It was suspected that the CaCl2 was being adsorbed onto the glass of the vial body. We agreed with the researchers’ suspicions regarding adsorption of the 45Ca onto the glass in the vial. The sample of interest was aqueous CaCl2 (0.00000375 M) and the assay was being performed in 7 mL glass vials (PerkinElmer part number 6000167). This effect is known to happen and with the incredibly low concentration of the sample, this is a very distinct possibility. The sample preparation steps were not complex: mix 0.5 mL of the sample with 3 mL of liquid scintillation cocktail. After preparation, about 50,000 counts (vial A) were present, and expected. Subsequently, three 0.35 mL aliquots were taken from vial A and these were used to fill three additional vials: B, C and D. After these preparation steps, vial A should contain about 35,000 counts while vials B, C and D should each contain about 5,000 counts. Discussion Recommendations We recommended switching to polyethylene vials to avoid this problem. In addition, if glass vials are preferred, we recommend the addition of nonradioactive CaCl2 to the cocktail prior to the addition of the sample (e.g., 0.1 mL of 0.1 M CaCl2). The addition of the CaCl2 will “precoat” the glass vial surface with Ca and help prevent the sample from adhering to the glass. Unfortunately, the actual counting results were as follows: Vial A = 50,000 counts Vial B = 0 Vial C = 0 Vial D = 0 PerkinElmer, Inc. 940 Winter Street Waltham, MA 02451 USA Phone: (800) 762-4000 or (+1) 203-925-4602 www.perkinelmer.com For a complete listing of our global offices, visit www.perkinelmer.com/lasoffices ©2007 PerkinElmer, Inc. All rights reserved. The PerkinElmer logo and design are registered trademarks of PerkinElmer, Inc. All other trademarks not owned by PerkinElmer, Inc. or its subsidiaries that are depicted herein are the property of their respective owners. PerkinElmer reserves the right to change this document at any time without notice and disclaims liability for editorial, pictorial or typographical errors. 007902_23 Printed in USA N O T E Our field sales engineer told us about a laboratory that was measuring 45Ca and had encountered unexpectedly low counts. The researchers asked for assistance, suspecting sample preparation to be the primary problem. A P P L I C A T I O N Introduction L S C C O C K TA I L S LSC in Practice 45 Ca Adsorption onto Glass Vials