The objective of this research is centered on fundamental studies to improve the analytical performance of plasma based elemental mass spectrometry and optical emission spectrometry with an emphasis on the development of liquid sample introduction devices suitable for the analysis of limited, expensive, and toxic materials.
The use and improvement of the demountable-direct injection high efficiency nebulizer (d-DIHEN) is investigated as a suitable interface for high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) to detect toxic arsenic species at nano-liter solution flow rates and sample volume. Separation of five arsenic species is achieved in less than 12 minutes at a solution flow rate of 0.9 μL min-1 using a 50 nL sample injection. Precision values for peak height and area of five arsenic species range from 0.5% to 6.5% RSD and absolute detection limits are within 0.4 pg to 5.4 pg arsenic, which are comparable to previously reported data at higher solution uptake rates (20 μL min-1 to 1 mL min-1 ) and larger sample injection volumes (20 μL to 100 μL).
To increase the potential for the d-DIHEN to be used more widely, an automated sample introduction system is successfully incorporated for the first time, making the d-DIHEN a universal direct injection micronebulizer. The measurement of the phosphorus content in acid-digested nucleotides and deoxyribonucleic acid (DNA) is performed with an inductively coupled plasma optical emission spectrometer (ICP-OES). With this experimental setup, the solution uptake rate and volume are reduced from 170 μL min-1 to 30 μL min-1 and 10 mL to 2.4 mL, respectively, thereby reducing the required DNA sample mass for solutions containing 3 μg g -1 P, from 300 μg to 72 μg DNA, in comparison to previous analyses. The use of direct injection also improves P (I) 213.617 nm sensitivity by a factor of 4 on average. The d-DIHEN with high performance-ICP-OES methodology allows for the quantification of DNA mass at P mass fractions as low as 0.5 μg g-1, further reducing the required DNA mass to 12 μg, with small uncertainty (≤ 0.4%). This successful approach will aide in the development and certification of nucleic acid certified reference materials (CRMs), particularly for these samples that are typically limited in volume.
The measurement of key aerosol parameters is essential for the development of an efficient low-flow nebulizer. Interferometric Droplet Imaging (IDI) with the combination of particle tracking velocimetry (PTV), is investigated to provide spatial mapping of surviving droplets in an ICP while simultaneously determining droplet size, velocity, and evaporation rate. Key findings include: (1) droplets traveling at velocities of 15 ms-1 and higher are more likely to survive the high temperature plasma, causing local cooling effects, (2) surviving droplets have a size distribution of 3 μm to 35 μm, and (3) the droplets inside an argon plasma evaporate at a rate of 0.26 mm2 s-1 to 0.36 mm 2 s-1, confirming the results of theoretical modeling and predicting a maximum droplet size of ∼18 μm for complete evaporation.
To overcome the fundamental limitation of pneumatic nebulization a heated assisted argon laminar flow interface has been designed to utilize electrospray for low-flow liquid sample introduction in plasma spectrometry. This approach improves the transport efficiency of charged droplets to the ICP over previous methods by eliminating the turbulence and the consequent droplet loss caused by the high gas velocity around the electrospray capillary. The electrospray interface has been successfully installed on an ICP-OES and ICP-MS. With the current design and implementing a heated chamber to approximately 90°C, a stable spray in a 100% argon environment with the solvent having only 5% methanol content has been achieved.
|Advisor:||Turk, Gregory C., Montaser, Akbar|
|Commitee:||King, Michael M., Nagel, David, Ramaker, David E., Teng, Henry, Vertes, Akos|
|School:||The George Washington University|
|School Location:||United States -- District of Columbia|
|Source:||DAI-B 70/02, Dissertation Abstracts International|
|Keywords:||Aerosol generation, DNA, Direct injection, Electrospray, Limited sample, Phosphorus, Plasma spectrometry|
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