Adsorbent Cartridge Capable of Long-Term Storage

Abstract

Disclosed in this abstract is an adsorbent cartridge, a first layer made of activated carbon, and a second layer in direct contact with the first layer, the second layer including a second layer made of one or both of zirconium hydroxide and zirconium phosphate, wherein the first layer has a moisture content of X wt%, the second layer has a moisture content of Y wt%, and the difference in moisture content between the first layer and the second layer is 8 wt% or less.

Description

Technical Field

[0001] The present invention relates to an adsorbent cartridge that can be stored for a long time. The improvement of the storage period is achieved by applying the adsorbent in the form of a layer with the smallest difference in water content between layers.

Background Art

[0002] The description or consideration of prior published documents in this specification should not necessarily be construed as an admission that such documents are part of the art or common general knowledge.

[0003] Adsorbents are useful for kidney dialysis, particularly for removing toxins present in dialysis fluid. Examples include ion exchangers such as zirconium phosphate (ZP) and hydrated zirconium oxide (HZO), uremic toxin removing components such as activated carbon (AC) and (immobilized) urease. Various components contained in the adsorbent are often provided as part of separate layers within the cartridge. A cartridge composed of an adsorbent is known as an adsorbent cartridge.

[0004] Patients who require dialysis often undergo treatment at home overnight because they can lead a relatively normal life during the day and avoid frequent visits to the dialysis center. For this purpose, it is necessary to store all the materials required for dialysis, such as the dialysis device, dialysis fluid, and adsorbent cartridge, at home. The ability to store these components for a long time is convenient for patients to reduce the frequency of receiving bulk deliveries.

[0005] Problems associated with layered adsorbent cartridges are that the layers may separate or cracks may occur, and other adsorbent incompleteness or non-uniformity may occur during storage (e.g., after just two weeks). The gaps formed by such layer separation or cracks, and the incompleteness or non-uniformity greatly affect the flow of dialysis fluid through the adsorbent, thereby reducing the effectiveness of the adsorbent in removing toxins from the dialysis fluid and impairing the effectiveness of the treatment.

[0006] Therefore, there is a need for an adsorbent cartridge that can be stably stored for at least 8 weeks, preferably up to 12 months or more. SUMMARY OF THE INVENTION

[0007] The water content of the ion exchange material in the adsorbent plays an important role in the effectiveness of ion exchange. For example, the inventors have found that the ion exchange efficacy of zirconium phosphate and zirconium oxide can be optimized when their water contents are about 20-23 wt% and 35-40 wt% respectively. In contrast, the inventors have found that the water content of the activated carbon layer, which is another central component of the adsorbent, is usually provided at a much lower water content of about 8 wt%.

[0008] The inventors have surprisingly found that minimizing the difference in water levels between the layers of zirconium phosphate / zirconium oxide / activated carbon in the adsorbent results in much longer-term stability of the adsorbent. This can be achieved without significantly affecting the ion exchange capacity of the adsorbent. Without wishing to be bound by theory, it is believed that a substantial difference in water levels leads to layer separation of the adsorbent having adjacent layers of zirconium phosphate / zirconium oxide / activated carbon during longer-term storage, and this problem can be avoided by minimizing this difference.

[0009] Accordingly, the present invention provides the following numbered clauses.

[0010] 1. An adsorbent cartridge comprising: a first layer consisting of activated carbon, and a second layer in direct contact with the first layer, the second layer comprising a second layer consisting of one or both of hydrated zirconium oxide and zirconium phosphate, wherein the first layer has a water content of X wt%, the second layer has a water content of Y wt%, and the difference in water content between the first layer and the second layer is 8 wt% or less.

[0011] 2. The adsorbent cartridge according to clause 1, wherein the second layer contains both zirconium hydroxide and zirconium phosphate.

[0012] 3. The adsorbent cartridge according to clause 2, wherein the second layer consists of a homogeneous mixture of zirconium hydroxide and zirconium phosphate.

[0013] 4. The adsorbent cartridge according to clause 1, wherein the second layer consists of one of zirconium phosphate and zirconium hydroxide, the adsorbent cartridge further includes a third layer consisting of the other zirconium that is not present in the second layer among zirconium phosphate and zirconium hydroxide, the third layer has a moisture content of Z weight %, and the difference in moisture content between the second layer and the third layer is 8 weight % or less.

[0014] 5. The adsorbent cartridge according to clause 4, configured such that during use, the dialysate passes through the layer consisting of zirconium phosphate before passing through the layer consisting of zirconium hydroxide.

[0015] 6. The adsorbent cartridge according to any one of the preceding clauses, wherein the difference in moisture content between the first layer and the second layer is 5 weight % or less.

[0016] 7. The adsorbent cartridge according to clause 6, wherein the difference in moisture content between the first layer and the second layer is 4 weight % or less, and optionally 3 weight % or less.

[0017] 8. The adsorbent cartridge according to clause 4 or clause 5, wherein the difference in moisture content between the second layer and the third layer is 5 weight % or less.

[0018] 9. The adsorbent cartridge according to clause 8, wherein the difference in moisture content between the second layer and the third layer is 4 weight % or less, and optionally 3 weight % or less.

[0019] 10. The difference between the moisture content of the first layer and the weighted average of the moisture contents of the second and third layers is 8% by weight or less, optionally 5% by weight or less, more optionally 4% by weight or less, for example 3% by weight or less, the adsorbent cartridge according to any one of items 4, 5, 8, and 9, wherein the weighted average of the moisture contents of the second and third layers is based on the mass of zirconium hydroxide and the mass of zirconium phosphate.

[0020] 11. The adsorbent cartridge according to any one of the preceding items, wherein the first layer has a moisture content of 20 to 35% by weight, optionally 23 to 30% by weight, or 25 to 35% by weight.

[0021] 12. The adsorbent cartridge according to any one of the preceding items, wherein the second layer has a moisture content of 20 to 35% by weight, optionally 23 to 30% by weight, or 25 to 35% by weight.

[0022] 13. The adsorbent cartridge according to any one of items 4, 5, and 8 to 12, wherein the third layer has a moisture content of 20 to 35% by weight, optionally 23 to 30% by weight, or 25 to 35% by weight.

[0023] 14. The adsorbent cartridge according to item 4, or any one of items 5 and 8 to 13 dependent on item 4, wherein the layer composed of zirconium hydroxide has a moisture content of 25 to 35% by weight.

[0024] 15. The adsorbent cartridge according to item 3, or any one of items 6, 7, 11, 12, or 13 dependent on item 3, wherein the moisture content of the second layer composed of a homogeneous mixture of zirconium hydroxide and zirconium phosphate is 23 to 30% by weight.

[0025] 16. The adsorbent cartridge according to any one of the preceding items, further comprising a urease layer composed of immobilized urease.

[0026] 17. The adsorbent cartridge according to item 16, wherein the urease layer has a water content of 17 to 27% by weight, for example 19 to 25% by weight, for example 20 to 24% by weight.

[0027] 18. The adsorbent cartridge according to item 16 or 17, wherein the urease layer is in direct contact with at least one of the first layer, the second layer, and, if present, the third layer, and the difference in water content between the urease layer and the layer with which the urease layer is in direct contact is 8% by weight or less, for example 5% by weight or less, 4% by weight or less, or 3% by weight or less, and optionally, the adsorbent cartridge is configured such that, during use, the urease layer is located upstream of the layer composed of zirconium phosphate. Optionally, the adsorbent cartridge is configured such that, during use, the urease layer is located upstream of the layer composed of zirconium phosphate.

[0028] 19. The adsorbent cartridge according to any one of the preceding clauses, wherein the water contents of the first layer, the second layer, and, if present, the third layer and the urease layer are determined by loss on drying.

[0029] 20. The adsorbent cartridge according to item 19, wherein the water contents of the first layer, the second layer, and, if present, the third layer and the urease layer are determined by loss on drying using a Radwag MA200.3Y moisture analyzer at a temperature of 180 to 220 °C, optionally about 210 °C.

Brief Description of the Drawings

[0030]

Figure 1

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Figure 6

[0031] As described in this specification, the binding ability of the ion-exchange substances (e.g., zirconium phosphate and hydrated zirconium hydroxide) in the adsorbent depends on the water content of the ion-exchange substances, as shown in Table 1. [Table 1]

[0032] Activated carbon is a common adsorbent component and is commercially available with a water content of about 8% by weight. This is significantly different from the preferred water content of ZP and HZO when used in peritoneal dialysis. Without wishing to be bound by theory, the inventors believe that an adsorbent formed from commercially available AC and layers of ZP and HZO with the desired water content is likely to crack or separate during long-term storage (Comparative Examples 1 and 2). As used in this context, the terms "crack" and "separation" are intended to refer to gaps or voids formed within a previously compressed solid powder, at any angle, vertical, horizontal, or intermediate. Such gaps or voids may form between different layers of the adsorbent or within the layers of the adsorbent.

[0033] The present invention solves the problems associated with the prior art. Accordingly, the present invention provides an adsorbent cartridge having the following configuration: a first layer made of activated carbon, and a second layer in direct contact with the first layer, the second layer including a second layer made of one or both of hydrated zirconium hydroxide and zirconium phosphate, wherein the first layer has a water content of X% by weight, the second layer has a water content of Y% by weight, and the difference in water content between the first layer and the second layer is 8% by weight or less.

[0034] In the embodiments of this specification, the term "consisting of" can be interpreted as requiring the described features but not limiting the presence of other features. Alternatively, the term "comprising" may be relevant in situations where it is intended that only the listed components / features are present (for example, the term "comprising" can be replaced with the expressions "comprises of" or "comprises essentially of"). It is explicitly contemplated that both a broader interpretation and a narrower interpretation can be applied to all aspects and embodiments of the present invention. In other words, the term "comprising" and its synonyms can be replaced with the term "consisting of" or the term "consisting essentially of" or their synonyms, and vice versa.

[0035] As used herein, the "adsorbent cartridge" refers to a container made of a material capable of removing toxins from the dialysate, that is, an adsorbent cartridge for kidney dialysis. More specifically, the adsorbent cartridge for kidney dialysis of the present invention may be suitable for use in peritoneal dialysis.

[0036] The adsorbent cartridge of the present invention comprises at least two layers, namely a first layer made of activated carbon and a second layer made of one or both of zirconium hydroxide hydrate and zirconium phosphate. The second layer is in direct contact with the first layer.

[0037] Both the first layer and the second layer have a moisture content, which is denoted as X wt% and Y wt% respectively herein. The difference in the moisture content between the first layer and the second layer is 8 wt% or less. In other words, the difference between X and Y is 8 or less.

[0038] As used herein, the "water content" of a layer refers to the amount of liquid adsorbed or absorbed in the solid components of the layer. Typically, the water content is mainly composed of water, but other liquids may also form part of the overall water content. In some embodiments of the invention that may be referred to herein, the water content of a layer may refer to the water content of that layer. In some embodiments of the invention that may be referred to herein, the water content of a layer is the same as the weight loss on drying of that layer, for example, the weight loss on drying at a temperature of 210°C of that layer (e.g., measured by a Radwag MA200.3Y moisture analyzer at 210°C). For example, a solid sample (e.g., 1 - 2 g) can be placed in a Radwag MA200.3Y moisture analyzer and a weight loss on drying experiment can be carried out at a temperature of 210°C. In this experiment, the sample is heated at a temperature of 210°C until the instrument determines the weight loss on drying.

[0039] In some embodiments of the invention that may be referred to herein, the second layer may consist of zirconium hydroxide hydrate. Then, the adsorbent cartridge may include a third layer consisting of zirconium phosphate. An example of such an embodiment is shown graphically in FIG. 1, where 101 represents activated carbon, 102 represents zirconium hydroxide hydrate, and 103 represents zirconium phosphate.

[0040] In some embodiments of the invention that may be referred to herein, the second layer may consist of zirconium phosphate. Then, the adsorbent cartridge may include a third layer consisting of zirconium hydroxide hydrate. These embodiments correspond to those shown in FIG. 1 where layers 102 and 103 are reversed.

[0041] When the third layer is present, it has a water content of Z wt%, and may be in direct contact with the second layer. In such embodiments of the invention, the difference in water content between the second layer and the third layer may be 8 wt% or less. In other words, the difference between Y and Z may be 8 or less.

[0042] In an embodiment of the present invention in which the adsorbent cartridge comprises separate layers of zirconium phosphate and hydrated zirconium hydroxide, during use, the dialysate may pass through the layer of zirconium phosphate before passing through the layer of hydrated zirconium hydroxide. Thus, in the embodiment shown in FIG. 1, the dialysate may first pass through layer 103, then through layer 102, and finally through layer 101. If layers 102 and 103 are reversed such that zirconium phosphate is present in the intermediate layer, the dialysate may first pass through the activated carbon layer, then through the zirconium phosphate intermediate layer, and finally through the hydrated zirconium hydroxide layer.

[0043] In some embodiments of the invention that may be referred to herein, the second layer may consist of hydrated zirconium hydroxide and zirconium phosphate (e.g., a homogeneous mixture of hydrated zirconium hydroxide and zirconium phosphate). An example of such an embodiment is shown graphically in FIG. 2, where 201 represents activated carbon and 202 represents a layer consisting of both hydrated zirconium hydroxide and zirconium phosphate.

[0044] In embodiments of the invention that may be referred to herein, the difference in moisture content between adjacent layers (e.g., the first layer and the second layer, or the second layer and the third layer) may be 8 wt% or less. In further embodiments of the invention that may be referred to herein, the difference in moisture content between adjacent layers may be 5 wt% or less, 4 wt% or less, or 3 wt% or less. As will be correctly understood by those skilled in the art, these values apply equally to the difference in moisture content between the first layer and the second layer and to the difference in moisture content between the second layer and the third layer. All possible combinations of moisture content differences between layers are explicitly contemplated herein.

[0045] In an embodiment of the present invention in which the second layer consists of one of zirconium phosphate and hydrated zirconium hydroxide and the third layer consists of the other of zirconium phosphate and hydrated zirconium hydroxide, the difference between the moisture content of the first layer and the weighted average of the moisture contents of the second and third layers may be 8 wt% or less (e.g., 5 wt% or less, e.g., 4 wt% or less, e.g., 3 wt% or less).

[0046] In such an embodiment, the weighted average of the water content rates of the second layer and the third layer is based on the mass of zirconium hydroxide hydrate and the mass of zirconium phosphate in these layers.

[0047] In some embodiments of the present invention that may be referred to herein, the small difference in water content rate between the first layer and the second layer can be obtained by using an activated carbon layer (first layer) having a higher water content rate than commercially available activated carbon. By increasing the water content rate of the activated carbon, the difference in water content rate between the layers can be reduced without significantly reducing the water content rates of zirconium hydroxide hydrate and zirconium phosphate. In this way, the difference in water content rate across the layer boundary can be reduced without impairing the ion exchange ability of the ion exchange compounds (zirconium hydroxide hydrate and zirconium phosphate). On the other hand, if the water content rates of zirconium hydroxide hydrate and zirconium phosphate are too low, as shown in Table 1 above, the ion exchange ability may be impaired.

[0048] In some embodiments of the present invention that may be referred to herein, the first layer may have a water content rate of 20 to 35% by weight, for example 23 to 30% by weight or 25 to 35% by weight. As will be correctly understood by those skilled in the art, when the first layer has the water content rate according to this embodiment, the difference in water content rate between the first layer and the second layer is 8% by weight or less (for example, the second layer may have a water content rate of 12 to 43% by weight). In some aspects of this embodiment of the present invention, the second layer may also have a water content rate of 20 to 35% by weight, for example 23 to 30% by weight or 25 to 35% by weight.

[0049] In some embodiments of the invention that may be referred to herein, the second layer may have a water content of 20 to 35% by weight, such as 23 to 30% by weight or 25 to 35% by weight. As will be correctly understood by those skilled in the art, when the second layer has a water content according to this embodiment, the difference in water content between the first layer and the second layer is 8% by weight or less (for example, the first layer may have a water content of 12 to 43% by weight). In some aspects of this embodiment of the invention, the first layer may also have a water content of 20 to 35% by weight, such as 23 to 30% by weight or 25 to 35% by weight.

[0050] In some embodiments of the invention that may be referred to herein, the third layer, if present, may have a water content of 20 to 35% by weight, optionally 23 to 30% by weight or 25 to 35% by weight. As will be correctly understood by those skilled in the art, when the third layer has a water content according to this embodiment, the difference in water content between the second layer and the third layer is 8% by weight or less (for example, the second layer may have a water content of 12 to 43% by weight). In some aspects of this embodiment of the invention, the second layer may also have a water content of 20 to 35% by weight, such as 23 to 30% by weight or 25 to 35% by weight.

[0051] In an embodiment of the invention consisting of separate layers of zirconium phosphate and hydrated zirconium hydroxide that may be referred to herein, the layer consisting of hydrated zirconium hydroxide may have a water content of 25 to 35% by weight.

[0052] In an embodiment of the invention in which the second layer consists of both zirconium phosphate and hydrated zirconium hydroxide (for example, a homogeneous mixture of zirconium phosphate and hydrated zirconium hydroxide) that may be referred to herein, the water content of the second layer consisting of the homogeneous mixture of hydrated zirconium hydroxide and zirconium phosphate may be 23 to 30% by weight.

[0053] The above weight % values are considered advantageous as they avoid cracks or separation between layers while providing a water content sufficient for the effective ion exchange of zirconium phosphate and zirconium oxyhydroxide during dialysis.

[0054] As will be correctly understood by those skilled in the art, the adsorbent cartridge of the present invention may include additional layers. For example, in some embodiments of the present invention that may be referred to herein, the adsorbent cartridge may include a urease layer composed of immobilized urease. In some such embodiments, the urease layer may have a water content of 17 to 27 wt%, such as 19 to 25 wt%, such as 20 to 24 wt%.

[0055] In embodiments of the present invention where a urease layer is present, the urease layer may be in direct contact with at least one of the first layer, the second layer, and, if present, the third layer. The difference in water content between the urease layer and the layer with which the urease layer is in direct contact may be 8 wt% or less, such as 5 wt% or less, 4 wt% or less, or 3 wt% or less.

[0056] In embodiments of the present invention where a urease layer is present, the urease layer is preferably located in the upstream layer as compared to the layer composed of zirconium phosphate. This is because the urease layer generates ammonia, and this ammonia needs to be removed from the fluid passing through the adsorbent and not passed on to the patient. Ammonia may be removed by zirconium phosphate, and thus the urease layer is preferably disposed upstream of the zirconium phosphate layer.

[0057] The present invention is illustrated by the following examples, which should not be construed in a limiting sense.

Examples

[0058] Abbreviations: AC = activated carbon ZP = zirconium phosphate HZO = zirconium oxyhydroxide LOD = Loss on drying All materials were obtained from commercial suppliers and used without further purification.

[0059] General method

[0060] In the following examples and comparative examples, the layered adsorbent was prepared according to the following method.

[0061] Layer 1 (activated carbon) with a loss on drying (LOD) of 8 - 10% was obtained from a commercial supplier.

[0062] Layer 1 (activated carbon) with an LOD of 20 - 25% was prepared by adjusting the moisture content of the AC. Deionized water was added to the AC with an LOD of 8%, and the mixture was stirred at 25 °C for 5 - 10 minutes using an overhead stirrer. Next, the LOD was measured at a temperature of 210 °C using a Radwag MA200.3Y moisture content analyzer.

[0063] The following equation was used to obtain activated carbon with an LOD of 25% from 100 g of activated carbon with an LOD of 8%.

Equation

[0064] The layer composed of zirconium phosphate and hydrated zirconium hydroxide was prepared by mixing specified amounts of ZP and HZO. ZP with an LOD of 20 - 25% and HZO with an LOD of 35 - 40% were obtained from commercial suppliers. HZO with an LOD of 25% was obtained by heating commercially available HZO with a known LOD until the required weight loss occurred.

[0065] The weight loss on drying was analyzed as follows. A solid sample (e.g., 1 - 2 g) was placed in a Radwag MA200.3Y moisture content analyzer, and an experiment on weight loss on drying was conducted at a temperature of 210°C. In this experiment, the sample was heated at 210°C until the instrument determined the weight loss on drying.

[0066] Comparative Example 1

[0067] Two - layer comparative adsorbent 1 was prepared with the layers shown in Table 2 below.

Table 2

[0068] Comparative adsorbent 1 is a conventional adsorbent, and different layers have typical moisture levels known in the art. The difference in moisture content between layer 1 and layer 2 is about 12%.

[0069] Photographs of the results of a 9 - week storage test at ambient conditions / room temperature are shown in Figure 3. (A) shows comparative adsorbent 1 at week 0, and (B) shows comparative adsorbent 1 at week 9. The black part in this figure is the AC layer, and the white part is the ZP / HZO layer.

[0070] After 9 weeks, as shown within the dashed line, visible cracks and non - uniformity were formed between the layers. Therefore, comparative adsorbent 1 had no 9 - week storage stability.

[0071] Example 1

[0072] Two - layer adsorbent 1 was prepared with the layers shown in Table 3 below.

Table 3

[0073] Adsorbent 1 is the adsorbent described in the present invention, and the difference in moisture content between the two layers is minimized. The difference in moisture content between layer 1 and layer 2 is 0 - 5%.

[0074] Photographs of the test results of storage for 9 weeks under ambient conditions / at room temperature are shown in Fig. 4. (A) shows adsorbent 1 at week 0, and (B) shows adsorbent 1 at week 9. The black part in this figure is the AC layer, and the white part is the ZP / HZO layer.

[0075] After 9 weeks, there were no visible cracks or other non-uniformities between the layers.

[0076] Therefore, it was shown that adsorbent 1 was stable in storage for at least 9 weeks under ambient conditions.

[0077] Comparative Example 2

[0078] Comparative adsorbent 2 was prepared according to Table 4 below.

Table 4

[0079] The difference in moisture content between layer 1 and layer 2 was about 17 - 20%.

[0080] Photographs of the test results of storage for 8 weeks under ambient conditions / at room temperature are shown in Fig. 5. (A) shows the adsorbent cartridge after 2 weeks, (B) shows the adsorbent cartridge after 4 weeks, and (C) shows the adsorbent cartridge after 8 weeks. The black part in this figure is the AC layer, and the white part is the ZP / HZO layer.

[0081] After 2 weeks, defects with different moisture levels and appearances were visible from the boundary between layer 1 and layer 2 to layer 2 (ZP + HZO). These defects grew larger during the 8-week test period. The boundaries of the defects in each period are indicated by the dashed lines in Fig. 4.

[0082] Therefore, comparative adsorbent 2 had no storage stability even for 2 weeks, let alone 8 weeks.

[0083] Example 2

[0084] Adsorbent 2 was prepared according to Table 5 below.

Table 5

[0085] The difference in moisture content between layer 1 and layer 2 is about 1 - 4%.

[0086] Photographs of the test results after storage at ambient conditions / room temperature for 8 weeks are shown in Fig. 6. (A) shows the adsorbent cartridge after 2 weeks, (B) shows the adsorbent cartridge after 4 weeks, and (C) shows the adsorbent cartridge after 8 weeks. The black part in this figure is the AC layer, and the white part is the ZP / HZO layer.

[0087] During the 8 - week test period, no defects, delamination, or cracks were observed between the layers.

[0088] Therefore, it was shown that adsorbent 2 is stable for at least 8 weeks under ambient conditions.

[0089] The above - mentioned examples and comparative examples show that the adsorbent cartridge of the present invention has excellent long - term storage stability and improved stability compared with conventional dialysis adsorbent cartridges in which the difference in moisture content across the layer boundary is not controlled.

Claims

1. Adsorbent cartridge, A first layer made of activated carbon, and A second layer in direct contact with the first layer, wherein the second layer contains either or both of hydrated zirconium oxide and zirconium phosphate. An adsorbent cartridge wherein the first layer has a water content of 20 to 35% by weight, the second layer has a water content of 12 to 43% by weight, the difference in water content between the first and second layers is 8% by weight or less, and the water content of the first and second layers is determined by the drying loss of each layer at a temperature of 210°C.

2. The adsorbent cartridge according to claim 1, wherein the second layer comprises both hydrated zirconium oxide and zirconium phosphate.

3. The adsorbent cartridge according to claim 2, wherein the second layer comprises a homogeneous mixture of hydrated zirconium oxide and zirconium phosphate.

4. The adsorbent cartridge according to claim 1, The second layer consists of one of zirconium phosphate and hydrated zirconium oxide. The adsorbent cartridge further comprises a third layer consisting of the other of zirconium phosphate and hydrated zirconium, which is not present in the second layer. The third layer has a water content of 20 to 35% by weight, and An adsorbent cartridge in which the difference in moisture content between the second layer and the third layer is 8% by weight or less, and the moisture content of the third layer is determined by the loss on drying at a temperature of 210°C.

5. The adsorbent cartridge according to claim 4, configured such that, during use, the dialysis fluid passes through a layer made of zirconium phosphate before passing through a layer made of hydrated zirconium oxide.

6. The adsorbent cartridge according to claim 1, wherein the difference in water content between the first layer and the second layer is 5% by weight or less.

7. The adsorbent cartridge according to claim 6, wherein the difference in water content between the first layer and the second layer is 4% by weight or less, and optionally 3% by weight or less.

8. The adsorbent cartridge according to claim 4, wherein the difference in water content between the second layer and the third layer is 5% by weight or less.

9. The adsorbent cartridge according to claim 8, wherein the difference in water content between the second layer and the third layer is 4% by weight or less, and optionally 3% by weight or less.

10. An adsorbent cartridge according to any one of claims 4, 5, 8, and 9, wherein the difference between the water content of the first layer and the weighted average of the water content of the second and third layers is 5% by weight or less, and more optionally 4% by weight or less, for example 3% by weight or less, An adsorbent cartridge in which the weighted average of the water content of the second and third layers is based on the mass of hydrated zirconium oxide and the mass of zirconium phosphate.

11. The adsorbent cartridge according to claim 1, wherein the first layer has a water content of 23 to 30% by weight or 25 to 35% by weight.

12. The adsorbent cartridge according to claim 1, wherein the second layer has a water content of 20 to 35% by weight, optionally 23 to 30% by weight, or 25 to 35% by weight.

13. The adsorbent cartridge according to claim 4, wherein the third layer has a water content of 23 to 30% by weight or 25 to 35% by weight.

14. The adsorbent cartridge according to claim 4, wherein the layer made of hydrated zirconium oxide has a water content of 25 to 35% by weight.

15. The adsorbent cartridge according to claim 3, wherein the moisture content of the second layer, which consists of a homogeneous mixture of hydrated zirconium oxide and zirconium phosphate, is 23 to 30% by weight.

16. The adsorbent cartridge according to claim 1, further comprising a urease layer containing immobilized urease.

17. The adsorbent cartridge according to claim 16, wherein the urease layer has a water content of 17 to 27% by weight, for example 19 to 25% by weight, for example 20 to 24% by weight, and the water content of the urease layer is determined by the loss on drying at a temperature of 210°C.

18. The adsorbent cartridge according to claim 16 or 17, wherein the urease layer is in direct contact with at least one of the first layer, the second layer, and, if present, the third layer, and the difference in water content between the urease layer and the layer in direct contact with the urease layer is 8% by weight or less, for example, 5% by weight or less, 4% by weight or less, or 3% by weight or less, An adsorbent cartridge, optionally configured such that, when in use, the urease layer is located upstream of the layer made of zirconium phosphate.

19. The adsorbent cartridge according to claim 1, wherein the water content of the first layer, the second layer, and the third layer and urease layer, if present, is determined by the loss on drying using a Radwag MA200.3Y water content analyzer at a temperature of 210°C.

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