The value of n should be chosen such that the operator is sure the finite tube blank has been reached. In Exp. 2 as part this of the intermediate-term blank memory effect investigation, we did not observe any significant increment of blank levels after day 8 and day 15. Thus, it can be said that stored blank tubes should have been maintained under good condition providing that enough blank cycles were run following initial analysis. By contrast, according to Brown et al. [14], tubes should be cleaned at day 8 to minimize memory effect, as they found elevated level of mercury at that time (about 0.42ng in the first heating cycle). The results of Exp. 3 suggest that up to 30ng of initial loading, liberation of excess mass from the second heating cycle (at day 8) was below 0.53%.

By contrast, the increment at day 8 was about seven times higher for the 50ng initial loading. Brown et al. [14] measured an effect in the range between 0.16 and 0.21% at day 7 for initial loadings in excess of 25ng. However, in both studies, liberation of excess mass during the third heating cycle was consistently insignificant (<0.02%), except at 50ng (Figure 4). Overall, the combination of low standard injection masses and the liberation of any remaining excess mass from second heating cycle can enhance analytical accuracy significantly. Considering this effect, it is not good practice to keep tube for prolonged period of time without a second blank run step. It should be noted that, in this investigation, when we analyzed mass at 50ng or above 50ng, the system was contaminated and internal cleanup was needed to stabilize the system.

To measure accurately at these high masses tubes should be cleaned rigorously after GSK-3 analysis using repeated blank runs to maintain blank level mass below 0.01ng in CVAAS system. If we keep tubes for long periods of time (about 45 days) after standard or real sample analysis without intermittent tube cleaning, excess Hg mass will be liberated. This excess mass will increase as the time gap between analysis increases (Figure 5). Such effects can be significant, as the pattern became highly unpredictable after long storage periods. 4. ConclusionIn this study, to quantify memory effect patterns of mercury adsorption tubes containing gold-coated quartz sand on short (1 day), intermediate (15 days), and long (45 days) timescales, liberation of excess mass of gaseous mercury from blank heating cycles has been investigated by CVAAS system. Due to fairly limited previous work on the memory effect, this study has been designed to allow direct comparison with our previous investigation [14] using CVAFS. In this research, four different types of experiments were conducted to quantify the memory effect over different time cycles.