SPSFAM Heavy Metals ERP Book

1082 K ubachka et al .: J ournal of AOAC I nternational V ol . 100, N o . 4, 2017

Figure 1. Speciation results for RTD and concentration juice samples from each laboratory. (a) RTD apple juice; (b) apple juice concentrate; (c) RTD grape juice; and (d) RTD pear juice.

values for As(III) and As(V) were 6.3 and 6.1%, respectively, whereas the iAs RSD R was only 3.9%. Similarly, for sample GJ3, the RSD R values for As(III) and As(V) were 7.6 and 8.5%, respectively, whereas the iAs RSD R was 4.9%. One of the 13 samples was fortified by the originating laboratory at a level of 30 µg/kg DMA. All other samples were not found to contain DMA at a concentration above the method LOQ. The RSD r , RSD R , and HorRat values for this sample were 3.3%, 6.7%, and 0.24, respectively. Four RTD juice samples contained trace levels of DMA that were >2 times the method LOD. For these samples, the RSD R ranged from 28 to 33% and the HorRat values ranged from 0.60 to 0.73. Four of the 13 samples were found to have MMA concentrations above the method LOQ; however, three of those were fortified by the originating laboratory. For these samples, the MMA RSD r values ranged from 2.2 to 4.4% and the RSD R values ranged from 6.0 to 9.3%. The HorRat values were all less than 0.5. One sample, AJ3, contained a trace level of MMA that was >2 times the method LOD. For this sample, the RSD R and HorRat values were 58% and 1.24.

Sample Fortification Recovery

Each laboratory participating in this MLV study prepared fortified samples representing each matrix (AJ1, GJ1, PJ1, and AJC1) in duplicate at three spike concentration levels and then determined spike recoveries. The nominal spike concentrations in the RTD juices were 5, 25, and 50 µg/kg for As(III), As(V), DMA, and MMA. Thus, in calculating the recovery for iAs, the fortification concentrations and determined concentrations for both As(III) and As(V) were taken into account. The results of this fortification study are shown in Table 3. Overall, fortification recoveries in RTD juice samples of apple, grape, and pear were very good, with averages ±1 SD of 100 ± 8, 100 ± 7, and 100 ± 8% for iAs ( n = 144), DMA ( n = 126), and MMA ( n = 126), respectively. Only one recovery values for iAs and one recovery values for MMA were outside the 80–120% acceptable range set forth in the QC criteria for the method, and each of these values was >120% but ≤130% recovery. Again, due to a known standard issue, the data for DMA and MMA for one laboratory were rejected from these results.