Integrated sample preparation, separation and introduction...

Details Integrated sample preparation, separation and introduction... Integrated sample preparation, separation and introduction...

2001-03-27

2003-08-26

Lee, John R. (Department: 2881)

Radiant energy

Ionic separation or analysis

With sample supply means

C422S068100, C250S281000, C250S252100

Reexamination Certificate

active

06610978

ABSTRACT:

TECHNICAL FIELD
The present invention relates to sample preparation and analysis. More specifically, the invention relates to integrated microdevices for preparing and introducing a small volume of a fluid sample into an ionization chamber of an analytical device, such as a mass spectrometer, an absorption spectrometer or an emission spectrometer. The invention also relates to methods for sample introduction using the novel integrated microdevices.
BACKGROUND
Atomic or elemental analysis techniques allow for precise measurements of minute quantities of sample materials. Common analytical techniques include mass spectrometry, inductively coupled plasma spectrometry, inductively coupled plasma atomic emission spectrometry, and so forth. Elemental analysis by mass spectrometry is a generally well established technique. Inductively coupled plasma mass spectrometry (ICP-MS), in particular, is a powerful elemental analysis tool used in a variety of applications, such as environmental, geological, semiconductor and biological sample analyses. Various aspects of plasma mass spectrometry technology are described in patents such as in U.S. Pat. No. 5,334,834 to Ito et al., U.S. Pat. No. 5,519,215 to Anderson et al., and U.S. Pat. No. 5,572,024 to Gray et al. For example, U.S. Pat. No. 5,334,834 to Ito et al. describes a device for controlling the plasma potential in an ICP-MS. In ICP-based methods, the test sample is typically converted into an aerosol and transported into a plasma where desolvation, vaporization, atomization, excitation and ionization processes occur.
For fluid samples, sample introduction is a critical factor that determines the performance of analytical instrumentation such as a mass spectrometer. Analyzing the elemental constituents of a fluid sample generally requires the sample to be dispersed into a spray of small droplets. For instance, in mass spectrometry, atomic emission spectrometry or atomic absorption spectrometry, the sample is ionized. In ordinary ICP-MS, a combination of a nebulizer and a spray chamber is used in sample introduction because of the simplicity and relative low cost of the combination. The nebulizer produces the spray of droplets and the droplets are then forced through a spray chamber and sorted. However, use of this combination only introduces a small fraction of the aerosol into the plasma of the ICP-mass spectrometer because the larger droplets may condense on the walls of the spray chamber. As a result, this combination suffers from low analyte transport efficiency and high sample consumption. In addition, the use of the combination produces a memory effect, i.e., the sample signal will persist for a long period after the sample introduction is over (more particularly, “memory effect” may be defined to encompass the persistence of a signal as a result of release of adsorbed or residual fluid sample in either any portion a nebulizer or spray chamber). This analyte carry-over memory phenomenon in ICP-MS has been described, e.g., in U.S. Pat. No. 6,002,097 Morioka et al. The memory effect is especially problematic when a mass spectrometer is employed to analyze different fluid samples in sequence. Cross contamination compromises analytical results. Consequently, efforts in improving sample introduction for ICP-MS have focused on increasing spray efficiency and reducing memory effect. To obtain accurate and reliable results from an instrument that has the aforementioned memory effect, sufficient time must be provided to allow for a wash-out before a subsequent sample can be introduced. For these reasons, the throughput of instruments such as ICP-mass spectrometers using a combination of a nebulizer and a spray chamber has previously been low.
Many nebulization methods and devices are currently known in the art and include pneumatic, ultrasonic, direct injection, high-efficiency and electrospray nebulization. Two different geometries are the most common in pneumatic nebulization: the concentric type and the cross flow (including V-groove and Babington) type. Some nebulizers employ multiple nebulization methods. For example, an electrospray nebulizer may include an electrospray needle having a concentric gas flow. A concentric nebulizer with a small orifice (i.e., a microconcentric nebulizer) has been successfully used to increase spray efficiency, but tends to clog when spraying samples with a high concentration of dissolved solids. The direct injection nebulizer (DIN) is useful for reducing memory effect. It is also useful when the amount of the sample is limited or when maintaining the spatial or temporal resolution of chemical species is important, such as when coupling liquid chromatography (LC) or capillary electrophoresis (CE) to ICP-MS. However, none of these approaches correct for all known problems associated with nebulization.
It is clear, then, that the performance of a sample introduction system is evaluated with regard to parameters such as transport efficiency, precision, reproducibility, reliability, detection limits, sample size demand, liquid flow demand, spectral and nonspectral interference and wash-out time. The following patents and publications describe various aspects of sample introduction systems.
Published reports of nebulization methods and devices include Tangen et al., “Microconcentric nebulizer for the coupling of micro liquid chromatography and capillary zone electrophoresis with inductively coupled plasma mass spectrometry,”
JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY
, 1997, 12(N6):667-670; Taylor et al., “Design and characterisation of a microconcentric nebuliser interface for capillary electrophoresis-inductively coupled plasma mass spectrometry,”
JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY,
1998, 13(N10):1095-1100; and Mclean, J. A. et al., “A direct injection high-efficiency nebulizer for inductively coupled plasma mass spectrometry,”
ANALYTICAL CHEMISTRY,
1998, 70(N5):1012-1020; Kirlew et al., “Investigation of a modified oscillating capillary nebulizer design as an interface for CE-ICP-MS,”
APPLIED SPECTROSCOPY,
1998, 52(N5):770-772; and Haraguchi et al., “Speciation of yttrium and lanthanides in natural water by inductively coupled plasma mass spectrometry after preconcentration by ultrafiltration and with a chelating resin,”
ANALYST,
1998, 123(N5):773-778.
Ultrasonic energy has also been used to nebulize samples, and such use has been described in such publications as Kirlew et al., “An evaluation of ultrasonic nebulizers as interfaces for capillary electrophoresis of inorganic anions and cations with inductively coupled plasma mass spectrometric detection,”
SPECTROCHIMICA ACTA PART B
-
ATOMIC SPECTROSCOPY,
1998, 53(N2):221-237.
U.S. Pat. No. 5,868,322 to Loucks et al. describes methods and systems for nebulization of samples and for introduction of the samples into gas-phase or particle detectors. The patent describes a device having an outer tube and at least one inner tube, with fluid sample flowing out of the inner tube(s) during use. Either gas or liquid may flow in the outer tube. Liquid flowing in the outer tube may serve as “make-up fluid” and may also serve to stabilize flow in a buffer region.
U. S. Pat. No. 5,259,254 to Zhu et al. describes a method and system for nebulizing liquid samples and introducing the resulting sample droplets into a sample analysis system. Nebulization is performed with an ultrasonic nebulizer comprising a piezoelectric crystal or an equivalent ultrasound source covered with a barrier, such as a polyimide film, which serves as an interface between the ultrasound source and a heat sink. The system further comprises a solvent removal system. Any gas phase or particle sample analysis system may be used, including ICP-MS.
In addition, samples separated by high performance liquid chromatography have been nebulized and introduced into atomic emission spectrometers, as is disclosed in Elgersma et al., “Electrospray as interface in the coupling of micro high-performance liquid chromatography to inductively coupled plasma atomic emission spectrometry,”
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