Jarmo

Yes and no! The difference between 75% and 65% solutions should not be very
significant. As you are probably aware, 50% is used a great deal in Europe and is,
indeed, specified in UK DEF specs. Of course, the conversion factors are different.

50% has a number of advantages but, above all, it doubles the sensitivity of the test
and reduces the risk of saturation by half. In the USA, 75% is more popular because the
original tests done by Hobson et al. in the NAFI had extremely short integration times
(about 1 min) and they needed the solubilisation that a high IPA offered. OTOH, as
resistivity, rather than conductivity, was used and most of the resistivity meters of
that time were limited to 20 megohm-cm, the high resistivities offered by a 75%
solution allowed a great deal of cheating to occur, as it was possible to work
off-scale. This is a legacy that still exists today, to a slightly less extent, on
resistivity type instruments.

However, a point that is relatively little appreciated is the differences as to how the
solutions are made up. If you take:
a) 250 ml of water at 20 deg C and 750 ml of IPA at 20 deg C
b) 250 ml of water at 25 deg C and 750 ml of IPA at 25 deg C
c) 250 ml of water at 20 deg C and make it up to 1 l with IPA at 20 deg C
d) 750 ml of IPA at 20 deg C and make it up to 1 l with water at 20 deg C
e) 250 g of water and 750 g of IPA (temperature not material)
you will obtain 5 totally different solutions, which will give significantly different
results. Only a) is correct, according to the specs v/v wording, although e) is the
most scientific. At first sight, this may seem astonishing, until one realises that
mixing alcohols and water causes a diminution of volume by somewhat more than 10% and
that the coefficients of volume expansion of the two liquids are totally different.

Hope this helps

Brian

Kiiski Jarmo wrote:

> Are the results of contamination testing comparable if different solvent
> mixtures (75% v/v 2-propanol/water and 65% v/v 2-propanol/water) are used in
> static test (omegameter)? The exact solvent mixture is known and used in
> calculation of surface ionic density.
>
> B.R.
> Jarmo Kiiski
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
> the body:
> To subscribe:   SUBSCRIBE TECHNET <your full name>
> To unsubscribe:   SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
> information.
> If you need assistance - contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> ##############################################################

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################