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Assessment of the Potential of Chemometric Methods in the Analysis of Mass Spectrometry Images Towards Obtaining Pure Spectral and Spatial information

Mohammadi Tanouraghaj, Saeedeh | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50533 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Parastar Shahri, Hadi
  7. Abstract:
  8. Recently, the use of mass spectrometry imaging (MSI) has been introduced as a powerful tool to study the compounds in biological and environmental samples. The lack of need to sample preparation have made it possible to quantify and qualify these compounds in complex matrix such as biological matrices. This technique will also allow analyzing the compounds in a very wide mass range and precise structural information this method gives leads to employ this method widely for quantification and qualification of wide variety compounds. Accuracy and precision of results obtained by this method beside unique information it gives about system lead to wide use of this method in scientific researches. The high complexity and huge size of data obtained by this technique is where the interpretation and extraction of desired information from raw data runs into bottlenecks. Moreover, there are some major drawbacks inherent to quantitative analysis using MSI, due to the heterogeneity of matrix crystallization and also ion suppression effects. Therefore, chemometrics can play an important role in different steps of MSI data analysis. The objective of this work was quantification of chlordecone (C10Cl10O) as a carcinogen pesticide in the mouse liver using matrix assisted laser desorption ionization MSI (MALDI-MSI) combined with multivariate chemometric techniques. On this matter, the data sets related to images from the livers of exposed mice to chlordecone in 1, 5 and 10 days of exposure (Data sets I-III) were analysed. In these data sets, there were seven spots related to the standard of chlordecone in quantity range of 0 to 450 g/g and four unknown ones. As a first step, MSI images were compressed using binning approach in 3 different bin sizes: 0.25, 0.5 and 1.0. Then, MSI images for calibration and unknown samples were column-wise augmented and analyzed by multivariate curve resolution-alternating least squares (MCR-ALS) under application of proper constraints of non-negativity, spectral normalization. The resolved spectral profiles were used for identification of chlordecone and other interferences. Also, the augmented spatial profiles were post-processed and 2D images for each component were obtained in calibration and unknown samples. The sum of these profiles was utilized to set the calibration curve and to obtain analytical figures of merit (AFOMs). Inspection of the results showed that the lower bin size (i.e., 0.25) provides more accurate results. Finally, the obtained results by MCR for three data sets were compared with those of gas chromatography (GC) and MALDI-MSI. The results showed that MCR-assisted method gives chlordecone amount higher than single MALDI-MSI and lower than GC. It is concluded that combination of chemometric methods with MSI can be considered as an alternative way for MSI quantification
  9. Keywords:
  10. Gas Chromatography ; Mass Spectrometery ; Chemometrics Method ; Multivariate Curve Resolution-Alternative Least Square (MCR-ALS) ; Image Analysis ; Chlordecone

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