食物接触的表面积可按下列方法（Schlegel法）测量： Schlegel method of determining surface area A.1 Principle Under controlled conditions, the test item is coated with an adhesive and dipped in a fluidised bed of water-repellent or perfectly dry glass beads of uniform size. The mass of beads adhering to the item is proportional to the surface area of the test item. The relationship between the mass of beads and the surface area of the item is determined by applying the test to a standard specimen of regular shape and known area. A.2 Apparatus and materials A.2.1 Fluidised bed, bed of glass beads (see A.2.5) with a supply of fluidising air and means for heating the income air if water repellent beads are not used. This may be in the form of an electric heating element, near to the bottom of the bed, regulated by a voltage control, which is sufficient to raise the temperature of the fluidised beads to between 50 °C and 80 °C. Note: it is not advisable to control bead temperature by means of a thermostatic device because, when the power supply is disconnected from the heating element, the beads can pick up moisture from air supply. A.2.2 Laboratory balance capable of weighing to an accuracy of ± 2 mg. A.2.3 Hoist for withdrawing the test item from the adhesive at 20 mm/min. A.2.4 Adhesive composed of: Alkyl resin 1 part by mass Toluene (sulphur free) 1 part by mass A.2.5 Glass beads, graded from 200 mm to 250 mm, preferably of water repellent type. Note: Commercially available glass beads nominally graded to these limits may contain an undesirable proportion outside the limits; normally they should be regraded. A.2.6 Specimens of known area, (at least two) in stainless steel, as follows: a) a cylinder, of approximately 16 mm diameter and 110 mm in length, to indicate the mass of glass beads per square centimetre picked up by hollow handles; b) a rectangle, of approximately 100 mm × 30 mm × 1 mm, to indicate the mass of glass beads per square centimetre picked up by areas other than hollow handles. A.3 Procedure A.3.1 Ensure that the glass beads (see A.2.5), not of the water-repellent type, are thoroughly dry so that they do not adhere to each other. These beads should be prevented from reabsorbing moisture from air supply by preheating them in the fluidised bed at between 50 °C and 80 °C until no beads will adhere to a clean, dry item of cutlery that is dipped into them. Usually a drying time of 1 hour is adequate. Note: It has been found that once moisture has been eliminated, the beads will stay dry while the heating elements remain switched on. Maintain the temperature of the fluidised bed of glass beads at between 50 °C and 80 °C until the procedure described in A.3.8 has been reached. If water-repellent beads are used, the bed may be used at ambient temperature for the procedure described in A.3.7. A.3.2 Attach a thin wire hanger to the test specimen with a loop for suspension during weighing etc. A.3.3 Thoroughly clean the test specimen with methylated spirits. A.3.4 Dip the test specimen in the adhesive (see A.2.4) and withdraw at a rate of 20 mm/min using the hoist (see A.2.3). Do not allow the test specimen surface to come into contact with anything until stage A.3.7 is reached. A.3.5 Allow the adhesive to dry for 60 min ± 5 min. A.3.6 Weigh the test specimen to the nearest 2 mg. A.3.7 Immerse and continuously agitate the test specimen in the fluidised bed of glass beads for 10 s ± 1 s. During immersion the air flow should be vigorous enough to raise mounds of beads to a height of at least 40 mm above the bed of fluidised beads. Do not immerse more suspension wire than necessary. A.3.8 Reweigh the test specimen to the nearest 2 mg. A.3.9 Carry out a duplicate test on each test specimen; include at least two specimens of known area (see A.2.6) in each batch of specimens tested. A.4 Expression of results A.4.1 Method of calculation Calculate the area, A, in square centimetres, of the test specimen using the formula:
A =m/QA
where: m is the mean mass, in grams, of beads adhering to the test specimen; QA is the mean surface mass density, in grams per square centimetre, of beads corresponding to the mass adhering to the relevant specimen of known area.
我的社区
签到
赛默飞实验室产品焕新计划有奖调研！
【七月征文】不一YOUNG实验“猿”
报名开启：ICS2024第十三届光谱网络会议！
推荐收藏！盘点中药材及饮片检测解决方案
