The use of pencil lead as a matrix and calibrant for matrix‐assisted laser desorption/ionisation

Abstract

Pencil lead is shown to be an effective matrix and calibrant in matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry. Various groups of analytes, including peptides, polymers and actinide metals, can be readily ionised using MALDI when deposited onto a pencil lead matrix. The matrix is seen to have advantages in sample preparation relating to its hydrophobic properties and almost complete suppression of the matrix during analysis. Using pencil lead as a matrix is a quick and convenient method of qualitative analysis and has been shown to be quantitative for the isotope ratio analysis of actinide metals.

2B or not 2B, that is the question: further investigations into the use of pencil as a matrix for matrix‐assisted laser desorption/ionisation

“…This was reaffirmed where graphite rod (99.9%) was found to be an inferior graphite matrix source due to poor transfer and poor adhesion of graphite to the metal target. 15 The glide agents vary from mainly mixtures of long-chain hydrocarbons (C12-18), these occasionally mixed with phthalates, to mixtures of hydrocarbons and long-chain acids. In the case of the latter, the saturated C16 and C18 carboxylic acids are observed in the PL-MALDI spectrum at m/z 295 and 323, respectively, for the potassiated molecules (see Fig.…”

“…Notably some sugars have been successfully analysed using this method but the specific data cannot be reported here for confidentiality reasons. Initial analysis of actinides proved successful using PL-MALDI 15 and the scope for the analysis of transition metals has now been expanded to cover the lanthanides. 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 Time ( Dysprosium, erbium, gadolinium, lanthanum, praseodymium and ytterbium nitrate were all analysed successfully from the pencil matrix.…”

“…More recently, the use of ionic liquid matrices has become widespread 9 and the conditions required for the effective use of the matrix suppression effect (MSE) have been investigated. 10 The use of graphite as a matrix [11][12][13] and the utilisation of graphite target plates, without the addition of a standard crystalline matrix, 14 was discussed in our earlier publication, 15 where graphite powder and graphite rod were investigated as possible matrices for the analysis of actinides. Difficulties in handling and deposition of the graphite were highlighted and a simplified method utilising pencil lead (PL) as a new MALDI matrix was developed in this laboratory to address these problems.…”

“…The pencil is simply scribbled onto the target spot producing a hydrophobic surface that allows a sample droplet to dry to a concentrated spot. 15 As well as proving to be an excellent matrix for actinide analysis, some promise was shown for a few small organics, peptides and small polymers studied. To investigate this further, a diverse library of small molecules has been analysed to determine the breadth of application of PL-MALDI and the results are presented here.…”

“…It has previously been discovered that it was easier to obtain increased ion signal intensity with pencils of a higher black rating (higher B numbers). 15 However, pencils do not only contain clay and graphite. In order to give a smooth writing tool, waxes and oils are impregnated into the pencil leads during manufacture; these have been termed 'glide agents'.…”