APPLICATION NOTES

Glass Expansion HydraMist Spray Chamber

Simultaneous Multi-Element Analysis by Pneumatic Nebulization and Hg by Cold Vapor with the
Glass Expansion HydraMist Spray Chamber

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Introduction Instrument Results & Discussion Conclusion Related Documents

Introduction

While Hg can be determined by Inductively Coupled Plasma Optical Emission Spectrometry, (ICP-OES) with conventional pneumatic nebulization, the low μg/L detection limits typically achieved are not adequate for most environmental applications. The Cold Vapor technique, using an acidified stannous chloride reductant (SnCl2) solution, is a widely-used technique to improve the sensitivity of Hg in atomic spectroscopy. The Cold Vapor process traditionally uses a dedicated instrument, or a Cold Vapor/Hydride Generation accessory connected to the ICP. However, for laboratories that routinely determine Hg and other elements in the same sample, switching between a cold vapor and conventional nebulization modes adds complexity, increases argon (Ar) consumption and reduces laboratory productivity.

HydraMist
Figure 1. HydraMist - Simultaneous Cold Vapor/Pneumatic Nebulization Spray Chamber

Glass Expansion, world leaders in sample introduction systems for ICP-OES and ICP-MS have made a single-pass cyclonic spray chamber with conventional pneumatic nebulization capabilities and a secondary inlet port to inject a stream of SnCl2 into the nebulizer aerosol plume. The aerosol/liquid interaction ensures a rapid mixing of the aerosolized Hg in the nebulizer plume with the acidified SnCl2, efficiently converting Hg into a volatile form to improve Hg sensitivity. In this simple arrangement, the HydraMist gave a 20-fold improvement in Hg detection limits compared to conventional pneumatic nebulization setup, without degrading the precision or sensitivity of the other elements being conventionally nebulized through the SeaSpray nebulizer.

Instrument

The ICP-OES used in this work was an Agilent Technologies® 5100 SVDV ICP-OES, with a HydraMist spray chamber and Glass Expansion SeaSpray nebulizer with operating conditions indicated in Table 1 below. To compare the performance of the system without the Cold Vapor process the analysis was repeated using a standard Tracey single-pass spray chamber from Glass Expansion instead of the HydraMist spray chamber.

Experimental Parameter Setting
RF power 1.4kW
Nebulizer gas flow rate 0.60 L/min
Plasma gas flow rate 12 L/min
Auxillary gas flow rate 1.0 L/min
Real-time 30 sec
Number of replicates 3
Peristaltic pump speed 20 rpm
Stabilization time 30 sec
Sample line pump tubing White/white
SnCl2 line pump tubing Black/black
Drain tubing Black/white
Nebulizer 2 mL/min Direct Connection SeaSpray
Table 1. Instrumental conditions

The instrument was operated at a constant sample uptake with the option of the fast rinse between samples disabled.

SnCl2 Preparation

As SnCl2 can form an insoluble salt when dissolved in water, it is usually dissolved in concentrated HCl acid first and then diluted with H20 to form a 5% SnCl2 solution in 5% HCl.

Sample Preparation

The sample was Standard Reference Material 1643f Trace Elements in Water from the National Institute of Standard Technology (NIST) Gaithersburg, MD. SRM 1643f does not naturally have detectable Hg so it was spiked with 5ppb for this work.

Results & Discussion

As can be seen in Figure 2, the optimum concentration of SnCl2 reaches a maximum of about 5% and plateaus after that.

Figure 2
Figure 2. Sensitivity of Hg 194 with SnCl2 concentration.

In Figure 3, the intensity of Hg at 194nm is measured as a factor of sample uptake rate. The sample uptake rate is adjusted by varying the instrument peristaltic pump speed. The intensity of Hg increases as the volume of the sample aspirated is increased, indicating the Cold Vapor process is sample-limited, not reductant limited.

Figure 3
Figure 3. Hg 194nm intensity versus sample uptake rate.

In Figure 4, the Signal to Root Background Ratio (SRBR) and Net Intensity of Hg at 194nm was evaluated as a function of nebulizer flow. The nebulizer gas flow not only aspirates the analyte solution but it is also used to transport the sample aerosol and Hg Cold Vapor into the plasma. SRBR is used to optimize nebulizer flow, as it is a good proxy for detection limit performance in a solid-state detector-based ICP-OES. As can be seen in Figure 4, the optimum nebulizer flow rate is around 0.6 L/min Ar.

SRBR and Net Intensity
Figure 4.  SRBR and Net Intensity of Hg 194nm versus Nebulizer gas flow rate (L/min).

Figure 5 shows a comparison of blank intensity, and 5ppb and 10ppb Hg intensities with and without SnCl2 showing Hg sensitivity enhancements due to cold vapor generation using this SnCl2 - HydraMist method.

Mercury sensitivity with and without SnCl
Figure 5. Mercury sensitivity with and without SnCl2.

Table 2 presents 3σ Detection Limits (ppb) comparison between HydraMist and Tracey spray chambers.

Analyte λ (nm)
 HydraMist 3σ Detection Limits (ppb)
 Tracey 3σ Detection Limits(ppb)
As 188
2.3 2.5
Be 313
0.001 0.01
Cd 214
0.1 0.1
Co 233 0.6 0.6
Cr 268 0.3 0.3
Cu 327 0.7 0.5
Hg 194 0.2 4.2
Mn 257 0.03 0.03
Mo 202 0.5 0.6
Ni 232 0.6 0.8
Pb 220 2.1 2.4
Sb 217 2.8 2.6
Se 196 3.6 3.5
Tl 191 2.4 2.4
V 292 0.4 0.4
Zn 231 0.2 0.2
Table 2.  3σ method detection limits using a HydraMist spray chamber with SeaSpray nebulizer simultaneously determined using pneumatic nebulization and Cold Vapor analysis. The results are an average of 3 separate runs, measured using 3 replicates per sample of 10 blank samples.

The measured concentration of 16 elements in SRM 1643f “Trace Elements in Water” using the HydraMist spray chamber and SeaSpray nebulizer under the conditions listed in Table 1 are shown in Table 3 below. As the SRM does not contain measurable concentrations of Hg, a 50 mL aliquot of the SRM was spiked with 25 μL of 10 ppm Hg, for a 5 ppb spike concentration.

Analyte λ (nm)
 SRM 1643f Found (ppb)
 SRM 1643f Certified (ppb)
 Recovery %
As 188 60.5 57.4 105
Be 313 13.6 13.7 100
Cd 214 5.8 5.9 99
Co 233 25.5 25.3 101
Cr 268 18.5 18.5 100
Cu 327 22.9 21.7 106
Hg 194 5.3* 5.0 106
Mn 257 37.1 37.1 100
Mo 202 121.9 115.3 106
Ni 232 65.1 59.8 109
Pb 220 19.0 18.5 103
Sb 217 56.3 55.5 102
Se 196 11.9 11.7 103
TI 191 6.3 6.9 91
V 292 37.3 36.1 103
Zn 231 74.8 74.4 101
Table 3.  Measured concentration of 16 elements in SRM 1643f spiked with 5 ppb Hg using the HydraMist spray chamber and SeaSpray nebulizer.

The 5.3 ppb measured value for the 5 ppb Hg spike, represents a 106% recovery using the cold vapor mode of the HydraMist spray chamber. The measured values of all 15 naturally occurring elements were within 10% of the certified values, indicating the HydraMist spray chamber is not only sensitive for Hg by cold vapor, but also suitable for measuring trace elements in waters using conventional pneumatic nebulization mode.

Conclusion

When using the Agilent Technologies® 5100 SVDV ICP-OES with HydraMist spray chamber in cold vapor mode, the 3σ detection limits of Hg were found to be 0.2 μg/L compared to the 4.2 μg/L detection limits with a conventional Tracey single-pass spray chamber. The measured results for the “naturally occurring” elements and the 5 μg/L Hg spike in SRM 1643f Trace Elements in Water were all found to be within 10% of the expected values, demonstrating the HydraMist spray chamber is a simple and sensitive sample introduction system suitable for the simultaneous detection of Hg using Cold Vapor and other trace elements by conventional pneumatic nebulization.

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