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frogfot
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Thin layer chromatography (TLC)
TLC seems to be one of the few effective analysis techniques that are realistic to obtain for an amateur chemist (comparing with expencive HPLC, GC
etc).
For those that are not familiar with this chromatography technique, google have lots of pages on it..
Now of caurse the reason I post, is to ask if people have done their own TLC plates and if not, maby we can come up with some easy/cheap way to do
them.
The coating of the TLC plate (stationary phase) is mainly composed of porous silicone dioxide or aluminium oxide. A fluorescent compound (ZnS) is
added together with a binder to keep the coating together. ZnS is optional (there are other ways to develop the plate than UV), though using a UV lamp
would be neat.
In the old days, they mixed SiO2, gypsum and ZnS with water and drawed out this goo with a rod, like dough over a piece of glass.
Now, I dunno about porous silicone dioxide but it feels like porous aluminium oxide is easier to prepare.. any idea on this... maby precipitating an
Al(III) salt with a hydroxide and heating the obtained hydrate salt would do, or?
Another stationary phase could be usual activated carbon. The only problem is how to detect something on the plate..
This would give a type of "reversed phase" TLC (nonpolar stationary phase). If one had a simple way to develop this plate one would have a
huge advantage: using aqueous solvents!! Just think of it.. one could do chromatography of most things with simply an aqueous solution of ethanol or
methanol. Or did I miss something..
Developing white plates is very easy.. there are different oxidising liquids used that leaves stains on heating if organic material is present. Simply
dipping plate into H2SO4 and heating will do also. But I would most likely prefear developing it with iodine.
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solo
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Re:TLC
Here is a thread that covers TLC as well as other methods of chromatography.........solo
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https://synthetikal.com/synthforum/viewtopic.php?t=345
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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mick
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Adding fluorescene to the mix works for UV detection with organic solvents. I have thought about some of heavily embossed (I think that is what they
are called) shiney paper that you can get from art places. There is a fair amount of filler between the glossed surface. It might be possible to take
the shiney surface of with some fine sand paper or maybe better some wet or dry with a solvent and give some thing that could be used for TLC. I am
not sure what the filler is or whether it would work as an adsorbent layer. Just a guess. A good general developing method is dipping in a solution of
vanallin in ethanol + a bit of sulphuric acid (2.5g + 100ml + 1ml, I think without checking) and heating with a heat gun.
mick
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12AX7
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Filler is usually something like kaolin, a white clay. Clay is a hydrated aluminosilicate with small particle size, so it might have some adsorbancy
to it. Ball clay is finer, but that's getting into manufacturing more than using something as-is...
Paper also fluoresces under UV so you might have the fluo right there, too.
Tim
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frogfot
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Would be nice if clay alone could be used for this, though I doubt that it has much smaller particle size than say gypsum..
Made some chromatography experiments on usual printer paper using benzamide as analyte, and different mixtures between heptane, ethyl acetate and
ethanol, as solvents. The analyte travelled through the paper, but dot had large broadening along the travel path. Decreasing the amount of sample
made it nearly invisible.
I used only iodine to develop the "plate". The poor detection sencitivity is probably due to discoloring of the paper.. it's not that
good idea to stain an organic compound on the organic cellulose..
Gonna by a UV lamp for 10$ and give it a try. I heard that it'll require a filter to remove unwanted light (visible), though that specific lamp
I'll by has some dark glass around it..
Have also precipitated some aluminium hydroxide from AlCl3 soln with NaOH soln. Though it seems to take a while for it to attain crystalline form..
it's still partially amorphous.. gonna mix dried product with 10% gypsum and see how it will perform..
Anyway, addition of a fluorescent compound seems to be a next level...
The synthetika thread on chromatography seems to have lots of broken links to hive..
It's also hard to search google for relevant info since it's hidden quite well behind all pages with practical info where they use
commercial plates..
Heres something about paper chromatography:
http://www.agsci.ubc.ca/fnh/courses/food302/chromato/schroma...
Their list of adsorbents shows also applications:
http://www.agsci.ubc.ca/fnh/courses/food302/chromato/schroma...
So, it means cellulose can't be used on everything.. and alumina has a much broader scope of analytes, closer that of silicone oxide.
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Tacho
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frogfot,
I´m glad to see that someone with a hands-on aproach is researching homebrew TLC. I gave up.
I tried many different powders on large microscope glass plates. Tried to bond them with gipsum, sodium silicate, spit...
I never got any decent, useful, repeatable procedure.
Well, yes, one can separate black ink into its component colors but, in real lab life, that's far from enough.
Any UV "black" light will work. Not the germicide kind, I'm sure you know that. The the dark blue one. Of course, it only works if your
sample is fluorescent or you TLC plate have fluorescent aditive, otherwise it's of no use.
The great thing is still iodine. It really darkens any organic on your inorganic plate. And its easy to use.
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mick
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Couple of comments
I think with TLC 90% of the separation seems to be in the first 3-4 cm, after that the solvent front starts slowing (evaporation, gravity etc) and
that could be when things start diffusing.
Using small plates (6 cm) tilted so the solvent travels fast might stop that.
Commercially there are glass, plastic and aluminium backed plates. I like the Al ones, the layer seems to bond better to Al, you can cut them up with
a sharp knife without damaging the layer and heat them up to develop them (a bit of acid or alkali in the mixture does not seem to be a problem).
I have tried silica, alumina and cellulose plates, for general stuff most of the time silica has been best.
You can use silica with aqueous solvents (took me years to find that out because every one said you can not) if the TLC is developed fast. A good
general solvent system is some thing like ethyl acetate plus a 1 to1 ratio of methanol (alcohol maybe) and conc ammonia. Good for amines and the
hydrochlorides.
I can not think of an OTC source of some good silica.
The blue UV lamp shows up stuff that fluoresce, aromatics and stuff.
Adding a fluorescent agent (I think it is usually fluorscein but not sure) to the layer mix shows up stuff that quench the fluorescence, that is at
the other wave length (254). I think they are sold as germicidal, UV curing or some thing lamps.
254 is worse for the eyes but most plastics will take it out (not glass)
The developing tank needs to be saturated with the solvent, filter paper round the edge, to keep the solvent moving, as above tilting the plate seems
to be better that setting it upright.
The mix you are trying might stick to Al if you primed the Al just before (alkali)
If you are using the TLC with organic solvents maybe a flour mix might work.
(a feeler gauge to check the layer thickness ??)
mick
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frogfot
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I never use longer plates than 5 cm. Though I never thoat that efficiency would be increased if plate is tilted, sounds logical.
Seems like UV will not be the poblem anymore.. just thoat that ZnS can be most probably made easily by burning Zn prills in molten S..
Made new experiments with homemade Al2O3. It was a pain to filter, so that was excellent! (soln wasn't basic at all)
I tried two binders: gypsum (10%) and dextrine (5%). The plates with gypsum gave very high visibility under iodine (hight contrast) but I wasn't
able to do actual separation since I didn't have enough plates and they broke annoyingly..
Plates binded with dextrine was basically the opposite: poor visibility due to discoloring of dextrine but the layer held very tightly.. and it was
much easier to spread on the aluminium foile..
IMO, the dextrine plates could be used with UV, but the rest of staining methods wouldn't work that good.
So, one needs some effective inorganic binder.. I could try to increase gypsum concentration but I have a feeling that this wouldn't make any
good..
Sodium silicate do sounds like a solution, but as I understand it will form an amorphous, nonporous mass.. that will cover all the small Al2O3
particles and make them nonaccessible for the solvent/analyte..
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frogfot
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Alrighty, got myself an UV lamp, 4W, powered from 4X1,5 AA baterries. Originally used to check the money..
After applying some benzamide (dissolved in methanol) on white printer paper I couldn't see a squat.. except for very bright violet
fluorescenting paper...
Since the lamp also gives some visible light I'm wondering what daylight filters one can use? Maby it will help to increase the contrast.. Cheap
and homemade filters that is.. I was thinking in lines of a solution of some salt as the filter...
For some reason I couldn't find this info on google.. 
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chemoleo
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Re that UV lamp, did you check the emission spectrum? I suspect it is 'soft' UV, i.e. the less hazardous one, which is the type that is less
useful.
I believe you need hard UV, very short wavelenghts (look up the range, its probably around 220 nm), which is the range where most organics absorb.
Additionally, often filters are applied that only transmit a small section of the visible spectrum, and that way you can pick up the fluorescence
from the background.
For instance, try i.e. a red-coloured transparent sheet, and see if you can see a spot then. If it is red coloured, it means it absorbs in the blue
range, and thus you filter out the background from the light, so you might be able to see a spot.
But it really depends on the compound.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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frogfot
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Thanks for that advise, I forgot about complmentary colors. I'll dig up some red plastic sheets tomorrow, had one somewhere.
There's no info on the package about the wavelength..
Holy cow, I just found ways to activate Al2O3 and preparation of silica gel!!! The technical aluminium oxide (hydrated, precipitated will probably do)
is preferrably neutrolised by dilute mineral acid, dried and heated at 400-450*C for 3-5 hours while stirring occasionally. I can post the detailed
methodics if people are interested.. but that drying step seems to be tedious.. too high temp will make less active form of aluminium oxide..
Now preparation of silica gel is unbeliveably simple:
Usual liquid glass (prolly prepared from sodium silicate) is diluted with water to density of 1,19 g/ml, placed into a thickwalled jar and cooled to
5*C in ice bath. While vigurously stirring, conc HCl is added in portions and temp is kept below 5*C.
Forming silicone acid (eng?) will give liquid and then thick mass, which will make stirring harder. All mass should be stirred throughly.
On further addition of HCl, mass will liquify again. When mix shows acidic reaction (thymol blue) stirring is continiued and soon acidic reaction will
dissapear. HCl is added in portions untill solution becomes constantly acidic. Untill this step temperature must not raise above 5*C (use external
cooling or add ice into the reaction mix).
Mix is left at room temp for 3 hours and filtered on Buchner funnel making sure that solids doesn't get cracks. Wash with 8-10 vol amounts of
distilled water.
Solids are suspensed into excess of 0,2 M HCl and left for 2-3 days while stirred occasionally. This step reflects on the activity of final product.
Given conditions was found empirically and was confirmed by repeated tests.
After filtering on Buchner funnel, solids are washed with 20 vol amounts of distilled water. The product is spread in thin layer and dried first at
room temp and then in an oven at 110*C. Obtained silica gel is stored in air tight bottle.
Reference:
Lab techniques in organic chemistry, B. Keil, 1966
Russian translation of:
Laboratorni technika organicke chemie, B. Keil, 1963
Well how cool is that.. First thing I will do tomorrow is silica gel. I've also found lots of info on TLC in my old org books.
[Edited on 29-3-2005 by frogfot]
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neutrino
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What do you mean by neutralizing aluminum oxide? Just adding a small amount of acid and washing away what dissolves?
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Dave Angel
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Hi frogfot!
I would agree with chemoleo that you need shorter wavelength UV, but in addition to the longer wavelength you have. I remember our UV units in labs
have a switch for long and short and in fact...link.
I also found this; one device does both wavelengths so you may be able to get a reader that does both second hand. Actually it's 'only' (I say
'only' as I usually find these sort of things to be prohibitively expensive) 159 euros for a new unit which does both wavelengths, assuming
they will sell to people without a company / institution - but then I'm sure many of us here have had to find ways around that particular
limitation. 
My only concern would have been that it is not a question of wavelength but that you may need higher power bulbs than those in bank note checkers.
This is not the case, however, as my lab supply catalogue states their UV lamps take 8W bulbs, just like the checkers at that link I gave.
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mick
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Polycarbonate glasses should protect from UV, but put what you are looking at on matt black.
Precipitated silica can be made from sodium silicate but the commercial grade is more uniform and can be recycled.
After stripping the silica with alcohol or a polar solvent add some water mix and decant. Activate at 400-600 oC for a few hours.
mick
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frogfot
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Soz for taking so much time to reply... just wanned to post the next time I had some decent results.. which I still havn't.
| Quote: |
What do you mean by neutralizing aluminum oxide? Just adding a small amount of acid and washing away what dissolves?
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Soz, I mixed up things.. there weren't any unique neutralization procedure.. you're right, it's washed in dilute HCl or HNO3 and then
activated by heating as mentioned previously (400-450*C). At higher temps aluminium oxide becomes less useful in chromatography, since it will become
reactive against many org compounds. At very high temps it looses it's adsorbtion activity.
I wrote up a text on silica gel preparation here:
www.frogfot.com/synthesis/silicagel.html
(dunno if self-advertisement is ok in here.. rolleyes..)
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After stripping the silica with alcohol or a polar solvent add some water mix and decant. Activate at 400-600 oC for a few hours.
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Thats way to high for the activation of silica gel. It will lose it's activity. I've read that if silica gel will be used in adsorbtion
chromatography (especially of hydrocarbons) the recommended activation temp is 160-180*C. Lower, if more polar analytes will be used. Higher than this
will deactivate product.
As for the TLC plates, I really thik that stable plates is a must, either thick Al or glass. The Al foil is a joke... I only have 3 microscope plates
to play with so experimenting is taking time. (I'm currently trying to cut glass.. and make lots of theese plates).
Sofar I've made plates with homemade silica and 5% gypsum. Quite fragile I might add.. Feels like commercial plates uses other binders.
Used same analyte and solvents, and this time actually I got quite ok spot transported to half of plate (some tailing). Iodine gave decent visibility.
Problem is that solvent didn't travel that fast (not like in commercial plates that is). This could be due to small particles.. Gonna remove them
as mick (and my org book) suggested.
As for UV I gotta first produce some ZnS to test if my lamp excites it..
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mick
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The activation temperature came from some one who was trying to recycle silica and only went upto 250 oC and it did not work. I mentioned heating it a
bit more and I think it is working. The 400+ came from a book called Advanced Practical Organic Chemistry. I have tried re-running a column or tlc
with a quick wash and a dry and the separation is crap compared to the original.
mick
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mick
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Using a cheap web cam you can take some nice pictures of the TLC plates under UV.
mick
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microcosmicus
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In the thread "Unknown Copper Compound", blogfast25 pointed out an instructable
for homemade TLC plates:
http://www.instructables.com/id/Preparing-your-own-thin-laye...
To this, I would like to add two observations:
Rather than grinding up the silica gel from drying packets (which, as mentioned there,
often has gook added) why not just prepare some from sodium silicate. For instance,
you can get sodium metasilicate as "TSP substitute" in the paint aisle of the hardware
store. Add your favorite acid (even vinegar will do) to precipitate the gel, filter out, wash,
dry (details given above) and you're set to go without the tedious grinding.
Also, to get the thickness of the layer even, one trick is to put one or more layers of
tape on both sides of the slide, then go over it with some sort of squeegee to even
out the layer.
[Edited on 17-2-2008 by microcosmicus]
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chemrox
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Pass on some of the diy stuff and get some silica and gyspum. You can buy the silica already ground to a spec that you can look up. I make them from
slides as others have shown here and in the cited threads (@Solo-thanks). I use an iodine vapor tank to visulize spots. Its a jar with a few I2
crystals in it and the I2 attaches to almost everything. Another method to visulaize a large number of materials is acid. A strong H2SO4 solution is
sprayed on the plates after they've been run. I have glass sprayers (ebay) for the purpose. I may have an extra one. Getting a little more spendy,
ninhydrin reveals a large number of compounds. (Note) Both ninhydrin and I2 are used for visulizing fingerprints.
For 2 dimensional work I have a tank and some prepared glass plates (surplus). It's nice to have a good tank and some large squares of filter paper.
The biggest challenge will prove to be solvent selection. Read the sections on this in a number of O chem lab manuals including the "O-chem Survival
.."
[Edited on 17-2-2008 by chemrox]
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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12AX7
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How about clay? Plenty of OH sites, sticky, readily available.
Tim
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chemrox
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I think clay is way to sticky an adsorbant for most things. Were you thinking of clay mixed with silica? Getting nice white porcellaneous clay might
be more spendy than gypsum. I might try it though and let everyone know-I have to make mini-plates next week. And I need a trip to the pottery
supply for the kids' crystal set.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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12AX7
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Hardly- I have a 50lbs sack each of EPK, #4 Tennessee and 325 mesh ground flint, about $10 each. EPK is really clean stuff, and coarse enough
(kaolins are coarse, as clays go) that I wouldn't say it's "to [sic] sticky". With a variety of fillers, like ground flint, silica sand, etc., you
can certainly blend whatever consistency you like.
Tim
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bfesser
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I've had bad experiences in the past with grinding silica gel from desiccant sachets into fine powder in a mortar and pestle. I find that it
generates a cloud of nuisance dust, which you'd probably want to avoid breathing at all costs. I've found a pretty simple and convenient way for
eliminating this problem today, and it probably costs less than 15 cents.
I have a medium sized Coors mortar and pestle--see the pictures below. You'll want a high form mortar for this procedure, as the silica beads tend to
jump, and the higher walls help to reduce loss. I found a Ziploc bag that comfortably fits the entire mortar. You probably don't want a bag that's
too large, because it will just get in the way. Then I cut a short slit right in the middle of the bottom crease, going along the crease, maybe about
2.5 cm long. Then, from the inside of the bag, I pushed the handle of my pestle through the slit (it stretched out the slit, making a nice seal) and
wrapped around the joint a couple times with black electricians tape (truly one of mankind's greatest creations). Then I put a few silica gel beads
in the mortar, carefully slid it into the bag so that the business end of pestle was resting inside, sealed the bag shut with the zipper thingy, and
ground away without the annoying cloud.
It worked surprisingly well. The beads, which have a tendancy to bounce everywhere, were kept in the mortar by holding the mortar like a cup through
the bag, forming a sort of C shaped seal. It was a little difficult to see what was going on inside the bag, as the dust accumulated on the inside of
the bag, but with a little practice I was able to obtain a nice uniform powder just by feel. And the best part, absolutely no dust escaped! It's
probably also a good idea to wear cheap thin gloves when removing the mortar from the bag, and be careful not to disturb it too much.
Someone try it out and let me know what you think--especially suggestions for improvement.
Now I just need to figure out how to dry this stuff and where I can get some good solvents.
<table align='center'><tr><td><img src='http://www.geol.umd.edu/pages/facilities/rockprep/alumina_mortar_pestle.jpg'
width='250px' /></td><td><img src='http://www.thesciencefair.com/Merchant2/graphics/00000001/Mortar&PestleCNC1_M.jpg'
width='250px' /></td></tr><tr><td><div
align='center'><strong>Good</strong></div></td><td><div align='center'><strong>Bad<br />(Too
shallow.)</strong></div></td></tr></table>
[Edited on 2/18/08 by bfesser]
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chemrox
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workup media for PEA
I'd like to hear from anyone who has TLC experience with PEA. I'm thinking a MeOH/DCM/NH4 mixture but want to know if anyone has worked out the
percentages. Or a better mixture. I would be shooting for an RF of about 0.5 as the PEA is a reactant and I'm monitoring a reaction with its
disapearance.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Magpie
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Silica gel as a common moisture absorbant is relatively cheap and OTC. But chromatographic grade silica gel 60 (40-63 micron) is $403/kg
(ArtChemicals.com) and up.
Assuming that the common silica gel beads can be ground to the same particle size as that of the chromatographic grade, is there any difference?
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