## 3 MALDI Non-Imaging MS Analysis of GSLs
### The Influence of Matrices Used in MALDI Non-Imaging MS Analysis of GSLs
\begin{table}
\begin{tabular}{c l l l l} \hline \hline
**Matrix** & **Advantage** & **Reference** & **Disadvantage** & **Reference** \\ \hline \multirow{6}{*}{DHB} & Higher signal-to-noise ratio (S/N) & [116] & Resolution is considerably low & [117; 118; 119; 120] \\ \cline{2-5}  & Decreased fragmentation in negative ion mode & [121; 122] & Altered sample geometry & [117; 118; 119; 120] \\  & compared to positive ion mode & & & \\ \cline{2-5}  & Minimizes loss of sialic acid & [123] & Increased fragmentation the higher the molecular mass is & [117; 118; 120] \\ \cline{2-5}  & Minimizes loss of CO\({}_{2}\) & [121] & & \\ \cline{2-5}  & Addition of butylamine reduces fragmentation & [124] & & \\ \hline \multirow{6}{*}{DHA} & Increase in resolution & [125] & Decrease in the signal-to-noise & \multirow{2}{*}{[125]} \\  & Increase in resolution & [125] & & \\ \cline{2-5}  & Negative ion mode improved detection of & [125] & & \\ \cline{2-5}  & O-acetylated GT1 forms & & & \\ \cline{2-5}  & THAP & High-quality Gb4 Cer spectra & [126] & Low-quality spectra & [126] \\ \hline \multirow{6}{*}{ATT} & Enhanced crystal formation by adding lithium citrate & [127] & Inhomogeneous distribution of crystals & [126] \\ \cline{2-5}  & Superior S/N ratio (in positive ion mode) & [117] & & \\ \cline{2-5}  & Significantly reduced fragmentation & [120] & & \\ \cline{2-5}  & at high pressure & & & \\ \hline \multirow{6}{*}{CHCA} & Formation of homogeneous crystals & [117] & Considerable fragmentation & [117] \\ \cline{2-5}  & Differentiation of GD1a compared to GD1b & [115] & Trisialogangliosides & \multirow{2}{*}{[117]} \\  & Lysogangliosides are analyzed better & [128] & & \\ \hline \multirow{6}{*}{MSA} & High-quality ganglioside profiles (in positive ion mode) & [129] & & \\ \cline{2-5}  & Minimal loss of sialic acid (in positive ion mode) & [129] & & \\ \cline{2-5}  & Detects the isomer specific fragment ions for both & [129] & & \\ \cline{1-1} \cline{2-5}  & GD1a and GD1b & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Advantages and drawbacks of main matrices used for MALDI non-imaging MS.  
Figure 2: Common matrices used for MALDI non-imaging GSL analysis: DHB—2,5-dihydroxybenzoic acid, DHA—2,6-dihydroxyacetophenone, CHCA——cyano-4-hydroxycinamic acid, MSA—5-methoxysalicylic acid, ATT—6-azo-2-thiothymine, THAP—trihydroxyacetophenone. Glycoprotein, glycans, and frequently peptides are usually analyzed in this matrix, soluble in both organic solvents and water. DHB's most important disadvantage is the formation of big crystal needles which modify the spot-to-spot sample geometry on a preparation. When summing up spectra from various sample preparation spots, the result is a significantly lowered resolution. Preparations of DHB will make up a crystalline ring on the steel plates. Krutchinsky et al. [116] studied a phenomenon called \"chemical noise background\" in MALDI MS. Sample impurities, desorption and ionization of the sample, and matrix impurities have been linked with this \"chemical noise\". The sensitivity of the mass spectrometer is constrained primarily by background ions present in the mass spectrum rather than its inherent sensitivity. Background ion signals can be discerned at virtually every \(m/z\) value. A detailed analysis of these distinct background peaks at higher resolutions reveals the existence of numerous diverse ion species at each \(m/z\) value. Impurities can be removed to a certain degree by using highly purified reagents, as well as by analyzing purified MALDI substrates obtained by using different analytical separation methods. Krutchinsky et al. [130] used a polycarbonate compact disc as the MALDI target and found that using this type of target produced the lowest background \"chemical noise\" out of all their samples tested (approximately 20). Even though there are ways to decrease the background noise arising from impurities, elimination of this \"noise\" completely is very difficult.