264 Analyst, April, 1968, Vol. 93, $$. 264-265 Accurate Dispensing of Small Volumes of Volatile Liquids with a Micro Syringe and Aluminium Capillary Tubes BY M. ELLISON (Fiscms Ltd., Cambridge Division, Chesterfwd Park Research SM'on, Near Saflron Walden, Essex) A device for delivering and sealing accurate volumes of volatile liquids into aluminium capillary tubes is described. THE need for dispensing liquids within fairly close limits of weight arises from the more recent use of automatic analysers, with which elements in organic compounds are determined on small sample weights, viz., less than 1 mg. More specifically, with an F. & M. 185 CHN Analyzer it is important that during opera- tion sample weights must be kept within certain limits. The design of this instrument also requires that a sample container must not be greater than 1-5 cm in length, thus making a scaled-down version of the well known semi-micro sealed-tube technique difficult, if not impracticable, to carry out.Open-ended glass capillaries holding about 1 p1 can be used for liquid samples, but this simple technique of filling by capillarity can be tedious if a weight within 50 pg is required, and even more difficult with a volatile compound. EXPERIMENTAL APPARATUS- Fig. 1 shows a sealed-tube liquid dispensing device for overcoming this particular problem. Essentially, a 1-pl Hamilton micro syringe is mounted through two sliding supports; the rear or right-hand support carries a screw clamp so that the syringe may be held rigidly when required. The front or left-hand support consists of a length of glass tubing with a capillary just large enough to allow movement of the syringe needle.This glass tube is rigidly supported at both ends, and radial movement of the needle for aligning purposes is carried out with three radially mounted worm screws on the left-hand support. A tube-crimping device is shown in Fig. 2. It consists of a grooved platform to hold aluminium capillaries (0.d. 0.025 inch, i.d. 0-020 inch). A short length of rod is mounted vertically through a hole over this recess and, during operation, a capillary is crimped by pressure on this rod. The sample holder shown in the diagram is L-shaped and has five holes in one face, into which melting-point tubes containing samples can be inserted. ALIGNMENT OF THE MICRO SYRINGE- following adjustments before use.out of this tube by about half an inch when the syringe is moved fully to the left. position. can be carried out. As individual syringes differ slightly in dimensions it is necessary to carry out the Put the needle-guide tube into position longitudinally so that the syringe needle protrudes Place an aluminium capillary in the crimper groove and slide the crimper into load Check the radial position of the needle, as described earlier, so that free capillary entry 0 SAC and the author.Fig. 1. Sealed-tube liquid dispensing device [To face page 264ELLISON 265 (a) Plan view Countersunk slot Countersunk groove 0.02 deep x 0.025 wide ' Soft rubber base (b) Side view Details of crimper, sample holder and needle guidc.Fig. 2. Construction material was Tufnol, except where indicated; all measurements arc in inches PROCEDURE FOR WEIGHING A SAMPLE- Fill a melting-point sample tube three quarters full with sample and place the sample- holder tube in position. The holder is then put into position as shown in Fig. 2 (side view). Slide the syringe fully forward and pump the syringe piston several times. When the air has been expelled from the needle draw the piston back to the required volume (this can be calculated from the sample density if it is already known), then draw the syringe back until the needle is clear of the sample tube, and withdraw the piston a further 0.1 pl. Remove the sample holder from the stage, place a tared aluminium capillary in the crimper groove and slide the crimper into load position. Slide the syringe fully forward and inject sample into the capillary, then depress the crimping rod. Withdraw the syringe and carefully reverse the capillary in the crimper groove with forceps; seal the capillary tube by depressing the crimping rod. The capillary tube can then be transferred to a balance for weighing. Received August 30th, 1967