Patent Application: US-78627504-A

Abstract:
this invention provides a spherical lens optical immersion probe for use in analysis of solids , liquids , gases , powders , suspensions , slurries , particles and other homogeneous or heterogeneous samples . the use of a spherical lens in an optical immersion probe confers many advantages over traditional immersion probes including ease of use and accuracy of focus . the probe of this invention has applications to many types of optical spectroscopy methods including ultraviolet / visible , near - infrared , mid - infrared , fluorescence , and raman spectroscopy . the spherical lens used in this invention is both the optical and sample interface in the analytical system , and may be used to both focus the excitation source and to collecting signal . importantly , this invention has broad applications to any optical analytical technology that necessitates an optical immersion probe .

Description:
as used herein , the term ‘ proximal ’ refers to the end of the device or any of the device components that is nearer to the interface with a sample . the term ‘ distal ’ refers to the end of the device or any of the device components that is opposite the proximal end , and nearer the instrument interface . the simplest embodiment of the immersion probe of this invention is illustrated in fig2 . in this embodiment , probe 100 comprises spherical lens 140 seated within cylindrical probe tip 110 at lens opening 118 . a seal between the probe tip and the lens is formed at the opening by any means known in the art , including all forms of welding or braising and the use of epoxies or other adhesives . probe tip 110 may be any length . optionally , probe tip 110 may have threads 214 on its interior surface and may be extended using probe tube 130 , which has threaded collar 132 for threading into probe tip 110 . a seal is optionally formed between probe tube lip 137 and the distal end of probe tip 110 . fig3 illustrates a preferred embodiment of the optical immersion probe of this invention . probe 200 comprises 4 components : spherical lens 240 , probe tip 210 , fastener 220 and probe tube 230 . additional elements such as gaskets , o - rings , and other sealing means may be present to provide a leak proof system . in this embodiment , o - ring 213 is placed inside probe tip 210 such that it is seated around lens opening 218 on chamfered edge 216 at the proximal end of probe tip 210 . lens 240 is also placed inside probe tip 210 such that it is seated on top of o - ring 213 and a portion of the lens extends through lens opening 218 and is external to probe tip 210 . lens 240 is held in place , and a seal between the lens and the probe tip is formed , by fastener 220 . o - ring 223 is seated in probe tip 210 on top of lens 240 . fastener 220 has fastener threads 224 on its exterior surface and has chamfered edge 226 , around which o - ring 223 is seated when fastener 220 is inserted into probe tip 210 . threads 224 on fastener 220 are mated with tip threads 214 on the interior surface of probe tip 210 . fastener 220 is threaded into probe tip 210 such that o - ring 223 is seated between lens 240 and chamfered edge 226 of fastener 220 . this applies pressure on lens 240 such that a seal is formed at lens opening 218 . notch 225 is provided so that a screwdriver or other such device can be used to turn fastener 220 and provide greater force to the interfaces between the probe tip , o - rings , and spherical lens . the amount of force applied is a function of the type of o - ring material used as well as the experimental conditions , including pressure . this force would be readily determined by one skilled in the art . furthermore , the chamfered edges as illustrated in fig2 and 3 are examples only . the pitch of the chamfered edges may be steeper or shallower , or the edge may be beveled , slanted , rounded , square . probe tube 230 is connected to the probe tip by mating threads 234 on threaded sleeve 232 with tip threads 214 located on the interior surface of probe tip 220 . this mating may provide additional force to the seal system . the interface between probe tip 210 and probe tube 230 may be welded or otherwise sealed using epoxies or other adhesives . alternatively , an additional o - ring ( not shown ) may be provided between probe tube lip 237 and probe tip 210 . in another embodiment , fastener 220 may be made as one piece with probe tube 230 at the proximal end of threaded sleeve 232 . the opening at the distal end of probe tube 230 is provided as an instrument interface ( 239 ). instrument interface 239 is coupled to an analytical instrument using any means known in the art including threads , mechanical couplers such as swage connectors , quick connectors , and other connectors . these and other interface mechanisms would be readily known to one skilled in the art . the following examples illustrate the use of the optical immersion probe of this invention for raman spectroscopy . these examples are not meant to limit the use of the spherical lens optical immersion probe to raman spectroscopy and those skilled in the art will recognize the utility of the probe of this invention to other spectroscopic and optical measuring techniques . in the following section , the use of the spherical lens optical immersion probe of this invention for performing high precision raman measurements of various solid sample systems is discussed . the optical and mechanical design of the probe has been described above . in one example , the analytical performance of the probe is demonstrated by comparing the data from the spherical lens probe to that of a commercially available immersion probe . the commercially available probe had a flat faced window in contact with the sample . an adjustable plano - convex focusing optic was behind the window and adjustable with respect to the window surface so as to change the depth of focus into the sample to be analyzed . raman spectra were collected with a kaiser optical systems hololab series 5000 raman instrument consisting of a holoprobe transmission holographic spectrograph interfaced with fiber - optics to a mark ii ™ holographic probe head . the fiber - optic probe head was equipped with a custom - built immersion probe incorporating a spherical sapphire lens . the raman system was equipped with a 785 nm stabilized external cavity diode laser ( sdl inc .) operating at an average power of 90 mw at the sample . the mark ii ™ holographic probe head was coupled to the laser with an 8 μm i . d . single mode excitation fiber and the scattered signal was collected using a 50 μm i . d . multimode fiber . the immersion probe was 10 . 5 inches long and the spherical sapphire lens was used to both focus the laser and collect the scattered radiation in an epi - illumination configuration . all raman spectra were collected using a 50 μm slit width and a detector temperature of − 40 ° c . all spectra were acquired while vigorously stirring the sample volume unless stated otherwise . in this experiment , raman spectroscopy was performed in a sample of white acrylic paint to compare the performance of the spherical lens optical immersion probe of this invention to a commercially available raman immersion probe , using the same raman instrument described above . the data from the experiment are shown in fig4 . the raman peaks of the whitening agent , tio 2 , were used for comparison in the experiment . the initial results from this experiment were very promising . the spherical lensed immersion probe was placed into the paint sample five separate times with no alignment or adjustment of its position / focus . a spectrum ( 5 sec . exposure , 10 accumulations ) was collected after the probe was submerged in the white acrylic paint sample . the same was done with the commercial probe , after it was aligned for optimal focus before the first measurement . the relative sensitivity of the two probes was comparable , however the measurement reproducibility of the two probes was significantly different . over the five measurements performed , the tio 2 peak intensities with the commercial probe had a relative standard deviation ( rsd ) of 1 . 84 % compared to the spherical lensed immersion probe &# 39 ; s 0 . 24 % rsd . the spherical lensed immersion probe performed well in this experiment , especially since no operator input was needed to perform the analysis compared with the commercial probe . the optical design of the spherical lens optical immersion probe worked very well in a high weight percent slurry sample such as paint . the sampling apparatus for the mixing experiments described in examples 2 and 3 below is shown in fig5 . the sampling apparatus consisted of a tubular fluidized bed reactor 560 equipped with a dry nitrogen gas inlet 550 for mixing . the spherical lens optical immersion probe 500 was compression sealed in the reactor from above with a swagelok pressure fitting 580 . agglomerates of & lt ; 1 μm silica particles powder coated with polydimethylsiloxane ( pdms ) polymer were analyzed with raman spectroscopy . the silica particles were placed in the vessel and fluidized ( actively mixed ) by flowing dry nitrogen through the vessel . the immersion probe was positioned in the fluidized sample to ensure constant contact with the turbulent sample . the results of five spectra taken over a five minute time period during this experiment are shown in fig6 . each spectrum was the average of five , five - second accumulations . the spectra consisted of raman peaks corresponding to both the silica substrate and the pdms polymer coating on the particles . interestingly , the rsd of the silica band intensities was only 2 . 4 % compared to the pdms bands that exhibited a rsd of 15 . 1 %. after repeated experiments using this sample it was apparent that the pdms coating on the silica particles varied greatly when compared to the silica particles themselves . when the fluidized sample data was compared to the data taken of the sample not actively mixing , the rsds of the silica and pdms are 0 . 76 and 0 . 72 % respectively , for five replicate measurements . these consistent results demonstrated that the raman spherical lens optical immersion probe was a reproducible means for monitoring coating uniformity of these actively mixed particles . the optical immersion probe of this invention was used to monitor the active mixing of different concentrations of citric acid in 25 g of sucrose . these samples were chosen for their relatively similar densities , particle sizes and ease of disposal . the standard raman spectra for both citric acid and sucrose are demonstrated in fig7 a . the two raman spectra are quite similar except for the citric acid peak that occurs near 800 cm − 1 . each spectrum was the average of five , five - second accumulations . the mixing experiment entailed placing both powdered samples into the fluidized bed , creating a 2 - layer system . the data collection was then started followed by the start of the gas flow to begin the mixing process . a total of 60 raman spectra were obtained for each concentration of citric acid ( 1 – 30 %). the citric acid concentration range was 1 – 30 % ( w / w ) in 25 g of sucrose . the performance of the raman immersion probe for measuring citric acid in a citric acid / sucrose mixture is illustrated in fig6 b . the calibration results from the pls analysis were r 2 = 0 . 987 , rmsc = 1 . 2 % and correlation of 0 . 993 . the distribution of data points for each citric acid concentration is representative of the mixing of the citric acid into the sucrose . the fluidization of the 2 layers of powder was correlated with the onset of data collection . the mixing information is described primarily in the first scores plot of the 6 factor model as shown in fig6 c . from the loadings data for this factor it was determined that the data are describing the dilution of the initial concentration of sucrose as the two powders are blended . this is most apparent in fig6 c for the first two citric acid concentrations ( samples 1 – 60 , 61 – 120 ) where the scores plots level off indicating nearly complete mixing of the sample . this leveling off of the data is not as apparent at the higher concentrations . it is believed that this is primarily an experimental effect due to limited gas flow through the bed to completely fluidize the higher masses of powder . recent experiments have also shown that due to the limited volume of the fluidized bed that the higher mass samples should have been fluidized for longer periods of time to achieve complete mixing . therefore the data shown for the higher masses of citric acid in fig6 c had not achieved complete mixing when the experiment was stopped . because of the sample - to - sample reproducibility of the immersion probe of this invention , specific models and algorithms may be developed for describing and predicting the degree of mixing achieved in various mixers and blenders . two crystalline forms of a commercially available active pharmaceutical compound were vigorously stirred in a slurry over 24 hours at 40 ° c . the transformation of form 1 into form 2 was followed by raman spectroscopy . raman spectra of isolated forms of form 1 and form 2 are shown in fig8 a . fig8 b shows a series of raman spectra taken over 24 hours of vigorous mixing . this series shows the transformation of form 1 into form 2 . fig9 is an analysis of peak intensity . all references cited herein are incorporated by reference in their entirety to the extent not inconsistent with the disclosure herein . preferred embodiments described above are intended to be illustrative of the spirit of this invention . numerous variations and applications will be readily apparent to those skilled in the art . the range and scope of this patent is defined by the following claims and their equivalents . 1 . g . r . trott and t . e . furtak , “ angular resolved raman scattering using fiber optic probes ”, rev . sci . instrum , 51 , 1493 – 1496 , november 1980 . 2 . r . l . mccreery , m . fleischmann , and p . hendra , “ fiber optic probe for remote raman spectrometry ”, anal . chem , 55 , 146 – 148 , 1983 . 3 . s . d . schwab , r . l . mccreery , “ normal and resonance raman spectroelectrochemistry with fiber optic light collection ”, anal . chem , 58 , 2486 – 2492 , 1986 . 4 . s . d . schwab , r . l . mccreery , “ remote , long - 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