Abstract:
An improved sample chamber for laser assisted spectroscopy integrates valve mechanisms into the sample drawer, permitting the sample chamber to automatically bypass, purge and resume flow as the sample drawer is opened and closed to insert samples for processing. Integrating valve mechanisms into the sample drawer in this manner eliminates the need for external valves to be operated to bypass, purge and resume flow, thereby increasing system throughput and reducing system complexity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of U.S. patent application Ser. No. 12/752,788, filed on Apr. 1, 2010, now U.S. Pat. No. 8,319,176 issued on 27 Nov. 2012, which is incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to spectroscopy. More particularly it relates to laser ablation inductively coupled plasma mass spectroscopy (LA ICP-MS), laser ablation inductively coupled plasma emission spectroscopy (ICP-OES/ICP-AES) and matrix assisted laser desorption ionization time of flight (MALDI-TOF) spectroscopy. Specifically, it relates to sample chambers associated with these and other laser-assisted spectroscopy (LAS) systems including some optical spectroscopes. More specifically, the present invention relates to improvements to sample chambers for LAS. LAS often has the sample to be examined be in a flow of fluids, typically an inert gas although sometimes a liquid. The present invention relates to an improved apparatus for automatically bypassing, purging and restoring flow when the sample chamber is opened and closed, for example when a new sample is introduced to the sample chamber. 
     BACKGROUND OF THE INVENTION 
     LAS involves directing laser energy at a sample of matter in order to disassociate its constituent parts and make them available to a spectrometer for processing. Operation of LAS systems and other laser assisted spectroscopy systems typically apply this energy to the sample while passing a fluid, typically an inert gas, over the sample to capture the disassociated species and carry them to a spectroscope for processing. Sampling and detecting constituent parts of a sample with mass or optical spectrometry using an inert gas flow is necessary since, for example, an inductively coupled plasma instrument depends upon a plasma torch to ionize the laser ablated material for subsequent processing. This plasma torch can only operate in an inert atmosphere since regular open atmosphere extinguishes the plasma torch. Another advantage to using inert gas flow for laser assisted spectroscopy is that certain inert gases are transparent to desired laser wavelengths whereas regular room atmosphere is not. In addition, inert atmospheres can prevent 
     Commonly, LAS systems require opening their sample chambers to remove old samples and insert new samples. While this is happening, it is important to maintain the flow of inert gas to the spectrometer and prevent air from reaching the plasma torch and extinguishing it, among other reasons. For the same reasons, the sample chamber must be purged of air prior to connection to the spectrometer following opening and closing. Once the plasma torch is extinguished, the system must be restarted and recalibrated, taking time and expertise. In order to prevent room atmosphere from entering the instrument, care must be taken when the sample chamber is opened to insert a new sample. The problem of purging a sample chamber of room atmosphere following insertion of a new sample has been previously considered with varying results. 
     Laser assisted mass spectroscopy is described in U.S. Pat. No. 5,135,870 LASER ABLATION/IONIZATION AND MASS SPECTROSCOPIC ANALYSIS OF MASSIVE POLYMERS, inventors Peter Williams and Randall W. Nelson, Aug. 4, 1992. This patent describes using a laser to ablate a thin film of organic material in a vacuum and thereafter analyze it using a mass spectrometer. A more recent publication, US patent application No. 2009/0073586A1 ANALYTICAL LASER ABLATION OF SOLID SAMPLES FOR ICP, ICP-MS, AND FAG-MS ANALYSIS, inventors Robert C. Fry, Steven K. Hughes, Madeline J Arnold, and Michael R. Dyas, Mar. 19, 2009 describes in detail a radiation-hardened sample chamber design for a laser ablation system. A reference which discusses the issue of purging sample cells is U.S. Pat. No. 4,640,617 SPECTROMETERS HAVING PURGE RETENTION DURING SAMPLE LOADING, inventors Norman S. Hughes and Walter M. Doyle, Feb. 3, 1987. This patent discloses and claims a means for minimizing the amount of air introduced into the sample chamber during sample loading by using a spring-loaded plunger to seal the sample chamber while loading a sample. U.S. Pat. No. 5,177,561 PURGING OF OPTICAL SPECTROMETER ACCESSORIES, inventors Milan Milosevic and Nicolas J. Harrick, Jan. 5, 1993 discloses a means to minimize purging by separating the sample chamber atmosphere from the spectrometer atmosphere, thereby eliminating the need to purge the spectrometer when samples are changed. 
     These patents have considered issues associated with purging sample chambers, mainly by minimizing the amount of room atmosphere introduced into the sample chamber as a new sample is introduced but have not considered solutions which alter the fluid flow through the system as the sample chamber is opened and closed.  FIGS. 1   a - c  show an example of a prior art solution to the problem of providing: 1. Gas bypass when the sample chamber is open; 2. Gas purge when the sample chamber is initially closed; and, 3. Restoring gas flow after the sample chamber is purged. In  FIG. 1   a , fluid flow  14  (represented by the arrows marked “IN”: and “OUT”) enters the system via fluid inlet  12 . This fluid flow  14  then enters inlet valve  16 , which is in the “input bypass” position, sending the fluid  14  through the bypass tube  22  to the fluid outlet  24 . The outlet valve  20  is in the “output bypass/purge” position closing communication between the sample chamber  10  and the fluid outlet  24 . In this position, the sample chamber door  11  can be opened to remove or insert samples without risking contamination of the instrument (not shown) attached to the fluid outlet  24 . In  FIG. 1   b , the inlet valve  16  is set to the “purge/restore” position, sending fluid  14  from the fluid inlet  12  to the sample chamber  10  via the inlet tube  18  and then onto the outlet valve  20  via the outlet tube  28 . The outlet valve  20  is set to the “bypass/purge” position, sending the fluid from the sample chamber to the vent  26 , thereby purging the sample chamber  10 . In this mode, the sample chamber door  11  is closed. In  FIG. 1   c , the inlet valve  16  is set to the “purge/restore” position, sending the fluid  14  from the fluid inlet  12  to the sample chamber  10  via the inlet tube  18 . The outlet valve  20  is set to the “restore” position, sending fluid  14  from the sample chamber  10  to the fluid outlet  24  via the bypass tube  22  while the sample chamber door  11  is closed. This exemplary prior art solution involves adding valves or other mechanisms to the sample chamber and the input and output gas ports. These valves or mechanisms are then operated or opened and closed manually in specific sequences prior to the sample chamber being opened and closed in order to create the bypass, purge and restore functions. Providing these functions manually requires additional time to open and close valves between samples, thereby reducing system throughput. In addition, requiring such a sequence of steps each time a sample is introduced increases system complexity, increases system and maintenance cost, and makes mistakes in operation more likely. 
     Accordingly, there is a continuing need for a way to introduce samples to a sample chamber including gas bypass, purge and restored flow in a laser ablation mass spectroscopy system automatically as the sample chamber is opened and closed to obviate the need for slow and error prone manual processes. 
     SUMMARY OF THE INVENTION 
     Aspects of this invention are improvements to sample chamber design for laser assisted spectroscopy (LAS). These aspects improve sample chamber design by automatically redirecting flow of fluids to permit the sample chamber to be opened and closed to introduce new samples without allowing room atmosphere to be passed from the sample chamber to the spectroscope. In addition to LAS, these sample chamber improvements could be advantageously applied to other instruments or devices that desire processing a sample in a gas flow while also desiring to open and close a sample chamber, including mass spectrometers and some optical spectrometers or spectrophotometers. These aspects include a sample chamber having a gas inlet, a gas outlet, a vent and a sample drawer having first, second and third positions. These aspects also include having an inlet valve connected to a gas inlet and operatively connected to a sample drawer so that: 1. when the sample drawer is set to the first or open position the inlet valve directs the gas flow from the gas inlet to the gas outlet thereby bypassing the sample chamber; 2. when the sample drawer is set to the second or partially open position the inlet valve directs the gas flow from the gas inlet to the partially open drawer thereby purging the sample chamber; and, 3. when the sample drawer is set to the third or closed position the inlet valve directs gas flow from said gas inlet to said sample chamber thereby restoring gas flow to the sample chamber. These aspects further include a sample chamber having an outlet valve connected to a gas outlet, a sample chamber and a vent, and operatively connected to a sample drawer so that: 1. when the sample drawer is set to a first or open position the outlet valve directs the gas flow from the inlet valve to the gas outlet thereby bypassing the sample chamber; 2. when the sample drawer is set a second or partially open position said outlet valve closes the gas outlet thereby purging the sample chamber; and, 3. when the sample drawer is set to a third or closed position the outlet valve directs the gas flow from the sample chamber to the gas outlet thereby restoring the flow of gas through the sample chamber. These aspects of the invention cooperate to automatically alter the flow of inert gas within the sample chamber as the sample door is opened and closed between bypass, a purge and a restored flow position in order to maintain the flow of inert gas to the mass spectrometer and prevent outside atmosphere from entering the sample chamber. 
     Aspects of this invention which accomplish bypass, purge and restored flow automatically as a sample chamber is opened and closed are illustrated in  FIGS. 2   a - c . In  FIG. 2   a , the sample drawer is fully opened, causing the sample chamber to bypass the inert gas around the sample drawer while preventing room atmosphere from entering the sample chamber. In  FIG. 2   b , the sample drawer is partially opened, allowing inert gas to pass from the gas inlet through the sample drawer to the room atmosphere while keeping the outlet port closed, thereby purging the sample chamber. In  FIG. 2   c , the drawer is closed, and both the inlet and outlet ports are opened, thereby restoring normal flow to the system. In this way, aspects of the current invention are able to automatically maintain a bypass flow of inert gas while the sample chamber is opened, purge the sample chamber as the sample drawer is closed and restore the flow of inert gas over a sample as the sample chamber is opened and closed, thereby allowing the sample chamber to be opened and closed while minimizing contamination from room atmosphere and without requiring any operation of additional valves or other equipment. 
     Accordingly, the invention is an improved method and apparatus for automatically re-directing the flow of a fluid through a sample chamber so that when the sample chamber is opened the flow of fluid is prevented from entering the chamber, when the chamber is partially opened the flow of fluid enters the chamber for purging and when the chamber is closed resumes fluid flow over the sample and on to an instrument. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a . Prior art sample chamber in bypass mode. 
         FIG. 1   b . Prior art sample chamber in purge mode. 
         FIG. 1   c . Prior art sample chamber in operating mode. 
         FIG. 2   a . Sample chamber in bypass mode. 
         FIG. 2   b . Sample chamber in purge mode. 
         FIG. 2   c . Sample chamber in operating mode. 
         FIG. 3 . Sample chamber with external controls. 
         FIG. 3   a . Alternate valve arrangement. 
         FIG. 4 . Flowchart showing operation of sample chamber. 
         FIG. 5 . Sample chamber with full time bypass. 
         FIG. 6 . Sample chamber without bypass. 
         FIG. 7 . Sample chamber with alternate purge. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 2   a ,  b  and  c , an embodiment of this invention is an improved sample chamber  40  for laser processing a sample (not shown) in a fluid flow (shown by the arrows marked “IN” and “OUT”, fluid flow is provided by a source not shown), the improved sample chamber  40  having a fluid inlet  42 , a fluid outlet  44 , and a sample drawer  46  (right-hand diagonal fill) having first ( FIG. 2   a ), second ( FIG. 2   b ) and third ( FIG. 2   c ) positions. The improvements further comprise an inlet slide  48  communicating with the fluid inlet  42 , a fluid outlet  44 , and operatively connected to the sample drawer  46  so that when said sample drawer  46  is set to the first or open  62  position ( FIG. 2   a ) the inlet slide  48  (cross hatch fill) directs said fluid flow from the fluid inlet.  42  to the fluid outlet  44 . When the sample drawer  46  is set to the second or partially open position ( FIG. 2   b ) the inlet slide  48  directs the fluid flow from the fluid inlet  42  to the sample drawer  46 . When the sample drawer  46  is set to the third position ( FIG. 2   c ) the inlet slide  48  directs the fluid flow from the fluid inlet  42  to the sample drawer  46 . 
     The improvements further comprise an outlet slide  58  (cross hatch fill) communicating with a fluid outlet  44  and the inlet slide  48  and operatively connected to a sample drawer  46  so that when the sample drawer  46  is set to a first position ( FIG. 2   a ) the outlet slide  58  directs the fluid flow from the bypass plenum  52  to the fluid outlet  44 . When the sample drawer is  46  set to the second position ( FIG. 2   b ) the outlet slide  58  closes the fluid outlet  44 . When the sample drawer  46  is set to the third position ( FIG. 2   c ) the outlet slide directs the fluid flow from the sample drawer  46  to the fluid outlet  44 . 
     In more particular, an embodiment of this invention is an improved sample chamber  40  for laser processing a sample (not shown) in a fluid flow (shown by the arrows marked “IN” and “OUT), the improved sample chamber  40  having a fluid inlet  42 , a fluid outlet  44 , and a sample drawer  46  having first ( FIG. 2   a ), second ( FIG. 2   b ) and third ( FIG. 2   c ) positions. The fluid flow, which may be an inert gas and which preferably may be one of helium or argon, enters the sample chamber  40  via the fluid inlet  42 , which passes through the drawer enclosure  54  (left-hand diagonal fill), which supports and encloses the sample drawer  46  (right-hand diagonal fill). When the sample drawer is in the first or open  62  position ( FIG. 2   a ) the bypass inlet opening  50  in the inlet slide  48  (cross-hatch fill) aligns with the fluid inlet  42  and the bypass plenum  52 , permitting fluid to pass front the fluid inlet  42  to the bypass plenum  52 . The dotted line  60  represents the bezel or front surface of the sample chamber  40 ; therefore when the sample drawer  46  extends beyond the front surface of the sample chamber  60  as in  FIG. 2   a , the interior of the sample drawer  46  will be open  62  and exposed to room atmosphere. With the sample drawer  46  in the first or open  62  position ( FIG. 2   a ) the bypass outlet opening  56  in the outlet slide  58  (cross-hatch fill) aligns with the bypass plenum  52  and the fluid outlet  44  to permit fluid to pass from the bypass plenum  52  to the fluid outlet  44  while preventing room air from the open  62  sample drawer  46  from entering the fluid outlet  44 . In this way the sample chamber can maintain a flow of fluid to the instrument (not shown) attached to the fluid outlet  44  while the sample drawer  46  is open  62  to room atmosphere without permitting contamination of the fluid flow. 
     When the sample drawer  46  is in the second or partially open  68  position ( FIG. 2   b ) the purge/restore inlet opening  64  in the inlet slide  48  aligns with the fluid inlet  42  and the sample drawer  46  to permit fluid to flow from the fluid inlet  42  to the sample drawer  46 . When the sample drawer  46  is in the partially open  68  position, the fluid entering the sample drawer via the purge/restore inlet opening  64  exits the sample drawer  46  through the opening  68  to the room atmosphere. With the sample drawer  46  in the partially open  68  position, the restore opening  66  in the outlet slide  58  is not aligned with the fluid outlet  44 , thereby preventing any room atmosphere from entering the fluid outlet and contaminating the fluid flow to the instrument (not shown). Note that in this position, the sample drawer  46  is open  68  only a small amount with respect to the sample chamber front surface  60 , restricting the flow of fluid, therefore fluid flow will not have to be increased to successfully purge all room atmosphere from the sample drawer  46 , nor will flow have to be increased to prevent room atmosphere from reaching the instrument, since the fluid outlet  44  is closed by outlet slide  58 . 
     When the sample drawer  46  is in the third or closed  70  position ( FIG. 2   c ), the purge/restore inlet  64  in the inlet slide  48  aligns with the fluid inlet  42  allowing fluid entering the fluid inlet  42  to pass through to the sample drawer  46 . With the sample drawer  46  closed  70 , the fluid passes through the restore outlet  66  in the outlet slide  58  which is aligned with the fluid outlet  44  and permits fluid to pass through the sample drawer over the sample (not shown) and onto the instrument (not shown). Note that since the sample drawer  46  is closed  70  to room atmosphere (interior of sample drawer  46  is completely behind front surface of sample chamber  60 ), no contamination of fluid flow by room atmosphere is possible. With respect to room atmosphere contamination, it is worth noting that since these embodiments rely on fluid flow pressurized above normal room atmosphere pressure, application of seals to the mating surfaces of this invention is not critical. Any leakage that occurs will be leakage of pressurized fluid to the room atmosphere, therefore the application of seals to the mating surfaces of this invention will serve to prevent loss of possibly valuable fluids, not prevent contamination of the instrument. By constructing and using a sample chamber according to the disclosures herein, a sample chamber is created that will automatically provide bypass, purge and restored fluid flow to a sample chamber as the sample drawer is opened and closed without permitting contamination of the attached instrument or requiring additional steps to make the system ready for processing. It is also envisioned that embodiments of this invention may be constructed of fewer or more parts arranged in similar relationships without deviating from the spirit and intent of this invention. It is also envisioned that embodiments could use mechanical linkages or electrical sensor and actuators such as motors or solenoids to cause the opening and closing of valves to create bypass, purge and restored gas flow as the sample chamber door is opened and closed and thereby accomplish aspects of this invention. This is illustrated in  FIG. 3 , where the sample chamber  80  with access door  81  having a fluid inlet  82 , a fluid outlet  100 , fluid flow  84  from the fluid inlet  82  through the inlet valve  86 , to the sample chamber  80  via the inlet channel  88  and thence to the fluid outlet  100  via the outlet channel  98 , the outlet valve  94  and the bypass channel  102 . This embodiment has in addition a controller  110  operatively connected to inlet actuator  104 , outlet actuator  106 , and sample chamber actuator  108  which are operatively attached to inlet valve  86 , outlet valve  94  and sample chamber  80  respectively. In addition, the controller may have sensors (not shown) attached to the sample chamber  80 , sample chamber door  81 , inlet valve  86  and outlet valve  94  to detect the status of each. In this embodiment the controller  110  either detects the sample chamber door  81  opening or directs the sample chamber actuator  108  to open the sample chamber door  81 , and then directs inlet actuator  104  and outlet actuator  106  to assume positions as shown in  FIG. 1   a , thereby creating a bypass condition, When the controller  110  subsequently either detects the sample door  81  closing or directs the sample chamber actuator  108  to close the sample chamber door  81 , the controller  110  directs the inlet actuator  104  and outlet actuator  106  to set the inlet valve  86  and outlet valve  94  to the purge position as shown in  FIG. 1   b , thereby purging the sample chamber  80  via the outlet channel  98 , the outlet valve  94  and the vent  96 . When the controller  110  detects or predicts that the sample chamber  80  is fully purged, it directs inlet and outlet actuators  104 ,  106  to set the inlet valve  86  and outlet valve  94  to the restore flow position as illustrated in  FIG. 1   e . This embodiment could also operate by sensing the position of the sample door  81  without sample chamber actuator  104 . 
       FIG. 3   a  shows another embodiment of this invention, wherein any one of the complex valve mechanisms, for example valves  86 ,  94  from  FIG. 3 , may be replaced by simple on/off valves  112 ,  114 ,  116 , possibly connected by a connector “tee”  118 . Replacing a single complex valve mechanism with one or more simple valves provides the same fluid directing function as employed by other embodiments of this invention.  FIG. 3   a , valves  112 ,  114  and  116 , along with “tee” section  118 , direct flow from fluid inlet  82  to either the inlet channel  88  or the bypass channel  102  or neither. 
       FIG. 4  is a flow chart which illustrates the steps followed by embodiments of this invention as the sample chamber is opened to room atmosphere to insert samples and subsequently closed for processing. In step  120  the sample chamber is detected being opened or directed to open. Simultaneously or soon following, in step  122 , the gas inlet and outlet are set to the bypass position ( FIG. 2   a ). Subsequently, when the embodiment detects or directs the sample door in step  124  to either partially close or initially close, the inlet is set in step  126  to purge/restore while leaving the outlet valve in bypass position ( FIG. 2   b ). Then a pause ensues in step  128  to permit the sample chamber to fully purge. This pause may be automatically controlled by the embodiment or left to the user to perform. In step  130  the door is closed and purging is complete. At this point, in step  132  the inlet and outlet are set to restore the flow to the chamber ( FIGS. 2   c ,  3 ,  5 ). When the sample chamber is again opened, the flowchart returns to step  120 . 
     In another embodiment of this invention, the gas bypass is arranged so that gas is always flowing around the sample chamber and opening and closing the sample drawer causes the gas to purge and restore flow as the drawer is opened sand partially closed, and then fully closed. This is illustrated in  FIG. 5 .  FIG. 5  shows an embodiment of this invention that provides continuous bypass flow to the fluid outlet. This is accomplished by modifying the inlet and outlet slides  48  and  58  to permit flow through the bypass plenum  52  regardless of the position of the sample drawer  46 . This embodiment results in a slightly simpler design but at the cost of requiring increased fluid flow. 
     Referring to  FIG. 6 , another embodiment of this invention adds additional input slides  76 ,  78  to block bypass fluid flow, thereby preventing fluid flow through the chamber except when the chamber is closed  70 . This supports spectral analysis instruments that do not require bypass flow to remain in operation while the sample chamber is opened. 
     In  FIG. 7  an embodiment of this invention is constructed so that when the sample drawer  46  is in the purge position  92  the bezel  90  closes the drawer  46  from the room atmosphere. The modified outlet slide  138  has an additional opening, a purge outlet  134 , which, when the sample drawer  46  is in the purge position  92 , aligns with the restore outlet  66  and the outlet vent  136  to allow the sample chamber to purge room atmosphere prior to restoring flow with the sample chamber closed completely. 
     Having hereby disclosed the subject matter of the present invention, it should be obvious that many modifications, substitutions, and variations of the present invention are possible in view of the teachings. It is therefore understood that the invention may be practiced other than as specifically described, and should be limited in its breadth and scope only by the Claims: