[Histonet] Gravimetric Factor Equation

[lpwenk <@t> sbcglobal.net]

Gravimeter factor =

(conc of present dye)
__________________            X    (grams of  old dye used.)
(concentration of new dye)

Let's say your present dye is 75% dye (meaning 25% salts, fillers,
impurities - things that won't color the dye, but are a by-product or
possible needed to make the correct charge). And the solution you have been
making are working great. Now you buy a new bottle of the same dye. It's dye
concentration is 50% (meaning 50% salts, fillers, impurities, etc.).
Obviously, the new dye is much weaker, so in order for the new dye  to stain
as darkly as the old dye, hopefully it would make sense that MORE of the new
dye is needed.

If the solution you are to make is a 2% solution, that's 2 grams in 100 mL
of solvent (water, alcohol). (If the math doesn't show up right, make the
screen of your email full size)

(75%)
_____      X  (2 g) = (150) / (50) = 3 grams of new weaker dye are needed
(50%)

Conversely, if the old dye was 75%, and the new dye is 95%, then the new dye
is more concentrated. So for the new stronger dye to stain as pale as the
old dye, less of the new dye must be used.

(75%)
_____     X  (2 g) = (150) / (95) = 1.58 grams of the new stronger dye
needed
(95%)

(Percent signs cancel themselves out, leaving the grams.)

Just to let you know, in our lab, we usually  don't pay attention to GF.
First of all, many of our dyes seem fairly consistent in percentage from one
lot to another (87% vs 85% for example), so there isn't that big of a change
in amount needed. Second, for example, if we are make up a 1% light green
counterstain, we end up re-using it for 3-4 months. Therefore, by the end of
4 months, it's no longer 1%, it is a much lower percent/much weaker
solution. What used to take 1-2 seconds to stain when it was freshly made
up, now takes 30 seconds. As histotechs, we "eyeball" the quality of the
stained control (with or without the microscope), and adjust time
accordingly. And our procedures reflect that (stain in light green 2-30
seconds until background is pale).

But, yes, sometimes this can cause a problem (when the lot percentages vary
considerably) and adjustments are made. Someone puts a sign on the dye
bottle that says "Use 1.2 grams for every 1.0 grams needed", for example.

Hope this helps.

Peggy A. Wenk, HTL(ASCP)SLS
William Beaumont Hospital
Royal Oak, MI


----- Original Message -----
From: "Dave" <tynchas <@t> aol.com>
To: <histonet <@t> lists.utsouthwestern.edu>
Sent: Monday, June 14, 2004 12:11 PM
Subject: [Histonet] Gravimetric Factor Equation


Hello
In Freida Carson's book on histology, she has written to find the
gravimetric factor of a dye is   conc of present dye
                                                 conc of new dye

However study questions that I've been reviewing have the formula inverted.
I'm sure that Freida Carson is correct but I need to know for sure.  I
haven't had any luck on the internet and co workers don't have a clue about
what I'm talking about.  Thanks in advance.

Dave
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