The MALDI analysis is a diagnostic tool not a precise quantitative method. It cannot be used to confirm purity or identity of compound. But it is great for fast analysis/comparison of multiple closely related samples. The following examples are provided to illustrate possible applications of MALDI technique.

Let say, you are a strawberry grower. You grow 2 kind of strawberries, one regular and one organic, and you want to know if there are any difference between them. You take equal amounts of regular and organic strawberries, blend them to prepare homogeneous mixtures, mix them with a matrix and analyze them using MALDI technique. You should get similar but not identical data: slightly different amounts of sugars, flavors, metabolites. For regular strawberries you might see the presence of some pesticides or fertilizers. (But if you do not see them, it does not mean they are not there!) So, in the future, if you have an unlabeled box of strawberries, you should be able to say they are organic or regular.

Now, let say it takes 90 days for organic strawberries to become ripe. It is very difficult to transport ripe strawberries, and you would like to know if maybe you can collect them early as long as they are sweet enough. Again, you can use MALDI technique to get a good idea about relative content of sugars vs some other compounds.

Finally, you noticed that some animal bites off the ends of your strawberries, and you wonder, why? You take one strawberry, freeze it, cut a very thin slice of it, and put it in a slide glass. After adding some matrix compound you can use MALDI imaging technique to see the distribution of previously determined compounds through out one berry.

References:
Jin Wang, Ethan Yang, Pierre Chaurand, Vijaya Raghavan “Visualizing the distribution of strawberry plant metabolites at different maturity stages by MALDI-TOF imaging mass spectrometry”, Food Chemistry, Volume 345, 2021, 128838, ISSN 0308-8146, https://doi.org/10.1016/j.foodchem.2020.128838.

 To get started your lab should purchase one or two target plates from Bruker. There are two types: a ground steel plate (Part No.: 8280784) and a polished steel plate (Part No.: 8280781). A ground steel plate is supposed to be more universal but if your lab can afford it, buy both to see which one is better for your samples. At the moment, our local Bruker sales representative is Sengar, Raghvendra (Raj) (e-mail: Raghvendra.Sengar@bruker.com). Please, contact him to get a quote.

Using an appropriate matrix compound and technique prepare your samples.

After you prepared your plate, remember to keep it dry. Use some desiccant (e.g., USPak Silica Gel packets, 100 packets for ~$10 from Amazon) and a plate case to store your plate. Remember, if your sample plate is not completely dry, once you place it into the instrument under high vacuum, the remaining solvent/water will evaporate instantly, destroying your samples and contaminating the instrument.

Once your plate is ready, reserve a time slot at calendly.com/uhms.

 Three factors are important for the success in MALDI: the matrix, sample/matrix concentrations, and preparation technique.

The most popular matrix is α-cyano-4-hydroxycinnamic acid, but many different matrixes are available and widely used. The best approach is to check the literature to determine a good starting point.

The analyte should be soluble to at least about 0.1 mg/mL in some solvent. The solvent should have a normal evaporation rate: a drop of 1 μL should evaporate in 5-10 min at room temperature. The matrix is dissolved in the same solvent to yield either a saturated solution or a concentration of about 10 mg/mL. Around 0.5 – 1.0 μL of the analyte/matrix mixture is spotted onto a metal target plate for analysis and allowed to dry. After drying, the mixture of the sample and the matrix cocrystallizes and forms a solid deposit of sample embedded into the matrix. It is generally believed that the analyte is quite stable in the matrix; the sample plate can be prepared well in advance and stored for an extended period of time as long as any form of cross contamination is avoided.

The instrument uses 384 target plate. After the plate is loaded into the instrument, the analysis itself takes only a few seconds. The number of samples you can run in 1 hour depends on you.