[ken3009]

sample is evaporated from 200ml to 20ml and the concentrate then used for the test.

i use 3 tubes for each sample: one blank (10ml DI water+2ml sample), one standard (10ml Pb 2ppm solutino + 2ml sample), and one tube containing 12ml sample.

my question is, should i have 3 tubes for each and every sample if i have lots of samples?
should there be a blank and standard for each sample or is one balnk and standard enough.

at the end i have to compare the colors (std should be darker  brown than sample).

so if i do 10 samples, do i need to have 30 tubes??

[Arkcon]

It is really up to whoever's in charge.  You can do just one blank and standard per set of unknowns, or per day, or the test may require you to flank a series of unknowns, or yes you may be required to have a blank and standard for each sample.  Who's in charge of deciding may be you, or a supervisor, or the person who wants the test done, or a government agency.

[ken3009]

but if the method says to use 2ml of sample in each of the blank and standards...then how can i use just 4ml of one sample in the blank and standards and not the other samples? do u get what i mean?

because the sample goes in the blanks and standards i feel there should be a blank and standard for each sample,dont u think??

im trying to get my head around this and the purppose of it.

[Arkcon]

Sorry, I didn't read your O.P. carefully.  Yes, if a portion of your unknown goes into each blank and standard, then, of course you'll have to prepare a blank and standard for each unknown.