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Author Topic: Sodium Rhodizonate Question  (Read 29633 times)

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Offline fkonidaris

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Sodium Rhodizonate Question
« on: April 06, 2009, 07:59:24 AM »
Hey everyone!  I'm currently working on a project for school and am doing distance determination and GSR analysis.  I'm getting ready to do the sodium rhodizonate test (am currently doing the modified griess test).  Can anyone tell me exactly or approximately how much sodium rhodizonate in grams to use?  According to the procedure I have, it only states a sufficient amount of distilled water with a small amount of sodium rhodizonate.  Can someone please expand on this?  Thanks!

Offline Cole

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Re: Sodium Rhodizonate Question
« Reply #1 on: April 06, 2009, 08:29:39 AM »
About the color of strong tea.  This aspect of the sodium rhodizonate test is pretty qualitative, so if you can easily see that the solution is brown, you should be good.
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Offline fkonidaris

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Re: Sodium Rhodizonate Question
« Reply #2 on: April 06, 2009, 08:47:53 AM »
Thank you Cole!  Do you by any chance have an approximation of how much in grams that would be?  I'm wondering because I need to order the sodium rhodizonate still and my professor wants to know how much to order.  Would 5 g be enough to test 10 samples or would I need to go to the next size up of 25 g?

Offline Zak Carr

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Re: Sodium Rhodizonate Question
« Reply #3 on: April 06, 2009, 10:03:05 AM »
5g is plenty to process 10 samples.
Z.
Zak Carr
Johnson County Sheriff's Office Criminalistics Laboratory
Firearm and Toolmark Section
zachary.carr@jocogov.org

Offline Alison Quereau

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Re: Sodium Rhodizonate Question
« Reply #4 on: April 06, 2009, 10:12:09 AM »
Hi Friend,

The smaller 5g bottle will be plenty for your purposes.  Hopefully your sources have indicated to you that a Sodium Rhodizonate solution isn't viable for more than a day, so you need to mix up a new batch for each day you are going to use it.  Typically I start with 50-80ml of distilled water in a small beaker and add a small amount (less volume than the eraser on a pencil) of SoRho.  I stir and wait a few moments for the powder to dissolve, and see if there is any dark powder residue in the bottom of the beaker.  If not, I add another tiny amount.  When there are un-dissolved particles at the bottom of the mixture, it indicates a saturated solution and adding more doesn't nessaraily contribute to better results on your tests.  Be sure to do a control test on known lead (such as a scribble with the tip of a lead bullet on filter paper) and you're good to go!
« Last Edit: April 06, 2009, 01:02:17 PM by Alison Quereau »
Alison Quereau
Palm Beach County Sheriff's Office Crime Lab
West Palm Beach, FL

Offline Cole

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Re: Sodium Rhodizonate Question
« Reply #5 on: April 06, 2009, 11:59:41 AM »
The first time I made a NaRho soln., I saw it described as "saturated" and took it in the literal chemical sense.  I must've spent 15-20 minutes just dumping spatula-fuls of the stuff into the beaker. This is partially because it is so dark and fine that when you are constantly stirring it, it looks like it's dissolving when it really just hasn't settled out yet.  It was a waste, but I got good reactions...
The views expressed here do not necessarily reflect the views of anyone, anywhere, ever - including the author.

Offline Bob Shem

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Re: Sodium Rhodizonate Question
« Reply #6 on: April 06, 2009, 12:09:01 PM »
The stuff is expensive and considering the fact that the bottle looks almost empty when you first open it, use it sparingly.  Start with just enough water to get the job done.  I usually use about 30 ml (2.4321395464e-8 acre foot) of water in a 50 ml (4.0535659106e-8 acre foot)* beaker.  I add small amounts until no more will dissolve.  Then after letting the solution sit for a while to assure that the solution is fully saturated I will decant off the tea colored solution into a clean beaker, leaving the "mud" behind so that I don't spray the undissolved chemical on my tests or evidence.

As Alison mentioned, don't let the stuff sit overnight as it loses potency.  I haven't tried it, but I would avoid using hot water, as doing so might speed up the loss of potency.

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« Last Edit: April 06, 2009, 02:21:16 PM by Bob Shem »
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Offline fkonidaris

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Re: Sodium Rhodizonate Question
« Reply #7 on: April 06, 2009, 12:21:24 PM »
Thank you everybody for your help and advice!!!

Offline Jill Therriault

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Re: Sodium Rhodizonate Question
« Reply #8 on: April 06, 2009, 02:46:55 PM »
30 ml (2.4321395464e-8 acre foot) of water in a 50 ml (4.0535659106e-8 acre foot)* beaker. 
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http://en.wikipedia.org/wiki/Acre_foot

I about fell out of my chair, cracking up.  Bob, you rock.  :laugh:
« Last Edit: April 06, 2009, 02:48:42 PM by Jill Errickson »
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Offline Bob Shem

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Re: Sodium Rhodizonate Question
« Reply #9 on: April 06, 2009, 03:04:39 PM »
I don't want our farmer friends to feel slighted.
Robert J. Shem, 4900 Buckingham Way., Anchorage, AK  99503, ph 907 952-2254, bobshem@alaskan.com

Offline MaxYasko

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Re: Sodium Rhodizonate Question
« Reply #10 on: May 07, 2009, 02:34:58 PM »
Hello, colleagues! May I ask, why don't You use sodium sulphide solution? It's cheeper and, if stored in dark and cold place, keeps active quite long (about month or two).  It turns lead residues dark-brown.

Offline Jay Stuart

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Re: Sodium Rhodizonate Question
« Reply #11 on: May 07, 2009, 03:04:31 PM »
Off the top of my head (without seeing it used) I would say that the dark-brown color reaction color could quite easily be masked by blood/dirt on the clothing.  Again this is without ever having tried it.
 
Jay Stuart
Metro Crime Lab - Albuquerque, NM
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Offline MaxYasko

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Re: Sodium Rhodizonate Question
« Reply #12 on: May 07, 2009, 03:37:12 PM »
I apply it on a photographic paper samples (we call it contactogram), and any dirt from analyzed object (including blood) is simply washed away by a cotton wad. The smell is disgusting, although (H2S is a side product of Na2S  and H2O reaction).
« Last Edit: May 07, 2009, 03:39:01 PM by MaxYasko »

Offline Jay Stuart

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Re: Sodium Rhodizonate Question
« Reply #13 on: May 07, 2009, 05:53:27 PM »
Max,

Do you know if there is any published research on this technique.  I have not read about anywhere.  Are there any false positives to worry about?  How does the sensitivity of this technique compare to NaRho?

Thanks
Jay Stuart
Metro Crime Lab - Albuquerque, NM
505.823.4260

Offline MaxYasko

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Re: Sodium Rhodizonate Question
« Reply #14 on: May 08, 2009, 07:16:29 AM »
I'll answer anbout researches more exactly next week, but we use it  in Belarus (and our collegues in Russia, as I know) as official method. Sensitivity is quite enough to reveal lead residues (homogenous and speckle, forgive me my terminology  ::)). It's part of our standart procedure to determine, have shots from specific firearm  taken place after last cleaning or haven't,  to define the origin of a hole , and to determine (approximately, of course) the distance of a shot -- if the hole was  caused by bullet.  We also make tests to reveal copper (as a component of bullet jacket) and antimony (stibium, as part of prime composition).

 

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