Recommendations for quantitative analysis of small molecules by matrix-assisted laser desorption ionization mass spectrometry

Abstract

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) has been used for quantitative analysis of small molecules for many years. It is usually preceded by an LC separation step when complex samples are tested. With the development several years ago of “modern MALDI” (automation, high repetition laser, high resolution peaks), the ease of use and performance of MALDI as a quantitative technique greatly increased. This review focuses on practical aspects of modern MALDI for quantitation of small molecules conducted in an ordinary way (no special reagents, devices or techniques for the spotting step of MALDI), and includes our ordinary, preferred Methods The review is organized as 18 recommendations with accompanying explanations, criticisms and exceptions.

Determination of copper and lead in tequila by conventional matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and partial least squares regression

“…Two criteria were applied while setting experimental and instrument conditions: (i) homogeneity of sample co‐crystallization with matrix and (ii) as high as possible signal‐to‐noise (S/N) ratio. In accord with general recommendations and based on our previous study, α‐cyano‐4‐hydroxycinnamic acid was selected as the chemical matrix. A series of HCCA solutions was prepared using methanol, acetonitrile and acetone mixed in different proportions and containing or not 0.01% trifluoroacetic acid (TFA).…”

“…Figure S5 (supporting information) shows the effect of the HCCA concentration on the S/N ratio evaluated for peak height and peak area measurements and photos of sample co‐crystallized with matrix at different HCCA concentrations. As to the instrumental conditions, in line with previous experience, relatively low laser intensity (40%) and few shots per series (100) were used to keep spectral noise low and to obtain sound repeatability; to enhance sensitivity, summation of signals obtained in successive series was applied (25 × 100, details given in section ).…”

“…Two criteria were applied while setting experimental and instrument conditions: (i) homogeneity of sample co-crystallization with matrix and (ii) as high as possible signal-to-noise (S/N) ratio. In accord with general recommendations 11 and based on our previous study, 19 α-cyano-4-hydroxycinnamic acid was selected as the chemical matrix. HCCA concentration of 1.25 mg mL −1 was selected and it was decided to apply the peak area as the analytical signal mode because of the higher S/N ratios obtained for both elements as compared with the peak height measurements.…”

“…To counterbalance these limitations, a range of matrix‐free laser desorption/ionization techniques have been developed; however, the efficiency of analyte desorption/ionization strongly depends on the chemical nature and the size of nanomaterial applied to assist the process, and poorer sensitivity has often been reported in these new techniques as compared with conventional MALDI with organic matrices . In another approach for enhanced determination of small molecules, a considerable effort has been dedicated to the improvement of sample preparation and on the selection of instrumental conditions in conventional MALDI thus avoiding undesired matrix effects …”

“…[6][7][8][9][10] In another approach for enhanced determination of small molecules, a considerable effort has been dedicated to the improvement of sample preparation and on the selection of instrumental conditions in conventional MALDI thus avoiding undesired matrix effects. [11][12][13] Beyond any doubt, inductively coupled plasma mass spectrometry (ICP-MS) is the first-choice technique for the determination of trace metal/metalloids in any real-world sample; however, there have also been several applications of conventional MALDI-HRMS reported, [14][15][16][17][18] offering a memory-free, high-throughput, highresolution, micro-scale alternative with instrument operation costs much lower as compared with ICP-MS. In this regard, we have recently demonstrated the feasibility of conventional MALDI coupled to time-of-flight mass spectrometry (TOFMS) for the determination of mercury and copper in fish tissues.…”