Re: mass vs. volume measurement


"Andy Resnick" <andy.resnick@xxxxxxxxxxx> wrote in message
news:d6d7q5$od$1@xxxxxxxxxxxxxxxxxxxxxx
> Old Man wrote:
>> 0"Andy Resnick" <andy.resnick@xxxxxxxxxxx> wrote in message
>> news:d6cp2c$307$1@xxxxxxxxxxxxxxxxxxxxxx
>>
>>>Here's a simple question- why is vit much easier to dispense small
>>>volumes than to measure small masses?
>>>
>>>I routinely dispense single microliter volumes, and could do much better
>>>with a modest effort using common lab equipment, but it's very difficult
>>>to weigh a microgram of material.
>>>
>>>Andrew Resnick, Ph.D.
>>
>>
>> A lab balance isn't the only means: mass spectrometer.
>>
>
> No, that's not what I mean. I mean that if I want to prepare a 10 nM
> solution, I need to accurately weigh out some solid and accurately meter
> out some volume of fluid. Because I can't easily meter 10 ng of the solid
> (or however much I need), I have to prepare a concentrated (say) 1M
> solution and then dilute it down (in volume) to 10 nM.
>
> Never mind the other reasons to prepare concentrated stock solutions. My
> question is simply regarding the ease of metering an accurate small volume
> vs. metering an accurate small mass.
> --
> Andrew Resnick, Ph.D.

Old Man is amazed at the trust that microbiologists put
into their instruments. A lab balance is easily calibrated
with a set of standard weights, but do they ever think to
check their micro-pipettes ?

What of temperature effects ? What of abuse and of
improper technique ? They know not and care even less.

Old Man learned proper technique via checking micro-
pipetted samples with a calibrated lab balance. One
quickly learns the effects of technique and abuse, as
well as those of time and evaporation rate.

[Old Man]


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