A two‐point calibration method for quantifying organic binary mixtures using secondary ion mass spectrometry in the presence of matrix effects

Abstract

Quantification of the composition of binary mixtures in secondary ion mass spectrometry (SIMS) is required in the analyses of technological materials from organic electronics to drug delivery systems. In some instances, it is found that there is a linear dependence between the composition, expressed as a ratio of component volumes, and the secondary ion intensities, expressed as a ratio of intensities of ions from each component. However, this ideal relationship fails in the presence of matrix effects and linearity is observed only over small compositional ranges, particularly in the dilute limits. In this paper, we assess an empirical method, which introduces a power law dependence between the intensity ratio and the volume fraction ratio. A previously published physical model of the organic matrix effect is employed to test the limits of the method and a mixed system of 3,3′‐bis(9‐carbazolyl) biphenyl and tris(2‐phenylpyridinato)iridium (III) is used to demonstrate the method. This paper introduces a two‐point calibration, which determines both the exponent in the power law and the sensitivity factor for the conversion of ion intensity ratio into volume fraction ratio. We demonstrate that this provides significantly improved accuracy, compared with a one‐point calibration, over a wide compositional range in SIMS quantification and with a weak dependence on matrix effects. Because the method enables the use of clearly identifiable secondary ions for quantitative purposes and mitigates commonly observed matrix effects in organic materials, the two‐point calibration method could be of significant benefit to SIMS analysts.

Quantitative analysis of ToF‐SIMS data of a two organic compound mixture using an autoencoder and simple artificial neural networks

“…6 It contained two organic compounds, Irganox 1010 (C 73 H 108 O 12 , molecular weight 1176.8) and Fmoc-pentafluoro-L-phenylalanine (Fmoc-PFLPA; C 24 H 16 F 5 NO 4 , molecular weight 477.10). The methods for correcting matrix effects [3][4][5][6][7][8][9][10] are effective for quantitative analysis.…”

“…3,5,6,10 A two-point calibration method that is more accurate than existing correction methods has been proposed. 10 However, these methods require strict control in terms of concentrations and mixing conditions when preparing reference samples. Matrix effect correction methods 3,5,6,10 are effective only for secondary ions that exhibit lower matrix effects, and they require the selection of appropriate secondary ions out of numerous ions in the ToF-SIMS spectra.…”

“…As the matrix effects of the aforementioned organic materials can be expressed using reported mathematical equations, 3,5,6,10 the matrix effects that are described by continuous functions can be approximated by an ANN with one hidden layer, therefore the ANN method is used to indicate the appropriate ratios for the mixed samples and the autoencoder extracts the corrected features based on the pure components in a sample.…”

“…Quantitative and qualitative analyses of a complex sample through time-of-flight secondary ion mass spectrometry (ToF-SIMS) are challenging because of the multiorigin secondary ion overlap, interfering peaks, and matrix effects. [1][2][3][4][5][6][7][8][9][10] The matrix effects modulate ion intensity, irrespective of the concentration; they are often observed in the ToF-SIMS data of mixed-material samples.…”

“…Several mathematical equations have been proposed for matrix effect corrections. 3,5,6,10 A two-point calibration method that is more accurate than existing correction methods has been proposed. 10 However, these methods require strict control in terms of concentrations and mixing conditions when preparing reference samples.…”