Sequestering Agents.

Out of curiosity, how do the various sequesterers differ from one another in terms of function and performance? Sequestering agents such as those seen in the safety data sheets that are commonly mentioned are Sodium Hexametaphosphate, Sodium Tripolyphosphate and EDTA types.
It is used to be mentioned on the Ilford website before it was updated and of which I can no longer find the link to, that EDTA is not biodegradable and is not removed from waste water by water treatment plants.
EDTA has been successfully removed from Ilford products.
I know if distilled water is used, that a sequestering agent isn`t necessary (an expensive option for some), but I would like advice on the advantages/disadvantages of various sequestering agents.:confused:

I think the advantage is Kodak/Ilford/et all can create a formula that will work with a wide range of water. Good,bad or just average.

If your water is stable [distilled or not] I wonder how hard it would be to make some thing that worked without any EDTA.

Sequestering agents are classified chemically by the materials they sequester (isolate) and their environmental effects. The ability to sequester is sometimes referred to as the complexation constant. You can say that hypo is a selective sequestrant for silver ion for example.

The Dequest family of sequestrants is the strongest I have ever found. Phosphate salts are among the weakest, but best for calcium salts and others in hard water.

The effect varies, and must be gained by lab work and experience to understand what to use. Kodak has now begun using NTA or Nitrilo triacetic acid replacing EDTA in some formulas.

PE

Photo Engineer said:

Sequestering agents are classified chemically by the materials they sequester (isolate) and their environmental effects. The ability to sequester is sometimes referred to as the complexation constant. You can say that hypo is a selective sequestrant for silver ion for example.

The Dequest family of sequestrants is the strongest I have ever found. Phosphate salts are among the weakest, but best for calcium salts and others in hard water.

The effect varies, and must be gained by lab work and experience to understand what to use. Kodak has now begun using NTA or Nitrilo triacetic acid replacing EDTA in some formulas.

PE

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The stuff that I have is called CALGON (500 Grams) and in small print is Sodium Hexametaphosphate [HAZ-CLASS-NR/UN No-NRI] although I`m not sure if there are any other ingredients in the powder.
In the Ilford Manual of photography (page 404), it is suggested that one-half ounce per gallon (3 grams per litre) is a suitable concentration. Will this differ according to how the stock solution is diluted to make up a working strength solution of developer or fixer?
Sequestering agents don`t get mentioned much in the formulary section which is why I asked.
Thanks.

Nick Zentena said:

I think the advantage is Kodak/Ilford/et all can create a formula that will work with a wide range of water. Good,bad or just average.

If your water is stable [distilled or not] I wonder how hard it would be to make some thing that worked without any EDTA.

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Ilford seem to be using Sodium Tripolyphosphate in their powder-form chemicals and DTPA in their liquid concentrates.
http://www.ilfordphoto.com/healthandsafety/datasheet.asp?n=2

Keith;

Calgon comes in 2 forms. One does not work well in photographic processing solutions and the other does. That is why Kodak quit using it, among other things.

We actually used Quadrofos.

Phosphates were banned in many places due to their impact on the environment. That is why Calgon changed the formula.

The sequestering agent is present to compensate for varying types of soft and hard water around the world. It prevents sludge from forming or hazy precipitates. A sequestrant is an essential ingredient of Blixes and Bleaches now used in color film processing.

If you use Distilled Water throughout, or have soft water, no sequestrant is needed at all in the developer, stop or fix.

PE

Photo Engineer said:

Keith;

Calgon comes in 2 forms. One does not work well in photographic processing solutions and the other does. That is why Kodak quit using it, among other things.

We actually used Quadrofos.

Phosphates were banned in many places due to their impact on the environment. That is why Calgon changed the formula.

The sequestering agent is present to compensate for varying types of soft and hard water around the world. It prevents sludge from forming or hazy precipitates. A sequestrant is an essential ingredient of Blixes and Bleaches now used in color film processing.

If you use Distilled Water throughout, or have soft water, no sequestrant is needed at all in the developer, stop or fix.

PE

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I just checked the MSDS on Kodak`s website and they still list Sodium Hexametaphosphate in the MSDS for Dektol (CAT# 1464726).
http://www.kodak.com/eknec/PageQuerier.jhtml?pq-locale=en_US&pq-path=4648

I`ve not seen any mention of Quadrofos on the UK sites that sell photographic grade constituents (sound interesting). Distilled water is quite expensive over in the UK, although that might depend who is selling it.

I would have to look up quadrofos, but we moved to it when Calgon changed formulas, so it might be the alternative to Calgon with the same formula, ie. Hexametaphosphate. This is excellent for hard water.

DW is not a necessity. The water dispensers that use a charcoal or ion exchange filter on them will also dispense water clear of calcium and many other harmful ingredients such as iron.

PE

Keith Tapscott. said:

[...] I would like advice on the advantages/disadvantages of various sequestering agents.:confused:

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First of all, EDTA is not toxic and it is used as a food additive in many products. For example, store-bought mayonnaise often contains a small amount of EDTA. EDTA and other polyamine polycarboxylic acids and their salts are not biodegradable, and they are being phased out from many consumer chemical products. NTA (nitrilotriacetic acid) is only a small bit better in terms of biodegradability, but AGFA started using NTA many years ago. Now NTA is becoming more common among photographic chemical manufacturers.

Chelators like EDTA, NTA and their related compounds are also commonly used in color bleach baths. Although they are much less harmful to the environment than ferricyanide they replaced, more eco-friendly alternatives were developed by companies like AGFA and Konica. Generally speaking, these two companies were more aggressive in making processing chemicals environmentally more compatible than others. (Note: this is mostly in connection with R&D of chemicals for color processing minilabs as the most of the chemicals were consumed in this market.)

There are other chelators and sequestering agents. Inorganic polyphosphates are cheap and effective for calcium and magnesium in alkaline solution, and they used to be very common in laundry detergents. (Incidentally, even with all those stain-decomposing enzymes, only very recently did the phosphate-free laundry detergent become just as good as the old phosphate-containing ones.)

Another strategy to remove calcium and magnesium from water is to use ion replacement. There are many kinds of resin made for this purpose, often comes in granules, beads or in cartridges containing these forms. Zeolite is another thing.

In any case, the selection of chelating agent is not a very simple thing, because there are many variables. One big issue is the kind of metal you want to chelate. Very different kinds of chelators are required to chelate Fe(II) and Fe(III) for example, and also at different pH range. An excellent chelator at one pH can be (and usually is) a very crappy one at another pH. For this reason, if you have difficult needs, such as formulating practical ascorbate-based developers, it is often much easier to combine two or more chelating agents to deal with different metals rather separately.

Ryuji,
I`ve just checked the MSDS for Agfa Refinal Part `A` and it list two agents.
Sodium Hexametaphosphate (10124-56-8) and EDTA (60-00-4).
Is this becoming a common practice in commercial processing products?
It is the use of sequesterers/chelating agents in B&W developers that are of interest to me as I buy commercial stop-baths, fixers and sundries.
Thanks for replying.

Keith;

Sequestrants are needed only in areas of hard water. If you use water run through the carbon+ion exchange resin I mention above, that should work for you just fine.

Sequestrants don't change the qualities of the processing solutions, and if they are not used, the worst thing that can happen is a precipitate forms. In that case, you merely filter out the precipitate. Then the solution is ready to use.

The calcium or iron are present in such small amounts that they don't affect the formula at all. Once removed from filtration, there are no further problems.

PE

Photo Engineer said:

Keith;

Sequestrants are needed only in areas of hard water. If you use water run through the carbon+ion exchange resin I mention above, that should work for you just fine.

Sequestrants don't change the qualities of the processing solutions, and if they are not used, the worst thing that can happen is a precipitate forms. In that case, you merely filter out the precipitate. Then the solution is ready to use.

The calcium or iron are present in such small amounts that they don't affect the formula at all. Once removed from filtration, there are no further problems.

PE

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Thanks PE, that`s reassuring. Perhaps I will just continue to add that little pinch of Calgon though, just to be sure.

Cheers.

Do it. I did the same thing at EK before Calgon changed the formula and then I used Quadrofos, as I said previously. Most of the time I leave it out.

PE

Keith Tapscott. said:

Ryuji,
I`ve just checked the MSDS for Agfa Refinal Part `A` and it list two agents.
Sodium Hexametaphosphate (10124-56-8) and EDTA (60-00-4).
Is this becoming a common practice in commercial processing products?
It is the use of sequesterers/chelating agents in B&W developers that are of interest to me as I buy commercial stop-baths, fixers and sundries.
Thanks for replying.

Click to expand...

Inorganic polyphosphates (the name hexametaphosphate is often used, although it is not exactly correct name) are very cheap and effective but it has some limitations. A combination of EDTA broadens the effective spectrum of the chelation together, and it is a common strategy, but both phosphate compounds and polyamine polycarboxylate compounds are currently being phased out whenever possible. For example, Silvergrain darkroom chemicals use alternative compounds that are readily biodegradable and not EDTA, DTPA, NTA, polyphosphates, etc.

Another thing to note when you buy Calgon and other ingredients by brand name. Calgon is a trade name for sodium polyphosphate including hexametaphosphate. However, the consumer products traded with the same name often do not contain any of the polyphosphate but rather a combination of other chemicals and alkaline agents. (Another example is TSP in consumer packages that doesnt contain any trisodium phosphate but contains silicate or carbonate.) Both of these things work fine (perhaps slightly less well) as a cleaning product, but I recommend to specify chemicals for darkroom use by the name of the compound and be very careful when buying chemicals packaged for consumer use.

I`ve managed to find the Ilford link.
http://www.ilford.com/html/us_english/sds/ChemEnviro/chemenv1.html

If you want sodium hexametaphosphate look at www.chemistrystore.com. They have 10 lbs for 27 usd + shipping.

I'm not sure if an average darkroom user wants to buy 10lbs of it. Even if you make your own laundry detergent (which, I do) 10lbs is a lot.

Maybe several could split it. I can probably use it, but haven't yet. I have a large dehumidifier and lots of humidity in the summer, so I have contrived a simple drain on the condensate tank. But my well water is so hard I can stub my toe on it, but it's good for drinking and saves me from buying calcium and magnesium diet supplements, so I don't want a water softener. Usually I contrive developers that do not precipitate carbonates. PC-TEA is one that works well for my needs. To each his own.

Patrick,

I'm sure I brought this up before, but the water from dehumidifier is far from pure. It takes up all sorts of dust particles, impurities and pollutants from the air. It may be fine for some processing solutions but would not assume it is pure. It's just that it doesn't contain a lot of calcium or magnesium.

People who suffer from mineral scum and deposit on processed film or prints have a few possible options to try before giving up on the hard water. The simplest and effective way is to boil water and cool it down. A lot of minerals are dissolved with carbonic acid, and they will precipitate out once the carbonic acid is removed by boiling. Then use a washing aid bath containing rather generous amount of chelating agents. This is the most effective place to do so because of the neutral to slightly alkaline pH as well as being the final bath other than washing water.

It's sometimes undesirable to use phosphorous-containing compounds like Calgon, sodium tripolyphosphate, sodium hexametaphosphate, etc. where surface water pollution problem exists. In neutral to alkaline solutions, there are other compounds you can use to chelate calcium and magnesium. They include potassium sodium tartarate, potassium sodium saccharate, and sodium gluconate. Sodium gluconate, in particular, is used in some eco-friendly laundry detergents to replace polyphosphates (and successfully so, I'd say). These are all effective in alkaline pH, but the best pH varies depending on the agent. I personally prefer to use these sugar type chelating agents whenever possible, since they are biodegradable and does not cause surface water pollution.

I agree that water from a dehumidifier is bad to use.

Filtered water through a resin and charcoal is good, but not needed unless your water is quite bad.

But, I don't see any use in a wash aid. I've said it before. It adds steps to the process, and chemicals to wash out and dispose of. Stick with a good water wash.

PE

The purity of the water depends on the air that contained it and to which it was exposed after condensation, obviously. We cannot say absolutely that the water is unsuitable for photographic purposes. I had no problem with my well water for any use that did not involve precipitation of carbonates, and there was no scum on dried prints or negatives, probably because I wiped most of the water off before drying them. Even the precipitation of carbonates in the developer never caused an obvious problem, but I would rather not see it.

Reading my post makes me wonder how my scholarly English professor father ever had such a son. I meant to say that my well water has never given me any results that would show it was not suitable for photography. Where I live there is not the atmospheric contamination that one finds in many cities. We do have some bovine intestinal gas, but not as much as my grandfather had. There is more of my own gas, I suspect, as I am what we call an "old fart". I was not recommending the use of dehumidifier water but only saying it is what I have used without bad consequences.

The cost of driving to town to get distilled water is more than the cost of a gallon of the water. I have collected rain water for the purpose, which also seemed to be quite good.

Why don't you add a bit of carbonate to the water and wait for some time, decant the water and add the rest of the stuff to make up a developer?

I don't think driving to get distilled water is unnecessary and is against the principle of pollution reduction if the well water is easily workable. Indeed, even if you ride a bicycle, distilling takes a lot of energy.

Another alternative is reverse osmosis filter system or ion displacement resin.