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Sample concentration for MALDI

Maximum sensitivity is achieved in MALDI–TOF if samples are diluted to a particular

concentration range. If the sample concentration is unknown a dilution series may be

needed to produce a satisfactory sample/matrix spot of suitable concentration on the

MALDI plate.

Peptides and proteins seem to give best spectra at around 0.1 to 10 pmol mm^3

(Figs. 9.13, 9.14). Some proteins, particularly glycoproteins, may yield better results at

concentrations up to 10 pmol mm^3. Oligonucleotides give better spectra at around

10 to 100 pmol mm^3 while polymers require a concentration around 100 pmol mm^3.

(Note: 1 pmol nm^3 ¼ 10 ^6 mol dm^3 .)

Table 9.1Examples of MALDI matrix compounds

Compound Structure Application

a-Cyano-4-hydroxycinnamic acid
(CHCA)

HO

CN

O

OH

Peptides<10 kDa

(glycopeptides)

Sinapinic acid (3,5-dimethoxy-
4-hydoxycinnamic acid) (SA)

HO

CH 3

CH 3

O

O

O

OH

Proteins>10 kDa

‘Super DHB’, mixture of 10%
5-methoxysalycilic acid (2-hydroxy-
5-methoxybenzoic acid) with DHB

Proteins,

glycosylated

proteins

2,5-Dihydroxybenzoic acid (DHB)
(gentisic acid)
HO OH

OH

O Neutral

carbohydrates,

synthetic polymers

(oligos)

3-Hydroxypicolinic acid

N

OH

O

C OH

Oligonucleotides

2,-(4-hydroxy-phenlyazo)-Benzoic acid
(HABA)

O

OH

NN OH

C

Oligosaccharides,

proteins

367 9.3 Mass analysers