Performance comparison in the analysis of geological samples by ICP-OES using two novel nebulizers: MassNeb® and Micromist®

1. Introduction

Nebulizer selection is a critical but often overlooked aspect of ICP-OES analyses. There are many different nebulizers available for ICP-OES and ICP-MS, for this reason, choosing the optimal one can be confusing and misleading. To achieve peak performance from your ICP analysis, it is essential to choose the optimal nebulizer based on your sample matrix, precision and limits sensibility required. In addition to any necessary accessories and analytical strategies to maintain long-term performance, such as humidifiers, ultrafiltration, hydride generation, etc.
In the last decade, nebulizer selection has become challenging due to the relatively wide variety available. By far, concentric nebulizers are the most common type found on instruments today, as they generally provide the best performance. Even within the narrow category of concentric nebulizers, there is quite a range of different designs. In this study, we compare the performance of MassNeb® inert, robustness and durability nebulizer manufactured by Ingeniatrics Tecnologías S.L. and one of the most stablished nebulizers in the market, Micromist® (Glass Expansion) for analytical methodologies based on ICP-OES and ICP-MS detection.
MassNeb and Micromist

2. Experimental

Reagents and solutions

The aqueous calibration standards of 1, 5, 10, 50, 100 and 250 µg g-1 were prepared by appropriate dilution of a mono-elemental stock solution of 10000 mg L-1 of each Ag, As, Cu, Pb, Fe and Zn, analytes quantified in the present Application Note (ICP CetriPUR, Merck, Darmstadt, Germany) in deionized water (18 MΩ cm resistivity). All aqueous solutions are acidified by adding up to 5% nitric acid and 15% high purity hydrochloric acid (Merck, Darmstadt, Germany). An aqueous calibration blank is also prepared containing HNO3 and HCl in the same proportions, like the matrix samples, once mineralized.


All measurements were carried out using an inductively coupled plasma-optical emission spectrometer (ICP-OES) model Varian 710-ES (Agilent Technologies) and a SPS3 autosampler (Agilent Technologies). The instrument operating conditions are shown in table I.
MassNeb and Micromist

Table I. Operational conditions using ICP-OES Varian 710-ES, Agilent Technologies.

Sample Preparation

A microwave oven (CEM Matthews, C, USA, model MARS) was used for the mineralization of certified reference materials OREAS (geological matrix) used in this study. For this purpose, the CRM samples were exactly weighed (0.200 g) in 25-mL microwave PTFE vessels, and 5 mL of a mixture containing nitric acid and hydrochloric acid (1:3 v/v) was added. After 10 min, the PTFE vessels were closed and introduced into the microwave oven. The mineralization was carried out at 800 W from room temperature ramped to 160 °C for 15 min and held for 40 min at this temperature. Then the solutions were made up to 50 mL with ultrapure water and the metals analyzed by ICP-OES using axial acquisition mode of detection. All CRM were mineralized by triplicate.

3. Results and discussion

Sensitivity and signal stability

MassNeb® nebulizer uses Flow Blurring nebulization technology instead of the traditional Venturi effect, as Micromist® nebulizer. This allows the generation of a very fine droplet aerosol with a narrow size distribution (most droplets are smaller than 10 μm), which improves efficiency over a wide range of nebulization gas flow rates, especially 0.60-0.75 L min-1 (150-250 kPa nebulization pressure).
The optimal aerosol generated by the MassNeb® nebulizer is also more efficiently desolvated and excited in plasma, helping to improve precision values, typically less than 1% RSD between replicates of the same run analysis, even at low sample flow rates, which also explains why it is much more sensitive than conventional nebulizers. as well as a parallel-path nebulizer from other vendors.

To determine the optimal pump speed for sample introduction, a sensitivity study was conducted using a 5 µg kg-1 Mn solution monitored at a wavelength of 293.305 nm. A nebulization flow curve was generated for the Micromist® and MassNeb® nebulizers, with the best results obtained at 250 kPa and 10 rpm for Micromist® and 175 kPa and 7 rpm for MassNeb® (see Figure 1).
Performance comparison analysis

Figure 1. Nebulization flow curve for sensitivity evaluation using different nebulization gas pressure and pump speed for sample introduction represented as Intensity of 5 ppm Mn (cps) / Background signal (cps).

The purpose of this study was to evaluate the signal stability and plasma drift of the analytes of interest without using an internal standard for quantification.
To do so, a monitoring standard solution containing 25 µg g-1 of each element was prepared and analyzed once every 5 mineralized CRM samples. Recoveries were monitored to ensure they fell within the acceptable range of 90-108%.

Precision and reproducibility evaluation

Precision values were evaluated using geological matrix certified reference materials (CRM) after aqua regia mineralization using a microwave-assisted oven. Precision is expressed as the relative standard deviation percentage (RSD%).
Table II below, summarizes the experimental registered values for each monitored wavelength with both nebulizers evaluated, as well as the RSD obtained for 3 replicates of each of the CRMs used in the experimental development of this application note. Generally, MassNeb® shown better precision and reproducibility results in comparison with the results obtained with Micromist® nebulizer.
Performance comparison analysis

Table II. Experimental and certified values for each monitored wavelength, as well as the RSD obtained for 3 replicates of the different CRM using Micromist® and MassNeb® nebulizers used in this study.

4. Conclusions

The results obtained in this study using MassNeb® nebulizer provides better sensitivity at lower speed pump for sample introduction to the ICP-OES instruments in comparison with the results obtained by Micromist® nebulizer.
This fact makes MassNeb® nebulizer more appropriate for the analysis of samples with high contents of highly corrosive acids, especially hydrofluoric acid, favoring the product lifespan and minimizing the deterioration of instrumental accessories and consumables of ICP instruments, as well as reduce operational incidents caused by the corrosive effect of acids used in the mineralization of samples.

Moreover, the MassNeb® nebulizer’s lower sample consumption requirement makes it particularly appealing for clinical analysis, where the amount of sample needed for ICP analysis is a crucial factor due to the use of human tissues or biological fluids.
This feature allows for more efficient and costeffective analysis, making it an attractive option for clinical researchers and practitioners.

Finally, the increased precision in the results obtained with the MassNeb® nebulizer is due to its higher sensitivity and reproducibility compared to the Micromist® nebulizer. This is a consequence of the MassNeb® nebulizer’s ability to generate a very fine droplet aerosol with a narrow size distribution, resulting in greater precision in the analysis.

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