Interface for a photoionization mass spectrometer

Description of equivalent WO 2004061895 A1

INTERFACE FOR A PHOTOIONIZATION MASS SPECTROMETER

Cross Reference to Related Applications

This is an International Application claiming priority to U.S. Application No. 10/334,506, filed December 31, 2002, which is a continuation-in-part of U.S. Application No. 09/596,307, filed June 14, 2000, which is a continuation-in-part of U.S. Application 09/247,646, filed February 9, 1999 (U.S. Patent No. 6,211,516).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject matter disclosed generally relates to a

detector that can detect trace molecules .

2. Background Information

There are detectors that are capable of detecting a

trace molecule from a sample. The sample may be a gas or

liquid sample taken from a room or a fluid source,

respectively. It may be desirable to detect certain trace

molecules to determine whether the sample contains

contaminants, drugs, explosives, etc.

The detector may include an ionization stage and a mass

detector stage. The ionization stage ionizes molecules within the sample and then projects the ionized molecules

through the mass detector. The mass detector may be a time

of flight device that determines mass based on the time at

which the molecules strike a detector plate. The

ionization chamber may include a light source that ionizes

the sample through a photoionization process.

The sample is introduced into the ionization chamber

through a single inlet port. To obtain accurate readings

it is desirable to calibrate the detector before each

sample is run through the device. The detector is

calibrated by introducing a standard sample that may

contain the molecules under investigation. Obtaining

accurate readings therefore requires sequentially loading a

standard sample, calibrating the detector and then

introducing a test sample into the ionization chamber.

This sequence can be time consuming particularly when large

batches of samples are to be tested. Additionally, there

may be some degradation in the detector between the time

the detector is calibrated and -when the test sample is

actually loaded into the chamber. It would be desirable to decrease the run time and increase the accuracy of a

detector.

Liquid test samples typically include water or drug

samples stored in organic solvents. It is desirable to

vaporize the solvent before the sample is ionized. One way

to vaporize the solvent is to break the sample into aerosol

droplets with a nebulizer. A nebulizer includes a co-flow

of inert gas that breaks the liquid sample into an aerosol.

The detector may contain a heating element that vaporizes

the solvent within the aerosol.

Most nebulizers operate at atmospheric pressure because

higher pressure causes more molecular collisions and assist

in the vaporization process. It is sometimes desirable to

operate the ionization chamber at low pressure,

particularly for photoionizers . It would be desirable to

provide an inlet port for liquid samples that can introdude^"'

the sample to a low pressure ionization chamber.

BRIEF SUMMARY OF THE INVENTION

A detector system that includes a detector coupled to a

photoionizer. The system may also include a first inlet

port and a second inlet port that are both coupled to the

photoionizer.

BRIEF DESCRIPTION OF THE DRAWINGS^'

Figure 1 is an illustration of a detector system;

Figures 2A-B are graphs showing the detection of a

standard sample introduced to the detector;

Figures 3A-B are graphs showing the detection of a test

sample and standard sample simultaneously introduced to the

detector;

Figure 4 is an illustration of an alternate embodiment

of the detector;

Figure 5 is an illustration of an alternate embodiment

of the detector;

Figure 6 is an illustration of an alternate embodiment

of the detector;

Figure 7 is an illustration of a syringe used to

introduce a test sample into the detector;

Figure 8 is an illustration of a nebulizing inlet port

that receives a syringe;

Figure 9 is an illustration of a nebulizing inlet port

that receives a capillary tube. DETAILED DESCRIPTION

Disclosed is .a detector system that contains two inlet

ports coupled to a photoionization chamber. One inlet port

allows for the introduction of a test sample. The test

sample may contain contaminants, drugs, explosive, etc.

that are to be detected. The other port allows for the

simultaneous introduction of a standard sample. The

standard sample can be used to calibrate and/or diagnose

the detector system. Simultaneous introduction of the

standard sample provides for real time

calibration/diagnostics of the detector during detection of

trace molecules in the test sample. The photoionizer

ionizes the samples that are then directed into a mass

detector for detection of trace molecules. The detector

system may also include inlet embodiments that allow for

vaporization of liquid samples introduced to a low pressure

photoionizer.

Referring to the drawings more particularly by

reference numbers, Figure 1 shows a detector system 10.

The detector system 10 may include a housing 12,

electrostatic lenses 14 and 16, sealing elements 18 and an ionizer 20 that surround an ionization chamber 22. In one

embodiment the ionizer 20 is a light source that can

photoionize molecules within the chamber 22. By way of

example, the light source can emit light having photo-

energy between 8.0 and 12.0 electron volts (eV) . 8.0 to

12.0 eV is high enough to ionize most trace molecules while

minimizing molecular fragmentation within the sample.

The detector system 10 may include a first inlet port

24 and a second inlet port 26 that are coupled to the

ionization chamber 22. The inlet port 24 allows a test

sample to be introduced to the ionization chamber 22. The

test sample may contain contaminants, drugs, explosives,

etc. that are to be detected by the detector system 10.

The second inlet port 26 allows for the introduction of a

standard sample that can be used to calibrate and/or

diagnose the detector system 10. The standard sample may

be introduced in a continuous manner so that there is a

consistent flow of the sample. The test sample is

typically introduced through a -syringe. Consequently, the

introduction of the test sample is a transient event. Both the test sample and the standard sample may be either a

liquid or gas flow.

The first inlet port 24 may include a septum 28 and a

septum cap 30. The septum 28 can receive the needle of a

syringe (not shown) . The first inlet port 24 may be

coupled to the ionization chamber 22 by a channel 32. The

housing 12 may include a heating element 34 embedded in the

housing 12 to heat the channel 32. The heating element 34

may operate at a temperature that vaporizes solvents in the

test sample. For example, the heating element 34 may

operate between 100 and 400 degrees centigrade.

The second inlet port 26 may include a capillary tube

36 that extends through a tube fitting 38. The housing 12

includes another channel 40 that provides fluid

communication between the tube 36 and the ionization

chamber 22. The -heating element 34 also extends to the

channel 40 to vaporize the sample introduced through the

capillary tube 36. Although the first inlet port 24 is

shown as having a septum, it is to be understood that the

first port 24 may have the capillary tube arrangement of

the second port 26. The ionizer 20 ionizes the samples introduced to the

ionization chamber 22. The lenses 14 and 16 then pull the

ionized molecules of the samples through an aperture 42 and

into a mass detector 44. The mass detector 44 may be a

time of flight device that can detect the trace molecules

based on the time required to strike a detector plate (not

shown) within the detector 44. Although a time of flight

mass detector is described, it is to be understood that

other types of detector devices may be used in the system

10.

Figures 2A and 2B show a mass spectrum and a time

dependent profile, respectively, for a standard sample

introduced to the detector. The standard sample can be

used to calibrate and/or diagnose the detector system.

Figures 3A and 3B show a mass spectrum and a time

dependent profile, respectively, for a combined standard

sample and a test sample that contains diazepam in

methanol, introduced to the detector system 10. As shown

in Fig. 3B, the sample signal rises and falls with the

introduction of the test sample. Figure 4 shows an alternate embodiment, wherein the

detector 10' includes a pump 46 that removes a portion of

the samples. It is desirable to control the flow of the

samples from the ionization chamber 22 to the mass detector

44. An excessive flow may create an undesirably high

pressure within the mass detector 44. A pump-out channel

48 may be connected to a point between the ionization

chamber 22 and the aperture 42 to divert some of the

ionized molecules away from the mass detector 44. Figure 5

shows an embodiment of a detector 10" wherein the channel

48 terminates in the ionization chamber 22' .

Figure 6 shows another embodiment of a detector system

200 that includes a first ionization chamber 202 coupled to

a second ionization chamber 204 by a capillary tube 206.

The chambers 202 and 204 may be separated by interface

walls 208.

The first ionization chamber 202 may include a first ionizer 210. The first ionizer 210 may be of any type to

ionize molecules within the first chamber 202. The ionized

molecules within the first chamber 202 are focused into the

capillary tube 206 by electrostatic lenses 212 and 214. The first ionization chamber 202 operates at a higher

pressure than the second chamber 204. The pressure

differential drives the ionized molecules from the first

chamber 202, through the tube 206 and into the second

chamber 20 .

By way of example, the first chamber 202 may operate at

atmospheric pressure. Such a high pressure may induce

molecular collisions and reactions that can change the

identity of the ions. The second ionization chamber 204

may contain a second ionizer 216 that further ionizes the

sample. Further ionization may generate the original ions

and therefore restore the identity of the ions. The second

ionizer 216 may be a photoionizer. A photoionizer may

ionize molecules not ionized by the first ionizer 208 and

thus provide more information. Additionally, a

photoionizer is desirable because it does not use electric

fields and therefore such a device will not interfere with

ionized molecules traveling through the aperture 218 of the

focusing lens 220 to the mass detector 222.

A second capillary tube 224 can be placed adjacent to

the first tube 206. The second capillary tube 224 may provide a standard sample that is not ionized within the

first ionization chamber 202. The standard sample flows

into the second chamber 204 due to the differential chamber

pressure. The standard and test samples are ultimately

detected within the mass detector 222,

Figure 7 discloses a syringe 300 that can be used to

introduce a test sample into the detector system. The

syringe 300 may include a needle 302 that is attached to a

tube 304. The tube 304 has an inner chamber 306. A

plunger 308 extends into the inner chamber 306 of the tube

304.

The syringe 300 may be loaded with a liquid test sample

310 that is upstream from a volume of air 312. The air

mixes with and dilutes the liquid test sample to increase

the delivery time of the test sample into the detector

system. It is desirable to increase the delivery time to

improve the vaporization of the solvent in the sample. The

mixing of the air and liquid sample also allows for a

larger syringe needle 302 that is less susceptible to

clogging and condensation. The air volume may also

nebulize the liquid into an aerosol. An aerosol state is preferred to induce vaporization of the solvent within the

liquid sample.

A low pressure source can draw out the sample in a

syringe without using the plunger. It is sometimes

desirable to control the rate of sample delivery. The

combination of air and liquid reduces the total mass flow

rate into the detector system, which reduces the pressure

surge that can result from injection of a pure liquid

sample. The volume flow rate of a gas is typically about

30 times greater than for a liquid. However, because the

density of gas is about 1/600 of the density of the liquid,

the mass flow rate of the gas is about 20 times less than

for the liquid. It is desirable to have a significantly

high air to liquid ratio (much more air than liquid) , but

the ratio of gas to liquid should be no less than 1:1.

The syringe may contain a solvent slug 314 that washes"

out any residual sample within the needle 302. It has been

found that analyte may condense within the needle 302 of

the syringe 300. The solvent slug 314 will wash through

any such condensation. The solvent slug 314 may include

the standard sample used to calibrate and/or diagnose the detector system. By way of example, the syringe 300 may

contain 5 microliters of air 312, 1 microliter of sample

liquid 310 and 1 microliter of solvent slug 314.

Figure 8 shows an embodiment of an inlet port 400 with

an integrated nebulizer. The inlet port 400 is coupled to

an ionization chamber (not shown) . The inlet port 400

includes a septum 402 that receives a needle 404 of a

syringe 406. The syringe 406 can inject a sample into an

inner channel 408 of a housing 410. The housing 410 may

include a heating element 412.

The inlet port 400 may further have a co-flow port 414

that introduces a gas into the inner channel 408. The gas

introduced through the co-flow port 414 breaks the liquid

into an aerosol. The aerosol facilitates the vaporization

of solvents and analyte molecules on the heating element

412. The inlet port 400 may further includes a restrictof~

416 that induces a vigorous mixing of the air and liquid

sample into aerosol droplets. The aerosol droplets are

pulled through the restrictor 416 by the pressure

differential between the channel 408 and the ionization

chamber (not shown) of the detector system. Figure 9 shows an alternate embodiment of an inlet port

400' that utilizes a capillary tube 418 and tube interface

420 instead of the syringe 406 and septum 402 shown in Fig.

The generation of aerosol droplets and vaporization can

be augmented by a vibrator 422. The vibrator 422 may

contain piezoelectric elements or other means for shaking

either the syringe 406 or capillary tube 418. The

vibration may break the liquid stream into small aerosol

droplets.

While certain exemplary embodiments have been described

and shown in the accompanying drawings, it is to be

understood that such embodiments are merely illustrative of

and not restrictive on the broad invention, and that this

invention not be limited to the specific constructions and

arrangements shown and described, since various other

modifications may occur to those ordinarily skilled in the

art.