FI108674B - Method and apparatus for studying the moisture behavior of a powdered substance - Google Patents

Description

108674

METHOD AND APPARATUS FOR DETERMINING THE MOISTURE BEHAVIOR OF A POWDERED SUBSTANCE - METOD OCH ANORDNING FÖR UNDERSÖKNING AV ETT POWDER FORMULA BETEENDE I FUKT

The invention relates to a method and apparatus for studying the moisture behavior of a powdered substance. The term "moisture behavior" hereinafter refers to the moisture adsorption or desorption of a substance in an atmosphere of known relative humidity. The term also encompasses said rate of moisture adsorption or desorption and the equilibrium concentration of the substance.

Under a certain relative humidity atmosphere, the substance may be moisture-binding, i.e., hygroscopic, moisture-releasing, or weathering, or none of these phenomena will occur. In the latter situation, the substance is in equilibrium with the ambient atmosphere, and is then referred to as the equilibrium moisture content.

15 The equilibrium humidity of a substance depends not only on the substance itself::: own physical and chemical properties, relative humidity and temperature of the surrounding atmosphere. The adsorption isotherm is a curve that describes the equation, ···. weight moisture as a function of relative atmospheric humidity at constant temperature (Figure 1). The adsorption isotherm 'il.' Describes a situation in which the initial humidity of the substance has been * * lower than its equilibrium humidity in the atmosphere to which the substance is exposed. If, on the other hand, the substance has been conditioned: to equilibrium humidity in a well V: 25 high relative humidity, and the substance is exposed to a lower relative humidity, t ·, ···. the equilibrium moisture content will be set to a value above the adsorption isotherm, i.e. the desorption isotherm (Figure 1), which illustrates a situation in which the initial moisture content of the substance is higher than its equilibrium moisture content in the atmosphere to which the substance is exposed. Because of this phenomenon of hysteresis, the "history" of the substance, i.e., the humidity conditions in the 2,108,674 states in which it was stored before being exposed to the new atmosphere, is also an important factor affecting equilibrium.

For storage, handling and processing of powdered substances, it is important to know how the substance reacts to the humidity of the ambient air, i.e., to what moisture content the substance settles and how quickly moisture adsorption or desorption occurs. Figure 2 shows the weight change of one substance as a function of time when dry samples are exposed to 10 different atmospheres of relative humidity. If two or more powders need to be mixed and processed into a final product, it is essential to know how these substances affect each other's moisture behavior. For example, in the pharmaceutical industry, in the manufacture of solid dosage forms such as tablet-15, it has been found that powdered | the uncontrolled moisture behavior of raw materials causes many problems. Poor tabletability is often corrected by modifying the moisture of the tablet mass. The mechanical strength of the tablets and the theological properties of the powders can be controlled by changing the moisture content of the tabletting mass. Excessive moisture is detrimental in the sense that it enables microbiological growth. If known: the moisture behavior of the various components of the pulp can be selected in the formulation from substances which are suitable in this sense; 25 as well as possible.

On most commercial devices in use. . as a rule, the moisture content of the solid sample is measured. However, the moisture content is far from providing sufficient information on the moisture behavior of the substance in process or use situations. Commercial devices do not provide any information on the adsorption or desorption rates of the substance.

Pirttimäki and Laine, European Journal of Pharmaceutical Sciences 1 (1994) 203-8 describes a device capable of determining the adsorption-35 thio or desorption rates and equilibrium moisture values of small quantities. Device 3 108674 comprises a x-microbalance / scale-dependent sample container connected to a computer, an air-conditioning chamber, and a lifting device for lowering and raising the air-conditioning chamber so as to surround the test sample. The ventilation chamber is a container that opens upwards. The relative humidity of the air-conditioning chamber is adjustable by means of various saturated saline solutions by placing in the container a saturated saline solution which gives the desired relative humidity. Table 1 shows 10 suitable saline solutions and their relative humidity values. Silica gel gives 0% relative humidity and water 100% relative humidity. There is a water bath around the air-conditioning chamber, which can also be raised and lowered. The water bath can be used to regulate the temperature of the air-15 chamber. The apparatus is operated by placing a small amount of sample in a sample container on a microbalance and performing an initial weighing. The air conditioning chamber is then raised around the sample container. By monitoring and retrieving the sample readings 20 provided by the sample, the moisture erosion of the sample is obtained as a function of time. When the weight of the sample no longer changes, the equilibrium moisture content of the sample is. attained in relative humidity. By conducting a similar experiment on another sample and on an air-conditioning chamber, where:: there is another relative humidity (i.e., with another salt), it is obtained. equilibrium moisture content of the substance relative to one another; when moisture is present. Said equilibrium moisture values form points on the adsorption / desorption isotherm curve of the substance.

When studying the moisture behavior of a substance and making its' · '' 30 isotherm curve, several measurements should be used for each: ·: per point of the curve. With the device described above, this is done by performing several successive experiments in the same '. in relative humidity. However, this is very time consuming as it takes about several hours to reach the equilibrium moisture content.

5 4 108674 ί i

Table 1 Certain salts and relative humidities provided by their aqueous saturated solutions

Salt Relative Humidity,%

20 ° C 25 ° C 30 ° C

10 LiClxH20 12.4 12.0 11.8 CHjCOOK 23.3 22.7 22.0

MgCl2x6H20 33.6 33.2 32.8 K2C03x2H20 44.0 43.8 43.5 KN02 49.0 48.1 47.2 15 Mg (NO3) 2x6H20 54.9 53.4 52.0

NaN02 65.3 64.3 63.3

NaCl 75.5 75.8 75.6 (NH4) 2SO, 80.6 80.3 80.0 KN03 93.2 92.0 90.7 20 K2SOi SI .2 96.9 96.6 i

A solution has now been found whereby several samples can be placed simultaneously in a humidity chamber. This procedure allows the necessary parallel tests to be carried out during the same test period, thus significantly speeding up the examination of the substance.

The features of the invention are set forth in claims 1 and 30 3.

• · «» 1

The invention will now be described with reference to the accompanying drawings, in which *%. Figure 1 shows the adsorption and desorption isotherms of an agent

Figure 2 shows the weight change of one substance as a function of time when dry samples are exposed to various atmospheres of humidity • · »» · ·

Figure 3 shows a device according to the invention

Figure 4 shows a sample carousel of the device of Figure 3 according to one embodiment

Figure 5 shows another embodiment of the carousel of the device of Figure 3

Fig. 6 shows a sample container with a handle 5 Fig. 3 shows an apparatus solution for carrying out the iron method of the invention. The apparatus comprises a scale 1 coupled to a programmed processor 15 on which hangs a hanging wire 3 / on which a sample vessel 20 is suspended. Figure 4 shows in more detail how the different sample vessels 10 20a, 20b, 20c ... are positioned in the carousel 4. sample container 20 is provided with a handle for lifting 25 containers. The sample container is suitably wide-bottomed so that the sample can be applied in a thin layer so that the sample is effectively ventilated.

15 The air conditioning chamber 2 can be arranged around the carousel 4 by means of a lifting device 9. The desired relative humidity in the venting chamber 2 can be obtained by placing the drill bits 2 in a suitable saturated saline solution 7. The rotating movement of the vertical axis 16 coupled to the motor 5 · '·' is conveyed to: The temperature of the air-conditioning chamber 2 is adjustable by the surrounding water bath 8, i In Figure 3, the air-conditioning chamber 2 with the surrounding water bath 8 is shown in its raised state. The humidity and temperature la-sensors are designated by reference numeral 6. Reference numeral 13 telecommunication wires.

Reference numeral 14 denotes data for a processor and a motor 5 for a carousel 4 and a motor 10 for a crane 9 | Transport wires. Reference numeral 11 represents the body of the device and: 12 12 horizontal protective housing. Vertical connected to carousel 4. the shaft 16 is arranged to move the longitudinal direction indicated by the arrow ....

Here's how to use the device. With the crane 9, the air-conditioning chamber 2 with the water bath 8 is lowered 8. Samples N1, N2, ß 6 108674 Ν3 ... are placed in sample containers 20a, 20b, 20c ..., the tare of which has been weighed first. The motor 5 raises the vertical axis so that the plate 4 is positioned at such a height that the hook of the hanging wire 3 goes into the lug 5 25a of the sample container 20a when the plate 4 is rotated clockwise by the motor 5. When the sample container is hooked, the rotary movement of the plate 4 is stopped and the plate 4 is lowered, leaving the sample container suspended on the hanging wire 3 and weighing takes place. The weighing reading is transferred to the processor 15. After weighing 10, the plate 4 is lifted so that the sample vessel 20a is resting on the plate, rotated the plate slightly counterclockwise to release the hook of the hanging wire 3, lowered and rotated clockwise. The plate is then raised to a suitable height 15 to secure the next sample container 20b by means of a hook for the hanging wire 3 and the procedure described above is repeated for each container. For the successful weighing of the various containers as described above, it is important that the containers are located at the same distance from the center of the plate 20, and thus the plate 4 may have marked locations for the sample containers. The control is suitably such that the rotary movement of the plate is stopped during the lifting and lowering of the plate. The initial weighing of the various samples should be: · carried out in the shortest possible time so that the plate is rotated rapidly to the next sample to be weighed.

When the initial weighing of each sample N1, N2, N3 ... is completed, the air conditioning chamber 2 is raised so that it • surrounds the carousel with its samples and weighs the sample vessels alternately »· · as described above. The computer program records the weighing reading and the time of each 30 samples. The test can be; performs such that after the first weighing cycle, immediately following the next weighing cycle, etc. Then carousel. li is constantly on the move. Alternatively, a different break may be taken after the various weighing rounds. This can be well done if the weighing readings of the samples do not change very rapidly as a function of time in the atmosphere in the ventilation chamber. From the same test substance taken-! On the basis of the weighing readings of samples N1, N2, N3 ..., the processor can be used to calculate the respective weight. the moisture adsorption or moisture desorption curve of the substance which best corresponds to all the weights obtained.

5 If it is desired to study the moisture behavior of several different substances, the same can be sampled and examined in parallel during the same test period. On the basis of the weights N1, N2, N3 ... of the samples taken from the various substances under study, the processor calculates the moisture adsorption or desorption curves of the 10 different substances, with each curve being the most appropriate. substance weighing readings.

If the moisture content of the test substance is determined by a different test and the value is fed to the processor and if the weighing in the air-conditioning chamber is carried out until the weight of the different samples no longer changes over time, the processor can be calculated. equilibrium moisture content I of the substance at ambient temperature and relative humidity.

* · ”20 Alternatively, the carousel 4 may be a vertically-rotating, '·' circular plate as shown in Figure 5. The axis of the plate: through the center, passes through an axis (not shown in the figure) at right angles to the vertical axis 16 and transmits it; 'j'; rotary movement plate 4. In this solution, there are preferably trays for sample containers (trays not; shown in the figure). Suitably, the supports are mounted on the plate 4 i «· I !. 'so that their position remains constant in the rotational movement of the plate. despite who. This is simply an example of arranging weights,! 30 that prevent them from turning upside down.

'! »·· ... The method of the invention is, of course, practicable with hardware solutions other than those described above. For example, it is very possible that the plate on which the sample containers 35 rest is making a reciprocating motion instead of the rotating motion 8 108674 described above. It is also conceivable that the hanging wire connected horizontally is movable and the plate and the sample containers are stationary.

It will be apparent to one skilled in the art that various embodiments of the invention may vary within the scope of the following claims.

* i «*» ♦ ♦ * I * t * * I 't t I »» I ♦ »1 · · • * * l I I *

Claims (9)

A method for examining the moisture adsorption or desorption of a powdered substance, wherein a sample of the substance to be tested is weighed at the beginning of the experiment by a path connected to a programmed processor; the sample is subjected to an atmosphere of known relative humidity; the sample is weighed in this atmosphere for consecutive times and the weighing results are input to the processor, and the successive weights are performed for a desired time, whereby - at the beginning of the test, weights are performed by multiple samples N1, N2, N3 ... representing the same or various substances to be examined; 15. The samples are simultaneously exposed to an atmosphere of known relative humidity; - the repeated samples are weighed repeatedly in this atmosphere and the measured weights of the samples and the weighing time of the sample are recorded by the processor, characterized in that - the powdered sample is spread as a thin layer for effective air conditioning of the sample, the substance is calculated by the processor on the basis of the. The successive weights, which best correspond to all measured weights for the said substance, and • · · • II - at the beginning of the experiment, the moisture content of the samples is fed into the process and the weights are carried out until the weight of the different samples no longer changes as a function of time, and: the equilibrium moisture content of said substance is calculated in the rescuer; atmospheric temperature and relative humidity. Method according to claim 1, characterized in that the temperature of the atmosphere is controlled during the test time to a desired level. Apparatus for examining a powdered substance for adsorption or desorption by a method according to claim 1, wherein the apparatus comprises a sample vessel (20), a path (1), a programmed processor (15), an air conditioning chamber (2). ), a lifting device (9) for arranging the air conditioning chamber around the sample to be examined, a test vessel carousel (4), and the carousel's driving and control devices (5, 16), characterized in that - several test vessels (4) are arranged on the carousel (4) 20a, 20b, 20c ...) and that the 10. test vessels (20a, 20b, 20c ...) are broad-bottomed for propagating the powdered samples. 4. Apparatus according to claim 3, characterized in that the carousel is a circular disk rotating in a horizontal plane, around whose center a vertical axis (16) runs, the rotational movement of the shaft (16) being mediated to the disk (4). 5. Device according to claim 3, characterized in that the 2. carousel is a circular disc (4) rotating in a vertical pane, around which its center point runs an axis which is at a right angle to the vertical axis (16) and communicates. its rotational movement to the disk (4), and that sample vessel support is stored on the disk. (4) say that their position is constant independent of: the rotational movement of the disc. 6. Device according to claim 4 or 5, characterized in that the disk (4) has locations reserved for test vessels, all of which are arranged at separate distances from the center of the disk. Device according to claim 4, 5 or 6, characterized in that the vertical shaft (16) is arranged to be movable also 35 its longitudinal direction. »I t * · * Apparatus according to any of claims 3 to 7, characterized in that each test vessel (20) is provided with a handle (25) and that the road (1) is joined with a suspension tree (3) provided with a hook. . Device according to any of claims 3 to 8, characterized in that the temperature of the air-conditioning chamber (2) is adjustable, for example by means of a water bath (8) surrounding it. · • · · * a * · · • a * a * a * »* 1 a * · a * 1 1 · 1 1 · •« · 1 1 »a • 1 k ·