convection currents at the surface. Cold samples will appear heavier, and hot samples will be lighter. Humidity z If there is low humidity in the weighing environment, plast ssels should not be used, mainly for their propensity to gain electrostatic charges. Vessels comprised of 100% glass are pre ferred because they are nonconductive If high resolution is required(I mg or less), the sample should not make contact with the user's skin Traces of sweat add weight and attract moisture(up to 400 micrograms ug). The body will also transfer heat to the sample, creating problems addressed above Sample location The sample should be centered as much as possible on the weighing pan Off-center loading creates torque that cannot be completely counterbalanced by the instrument. This problem is called the off-center load error Hygroscopic samples Weigh these samples in a closed container. How Can You minimize service Calls? Ideally weighing equipment should be calibrated daily, and a certified technician should occasionally clean the balance and the internal calibration weights so that they keep their accuracy. More involved problems can be averted by minimizing the handling of the instruments If instruments must be handled or moved, apply great care a drop of inches can cause thousands of dollars of damage to an analytical balance For moves, use the original shipping packaging, which was specially designed for your particular instrument. Avoid any jarring movements, which can ruin an instruments calibration CENTRIFUGATION ( Kristin A. Prasauckas) Theory and strategy Do All Centrifugation Strategies Purify via One Mechanism? Zonal, or rate-zonal, centrifugation separates particles based on mass, which reflects the particles sedimentation coefficient. The How to Properly Use and Maintain Laboratory Equipmentconvection currents at the surface. Cold samples will appear heavier, and hot samples will be lighter. Humidity If there is low humidity in the weighing environment, plastic vessels should not be used, mainly for their propensity to gain electrostatic charges. Vessels comprised of 100% glass are pre￾ferred because they are nonconductive. Sample Handling If high resolution is required (1mg or less), the sample should not make contact with the user’s skin. Traces of sweat add weight and attract moisture (up to 400 micrograms [mg]). The body will also transfer heat to the sample, creating problems addressed above. Sample Location The sample should be centered as much as possible on the weighing pan. Off-center loading creates torque that cannot be completely counterbalanced by the instrument. This problem is called the off-center load error. Hygroscopic Samples Weigh these samples in a closed container. How Can You Minimize Service Calls? Ideally weighing equipment should be calibrated daily, and a certified technician should occasionally clean the balance and the internal calibration weights so that they keep their accuracy. More involved problems can be averted by minimizing the handling of the instruments. If instruments must be handled or moved, apply great care. A drop of inches can cause thousands of dollars of damage to an analytical balance. For moves, use the original shipping packaging, which was specially designed for your particular instrument.Avoid any jarring movements, which can ruin an instrument’s calibration. CENTRIFUGATION (Kristin A. Prasauckas) Theory and Strategy Do All Centrifugation Strategies Purify via One Mechanism? Zonal, or rate-zonal, centrifugation separates particles based on mass, which reflects the particle’s sedimentation coefficient.The How to Properly Use and Maintain Laboratory Equipment 55