LIBS analysis system and method for liquids

This application is a continuation-in-part of U.S. patent application Ser. No. 14/874,726 filed Oct. 5, 2015 and claims the benefit of and priority thereto under 35 U.S.C. §§119, 120, 363, 365, and 37 C.F.R. §1.55 and §1.78, which is incorporated herein by this reference.

The subject invention relates to laser induced breakdown spectroscopy (LIBS).

A handheld LIBS analyzer may include a housing enclosing a laser source, one or more spectrometers, and various optical and electronic components. The laser beam passes out of the housing via the nose section thereof. See U.S. Pat. No. 9,360,367; U.S. pending patent application Ser. No. 14/874,726; and U.S. Pat. Nos. 7,426,019; 8,436,991; 7,394,537; and 9,506,869 all incorporated herein by this reference.

In some instances, it would be desirable to use a handheld LIBS analyzer to analyze liquids. For example, in the field of lithium brines, currently a sample is taken from the brine location and sent to a laboratory to analyze the present lithium concentration. This process, however, can take several days or even weeks. The lithium content may also be an important variable in recovery methods. See U.S. Pat. No. 6,936,229 incorporated herein by this reference. Oil analysis, for example, is another area where a handheld LIBS analyzer could be used. See U.S. Pat. No. 9,366,634 incorporated herein by this reference.

As noted in U.S. Pat. No. 8,687,189, incorporated herein by this reference, analysis of liquids is difficult using a handheld LIBS device since the laser pulse dumps a large amount of energy which sends a shock wave and splatters the liquid which interferes with the physical observation of the emission due to liquid or dried residue on the device optics and which can also cross contaminate the next sample.

Still needed, then, is a LIBS analysis system for liquids which is easy to use and low in cost.

Liquid measurements are possible using bench top LIBS systems where the focal lengths are larger and optics are quite a distance from the plasma (several 10's of mm). With handheld LIBS, the focusing and protection optics are very close to the plasma, typically within a few mm. For this reason, small splashes of the water are more likely to coat the optics and cause laser defocusing and thus plasma inhibition. One the main causes of splashing is when a plasma is formed in water with bubbles present.

In this invention we describe several preferred means of insuring bubble are not present including low shot frequency and the use of convex meniscuses to help migrate bubble away from the plasma region.

Another problem with handheld LIBS is that the spectral intensities and intensity ratios of emission lines are strongly dependent on how far the water surface is from the focusing lens. In aspects of this invention, we describe the components and construction that allow for very reproducible water surface location relative to the focusing lens.

Featured is a LIBS analysis system for liquids comprising a handheld LIBS analyzer with a nose section through which a laser beam passes. A sample holder positioner is attached to the nose section of the hand held LIBS analyzer. A sample holder is receivable in the sample holder positioner and includes a container for a liquid and a top opening for filling the container with the liquid.

In one version, the nose section includes an end plate with an orifice therethrough for the laser beam and the positioner is affixed to the end plate. The end plate may be adapted for liquid samples and includes an enlarged orifice therethrough. The positioner may include a socket about the end plate orifice and receiving the sample holder therein.

Preferably, the sample holder top opening is non-circular (e.g., oval shaped) to dampen shock waves produced in the liquid by the laser beam. The sample holder may further include a standoff spacing the top opening from the end plate when the sample holder is placed in the positioner. In one example, the standoff includes a rim about the top opening. The sample holder may include a top surface and then the top opening may be located in the top surface.

Preferably, the sample holder is filled with liquid forming a liquid meniscus above the opening. Also, it may be preferred that the handheld UBS analyzer is configured to direct the laser beam at a location on the liquid meniscus other than at the apex of the liquid meniscus. Also, it may be preferred that the handheld LIBS analyzer is configured to produce a pulsed laser beam at a frequency sufficient to allow any bubbles created in the liquid meniscus to migrate and/or dissipate. The frequency may be 2 Hz or less. The liquid analyzed may be a lithium brine, oil or alcoholic beverage, for example. In some examples, the handheld LIBS analyzer is configured with a purge gas delivery subsystem.

In one design, the sample holder has a longitudinal axis and the top opening is tilted along an axis at an angle to the longitudinal axis. The system may further include a calibration standard receivable in the positioner. In one example, the calibration standard includes a top surface receivable into the nose section when the calibration standard is placed in the sample holder.

Also featured is a method of analyzing liquids using a handheld LIBS analyzer. The handheld LIBS analyzer is equipped with a sample holder positioner. A liquid is loaded into a sample holder configured to be inserted into the positioner. The sample holder is placed into the positioner the handheld LIBS analyzer is operated to analyze the liquid in the sample holder.

The positioner may be affixed to an end plate of the analyzer. One method includes tilting the handheld LIBS analyzer during the analysis to encourage any bubbles formed to migrate away from the laser beam location on the sample.

Also featured is a LIBS analysis system for liquids. A sample holder positioner is attachable to the nose section of a hand held LIBS analyzer and includes a socket. A sample holder is receivable in the sample holder positioner socket and includes a container for a liquid sample and an opening for filling the container with the liquid sample. The system may further include an end plate adapted for liquid samples and including an enlarged orifice therethrough. The end plate is attachable to the analyzer and the positioner is attachable to the end plate.

The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

FIG. 1 is a schematic three dimensional front view showing an example of a handheld LIBS analyzer which can be used in the invention;

FIG. 2 is a schematic front view showing an example of an end plate for use when the analyzer of FIG. 1 is used to analyze a liquid;

FIG. 3 is a schematic view showing the analyzer of FIG. 1 fitted with the end plate of FIG. 2 as well as a sample holder positioner;

FIG. 4 is a schematic view of a sample holder in accordance with one example of the invention;

FIG. 5 is a schematic view showing the sample holder of FIG. 4 filled with liquid forming a liquid meniscus surface at the sample holder top opening;

FIG. 6 is a cross sectional view showing how the sample holder of FIG. 1 is received in the positioner shown in FIG. 3 ;

FIG. 7 is a three dimensional view showing how the analyzer can be used to analyze a liquid sample present in the sample holder;

FIG. 8 is a schematic view similar to FIG. 7 but showing the sample holder now inserted into the positioner attached to the nose section of the analyzer;

FIG. 9 is a schematic view showing an example of a calibration standard useful in connection with the invention; and

FIG. 10 is a schematic cross sectional view showing another embodiment of a sample holder with an angled interior surface.

Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

FIG. 1 shows an example of a handheld LIBS analyzer 10 . See U.S. Pat. No. 9,360,367 and pending application Ser. No. 14/874,726 both incorporated herein by this reference.

The laser beam exits the nose section 12 which, in this particular example, includes removable end plate 14 a with small opening 16 a for the laser beam and fastened to the nose section 12 via fasteners 18 a , 18 b.

In one preferred embodiment, when the LIBS unit is to be used to analyze a liquid sample, these fasteners are removed and end plate 14 b , FIG. 2 is used instead with an enlarged opening 16 b . This end plate is secured to nose section 12 of analyzer 10 as shown in FIG. 3 using fasteners 18 a , 18 b . Enlarged opening 16 b may be about 1 cm in diameter.

In this particular embodiment, sample holder positioner 20 is also attached to the nose section of the analyzer, in this example using fasteners 18 a , 18 b , to a fix positioner 20 to nose plate 14 b . Positioner 20 includes socket 22 about enlarged nose plate opening 16 b configured to receive sample holder 30 , FIG. 4 therein. Other sample holder designs are possible.

If at any time liquid splashes onto the shield inside the analyzer nose section behind opening 16 b , FIG. 3 of the end plate 14 b , the enlarged opening 16 b of the end plate facilitates cleaning of the shield using, for example, a cotton swab.

The sample holder 30 , FIG. 4 , in this particular embodiment includes cylindrical container interior 32 for the liquid and top surface 34 with top opening 36 therein leading into the container for filling it with the liquid sample to be analyzed. The sample holder may take other forms but preferably is configured to be received in the sample holder positioner 20 , FIG. 3 (e.g., into the socket 22 thereof). Preferably, top opening 36 of holder 30 is not circular to dampen shock waves produced in the liquid 40 , FIG. 5 by the laser beam of the handheld analyzer. An oval shaped opening is shown in FIGS. 4-5 . The opening, however, may take other shapes. Also, when sample holder 30 container 32 is filled as shown in FIG. 5 , the liquid 40 forms a convex meniscus as shown. The handheld LIBS analyzer 10 , FIG. 1 can be configured to direct the laser beam at a location such as location 42 on the liquid meniscus other than the apex thereof. In this way, a bubble formed by the laser beam at location 42 will eventually migrate up to the apex of the liquid meniscus and not interfere with the next laser pulse at location 42 . As discussed in U.S. Pat. No. 9,360,367 and pending application Ser. No. 14/874,726, the handheld laser preferably includes an optics stage whereby the focusing lens can be moved in order to direct a laser beam to location 42 . In some embodiments, the sample holder is positioned in the positioner such that the long axis of the oval extends left to right across the nose section of the analyzer in order to more easily move the laser beam to a position such as position 42 shown in FIG. 5 . In some embodiments, there may be a keying arrangement between the positioner and the sample holder so that the sample holder can only be inserted into the positioner in one fashion.

Also, if the laser is pulsed at a frequency which allows the bubbles to migrate away from the target location on the fluid before the next laser shot, less splashing occurs. Accordingly, a laser pulse frequency of less than about 2 Hz may be chosen in order to allow the bubbles to migrate between pulsing of the laser. A 1 Hz firing rate may be used.

Holder 30 , FIGS. 4-5 preferably also include a stand-off of some kind such as rim 44 of a height sufficient to place the meniscus fluid at a predetermined and repeatable distance from the focusing lens of the handheld laser. As shown in FIG. 6 , when the top of rim 44 seats against the outside of end plate 14 b , the meniscus 40 is positioned about where a solid article would be located if the handheld analyzer was to be used as usual, to analyze a solid sample by engaging the end plate with the sample. Here, the distance between focusing lens 39 and the liquid sample meniscus is predetermined and repeatable.

In use, a liquid (e.g., lithium brine, oil, an alcoholic beverage, or the like) is loaded in the sample holder 30 as shown in FIGS. 5 and 7 using, for example, a pipette. As shown in FIG. 8 , the sample holder 30 is loaded into positioner 20 and then the analyzer 10 is triggered to fire the laser and process the resulting spectrum to report, for example, on screen 11 , the elements present in the liquid sample and their concentrations. In testing with lithium brine samples, the system reported lithium concentrations in known lithium reference samples with good accuracy. A purge gas such as argon may be used. U.S. Pat. No. 9,360,367 discloses a purge gas delivery system.

FIG. 9 shows a calibration standard 60 (e.g., made of stainless steel) receivable in the socket 22 , FIG. 3 of the positioner 20 for calibration of the analyzer. In the example shown, top post 62 has top surface 64 which is receivable through the opening 16 , FIGS. 2-3 of the end plate 14 b and into the nose section of the handheld analyzer spacing surface 64 a predetermined distance from the focusing lens of the analyzer.

In other examples, to move bubbles away from the site on the surface of the liquid to be analyzed which is struck by the laser beam, the handheld LIBS analyzer 10 , FIG. 8 may be tilted during operation of the analyzer so any bubble will naturally move up the surface of the liquid meniscus by gravity. The same result can achieved as shown in FIG. 10 for sample holder 30 ′ with surface 34 ′ having opening 36 ′ which lies on an axis 72 which is tilted at an angle θ relative to the longitudinal access 70 of the sample holder. Thus, θ may be greater than 90°.

The result, in one or more embodiments, is the system facilitating on-site liquid analysis using a LIBS analyzer. In preferred embodiments, the system is easy to use, cost effective, involves few or no moving parts, and provides accurate results. Besides analyzing the concentration of lithium and lithium brines, concentrations or impurities in oils or alcoholic beverages may a analyzed, and other liquids can be analyzed using the above described system and method.

Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.

In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.

Other embodiments will occur to those skilled in the art and are within the following claims.