Voyager DP-263-S Guia do Utilizador descarregar pdf (Página 148)

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Chapter 3 Preparing Samples

3-18 PerSeptive Biosystems

Note the following:

• When diluting sample, keep in mind that you will be

further diluting when you mix sample with matrix.

• If you are unsure of the starting concentration of sample,

make a serial dilution to prepare various dilutions of the

same sample.

• Different samples are soluble in different liquids. Try

water first, then add acetonitrile, and then add 0.1% TFA

to increase solubility if required.

• A higher concentration of TFA may enhance sample

ionization and improve sensitivity in samples prepared in

buffers.

• Many samples adhere strongly to plastic tubes and pipet

tips. You can minimize sample loss by preparing samples

in 30 percent acetonitrile with 5 to 10 percent TFA.

• Do not dilute sample with phosphate buffered saline

(PBS) or other buffer solutions. A high salt concentration

can interfere with sample ionization and may cause

increased sodium and potassium adduct peaks.

Preparing

samples for thin

layer application

Prepare samples in water. If samples contain organic solvents,

they will dissolve the matrix applied to the sample plate.

Internal standards

If you require mass accuracy greater than the accuracy

provided by external calibration, (for example, >0.05% on a

Voyager-DE system), use an internal standard. See

Appendix A, Specifications, for the mass accuracy on other

systems.

Add two standards of known molecular weight to the sample.

Standards should:

• Closely bracket the molecular weight of your unknown

• Be easily distinguished from the unknown

As a starting point, use an internal standard concentration in

the same range as your sample concentration. Because an

internal standard may affect the intensity of the sample signal,

it is a good idea to prepare sample with several different

internal standard concentrations.

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