Preparation of Gelatin Gel Calibration Standards for Semi-Quantitative Imaging of Elements with LA-ICP-MS

Abstract

In this work, we present the preparation of multi-element gelatin gel calibration standards for bioimaging of the elements in various biological samples with LA-ICP-MS. Homogeneity of the gelatin gel standards, linearity, sensitivity, and accuracy of the developed LA-ICP-MS method using gelatin gel standards are demonstrated in detail.

Introduction

Laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) is a powerful microanalytical technique for the direct elemental analysis of solid samples. This technique has several advantages such as wide elemental coverage, excellent limits of detection, linear dynamic range of up to 10 orders of magnitude, microanalysis, depth profiling analysis, and 2D and 3D elemental mapping. Recently, gelatin-gel calibration standards have been used successfully for quantitative bioimaging of the elements in animal tissue by LA-IC-MS due to their close resemble animal tissue [1,2].

Materials and Methods

Reagents and Instrumentation

Multi–element (Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Hg, and Pb) standard stock solution was prepared from their 1000.0 μg mL-1 standard solutions (hps, USA) in 2% (v/v) HNO3. Porcine skin gelatin (Sigma-Aldirch, USA) was used for preparation of gelatin gel calibration standards. Ultrapure water (resistivity of 18.2 MΩ cm) was used for materials cleaning and solutions preparation. All measurements and analyses were performed using a Teledyne Iridia 193 nm excimer laser with a Cobalt cell coupled to an Agilent 8800 ICP-QQQ-MS. The optimization was conducted by ablating a glass NIST SRM 612 to obtain the ThO/Th ratio <0.25% and the U/Th ratio close to 1. The images of elements, Calibration curves, LOD, and LOQ were generated by using HDIP software v1.8.5.148 (Teledyne Photon Machines, USA)

Preparation of Gelatin Gel Standards

Gelatin gel calibration standards were prepared according to the procedure outlined by Šala et al. [2] with some modifications using porcine skin gelatin at concentrations ranging from 0 to 50 μg g^-1.

Homogeneity of Gelatin Gel Standards

The homogeneity of gelatin gel calibration standards was tested by imaging elements individually in the standards with LA-ICP-MS. As shown in Figure 1, analyte elements were distributed homogenously in the prepared gelatin standards.

Figure 1. Homogeneity of gelatin gel calibration standards

Results

Calibration, sensitivity and accuracy

Linear calibration equations of calibration curves, linearity (expressed as R2), limit of detection (LOD), and quantification (LOQ) are given in Table 1. As can be seen in Table 1, satisfactory linearity and sensitivity were achieved.

Table 1. Linear calibration equations (concentration range: 0-50 μg g-1), determination coefficient (R2), precision (as RSD), limit of detection (LOD) and quantification (LOQ) of the LA-ICP-MS method.

The accuracy of the gel calibration standards was checked by analysis of pelleted certified reference materials (SRM1566 b: Pine Needles; SRM1547: Peach Leaves; SRM1575a: Oyster Tissue). Results are shown in Table 2. The recoveries were between 71% (for 208Pb) and 140% (for 59Co) which are acceptable for LA-ICP-MS.

Table 2. Results of the SRMs analysis by using LA-ICP-MS.

References

1. Limbeck, A., Galler, P., Bonta, M., Bauer, G., Nischkauer, W., Vanhaecke, F., (2015). Anal. Bioanal. Chem. 407, 6593–6617.

2. Šala, M., Šelih, V. S., & van Elteren, J. T. (2017). Analyst, 142(18), 3356-3359.