Chromatography Forum

I am not going to defend a peer reveiwed paper against the accusation of being "pointless".

Peter, I hope you did not misunderstand me - I was not saying that your arguments were pointless. We have another participant in this discussion...

I posted my comment before I read your reference to the article. I would be very intersted in reading it - would it be possible to send me a pdf (I dont't have access to the journal)?

But even if weighing is more precise and accurate - it is still a different situation if you're doing research or routine analysis in a commercial lab...

Hi, H Thomas
But about EPA 625?
METHODS FOR ORGANIC CHEMICAL ANALYSIS OF MUNICIPAL AND
INDUSTRIAL WASTEWATER
1) Problem of testing
Its nothing benz-a-peren and others cancerogens and pesticides in munitipal water . If carcinogens in "potentially drinking water" (for those who live downstream) - we must not precision calculate their concentration to three decimal count, but to sound the alarm at the first sign of poison detection , as people will not poisoned.
2)Object of testing - trap water.That consume hundreds of tons per hour - per liter or two liters of selected samples do not play any role in consumption and are not worth anything.
If you need to - you can have take at least (as minimum) a pail a water sample .
3)The final dimension-mg / liter. So why in the selection of the water we work with weights?

We have a slightly different system
Common GOST 51232-98 http://www.vashdom.ru/gost/51232-98/(government standard) and SNIP in drinking water specifies the general requirements as standard.Determine the specific substances to a group of pollutants (indicator) that are "markers"in accordance with the specifics of a given area, a regional sanitary-epidemiological laboratory by the method of matching, the department for a specific group of substances.
Example here
http://law7.ru/base07/part2/d07ru2957.htm
http://www.gosthelp.ru/gost/gost8984.html

As you can see not any mass spectrometric, is designed to run on very old equipment.
Here the problem is not found guilty, but always controlled object to prevent ingress of toxic products in the water piping system.

Analog (free translate) EPA625 use forensic experts and environmentalists. When it is necessary to establish the guilt of a particular company.

I am not going to defend a peer reveiwed paper against the accusation of being "pointless".

Peter, I hope you did not misunderstand me - I was not saying that your arguments were pointless. We have another participant in this discussion... I thought that was what prompted your comment

I posted my comment before I read your reference to the article. I would be very intersted in reading it - would it be possible to send me a pdf (I dont't have access to the journal)? If your e-mail address is on your profile I'll send you a copy. If not, can you e-mail me at peterjapps-at-gmail (suitably adjusted).

But even if weighing is more precise and accurate - it is still a different situation if you're doing research or routine analysis in a commercial lab...

In additon to the metrology level work in the paper I have also developed standard methods around gravimetrics - typically the scheme was to use autopipettes and dispensers to very quickly get close to any target addition, and then check weigh at every stage to get correction factors for what had actually been added (and to verify that an operation had been carried out !). Even with people writing the weights on paper this went much quicker than using "proper" volumetric glassware, and was much more repeatable and accurate than relying only on the autopipettes and dispensers - with balances hooked up to data processing I imagine that it would run even better. The jumping off point for this was the Zymark robots that have built in weighing to verify and correct their volumetric operations.

Using auto-volumetrics and check weighing also made results more robust to differences in operator skill.

Peter

[Using auto-volumetrics and check weighing also made results more robust to differences in operator skill.

OK, convinced. I will forward this discussion to our QA...

Method of making an internal standard is variable, and depends on many contributing factors - such as the purpose of analysis, concentration of substance in the sample, provability of operations for the external audit and others.
Without clarifying these introductory argue about which is better - microdoser, syringes, scales /balance/, finishing up volume with a solution of known IS concentration - can be infinite.
As argued medieval scholastics (using the proverbial respected Peter)
How many angels can dance on the end of the needle?
[quote= H.Thomas] OK, convinced. I will forward this discussion to our QA... [/quote]
100%+ OK, Finish disscus.

(...)
How many angels can dance on the end of the needle?
(...)

"Even a thousand szloty note can't tapdance."
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sorry for off topic, all these citations by DSP007 strongly remind me of Banacek:

http://www.thrillingdetective.com/trivia/triv265.html

İf you solve internal standart in %100 water, there is no problem with air displacement micropipette.
İf not or solve in organic(methanol etc.) , you should use positive displacement micropipette.

serifermis, I have seen water being lost by "air displacement pipets", because the hand holding the pipet warmed up the air.

I think an important question needs to be 'what level of accuracy/precision is actually required?'. There's no point going to extreme lengths to use the absolutely most accurate and precise method if it's completely overkill for the application.

For instance the Flexus Liquid Handler http://www.gilsonuk.com/flexus/introduction can have a balance or a nano-dispenser integrated into it but costs too much to use for simple internal standard addition only.

I'll take a Microman myself. The pipetting specs http://www.gilson.com/en/Pipette/Produc ... aspx?d=335 are excellent and plenty good enough for almost all applications. It's positive displacement and so will work well with volatiles. Quick, easy, simple and robust.

As my brother the engineer says: measure it with a micrometer, mark it with chalk and cut it with a chainsaw.
I often feel that QA wants to see the certificate of conformance for the micrometer.

just my two cents but our general rule of thumb is that when uL's are needed and are solvent based, use syringes. when adding solvents in mLs, like for extraction, use a finni/thermo but draw up, eject and then redraw each time but be aware that sometimes it can dry out the grease inside. anything aqueous can use either, but i prefer the finni/thermo in those instances.