Abstract:
A system for quickly and automatically extracting and analysing residual solvents is realised for operating directly in the premises where the packing materials are being manufactured, printed and/or laminated.  
     The system provides for a single unit equipped with a display and a keyboard, and comprises an extraction (desorption) chamber ( 1 ), an analysis chamber with valves and separating columns, a detection system ( 17 ), and a data processing system ( 19 ).  
     The extracting or desorption chamber comprises a desorption cell ( 1 ) for receiving a vial ( 36; 37 ) containing said sample, and means are provided to keep the inside of said cell ( 1 ) at a pressure higher that that of the surrounding environment until a new sample has been introduced into the cell, thus accomplishing a “washing” of cell for eliminating polluting solvents coming from the desorption of a preceding sample and/or solvents present in the surrounding environment.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
         [0001]    This invention relates to a system for quickly and automatically extracting and analysing residual solvents in material samples. Hereinbelow reference will be made particularly to preferred embodiments of the invention in which the samples are printed and/or laminated films, in general used as base supports for packing or packaging foodstuffs or pharmaceutical products, or liquid samples. Nevertheless, this is not to be understood as a limitation since the invention has several different applications, such as the analysis of residual monomers in polymers, the analysis of contaminated grounds, waters, and so on.  
           [0002]    More particularly, the invention can be advantageously employed directly in the premises or plants where the materials for packing foodstuff and pharmaceutical products are being manufactured or printed and/or laminated.  
           [0003]    As it is known the analyses of residual solvents present in printed and/or laminated packing materials, particularly those for packing foodstuffs and pharmaceutical products, are very important for the companies of this field.  
           [0004]    According to a prior art technique, the analysis of residual solvents, for example in a film of plastic material, is carried out in laboratories by using an analytical system comprising a head-space sample container or thermal desorber, coupled to a gas chromatograph. During the manufacturing of the printed and/or laminated support or at the end of such process, a sample is collected and sent to the laboratory. The analysis results from the laboratory are available after times that are not compatible with the manufacturing schedules. Besides the high costs, the non-availability in real time of the analysis results often brings to discard large amounts of product and to reprocess the materials with additional costs.  
           [0005]    This analysis is quite complex and requires high qualified technical personnel, and further has the following drawbacks:  
           [0006]    the handling of the samples from the manufacturing plant to the analysis laboratory,  
           [0007]    the use of test tubes, envelopes or other closed containers for transferring the samples to the laboratory with the associated risks of polluting the container content by the environment air, for example the air of the manufacturing plant when collecting the sample;  
           [0008]    extremely complicated calibration procedures and frequent calibration controls, particularly for systems carrying out a subdivision or splattering of the sample;  
           [0009]    long analysis times of the order of 45-60 minutes.  
           [0010]    A further trouble of the known systems comes from the need to provide a pressure source and a gauge, which nevertheless does not allow a real knowledge of the pressure inside of the desorption chamber.  
           [0011]    The scope of this invention is to eliminate the drawbacks and the limitations of the known systems, and more particularly to maintaining a higher pressure (overpressure) inside the desorption cell until a sample is introduced thereinto. By providing such overpressure or “washing” of the cell, it is possible to eliminate any pollutants coming from the desorption of a preceding sample and/or from the surrounding environment, whereby the system is suitable to be employed in the field still supplying reliable results. Preferably, the same fluid is used both as washing fluid and as fluid maintaining the high pressure, although this is not mandatory.  
           [0012]    The above objects of this invention are achieved through a novel analyser for quickly analysing the residual solvent of a sample which analyser can be directly used in the sites where the packing article is being manufactured, printed and/or laminated.  
           [0013]    The analyser according to the invention operates in a fully automatic manner and does not require highly trained personnel, reduces the handling of the samples to be analysed, and supplies results that are comparable with those obtainable in a laboratory by using the known procedures in times of the order of several minutes.  
           [0014]    More particularly, for analysing printed and/or laminated packing articles, the system according to the invention can be advantageously located in the manufacturing premises, thus allowing for both the on-line analysing and the monitoring of the article being manufactured. As for what concerns the samples of packing materials, the invention allows to obtain the automatic analysis of solvent on both the sides of the sample, that is both on the outer side and on the inner side (that contacts the foodstuff or pharmaceutical product).  
           [0015]    Moreover, the system according to the invention can operate on very small amounts of sample (the term “sample” being referred to the amount of the residual solvent) directly in the capillary column, thus eliminating sample splitting techniques that are subjected to introduce errors in the analysis.  
           [0016]    According to the invention, these objects are achieved through a system for automatically extracting and analysing residual solvents in materials samples as claimed in claim 1. Further advantageous features are recited in the dependent claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The invention will now be disclosed with particular reference to the attached drawings illustrating a non limiting embodiment thereof, in which:  
         [0018]    [0018]FIG. 1 is a schematic perspective view of an equipment implementing the system according to the invention;  
         [0019]    [0019]FIG. 2 is a general diagram of a system according to the invention;  
         [0020]    [0020]FIG. 2A schematically illustrates some steps of the method according to the invention;  
         [0021]    [0021]FIG. 3 is a cross section view illustrating with more details the desorption cell for a liquid or solid sample;  
         [0022]    [0022]FIG. 4 is a cross section view illustrating with more details the desorption cell for a film or a support of packing materials;  
         [0023]    [0023]FIG. 5 shows an analysis diagram obtained by a system according to the invention;  
         [0024]    [0024]FIG. 6 schematically illustrates a preferred embodiment for realising some of the system valves through a single small volume automatic valve assembly. 
     
    
       [0025]    Throughout all the Figures the same numerical references have been used to indicate equal or substantially similar parts.  
       DETAILED DESCRIPTION  
       [0026]    With reference to FIGS. 1 and 2, a system according to the invention preferably comprises a single equipment piece disposed inside a container or thermostatic case  50 , housing an analysis chamber equipped with valves and a separation column, and a data processing system. On the front panel of the equipment there are mounted an analysing or desorption cell  1 , preferably kept at a fixed temperature, and a graphic display  52 . A keyboard  51  for the controls is connected to the equipment, as well as a printer (not shown) to supply a hard copy of the analysis results.  
         [0027]    The diagram of FIG. 2 illustrates with more details the components and the system operation. Such a system comprises a desorption cell  1  for extracting the solvents from a sample, that can be connected to a high resolution capillary column  16  in order to separate from one another the solvents present in the sample to be analysed. The column  16  is connected to a detection system  17 , to a sampling loop  9 , and to a processing and control unit  19 . These components (as well as their modes of use) are known and however their functions could also be performed by different components so that they shall not be further described.  
         [0028]    Additionally, means (not illustrated in the drawings) are provided for heating the sample and extract the solvents. Several fittings are provided for in the system for connecting this latter to the outside, such as:  
         [0029]    a fitting  20  to be connected to a vacuum source;  
         [0030]    a fitting  21  to be connected to a source of washing gas;  
         [0031]    a fitting 22  for discharging the washing gas outside of the apparatus;  
         [0032]    a fitting  23  to be connected to a pressure source;  
         [0033]    a fitting  24  to be connected to a reference standard;  
         [0034]    a fitting  26  for discharging the loop.  
         [0035]    Moreover, a digital device  13  for controlling the vacuum level can be connected to the fitting  20 , this device acting on a valve  14  (or other component) for adjusting the vacuum level, such valve being inserted in the connection between the fitting  20  and the vacuum source.  
         [0036]    The fittings  20 ,  22 ,  23 ,  24  and  25  can be connected to the cell  1  through the corresponding valves  2 ,  4 ,  5 ,  6  and  7 . The inlet of column  16  is connected to the fitting  26  through the valve  11 , and to one end of loop  9  through the valve  8 . The other end of loop  9  is connected to fitting  25  through a valve  10 , to fitting  21  through a valve  3 , and to fitting  26  through a valve  12 .  
         [0037]    A device  15  for controlling and adjusting the pressure is located between valves  7  and  8 .  
         [0038]    The cycle phases, the switching of the valves as well as other operations such as integrations, display of the chromatogram, data storage and so on, are under the control of unit  19 , preferably realised through a PC located inside the analyser.  
         [0039]    Valves  2  to  6  are preferably realised as a monolithic (single) component comprising a single automatic valve assembly of small volume, schematically illustrated in FIG. 6, adapted to accomplish the required functions and installed into a thermostat system.  
         [0040]    The valve  7 ,  8 ,  10 ,  11  and  12  realise an automatic valve assembly adapted to directly sample volumes from the capillary column and capable to sample a few microliters of sample without requiring special splitting techniques of the sample, thus eliminating the analysis errors inherent to such techniques.  
         [0041]    With reference to FIG. 3 it will be illustrated an embodiment of a desorption cell which is adapted to be used with solid or liquid samples. Said desorption cell comprises a recess or seat  31  having a substantially cylindrical shape, formed in a properly insulated portion  32  of the equipment front panel and of a closing member or knob,  33  for sealingly closing the cell. A conduit  35 , connected to the above mentioned valve  4  of the washing fitting  21  opens into the front portion of the cell and a needle  34  is located at the inner end of the cell.  
         [0042]    The cell or seat  31  can receive test tubes or “vials” having a  20  cc capacity, said vials being either vials of the open type such as  37  or vials  36  for liquid or solid samples, that have been sealed through a ring carrying a pierceable septum. The thickness of the test tube or vial is such as the inner available volume of the cell is of 20 cc after the tube has been inserted into the seat.  
         [0043]    After the introduction into the cell of a test tube closed by a septum  35 , the closing knob  33  is screwed and sealingly tightened onto the test tube till the needle  34  perforates the septum.  
         [0044]    [0044]FIG. 4 illustrates a cell adapted for analysing residual solvents in bases of printed and/or laminated packing for foodstuffs and pharmaceutical products, both on the outer and the inner surface of the packing sheet, this latter being the surface that will come in contact with the packed product. The cell comprises a recess divided by a net  43  for supporting the sample to be analysed, and forming two hollows  41  and  42 , each one with a 20 cc volume. The recess is placed in an insulated volume  40  and the seal is ensured by circular gaskets (not shown) fitting along the whole surface of hollow  42 . Two conduits  46  and  47  for the connection to the washing and vacuum sources respectively, as well as two conduits  45  and  44  for the outlet of the vapour solvent, open in the hollows  41  and  42 . Clamps  48  and  49  lock the cell into the correct position.  
         [0045]    An analysis cycle of a system according to the invention will now be disclosed in detail.  
         [0046]    Initially, a calibration cycle is carried out—wherein the desorption is not activated—by inserting into the desorption cell a mixture having a known concentration, such mixture being inserted either through a test tube or a vial closed by a pierceable septum, or by injecting the calibration mixture directly into the cell  1  by means of a syringe, through a pierceable septum.  
         [0047]    A check of the calibration stability in the time can be carried out by using a reference standard by connecting to the fitting  24  a cylinder containing synthetic air with a known concentration of only one substance, such as for example methane. The reference calibration cycle is comparable with the cycle for analysing the sample and provides for a first analysis to store the value of methane area, and then a comparison of such value with a value that has been stored in subsequent reference calibration cycles.  
         [0048]    For the real analysis, from an initial condition of standby, the valves  3 ,  7  and  4  are opened, whereby the desorption cell and the sampling loop, as well as the valve  11  for conveying a gas or “carrier” to the capillary column, are subjected to a washing.  
         [0049]    Then the operator introduces the sample into the chamber  1  and starts the system, thus causing the closing the previously opened valves  3 ,  7  and  4 , and the opening of valves  2  and  7  that apply the vacuum to the cell  1 , to the loop  9  and to the valve  11 , according to a predetermined cycle for a duration of a few minutes. During this cycle, the partial pressure is measured and monitored by the device  15  for controlling and adjusting the pressure.  
         [0050]    The control of the partial pressure value inside the chamber during the sample desorption phase is very advantageous since it supplies an indication of the quantity of solvent desorbed (i.e. extracted) from sample. Of course, the value of such partial pressure shall be proportional to the amount of the desorbed solvent. Moreover this control allows for a later validation of the analysis results by verifying that the partial pressure value has always remained under the present pressure value for the sample pressurisation cycle.  
         [0051]    Once the solvent desorption has occurred, that is when the solvent present in the sample has been converted to a gas in the cell, the valve  7  is opened again for communicating the sampling loop with the desorption cell  1  and the valve  11  with the capillary column.  
         [0052]    The gaseous sample is therefore pressurised by opening the valves  5  and  7 , respectively towards the pressurisation fitting  23  and the discharge  25  fitting, and the valve  11  of carrier to the capillary column. Through this pressurisation cycle a sufficient amount of gaseous sample to perform the analysis is achieved.  
         [0053]    Then, the valves  7  and  10  are open to fill the loop with the gaseous sample and to bring the loop of the gaseous sample to the atmospheric pressure. Thereafter the valve  11  of the carrier is opened to the capillary column.  
         [0054]    Then the gaseous sample is admitted into the gas chromatography column  16 . By opening the valves  12  and  8  the carrier draws the gaseous sample from the sampling loop and introduces it into the analysis column. By using a quick capillary column, it is possible to obtain the separation of the solvents and the analysis printout and report in a time of about 2 minutes. At the end of the analysis cycle, the system comes back to the stand-by conditions.  
         [0055]    The cycle of the reference standard is carried out after the calibration cycle and is identical to the analysis cycle but for the opening of the valve  6  after the sample has been introduced, by introducing the sample without the vacuum cycle. The system stores the response signal of the reference standard and checks its reproducibility in the time, by comparing the data obtained with those stored: as long as this value is reproducible, the system is properly calibrated.  
         [0056]    [0056]FIG. 2A shows the values P of the pressure in the desorption cell as a function of time t. The AB section at a pressure p1 higher than the atmospheric pressure corresponds to the washing phase in which the gas keeps the cell at a pressure higher than the environment pressure to prevent the inlet of polluting solvents deriving either from the desorption of a previous sample or from the environment air containing solvents. The analysis starts at time AN.  
         [0057]    At the beginning of the operations, the connection with the source of high pressure is closed and the pressure in the cell drops to the atmospheric value (p0) in the CD portion, the cell is then opened and the sample to be analysed is introduced in the cell. If the test tube is of the closed type, the needle  34  perforates the closing. During the desorption phase (in which the sample is being heated), the pressure can be kept either at the atmospheric level (as shown by the DE portion), or to a lower value (as shown by the FG portion) by connecting the chamber to the vacuum source. At the end of the desorption, the pressure is raised again to p1 level and the analysis cycle starts.  
         [0058]    The valve assembly shown in FIG. 6 comprises a body  55  and a head  57  joined by a screw  58  with a diaphragm  59  interposed between the parts.  
         [0059]    Although the invention has been illustrated with reference to preferred embodiments, it is generally susceptible of further applications and modifications that fall within the invention scope as will be evident to the skilled of the art.