persons is not a problem. Even so, the mixture of catechol, phenidone and ascorbic acid is not to be imbibed no matter what the solvent. Glycerine can be used as well, but its viscosity may be a problem.

 

[Alan Johnson]

Most of the oxygen comes from the airspace. 22.4x5 litres of air contains 32g oxygen (Avogadro's law) so 1 litre airspace contains 286 mg oxygen. The liquid developer has oxygen at its solubility of 9mg/L so 1 litre developer can only dissolve at most 9mg oxygen at 20C.
Alternative to Zhenya's ingenious suggestion is to use canned air:
http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0073Re

 

[eumenius]

Alan,

your calculations would be true, if the oxidation reaction did not change the equilibrium - 9 mg oxygen per liter, about 0.0035 mole of oxidative equivalents, is the equilibrium concentration. When pyrocatechin gets oxidized, it attracts half a mole of oxygen per mole, so the equilibrium gets shifted until all the pyro is not converted to corresponding quinone. For example, one Combi-Plan tank contains 1250 ml of working developer - 600 mg of pyrocatechin, C6H602 (110 mg/mmol, about 0.005 moles in total). So theoretically, the developer can have dissolved in it almost two times more oxygen at r. t., than needed to fully oxidize all the catechol. If there were no sodium metabisulfite, chemically binding the oxygen, and if the oxidation rate was really high (like the one of highly alkaline pyrogallol solutions) all would be lost

Zhenya

Most of the oxygen comes from the airspace. 22.4x5 litres of air contains 32g oxygen (Avogadro's law) so 1 litre airspace contains 286 mg oxygen. The liquid developer has oxygen at its solubility of 9mg/L so 1 litre developer can only dissolve at most 9mg oxygen at 20C.
Alternative to Zhenya's ingenious suggestion is to use canned air:
http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0073Re

 

[danschmidt]

In a cleanroom that I used to work in, we used to have these great bottle top dispensers that had a syringe type mechanism built in and where very repeatable. They were at the acid bench for mixing up etches.

I thought they would be great for photographic chemistry, but then I discovered they were like 400 dollars each.

 

[gainer]

I think the phenidone would be oxidized first without either the bisulfite of the water solution of the ascorbic acid of the glycol solution. The same goes for the Metol of Pyrocat MC or the p-aminophenol of Pyrocat PC.

 

[Alan Johnson]

'Classic Black and White Formulas' by Patrick Dignan gives phenidone 1g/L sodium bisulfite 5g/L as a phenidone preserving solution. With 10g/L sodium bisulfite, Pyrocat HD stock should be quite a good preservative,the phenidone only oxidizing slowly.

 

[Tom Hoskinson]

'Classic Black and White Formulas' by Patrick Dignan gives phenidone 1g/L sodium bisulfite 5g/L as a phenidone preserving solution. With 10g/L sodium bisulfite, Pyrocat HD stock should be quite a good preservative,the phenidone only oxidizing slowly.

Based on my experience, Phenidone will oxidize and die in a Sodium Bisulfite solution - however, it will oxidize more slowly than it would if dissoved in water.

I keep a stock solution of Phenidone dissolved in Propylene Glycol. It is now over 3 years old and is still active.