Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
2002-04-04
2004-11-16
Lee, John R. (Department: 2881)
Radiant energy
Ionic separation or analysis
With sample supply means
Reexamination Certificate
active
06818888
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to atmospheric pressure chemical ionization (APCI) mass spectrometry (MS). More particularly, the present invention relates to an apparatus and method for improving vaporization of sample-containing droplets in the APCI source.
BACKGROUND OF THE INVENTION
Mass spectrometry is a highly sensitive method of molecular analysis. In general, mass spectrometry is a technique that produces a mass spectrum by converting the components of a sample into rapidly moving gaseous ions, and resolving the ions on the basis of their mass-to-charge (m/e or m/z) ratios. The mass spectrum can be expressed as a plot of relative abundances of charged components as a function of mass, and thus can be used to characterize a population of ions based on their mass distribution. Mass spectrometry is often performed to determine molecular weight, molecular formula, structural identification, and the presence of isotopes. The apparatus provided for implementing mass spectrometry, i.e., the mass spectrometer (MS), typically consists of a sample inlet system, an ion source, a mass analyzer, and an ion detection system, as well as the components necessary for carrying out signal processing and readout tasks. Many of these functional components of the mass spectrometer, particularly the mass analyzer, are maintained at a low pressure by means of a vacuum system. The ion source converts the components of a sample into charged particles. The negative particles are ordinarily removed from the process flow. The mass analyzer disperses the charged particles based on their respective masses, and then focuses the ions on the detector. The ion currents produced by the detector are then amplified and recorded as a function of spectral scan time. The designs of the components of the mass spectrometer, and the principles by which they operate, can vary considerably. Thus, components of differing designs have distinct advantages and disadvantages when compared to each other, and the desirability of any one design can depend on, among other factors, the nature of the sample to be analyzed.
One type of sample inlet system can be described as being chromatographic—that is, in some types of analytical systems, the effluent from a chromatographic column can be utilized as the sample source for a mass spectrometer. Stated differently, the mass spectrometer in such cases can be considered as serving as the detector for the chromatographic apparatus. Such an arrangement is commercially available in systems in which a gas chromatographic (GC) apparatus is directly coupled to the mass spectrometer (GC/MS systems), or a liquid chromatographic (LC) apparatus is directly coupled to the mass spectrometer (LC/MS systems). These combined systems are particularly useful for deriving complex spectra from mixtures, as it is known that mass spectrometers alone are more or less limited to handling pure compounds and relatively simple mixtures.
An ion source commonly serving as the interface between an LC apparatus and the mass spectrometer operates according to the principle of atmospheric pressure chemical ionization (APCI). Simply stated, APCI is a means for ionizing samples dissolved in a liquid. Typically, the sample-containing liquid emitted from the LC apparatus is pneumatically nebulized into numerous small droplets, typically below 100 microns in diameter. Heat is applied to the droplets to vaporize the liquid and sample matrix, and the resulting vapor is subsequently passed through a low-current corona discharge. In the discharge, ion molecule reactions occur between the charge-neutral sample and the ions formed in the primary discharge. The ion molecule reactions with the sample cause the sample to become charged, and the charged sample ions are passed through an opening in a vacuum chamber into the mass analyzer of the mass spectrometer for mass analysis.
FIG. 1
illustrates an example of a conventional APCI source, generally designated
10
, utilized in, for example, an LC/MS system. In general terms, APCI source
10
comprises an inlet section, generally designated
20
; a vaporization section, generally designated
30
; an ionization section, generally designated
40
; and an outlet section, generally designated
50
, that includes an aperture
53
through which ionized products are directed into the mass analyzer of the mass spectrometer. For simplicity, the mass analyzer and other typical components of the mass spectrometer, such as its ion detection, signal processing and readout systems, are collectively designated as MS in FIG.
1
.
Inlet section
20
comprises a capillary tube
23
that serves as the sample inlet system of the mass spectrometer, and which conducts the LC column flow from a liquid chromatographic apparatus LC. In addition, a length of conduit
27
for directing a suitable nebulizing gas such as nitrogen into vaporization section
30
is coaxially disposed about capillary tube
23
. Vaporization section
30
of APCI source
10
generally includes a vaporizing tube
33
, a heater
35
, and a conduit
37
for directing a suitable vaporizing gas such as nitrogen into vaporizing tube
33
. Heater
35
is situated so as to ensure sufficient thermal contact with the wall of vaporizing tube
33
. Capillary tube
23
is disposed along the central axis of vaporizing tube
33
. A portion of vaporizing gas conduit
37
is coaxially disposed about nebulizing gas conduit
27
as well as capillary tube
23
. Ionization section
40
of APCI source
10
generally includes an enclosed chamber (not specifically shown) into which an electrode, designated herein as a corona needle
43
, is inserted. Corona needle
43
typically operates at about 5 kV to strike a low-current corona discharge
45
within ionization section
40
.
In operation, a liquid sample comprising the LC column flow from liquid chromatographic apparatus LC is introduced into the heated vaporizing tube
33
via capillary tube
23
. Nebulizing and vaporizing gas streams are introduced into vaporizing tube
33
through nebulizing gas conduit
27
and vaporizing gas conduit
37
, respectively. The nebulizing gas flows concentrically around centrally disposed capillary tube
23
at high velocity flow, thereby nebulizing the liquid sample into small liquid droplets as the nebulizing gas and liquid sample enter vaporizing tube
33
. Because the wall of vaporizing tube
33
is heated by heater
35
and consequently transfers heat energy into the interior of vaporizing tube
33
, the liquid droplets of the nebulized sample entering vaporizing tube
33
are converted into vapor. The vaporizing gas is added to the system by means of vaporizing gas conduit
37
to assist in transporting the liquid droplet and vapor phases of the sample through vaporizing tube
33
. The vapor then passes into the low-current corona discharge
45
established by corona needle
43
in ionization section
40
, where the charge-neutral sample is ionized by ion molecule reactions with ions formed in the discharge.
In a typical configuration of conventional APCI source
10
, vaporizing tube
33
has a 4-mm internal diameter and is 120-150 mm in length. A 1 ml/min liquid flow of sample-containing liquid corresponds to an approximately 1700 ml/min flow of vapor. The nebulizing gas flows at a rate of approximately 1000 ml/min, and the auxiliary vaporizing gas flows at a rate of approximately 1000-2000 ml/min. Thus, assuming a net gas flow rate of approximately 5000 ml/min through a 4-mm I.D., 120-mm long vaporizing tube
33
, a droplet entrained in the gas, moving at the average flow velocity of the gas, would require approximately 15-20 ms to traverse the entire length of vaporizing tube
33
. A liquid flow of 1 ml/min of water requires in excess of 40 W to heat and vaporize the water, neglecting any other heat losses. Because the flow through vaporizing tube
33
is laminar, the nebulized droplets will flow principally down the center of vaporizing tube
33
where the linear gas velocity is the greatest. It follows that the heat tr
Schachterle Steven D.
Wells Gregory J.
Fishman Bella
Gloekler David
Kalivoda Christopher M.
Lee John R.
Varian Inc.
LandOfFree
Vortex flow atmospheric pressure chemical ionization source... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Vortex flow atmospheric pressure chemical ionization source..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vortex flow atmospheric pressure chemical ionization source... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3303290