Prototyping of Automatic Dispensing Machine for Diluents and Liquid Media in Test Tubes

Abstract

Loading diluted solutions and liquid media into test tubes is typically done using plastic syringes or semi-automatic dispensers. However, these methods become problematic when preparing large amount of solutions, causing fatigue for the operator as the small size of the dispensing equipment leads to time-consuming preparations and inaccurate dispensing volumes. Additionally, the dispenser is an expensive and short lifespan of only 1-2 years, when we use it in the microbiology laboratory work, it is presented on error and showed less of accuracy and it was not suitable with the routine laboratory work. Therefore, the aims of this study were to design and create a prototype automatic liquid dispensing machine for pipetting the diluent solutions and liquid culture media packaging in test tubes with volumes of 9.00 and 10.00 mL, test tube size 16x160 mm with a total number of 100 tubes. The machine was designed and consisted of 3 parts: 1) a storage tank and a pump to pipette the diluent solutions and liquid culture media, 2) a movement mechanism to distribute the liquid and 3) a control unit for the pump and movement mechanism. The principle of using working volume was used a drive mechanism similar to an industrial CNC machine that moved along the x, y and z axes to distribute liquid into the designated location with precisely special volume by a peristaltic pump, that was used the G code command program to control the machine via MACH 3 software has two operating programs: (1) 9.00 mL 100 tubes and (2) 10.00 mL 100 tubes. The control of the liquid dispensing volume used the pulse with modulation (PWM), which was set by the speed controller and dispensed time with the G code program for a target volume of 9.00 mL, an optimal PWM value of 72%, and a dispense time of 1.4 seconds. Similarly, a target volume of 10.00 ml necessitated a PWM value of 83% while maintaining a dispense time of 1.4 seconds. The accuracy test results demonstrated that the average dispensed volumes for the target volumes of 9.00 mL and 10.00 mL were 8.89±0.7 ml and 9.99±0.7 ml, respectively. It was shown high accuracy, with relative standard deviations (%RSD) of 0.76 and 0.70 at n=10, respectively. A t-Test revealed no significant difference between the mean values of volume 9.00 mL and 10.00 mL (95% confidence level). Compared with the principle of calibration for preparing diluted solutions and culture media at a volume of 9.00±0.2 mL and 10.00±0.1 mL was found within the acceptance criteria. The results of this study indicated that the Automated Dispensing Machine (ADM) was highly capable for preparing diluent solutions and liquid culture media by using test tubes. The data showed the accuracy and reliability of the ADM. It could help the worker in laboratories with the convenience condition and reduce costs. Moreover, it could apply to the other field of works as well.