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Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a soft ionization technique used for the analysis of large nonvolatile molecules such as biopolymers and synthetic polymers. The goal of sample preparation in MALDI analysis is homogeneous cocrystallization of analyte and matrix molecules. The role of the matrix is very crucial in MALDI and many researchers have studied on what is a good matrix. Macha and Limbach discussed about the role of matrix in MALDI analysis. Matrix compounds are still discovered through trial and error because there has not been enough research to investigate what are the factors that affect the functioning of such compounds in MALDI process. The matrix dilutes and isolates polymers in the sample preparation step and plays a role in the analyte desorption and ionization process by absorbing the laser energy at the wavelength used. The ratio of the analyte to the matrix depends on the molecular weight and chemical properties of the analyte. The ratio increases when higher molecular weight sample is analyzed. In general, the molar ratio of the analyte to the matrix ranges from 1:10 to 1:10. Dihydroxybenzoic acid has many isomers such as 2,3-, 2,4-, 2,5-, 2,6-, and 3,4-dihydroxybenzoic acids. Among them, 2,5-dihydroxybenzoic acid has the most absorption coefficient at a wavelength of 337 nm. 2,5-Dihydroxybenzoic acid (DHB) is commonly used for the analysis of synthetic polymers as well as biopolymers. Some polar matrices such as 4-hydroxy-3,5-dimethoxy-cinnamic acid, α-cyano-4-hydroxy-cinnamic acid, and methyl salicyclic acid interact well with biopolymers while some polar matrices such as 2-(4-hydroxyphenylazo)-benzoic acid (HABA), all-trans-retinoic acid (RTA), and dithranol work for synthetic polymers. Nonpolar matrices such as anthracene, pyrene, acenaphthene, and terthiophene are suitable for nonpolar samples. In a MALDI mass spectrum, the protonated molecule and cation adduct of an analyte give an important information about the molecular ion mass. Some researchers reported that sliver clusters can be effectively produced under MALDI conditions from sliver salts in the presence of matrices. During the analysis of organic molecules when Ag is used as the cationizing agent, it can be recognized that besides the desired adduct ions, [M + Ag], an additional silver cluster ions, Agn . Study on metal cluster formation in gas-phase by mass spectrometry provides valuable information on the stability and electronic properties of the metal clusters depending on the sizes and this information can be utilized when the clusters are immersed into a liquid or solid environment. One of useful methods to generate silver cluster ions is MALDI using silver salts and matrices. Keki and coworkers studied the matrix effect on the formation of the silver cluster ions under MALDI conditions using reductive polar organic matrices and silver trifluoroacetate (AgTFA) and reported that the silver cluster ions were effectively produced and the matrix greatly influenced the resulting cluster ion abundances. Properties of metal salts are depending on the kind of the counter anions as well as the metal types. It can be expected that the formation of the silver cluster ions in MALDI will be affected by the counter anions of silver salts. However, this investigation has not been sufficiently carried out. In the present work, we investigated the influence of the silver salt types on the formation of silver clusters in MALDI conditions and experimental results were explained with the interactions and reactions between the silver salt and the matrix, DHB. The MALDI mass spectrum of the AgBz shows the silver cluster ion intensity distribution with an odd-even alternation pattern as shown in Figure 1. The intensity of the oddnumber cluster ions tends to be stronger than that of the neighboring even-number cluster ions. The mass spectrum also shows the clear magic numbers of n = 21 and 35 of Agn . The magic number of n = 21 is in good agreement

Influence of Silver Salt Types on Formation of Silver Cluster Ions in MALDI with DHB as Matrix