GB2429693A

GB2429693A - Chemical test apparatus

Info

Publication number: GB2429693A
Application number: GB0512730A
Authority: GB
Inventors: Richard Hudson; Mark Harding; Christian Berlind
Original assignee: Anachem Ltd
Current assignee: Anachem Ltd
Priority date: 2005-06-22
Filing date: 2005-06-22
Publication date: 2007-03-07
Also published as: GB0512730D0; JP2008547014A; WO2006136838A3; WO2006136838A2; EP1904825A2

Abstract

An apparatus (100) for testing the solubility of a chemical dissolved in a solvent (211). Particles (210) of undissolved chemical may be stirred in the solvent (211) to ensure that the solvent (211) is saturated with dissolved chemical. Samples of the solvent (211) are taken off for analysis, for example by a high performance liquid chromatography (HPLC) analyser (150). The sampling apparatus comprises a body having a lumen, a filter 430 for substantially preventing undissolved particles from entering the lumen and sealing means 420 between the filter and the lumen. Samples may be taken at different temperatures to determine the solubility profile of the chemical in the solvent (211). The apparatus (100) includes a filter 430 to prevent particles of undissolved chemical (210) forming part of the samples. The filter 430 may be provided with a recess (832) to reduce a "dead volume" of the filter. A computer (600) may be arranged to determine if a sample contains too much or too little chemical for analysis by the HPLC 150; samples may be diluted in an analytical vial (141) to ensure that the HPLC 150 is not saturated by excess chemical.

Description

CHEMiCAL TEST APPARATUS The present invention is concerned with an

apparatus for performing solubility testing.

In the field of chemistry, there is often the need to determine the solubility of a chemical in a particular solvent. For example, a researcher may wish to determine the solubility of 1- napthol in water at a particular temperature. Of course, the solubility of3-napthol in water is known. However, the solubility of a newly synthesised chemical in a particular solvent will not be known. l0

More usually, the researcher may wish to determine the solubility profile of the chemical in the solvent. The solubility profile is a curve which gives the solubility of the chemical in the solvent at different temperatures. For example, the solubility of the chemical 13- riapthol in water at 20 C, 35 C and 50 C is 0.75, 0.9 and 1.9 mg/mI, respectively. I5

Solubility profiles can be measured manually but this is time consuming, particularly because the temperature of the chemical, solvent and associated apparatus must be controlled.

A prior art apparatus for solubility testing operates by detecting turbidity in the solvent.

Initially, a known mass of the chemical and a known volume of the solvent are placed in a container. The container is heated until all the chemical has dissolved. The temperature of the container is then slowly reduced, and the turbidity of the solvent is measured by passing light through the container. As the temperature decreases, dissolved chemical comes out of solution, thereby reducing the amount of light that reaches a photodetector.

A disadvantage with this prior art apparatus is that the results assume that none of the known volume of solvent that was originally introduced into the container evapourates during the solubility testing; any evapouration will introduce errors. Another disadvantage is that a known mass of the chemical must be introduced which can require manual handling and weighing of the chemical. (

According to one aspect of the present invention, there is provided an apparatus for solubility testing, comprising: means for controlling the temperature of a container containing a chemical and a solvent saturated with the chemical; means for obtaining a sample of the saturated solvent form the container, wherein the means for sampling comprises a rigid filter for preventing the sampling of undissolved chemical; means for measuring the concentration of the chemical in the sample of saturated solvent.

According to another aspect of the invention, there is provided a sampling apparatus for a container.

According to another aspect of the invention, there is provided a method for automatically controlling an apparatus for solubility testing based on the measured concentration of a chemical in a sample of saturated solvent.

Description of Figures

Figure 1 shows a perspective view of the major components of an apparatus 100 for performing solubility testing, also shown is a sample needle 130.

Figure 2 shows a cross-sectional view of a test tube Ill that forms part of the apparatus 100, also shown are a body 240 and a nozzle 250 in a non-cross-sectional view.

Figure 3 shows an exploded view of the body 240 and the nozzle 250.

Figure 4 shows a detailed cross-sectional view of a portion of the body 240 assembled to the nozzle 250.

Figure 5 shows the lowermost portion of the body 240 and nozzle 250 as for Figure 4 but additionally shows the sample needle 130 inserted into the nozzle 250, additionally shows a narrowed region 200 of the lest tube 111, and additionally shows the nozzle 250 surrounded by solvent 211.

Figure 6 shows a schematic diagram of a computer 600 interfaced to various major components of the apparatus 100.

Figure 7 shows an example of an output signal from a high pressure liquid chromatography (I IPLC) apparatus 150 that forms part of the apparatus 100.

Figure 8 shows a modified frit filter 830.

Figure 9 shows an example of a series of solubility measurements at different temperatures, and illustrates a method that can be used to reduce the effects of "dead volumes" with the nozzle 250.

Figure 10 shows an example of a series of solubility measurements at different dilutions, and illustrates a method that can be used to avoid saturation of the HPLC 150 by adjustment of a dilution factor.

First embodiment of the invention Figure 1 shows an apparatus 100 for performing solubility testing. Major components of the apparatus are a temperature controlled block 110, an XYZ arm 120, a sample needle 130, a solvent rack 135, a sample rack 140 (in which dilutions are performed), a high pressure liquid chromatography (HPLC) apparatus 150 and a wash station 160. The major components of the apparatus 100 are mounted on a base (not shown). In this embodiment, the apparatus 100 has a width along the X axis of about 80cm, a depth along theY axis of about 60cm and a height along the Z axis of about 80cm.

In general terms, the apparatus 100 uses the sample needle 130 (which is hollow and in this embodiment has a flat tip) to draw a sample of saturated solvent (Fig 2: 211) from a test lube Ill in the temperature controlled block 110. The sample is then diluted at the sample rack 140 and then passed into the HPLC 150 for measurement. By diluting the sample before the sample is passed to the HPLC 150, saturation of a detector (not shown) inside the 1-IPLC 150 can be avoided. Finally, the wash station 160 is used to clean the sample needle 130 before the sample needle 130 is used to draw a sample of saturated solvent from a test tube Ill (or, if several different test tubes 111 are being used, to clean the sample needle 130 before drawing a sample from a different test tube Ill).

To set up the apparatus 100 for use, a user first introduces sample(s) of chemicals (whose solubility is to be tested) together with a solvent(s) into the test tubes 111. In each test tube Ill, the quantity of chemical must be sufficient so that not all of the chemical will be dissolved by the solvent. The user may also provide solvent(s) in the solvent rack 135 (in some situations, the apparatus 100 is arranged to automatically charge a test tube 111 with solvent). Each test tube I I I is stirred to ensure that equilibrium is reached between the chemical dissolving in the solvent and excess dissolved chemical precipitating out of solution. After allowing a time period for the solvent to become saturated with the dissolved chemical, samples of the saturated solvent at various temperatures are drawn off from the test tubes Ill for analysis by the HPLC 150.

The temperature controlled block 110 has a plurality of cylindrical cavities (not shown).

Each of the cylindrical cavities contains a test tube 111, with one test tube 111 being used for each combination of chemical and solvent that is being solubility tested. In this embodiment, each test tube ill holds about I to 3m1 of solvent. The temperature controlled block 110 allows a computer (not shown) to set the temperature of each test tube. The temperature controlled block 110 contains heaters and coolant for heating/cooling the test tubes Ill so that the test tubes are maintained at the required temperature. In this embodiment, the temperature of the test tubes II I may be set individually to a temperature in the range 30 C to 150 C. Once the solubility of the chemical in a test tube I I I has been measured, the computer commands the temperature controlled block 110 to a new temperature for that test tube 111. For example, to obtain the measurements mentioned above for the solubility of-napthol in water, a test tube Ill containing J3-napthol and water would be heated to the temperatures 20 C, 35 C and 50 C.

The temperature controlled block 11 0 also contains magnetic stirrers (not shown) for rotating stirring beads (Fig 2: 201); a respective stirring bead is placed at the bottom of each test tube 111. The magnetic stirrers ensure that undissolved chemical is stirred in the solvent, thus reducing the time required to reach saturation.

The XYZ arm 120 carries the sample needle 130 and moves the sample needle 130 between the test tubes Ill, the sample dilution block 140, the HPLC 150 and the wash station 160. The XYZ arm 120 is movable under computer control in orthogonal directions. As shown by Figure 1, movement along the Y axis allows the selection of a particular test tube 111 of the temperature controlled block 110. Movement along the X axis allows the sample needle 130 to be moved from the temperature controlled block Ill, to the sample dilution block 140, to the wash station 160 and finally the HPLC 150.

Movement along the Z axis corresponds to raising or lowering the sample needle 130. By means of the XYZ arm 120, the sample needle 130 is lowered into a test tube Ill and extracts a sample of saturated solvent from the test tube 111. The sample needle 130 is then raised, moved to a position above an analytical vial 141 in the sample rack 140, and then lowered into an analytical vial 141 in the sample rack 140. An analytical vial 141 is, in effect, a type of small test tube (which may or may no be sealed) and in this embodiment is sized to hold up to 2nil of liquid.

The sample needle 130 is connected via a flexible transfer tube (not shown) to a syringe pump (not shown) that allows liquids and ambient air to be drawn into/expelled from the sample needle 130. The syringe pump itself has an associated syringe pump reservoir (also not shown) of solvent which acts as a hydraulic fluid in the transfer tube and may be dispensed to test tubes Ill or analytical vials 141.

Once the sample has been deposited in an analytical vial 141, a predetermined quantity of diluent (i.e. solvent, e.g. water in the case of J3-napthol and water) that has previously been stored in the transfer tube (not shown) is dispensed out of the sample needle 130. The solvent (or solvents if the solubility of the chemical(s) is being measured in several different solvents) is provided in solvent vials 136 or may come from the syringe pump reservoir (not shown).

In this embodiment, solvent (water) from the syringe pump reservoir (not shown) is used to dilute the sample by a factor of fifty. The syringe pump (not shown) is activated so that in addition to the sample being expelled form the sample needle 130, sufficient water is also expelled into an analytical vial 141. A portion of the diluted sample in an analytical vial 141 may then be injected into the HPLC 150.

The quantity of solvent not only reduces the likelihood of the detector within the l-IPLC becoming saturated by the concentration of the chemical in the solvent, but also re- dissolves any chemical that may have precipitated inside the sample needle 130 during the transit of the sample needle 130 from a test tube 111 to an analytical vial 141. For example, if a sample of saturated solvent is drawn from a test tube 111 that happens to be at 50 C then, unless the ambient temperature of the apparatus 100 is 50 C or higher, some of the chemical (in the sample of saturated solvent in the sample needle 130) will precipitate as the sample needle 130 cools on the way from the test tube III to an analytical vial 141.

Although in the present embodiment water from the syringe pump reservoir (not shown) is used to dilute a sample in an analytical vial 141, in other embodiments solvent from a solvent vial 136 in the solvent rack 135 may be used to dilute a sample before injection of a portion of the diluted sample into the HPLC 150. In such cases, a "slug" of air (in the sample needle 130 and in the transfer tube) may be used as an air gap to separate (i) the solvent from a solvent vial 136 and (ii) the liquid (e.g. water) from the syringe pump reservoir (not shown), and thereby prevent mixing of the liquids in the sample needle 130 and transfer tube.

When a solvent from a solvent vial 136 is used it is preferred that the solvent is drawn up into the sample needle I 30 and the transfer tube before a sample is taken from a test tube Ill. Thus, when a sample is taken from a test tube Ill, solvent for flushing the sample needle 130 will already be positioned "above" sample in the sample needle 130 and transfer tube. Once the sample needle 130 is inside an analytical vial 141, the syringe puiiip is activated so that the sample and the previously stored solvent are expelled into the analytical vial 141. The use of a slug of air reduces mixing of the (i) solvent from a solvent vial 136 and (ii) the liquid from the syringe pump reservoir in the transfer tube. As those skilled in the art will appreciate, the use of slugs of air may be avoided by the use of a "guard" volume of excess solvent from a solvent vial 136; the guard volume is not dispensed into an analytical vial 141 but is instead disposed of in case of contamination with the liquid from the syringe pump reservoir (not shown).

As those skilled in the art will appreciate, the HPLC 150 comprises a pump (not shown), an oven (not shown), a detector (not shown) and a degassing unit (not shown). Samples are introduced into the I-IPLC 150 via an injection port 151 which operates in conjunction with a multi- position rotary switching valve (not shown). The sample needle 130 is lowered into the injection port 15 I and injects a sample of diluted solvent from an analytical vial 141 into the I-IPLC 150. In this embodiment, the multi-position rotary switching valve has a 20il sample loop (not shown) into which a sample is loaded. The HPLC ISO also comprises a column (not shown) which is maintained at a user definable temperature in the oven. Once the sample has been loaded via the injection port 151 into the sample loop, the multi-position rotary switching valve changes position, thereby allowing an IIPLC solvent (e.g. in this embodiment, a 50/50 mixture of water and acetonitrile) to force the sample out of the sample loop and along the column of the HPLC 150. The chemical (e.g. 3-napthol) will have a definitive residence time on the column (which time will depend on the temperature, HPLC solvent system and flow rate) and will then emerge from the column and into the detector to be distinguished from other components within the sample. Other components within the sample may be HPLC active solvents, which may have been used to dissolve the chemical in the test tube 111, or impurities arising from the preparation of the chemical or decomposition products.

In this embodiment, the detector (not shown) of the lIPLC 150 operates using UV (ultraviolet) spectroscopy at a wavelength that is suitable for the chemical whose solubility is being measured. In this embodiment, a wavelength of 220nm is used. As those skilled in the art will appreciate, many commonly used solvents do not have significant absorbance at wavelengths longer than about 200nm. Thus spectroscopy at a wavelength that is longer than 200nm, e.g. 220nm, will generally allow the detector of the lIPLC 150 to effectively ignore the solvent (e.g. water) yet respond satisfactorily to the chemical (e.g. 3-napthol). The chemical absorbs some of the UV light and thus reduces the amount of UV light incident on the detector. The detector provides an electrical signal in the form of a peak to a computer (Fig 6: 600). The area under the peak is proportional to the amount of chemical in the sample admitted to the 11PLC 150.

Figure 2 shows a cross sectional view through a test tube Ill. In this embodiment, the test tube Ill is generally cylindrical but has a narrowed region 200 towards the base of the test tube Ill. Figure 2 shows particles of undissolved chemical 210 and the solvent 211 in the narrowed region 200.

A stir bar 201 is shown at the bottom of the narrowed region 200. The use of a narrowed region 200 advantageously allows reduced quantities of chemical 210 and solvent 211 to be used. The use of reduced quantities is advantageous as chemicals of interest may not be available in large quantities for testing; for example, only several hundred milligrams may be available. The stir bar 201 is small enough to rotate freely in the narrowed region 200 and to be fully submerged in solvent 211 in order to ensure effective stirring.

Also shown is a thermal collar 215 which provides good thermal contact between the narrowed region 200 and the temperature controlled block 110. In this embodiment, the test tube Ill is formed of borosilicate glass and has a total length of 16cm and a diameter of 3cm; the narrowed region 200 has a length of 4cm and a diameter of 1.5cm.

The top of the test tube 111 has an external thread 270 onto which is screwed a cap 220.

The cap 220 has a hole through which passes a sample extraction assembly 230. The sample extraction assembly 230 is not shown in cross-section. The hole is sized so to provide a suitable clearance between the cap 220 and the sample extraction assembly 230 to allow the sample extraction assembly 230 to slide relative to the cap 220. In this embodiment, the sample extraction assembly 230 comprises a body 240 and a nozzle 250.

In this embodiment, the body 240 is formed of the thermoplastic polyetheretherketone (PEEK) which is resistant to a wide range of solvents. In this embodiment, the nozzle 250 is formed of stainless steel 250 which is also resistant to a wide range of solvents. The nozzle 250 is attached to the body 240 by an internal screw thread on the nozzle 250 and an external screw thread on the body 240. A coil spring 260 biases the sample extraction assembly 230 upwards so that the nozzle 250 is normally held clear, as shown, from the solvent 211.

The body 240 and the nozzle 250 each have axial through holes (Fig 3: 313, 323) that allow the sample needle 130 to be inserted so that the bottom of the sample needle 130 touches the bottom of the nozzle 250. Once the sample needle 130 touches the nozzle 250, further downwards movement of the sample needle 130 overcomes the upwards biasing lbrce from the coil spring 260, thus causing the sample extraction assembly 230 to move downwards so that the bottom of the nozzle 250 is just above the top of the stirring bead 201. In this position, the sample needle 130 can draw a sample of the solvent 211 through a hole (Fig 3:313,323) in the bottom of the nozzle 250. Once the sample has been drawn into the sample needle 130, the sample needle 130 is raised and may then be moved to the sample rack 140 so that the sample of solvent 211 may be placed into an analytical vial 141. As the sample needle 130 is raised, the coil spring 260 returns the sample extraction assembly 230 to the position shown at Figure 2 (i.e. with the bottom of the nozzle 250 clear of the solvent 211).

Figure 3 shows an exploded view of the body 240, nozzle 250, cap 220 and coil spring 260. The cap 220 and coil spring 260 are shown in cross-section. The body 240 comprises an upper body portion 3 10 and a lower body portion 320. The upper body portion 310 has a flange 311 towards the top of the upper body portion 310. The flange 311 prevents the upper body portion 3 10 from passing through the hole in the cap 220 and retains the upper rim of the coil spring 260. The bottom of the upper body portion 310 has an external screw thread 312 for attaching the upper body portion 310 to the lower body portion 320.

A through hole 3 13 allows the sample needle 130 to pass through the upper body portion 310.

l'he lower body portion 320 has a flange 321 towards the top of the lower body portion 320 which prevents the upper body portion 320 from passing through the hole in the cap 220. l'hus the flanges 3 11 and 321 ensure that the body 240 is captively mounted to the cap 220. A lip 322 on the upper surface of the flange 321 is provided for forming an air seal against the underside of the cap 220. The coil spring 260 biases the sealing lip into contact with the cap 220. The seal between the sealing lip 322 and the cap 220 is not completely airtight but is sufficient to reduce escape of the solvent 211 from the test tube Ill. A through hole 323 allows the sample needle 130 to pass through the lower body portion 320. An internal screw thread 324 allows the lower body portion 320 to be secured, via the external screw thread 312, to the upper body portion 310. An external screw thread 325 allows the lower body portion 320 to be secured to the nozzle 250. The bottom of the lower body portion 320 has a projection 326 which, when the lower body portion 320 is attached to the nozzle 250, projects into the nozzle 250.

Figure 4 shows the nozzle 250 and part of the lower body portion 320 in more detail.

Figure 4 shows a cross section through the nozzle 250 and the lower body portion 320.

l'he nozzle 250 is tubular. The top of the nozzle 250 has an internal screw thread 401 for attachment to the external screw thread 325 of the lower body portion 320. The projection 326 of the lower body portion 320 extends nearly, but not quite, to the bottom of the nozzle 250. The projection 326 terminates in an annular face 410. Adjacent the face 410 is an injection port seal 420. As those skilled in the art of HPLC will appreciate, injection port seals are typically provided in HPLC apparatus to allow a sample needle (such as the sample needle 130) to inject a sample into injection port (such as the injection port 151) of an 1-IPLC (such as the HPLC 150). The injection port seal 420 comprises a rubber 0-ring 421 which is surrounded on three sides of a square (the three sides being the inner cylindrical surface and the two opposing faces of the 0-ring 421) by an annular poly-tetra- flouro-ethylene (PTFE) sheath 422.

The upper face of the PTFE sheath 422 forms a seal against the face 410. The lower face of the PTFE sheath 422 forms a seal against the upper face of a frit filter 430. As those skilled in the art of HPLC will appreciate, frit filters are commonly placed in-line before an I-IPLC column in order to prevent contamination of the HPLC column by particulate contaminants. The irit filter 430 comprises a discoidal frit 431 and a surround 432. The frit 431 is formed of sintered particles of stainless steel. In this embodiment, the frit 431 has a pore size of 2jim and thus prevents particles that are larger than 2tm from passing through the frit 43 1. The surround 432 is an annular plastic member that is bonded to the frit 431 and carries the frit 431.

The lower face of the frit filter 430 is adjacent a face 440 of the bottom of the nozzle 250.

A hole 450 allows the solvent 211 to reach the frit filter 430. When attaching the nozzle 250 to the lower body portion 320, the face 410 compresses the injection port seal 420 against the frit filter 430. This compression results in slight deformation of the injection port seal 420 which enhances the ability of the injection port seal 420 to form a seal with the sample needle 130.

The outer edge of the rubber 0-ring 421 abuts the interior wall of the nozzle 250. This abutment ensures that the injection port seal 420 is centred with regard to the nozzle 250 and body 240; the sample needle 130 is guided by the through holes 313, 323 of the body 240 and thus this centring also ensures that the sample needle 130 is guided to the centre of the PTFE sheath 422. (If the injection port seal 420 was not centred relative to the body 240 then there would be the risk of the sample needle 130 striking the PTFE sheath 422 and shaving a sliver of PTFE off the PTFE sheath 422.) Figure 5 shows the same parts as Figure 4 but additionally shows the sample needle 130 in contact with the frit filter 430. In Figure 5, the sample needle 130 has pushed the body 240 and the nozzle 250 into the narrowed region 200 of the test tube 111 and thus Figure 5 also shows the narrowed region and the solvent 211. As can be seen, the bottom of the nozzle 250 isjust clear of the stir bar 201.

The inner cylindrical surface of the PTFE sheath 422 forms a seal with the sample needle 130. Thus when a partial vacuum is applied to the sample needle 130 by the syringe pump (not shown) via the flexible transfer tube (not shown), ambient atmospheric pressure forces solvent 211 through the frit filter 430 and into the sample needle 130. The frit filter 430 ensures that substantially no particles 210 of undissolved chemical pass into the sample needle 130. The sample needle 130 can then be raised to transfer the sample to the sample dilution block 140.

The abutment between the rubber 0-ring 421 and the nozzle 250 forms a seal. This seal ensures that, when a partial vacuum is applied to the sample needle 130, air that may be present between the nozzle 250 and body 240 will not be drawn into the sample needle 130. Without the seal, air could pass between the between the faces of the injection port seal 420 and the frit filter 430.

Figure 6 shows a computer 600 (not shown in the earlier Figures) that forms part of the apparatus 100. The computer 600 comprises a processor and memory and is electrically connected to the temperature controlled block 110, the XYZ arm 120, syringe pump 610 (not shown in the earlier Figures) and the HPLC 150. The computer 600 communicates electrically with the temperature controlled block 110 to set the temperatures of the various test tubes 111 in the temperature controlled block 110. The computer 600 communicates with the XYZ arm 120 to command the XYZ arm 120 to various positions about the apparatus 100. The computer 600 communicates electrically with the syringe pump 610 and thus controls, via the syringe pump 610, the aspiration (induction) and dispensation (expulsion) of solvent and air to/from the sample needle 130. The syringe pump 610 comprises solenoid valves (not shown) for controlling the flow of liquids and gases within the sample needle 130 and transfer tube (not shown). The computer 600 communicates with the HPLC 1 50 to initiate analysis of a sample that has been injected into the injection port 151 of the HPLC 150. The computer 600 also receives data from the HPLC regarding the results of an analysis.

Figure 7 shows an example of the output from the HPLC 150. The detector (not shown) of the HPLC ISO produces an electrical signal. The HPLC 150 converts the electrical signal into a data format suitable for transmission to the computer 600. Figure 7 shows a single peak 710 that corresponds to the chemical (e.g. 3-napthol in the case of3-napthol in water).

Figure 7 shows that analysis of an injected sample began at time t=0. For example in the case of-napthol in water, after approximately 60 seconds, peak 710 occurs. The area under the peak 710 is proportional to the amount of chemical in the sample and is also proportional to the UV absorbance of the chemical at the wavelength of 220nrn. To convert the area under the peak 710 to a mass of the chemical, the absorbance of a known concentration (standard) of the chemical at 220nm must be known. The UV absorbance of the standard at 220nm can be measured using HPLC 150 under the same sample conditions either before or after using the apparatus 100.

Second embodiment of the invention The frit 43 1 as described above for the first embodiment has a "dead volume". The dead volume of the frit 431 is the volume of solvent that is retained in the pores of the frit 431 after the aspiration of a sample through the frit 431 (once the sample needle 130 has been removed). When the sample needle 130 returns to the frit 43 1 (for example to take a sample of solvent 2 11 at a new temperature compared to the last temperature), the initial sample of solvent 211 that is sucked into the sample needle 130 will be the solvent 21! from the previous temperature that has remained trapped in the pores of the frit 431 since the previous sample. As more solvent 211 in sucked into the sample needle 130, fresh solvent 211 from the test tube will pass into and through the frit 431.

The second embodiment is based on the first embodiment but uses a different design of frit and different software for the computer 600 in order to reduce the effects of the dead volume of the frit.

In the apparatus 1 00, the frit 431 was discoidal. In an alternative embodiment, shown at Figure 8, the frit 43 1 has an alternative shape.Figure 8 shows a frit filter 830 with a frit 831 and a surround 832. The frit 831 has a recess 832. The recess 832 is dimensioned to allow the recess to receive a portion of the tip of the sample needle 130 when the sample needle 130 contacts the frit 831. An advantage of this embodiment is that the "dead volume" of solvent 211 trapped in the frit 831 is reduced compared to the dead volume of the frit 43 1. Another advantage of a recess 832 is that the flow resistance of the solvent 211 through the frit 83 1 will be reduced (compared to the frit 431) as the solvent will have to traverse a thinner portion of the frit 831 compared to the frit 431.

To illustrate the method by which the software of the computer 600 reduces the effects of dead volume, consider Figure 9. Figure 9 shows nine solubility measurements 901 to 909.

Figure 9 illustrates an example in which the apparatus 100 is used to make three measurements of the solubility of a chemical for each of three different temperatures. The vertical axis of Figure 9 illustrates the measured solubility of the chemical. The horizontal axis of axis of Figure 9 indicates the measurement number; I indicates the 1st measurement while 9 indicates the final measurement of the nine measurements. Measurement numbers I to 3 are all solubility measurements performed at 20 C, measurement numbers 4 to 6 are all performed at 35 C and measurement numbers 7 to 9 are all performed at 50 C. As shown, for the new temperatures of 35 C and 50 C, the initial measurement (i.e. measurements 4 and 7) is lower than the last two measurements (measurement numbers 6 & 7 and 8 & 9, respectively). Measurement number I is not affected by the dead volume as the pores of the frit 431 initially contain air and not the solvent 211. The software of the computer 600 is arranged to discard the first solubility measurement at a new temperature in order to avoid the effects of the dead volume.

In this embodiment, after completing all the measurements, the computer 600 produces a data file (not shown) for a user. In one mode of operation, the computer 600 produces a data file which includes all of the solubility measurements. In a preferred mode, the data file contains the solubility profile of the various chemicals and solvents that were tested; when calculating the data file, the computer 600 discards measurements that may have been affected by dead volumes.

Third embodiment of the invention The third embodiment is based on the first (or second) embodiment and includes software on the computer 600 that allows the apparatus 100 to automatically avoid saturation of the I IPLC 150. If the computer 600 deduces that the detector (not shown) of the HPLC 150 has become saturated then the computer 600 arranges for the sampling needle 130 to aspirate an additional sample from the test tube 111 and ensures that the additional sample undergoes at least one dilution stage before injection into the I-IPLC 150.

To illustrate the method by which the software of the computer 600 reduces the effect of saturation, consider Figure 10. Figure 10 shows an example of a series of solubility measurements at different dilutions.

Figure IOA shows the output of the detector (not shown) of the 1-IPLC ISO when a sample of chemical and solvent is not diluted before injection into the HPLC 150 (i.e. the sample dilution block 140 is not used) and instead the sample of chemical and solvent is injected directly into the HPLC 150. As can be seen, the output of the detector is a peak 1010 with a flat top 1 011. The flat top lOll indicates that the detector has become saturated by the dissolved chemical and that the detector is no longer giving an output signal that is linearly proportional to the concentration of the chemical.

Figure lOB shows the output of the detector of the HPLC 150 when an additional sample (with the temperature controlled block 110 at the same temperature as used for Figure IOA) of chemical/solvent is diluted by a factor of fifty before injection into the l-IPLC 150.

The dilution by fifty is performed using an analytical vial 141 in the sample dilution rack 140. As can be seen, the peak 1020 also has a flat top 1021 but the peak 1020 is narrower than the peak 1010.

Figure lOC shows the output of the detector of the HPLC 150 for yet another sample.

Compared to the sample of Figure bA, the sample of Figure lOC is diluted twice by a lctor of fifty each time, for a total dilution of 2,500, before injection into the HPLC ISO.

A sample from the analytical vial 141 that was used for Figure lOB is drawn off and placed into another analytical vial 141. Further diluent is then added so that the sample in the second analytical vial 141 is also diluted by a factor of fifty. Two analytical vials 141 are therefore required. As can be seen, the peak 1030 has a rounded top which indicates the detector of the HPLC 150 has not been saturated. It can also be seen that the area under the peak I 020 is less than the areas under the peaks 1010 and 1020. This is because, due to the dilution, a reduced quantity of the dissolved chemical is being injected into the HPLC 150 compared to Figures bOA and I OB.

The computer 600 is programmed to monitor the output from the HPLC 150. If saturation of the HPLC 150 is detected then the computer 600 arranges for the sample needle 130 to obtain a new sample from the test tube Ill and to dilute the new sample before injection into the IIPLC ISO. If the new sample still results in saturation of the HPLC 150 then further rounds of dilution may be performed until the HPLC ISO is no longer saturated.

Alternative embodiments The apparatus 100 described above used an injection port seal 420 to form a seal between the sample needle 130 and the frit filter 430. In alternative embodiments an 0-ring (not shown) may be used to form a seal between the sample needle 130 and the frit filter 430.

An annular recess (not shown) may be used to locate the 0-ring relative to the body 240 and thus relative to the sample needle 130. An annular recess may also be used to locate the injection port seal 420 relative to the body 240 (whereas the apparatus 100 used the interior wall of the tubular nozzle 250 to align the injection port seal 420 relative to the body 420).

The sample needle 130 was described above as having a flat tip. As those skilled in the art will appreciate, sample needles having an angled tip are commonly available. Samples needles having an angled tip may be used but this may require modification of the sealing arrangement between the sample needle, the body 240 and the frit filter 430. For example, a plurality of adjacent injection port seals 420 may be provided between the body 240 and the frit filter 430 to accommodate sample needles having an angled tip.

The apparatus 100 described above used a frit filter 430 to preclude particles 210 of undissolved chemical from being aspirated into the sample needle 130. In alternative embodiments, a porous ceramic filter, a woven metal mesh filter or some other rigid filter may be used to prevent the entry of particles 210. A paper filter or some other type of flexible filter could be used in other embodiments. In such embodiments, the flexible filter is held trapped between the body 240 and the nozzle 250, in order to avoid the solvent passing around the edges of the filter and into the lumen (i.e. the through holes 313, 323) inside the body 240. For example, by clamping a paper filter against the body 240, particles 211 of undissolved chemical can be prevented from reaching the lumen.

The test tubes Ill were described as having a narrowed region 200. In alternative embodiments, test tubes that are generally cylindrical may be used instead. When using such test tubes, the body 240 and nozzle 250 may have a different shape from that shown by Figures 2 to 5. Test tubes which have a side pocket (not shown) for the insertion of a thermocouple may be used to improve the accuracy of measuring the temperature of the solvent 211. The inserted thermocouple may be used to directly monitor the temperature of the contents of the test tube Ill.

The temperature controlled block 110 was described above as stirring the test tubes 111 using a magnetic stirrer (not shown). In alternative embodiments, other means of stirring may be used instead. For example, the temperature controlled block may be arranged to vibrate the test tubes 111. Alternatively, the sample needle 130 may be used to stir the test tubes Ill by bubbling air through the test tubes 111. An overhead (mechanical) stirrer may be used to stir the contents of a test tube 111 and may be driven by a motor or by a magnetic drive. In other embodiments of the apparatus 100, no means of stirring the test tubes 111 is provided; such embodiments will take longer to reach equilibrium compared to embodiments that have a means of stirring.

Some embodiments of the apparatus 100 may be provided with a cooling manifold (not shown) above the temperature controlled block 110. The cooling block is arranged to cool the upper portions of the test tubes 111 and thereby allow avapourated solvent to condense and run down the inside wall of the test tube 111 back to the narrowed region 200. The use of a cooling block is preferred when the solvent is highly volatile or poisonous.

Some embodiments of the apparatus may be provided with means (not shown) for filling the test tubes 111 with an unreactive gas (such as nitrogen) or a noble gas. Such a means acts to exclude ambient air from the test tubes I 11 and is preferred when the solvent or the chemical reacts with ambient oxygen or adventitious moisture.

The apparatus 100 was described above in terms of a temperature controlled block 110 for controlling the temperature of two or more test tubes Ill. In alternative embodiments, the temperature controlled block may be capable of controlling the temperature of only a single test tube. The use of the temperature controlled block 110 is preferred as such a block allows many combinations of chemicals and solvents to be measured in one batch.

The apparatus 100 was described above as having an XYZ arm 120 that is capable of moving in three orthogonal directions. In alternative embodiments, other means may be used to allow the relative motion between the sample needle 130 and the various parts of the apparatus 100. For example, the temperature controlled block 110, the solvent block 135, the sample dilution rack 140, the wash station and the HPLC 150 may be mounted to a table (not shown) movable in the X axis relative to an "YZ" arm that is capable of moving in the Y and Z axis.

The apparatus 100 had coil springs 260 to bias the nozzles 250 out of the test tubes ill. In alternative embodiments, the coil spring 260 may be replaced with some other type of resilient means. In other embodiments, the coil spring 260 may be dispensed with.

However, it is preferred that the nozzles 250 are normally held out of the solvent 211 as in some circumstances, the stirring effect of the stir bar 201 can be impaired if the nozzles 250 are continuously dipped into the solvents 211 of their respective test tubes 111.

The apparatus 100 was described above as diluting a sample of solvent 211 with diluent (i.e. further solvent) before injection of the sample into the 1-IPLC 150 for analysis. This dilution was described as reducing the possibility of saturation of the detector of the 1-IPLC 150 (HPLC is a sensitive technique and so inadvertent saturation of the detector through an excessive concentration of dissolved chemical is an unwanted possibility). In some situations, the step of diluting the sample of solvent 211 may be dispensed with. For example, if a chemical is only slightly soluble in a solvent and the I-IPLC detection parameters are set to an insensitive setting then it may not be necessary to dilute the sample with additional solvent. In such cases a sample from a test tube 111 may be directed directly into the HPLC 1 50.

For the second embodiment, the software of the computer 600 was arranged to automatically discard the first solubility measurement at a new temperature (except for the First measurement where there was no dead volume). In alternative embodiments, the computer 600 is arranged to determine whether the first measurement for a new temperature is statistically similar to subsequent solubility measurement for that temperature. As those skilled in the art will appreciate, the computer 600 may automatically discard measurements not lying within the 95% confidence level (i.e. 2 standard deviations). The computer 600 may instead be arranged to automatically discard measurements not within some predetermined proportion of the later measurements for 1 0 that temperature.

[he third embodiment was described as taking a sample from a test tube 111 and injecting the sample directly into the HPLC 150 for analysis. If the concentration of dissolved chemical was such as to saturate the HPLC 1 50 then one or more rounds of dilution were performed until the computer 600 determined that the HPLC 150 was no longer being saturated. In many situations, the sensitivity of the HPLC 150 is such that dilution in an analytical vial 141 of the sample before injection into the HPLC 150 will almost always be required. An alternative embodiment may automatically dissolve the sample in an analytical vial 141. [he computer 600 then checks the output of the HPLC 150 to ensure that the 1-IPLC 150 has detected a peak corresponding to the dissolved chemical. If no peak has been detected then the computer 600 assumes that the (diluted) sample that was injected into the HPLC 150 was too dilute and the computer 600 arranges for another sample from the test tube Ill to be directly injected into the HPLC 150 for analysis.

The apparatus 100 had an HPLC ISO. [hose skilled in the art will appreciate that HPLCs are capable of discriminating between different chemicals as the different chemicals will have different transit times through the HPLC column. Those skilled in the art will also appreciate that the HPLC 150 was used for its ability to measure the quantity of a dissolved chemical (i.e. the area under a peak 710) rather than for its ability to discriminate between different chemicals. In alternative embodiments, some other means for measuring the amount of a chemical may be provided. For example, a gas chromatograph may use a flame ionisation detector, instead of a UV detector, to measure the amount of chemical.

The apparatus 100 had a temperature controlled block 110 for controlling the temperature of the test tubes Ill. In alternative embodiments, the temperature controlled block 110 may be dispensed with and the apparatus may be placed into a temperature controlled environment. In yet other embodiments, a temperature controlled environment is not required and the apparatus is used for making solubility measurements with the solvent and chemical at room temperature.

As those skilled in the art will appreciate, alternative embodiments may replace the 1 0 computer 600 with dedicated electronic circuitry. When a computer 600 is used, a program for programming the computer 600 to control the apparatus 100 may be distributed using a data carrier such as a floppy disk or as a signal, for example as a downloadable file from the Internet.

Claims

CLAIMS: 1. A sampling apparatus for obtaining a sample of a solvent from a

container, the apparatus corn pris ing: a body having a lumen; a filter for allowing solvent but substantially preventing undissolved particles of a chemical from entering the lumen; and sealing means for forming a seal between the filter and the lumen.
2. An apparatus according to claim I, wherein the sealing means comprises an injection port seal.
3. An apparatus according to claim I or 2, comprising a nozzle for urging the filter towards the body, wherein the nozzle comprises a hole for allowing solvent to reach the filter.
4. An apparatus according to any one of claims I to 3, comprising a cap adapted for engagement with the top of a container.
5. An apparatus according to claim 4, wherein the cap is captively secured to the body.
6. An apparatus according to claim 5, wherein the body comprises an upper part and a lower part and the cap is captively held between the upper and lower parts of the body.
7. An apparatus according to any one of claims 4 to 6, wherein the container is a test tube and the cap is adapted for engagement with a test tube.
8. An apparatus according to any one of claims 4 to 8, wherein the cap and body are adapted to impede the escape of solvent from the container when the cap is engaged with the top of a container.
9. An apparatus according to claim 8, wherein the body comprises a lip for engagement with the cap, thereby impeding the escape of solvent.
10. An apparatus according to any one of claims 4 to 9, comprising bias means to urge the body out of solvent within the container.
11. An apparatus according to claim 10, wherein the bias means comprises a coil spring.
12. An apparatus according to any preceding claim, wherein the filter comprises a substantially rigid filter.
13. An apparatus according to claim 12, wherein the filter comprises a frit.
14. An apparatus according to claim 12 or 13, wherein the filter comprises a recess.
15. An apparatus according to claim 14, wherein the recess of the filter is provided on the lumen side of the filter.
16. An apparatus for performing solubility measurements, the apparatus comprising: a container holder for holding a container, wherein the container contains a solvent with a dissolved chemical and particles of the undissolved chemical; a sampling apparatus comprising a filter for obtaining, from a container, a sample of solvent that is substantially free of undissolved particles; an analyser for determining the amount of a chemical dissolved in a sample of solvent, wherein the sample of solvent has been obtained from a container using the sampling apparatus; and liquid transfer means for transferring a sample of solvent from a container to the analyser.
1 7. An apparatus according to claim 16, wherein the sampling apparatus comprises a sampling apparatus according to any one of claims I to 15.
18. An apparatus according to claim 16 or 17, wherein the container holder comprises means for controlling the temperature of the container.
19. An apparatus according to any one of claims 16 to 18, wherein the container holder is operable to stir solvent and particles of undissolved solvent in a container.
20. An apparatus according to claim 19, wherein the container holder comprises a magnetic stirrer.
21. An apparatus according to any one of claims 16 to 20, wherein the liquid transfer means comprises an XYZ arm and a sample needle.
22. An apparatus according to any one of claims 16 to 21, wherein the analyser comprises an lIPLC.
23. An apparatus according to any one of claims 16 to 22, wherein the container is a test tube and the container holder is adapted for holding a test tube.
24. An apparatus according to any one of claims 16 to 23, comprising a container.
25. An apparatus according to any one of claims 16 to 24, wherein the container holder is adapted for holding a plurality of containers.
26. An apparatus according to any one of claims 16 to 25, comprising a controller for controlling the liquid handling means.
27. An apparatus according to claim 26 when dependent on claim 18, wherein the controller is operable to control the means for controlling the temperature of the container.
28. An apparatus according to claim 26 or 27, wherein the controller is operable to control the analyser.
29. An apparatus according to any one of claims 26 to 28, wherein the controller comprises a computer.
30. An apparatus according to any one of claims 16 to 29, wherein the container holder is a first container holder for holding a first container, comprising: a second container holder for holding a second container; and sample dilution means for diluting, in a second container, a sample of solvent from the first container with solvent, wherein the liquid transfer means is operable to transfer a sample of solvent from a first container to the analyser via a second container.
31. An apparatus according to claim 30, wherein the sample dilution means comprises the liquid transfr means.
32. An apparatus according to claim 30 or 31, wherein the second container is an analytical vial and wherein the second container holder is adapted for holding an analytical vial.
33. An apparatus according to any one of claims 30 to 32, comprising a second container.
34. An apparatus according to any one of claims 30 to 33, wherein the second container holder is adapted for holding a plurality of second containers.
35. An apparatus according to any one of claims 30 to 34 when dependent on any one of claims 26 to 29, wherein the controller is operable to receive a signal from the analyser that is indicative of the amount of a chemical that is dissolved in a sample of solvent, and wherein the controller is operable to selectively cause the dilution in a second container of a sample of solvent from a first container, in dependence on the signal from the analyser.
36. An apparatus according to claim 35, wherein the controller is operable to cause the dilution of a sample of solvent if the signal from the analyser indicates that the amount of a chemical dissolved in the solvent is such that the analyser has been saturated.
37. An apparatus according to any one of claims 16 to 36, comprising a cleaning station.
38. A method of performing a solubility measurement, comprising the steps of: using a filter, causing the extraction from a container of a sample of solvent containing a dissolved chemical; causing the transfer, as a first analysis sample, of at least a portion of the sample to an analyser; using the analyser to determine the amount of the dissolved chemical in the first analysis sample; receiving a signal from the analyser indicative of the amount of the dissolved chemical in the first analysis sample; determining whether the signal indicates that the amount of the dissolved chemical in the first analysis sample was one of too low and too high, for accurate analysis by the analyser; and if the amount was too low or too high, causing the transfer of a second analysis sample to the analyser, wherein the second analysis sample contains a different concentration of the dissolved chemical compared to the first analysis sample.
39. A method according to claim 38, wherein the step of determining comprises determining if the amount of the dissolved chemical was too high for accurate analysis, and wherein the step of causing the transfer of a second analysis sample comprises diluting the second analysis sample with respect to the first analysis sample.
40. A method of performing a solubility measurement, comprising the steps of: using a filter, causing the extraction from a container of at least first and second samples of solvent containing a dissolved chemical, wherein the at least first and second samples are extracted at substantially identical temperatures; causing the transfer, as analysis samples, of at least a portion of each of the at least first and second samples to an analyser; using the analyser to determine the amount of the dissolved chemical in each of the at least first and second analysis samples; receiving a signal from the analyser indicative of the amount of the dissolved chemical in each of the at least first and second analysis samples; comparing the respective amounts of dissolved chemical in each of the at least first and second analysis samples and, if the first amount differs from the at least second amount by more than a predetermined amount, discarding the measurement of the first amount.
41. A method according to claim 40, wherein the predetermined amount is two standard deviations.
42. A method according to claim 40 or 41 when dependent on claim 38 or 39.
43. A program product for programming a processor to perform the method of any one of claims 38 to 42.
44. An apparatus according to any one of claims 26 to 29 or 35 to 36, wherein the controller is programmed to perform the method of any one of claims 38 to 42.
45. An apparatus and method as hereinbefore described and/or with reference to the accompanying Figures.