A salt restored from discoloration and a method for this restoration

Abstract: A salt sterilized by radioactive radiation, e g gamma irradiation and/or beta irradiation of the type which obtains a discoloration on irradiation, characterized in that its original colour is wholly or partly restored. The invention relates also to the actual method for restoring the original colour of such a salt and the method is characterized in that it takes place with the help of heating to appropriate temperatures for appropriate durations of treatment.

Description: TECHNICAL FIELD The present invention relates to a salt sterilized by radioactive radiation e g gamma irradiation and/or beta irradiation of the type which obtains a discoloration on irradiation. In the first place this refers to salts intended to be used for medical purposes, e g in dialysis for the preparation of dialysis liquid. A probable explanation of the discoloration is that it is due to an electron displacement, that is to say to one or more electrons being made to change electron orbit and thereby getting into an excited state. BACKGROUND ART Unpublished experiments aimed at restoring the original colour of the irradiated salt have been carried out with the help of daylight, UV-ligt and microwaves. However, no evident effect was achieved. Alternatively it is possible to refrain from irradiation and use instead a bacteria filter for the filtering out of undesirable substances after the salt has been dissolved in water or other suitable liquid. Difficulties can arise here in maintaining this bacteria filter sterile. They may be overcome, though, in the manner which is described, for example, in the American patent specification 4 783 273. A further method consists in using a powder which is as pure as possible, and dissolving the same directly in connection with its utilization. See, for example, American patent specification 4 784 495. It is not possible here, however, to guarantee absolute sterility. DISCLOSURE OF INVENTION The salt in accordance with the invention, that is to say a salt sterilized by radio-active radiation, e g gamma irradiation and/or beta irradiation of the type which obtains a discoloration on irradiation is characterized in that its original colour is wholly or partly restored by heat during a time period depending on the temperature and long enough to restore the original colour at least partly or recrystallization in a wholly sterile environment. In this manner the problems mentioned above can be fully solved. In particular the invention relates in the first place to sodium hydrogen carbonate and sodium chloride, that is to say salts which are frequently used in connection with, for example, dialysis, hemofiltration and plasmaferes. The salts may be dissolved directly in conjunction with the medical treatment, as described in the above mentioned American patent 4 784 495. Also by such a use it is, however, desirable for the powder to be present in the form of a wholly sterile natural-coloured powder. The invention also related to the actual method for restoring the orginal colour of a salt sterilized by radioactive radiation of the type which obtains a discoloration on irradiation. This method is characterized in that it takes place with the help of heating during a time period depending on the temperature and long enough to restore the original colour at least partly. Insofar as the treatment of irradiated sodium hydrogen carbonate is concerned, the temperature and duration of treatment may be selected according to approximately the following relations: a) one day at 65°C resulting in a diminishing discoloration, b) three days at 75°C resulting in a natural-coloured substantially white powder, c) one day at 85°C resulting in a natural-coloured, substantially white powder, d) 6 hours at 95°C resulting in a natural-coloured, substantially white powder, e) 3 hours at 105°C resulting in a natural-coloured, substantially white powder. For information it may be added that one day's treatment at approximately 55°C did not produce any objectively detectable change of colour. Furthermore, it has been found that no changes of temperatures or durations of treatment were required when changing the irradiation dose for sodium hydrogen carbonate from 25kGy to 50 kGy. On the other hand it has been established that sodium hydrogen carbonate of analytically pure quality obtains a less pink coloration than the corresponding standard quality for medical usage. Insofar as the treatment of irradiated sodium chloride is concerned, the temperature and duration of treatment should be selected according to the following relation: one day at 150°C resulting in a natural-coloured, substantially white powder. For information it may be added that a treatment at 100°C during one day proved to have no effect on the powder coloured orange-brown as a result of irradiation. Alternatively the discoloration can be eliminated by means of recrystallization with the help of sterile water. In the process a saturated solution is produced from which the salt can be precipitated again, thereafter to be separated from surplus liquid and dried. The whole has to be carried out, of course, in completely sterile environment and the same applies to subsequent storage which may be done, for example, in small completely bacteria-tight packages. Naturally the invention is not limited solely to the examples described above but can be varied within the framework of the subsequent claims. For example it will be clear to those versed in the art that there are probably common properties of many salts which bring about the discoloration obtained on radioactive irradiation. For this reason is should be possible for many salts other than those mentioned as examples to be treated by the method in accordance with the invention.

Claims: A salt sterilized by radioactive radiation, e g gamma irradiation and/or beta irradiation, of the type which obtains a discoloration on irradiation, characterized in that its original colour is wholly or partly restored by means of heat or recrystallization in a wholly sterile environment. A salt in accordance with claim 1, characterized in that it consists of sodium hydrogen carbonate or sodium chloride. A salt in accordance with claim 1 or 2, characterized in that its original colour is restored by means of heat during a time period depending on the temperature and long enough to restore the original colour at least partly. A method for restoring the original colour of a salt sterilized by radioactive radiation of the type which obtains a discoloration on irradiation, characterized in that it is carried out with the help of heating during a time period depending on the temperature and long enough to restore the original colour at least partly. A method in accordance with claim 4 in the treatment of irradiated sodium hydrogen carbonate characterized in that temperature and duration of treatment are selected according to the following relations: a) one day at 65°C resulting in a diminishing discoloration, b) three days at 75°C resulting in a natural-coloured substantially white powder, c) one day at 85°C resulting in a natural-coloured substantially white powder, d) six hours at 95°C resulting in a natural-coloured, substantially white powder, e) three hours at 105°C resulting in a natural-coloured, substantially white powder. A method in accordance with claim 4 or 5, characterized in that duration and temperature are selected independently of the dose of radiation which may be, for example, 25 kGy or 50 kGy. A method in accordance with claim 4 in the treatment of irradiated sodium chloride, characterized in that temperature and duration of treatment are selected according to the following relation: one day at 150°C resulting in a natural-coloured, substantially white powder. A method for restoring the original colour of a salt sterilized by radioactive radiation of the type which obtains a discoloration on irradiation, characterized in that it takes place with the help of recrystallization in a wholly sterile environment. A method in accordance with claim 8, characterized in that the irradiation salt is dissolved with the help of sterile water, made into a saturated solution, caused to precipitate, separated from surplus water and dried.

Inventors: LINDQVIST STEN-BOERJE, LINDQVIST, STEN-BOERJE, Lindqvist, Sten-Börje
Applicants: GAMBRO AB
Application year: 1990
Main classification: A61L2
IPC codes: A61L2, C01D3, A61M1, C01D7