SPSFAM Heavy Metals ERP Book

1078 K ubachka et al .: J ournal of AOAC I nternational V ol . 100, N o . 4, 2017 limits capable of quantitating each arsenical at the low levels required for this method. Both ion-exchange and ion-pair chromatography have been used with ICP-MS detection for arsenic speciation in juice (9–11), but to our knowledge, these methods have not been subjected to a multilaboratory validation (MLV) study. In 2012, Conklin and Chen at the FDA published an ion exchange method and single-laboratory validation study for arsenic speciation in fruit juice (10). After some minor modifications, this method was added to the FDA Elemental Analysis Manual for Food and Related Products (EAM) as 4.10 High Performance Liquid Chromatography– Inductively Coupled Plasma–Mass Spectrometric

found in various FDA-related surveys of products. Samples were mixed thoroughly and kept refrigerated until needed for shipment. Due to the long window of time allowed for participation, samples sent out after more than 6 months from the time of preparation were stored frozen and then thawed by the organizing laboratory before shipping in a refrigerated condition to participating laboratories. All laboratories were sent 50–60 g each of the 13 juice samples. In cases in which cost or availability was an issue, the central laboratory provided additional supplies such as arsenobetaine (AsB), aliquots of Standard Reference Material (SRM) 1643e, mobile phase salt, and PRP-X100 guard columns. During the validation study, procedural clarifications and instrument- specific queries were addressed by the method authors. Each laboratory was provided with procedural guidance to supplement EAM 4.10, including specific instructions, e.g., regarding the number of replicates to analyze and the approximate fortification levels to use. A reporting template accompanied these instructions to unify data reporting. Upon request, data packets including calculations and raw data printouts were sent to the organizing laboratory. All laboratories were instructed not to discuss their results with other participating laboratories. The participating laboratories included three FDA laboratories and five state laboratories, for a total of eight data sets including the organizing laboratory. Participating state laboratories were all part of the Food Emergency Response Network (16). Data sets were not edited to ensure the most complete representation; however, two laboratories exhibited a calculation issue that required reprocessing of their initial data (explained later). This manuscript describes the MLV exercise carried out by the eight laboratories using EAM 4.10, which has recently been granted AOAC First Action Status (17), to analyze apple, pear, and grape juices for iAs, DMA, and MMA. Details regarding the apparatus and reagents can be found in AOAC First Action Official Method SM 2016.04 (17). Deviations from, or clarifications to, that method are explained below. All reagents should be of the highest purity available, e.g., Optima grade (or equivalent), to ensure the lowest blank levels of arsenic possible. National Institute of Standards and Technology (NIST) SRM 1643e Trace Elements inWater and/or SRM 1640a Trace Elements in Natural Water were used to evaluate the accuracy of the method. To our knowledge, a fruit juice SRM for total arsenic and/or arsenic species was not available at the time of this MLV study. Multiple vendors, depending on the laboratory, were used to supply the various standards and reagents. However, ammonium phosphate dibasic [(NH 4 ) 2 HPO 4 ] was purchased from Sigma- Aldrich (St. Louis, MO), and due to trace-but-detectable levels of arsenic in other sources, this source was used by all laboratories during the MLV study. Apparatus and Reagents

Determination of Four Arsenic Species in Fruit Juice, version 1.0 (EAM 4.10; 12) and was used as the basis for this MLV study, as well as subsequent FDA juice survey assignments (13). The data obtained from FDA juice survey assignments were used to generate the health hazard evaluation by the FDA and led to the proposed action level of 10 ng/g iAs in apple juice (14). The goals of this MLV study were to evaluate the accuracy, precision, and robustness of the method; to ensure that it meets the needs of the agency; and to fulfill the requirements for a Level 3–validated method according to the Guidelines for the Validation of Chemical Methods for the FDA Foods and Veterinary Medicine Program (15). Eight laboratories participated in this study. Prior to participating, selected personnel from each laboratory participated in a training exercise. This was necessary because the majority of the analysts had experience with total elemental analysis using ICP-MS, but few had experience using HPLC. Laboratories were instructed to obtain the necessary equipment for the method, obtain juice samples, analyze them for total arsenic, and determine the concentrations of the individual arsenic species using EAM 4.10. Each laboratory was encouraged to coordinate with the method authors to ensure their readiness before beginning the validation exercise. When analysts were comfortable with the method and achieved satisfactory mass balances for their samples, they were able to start the validation exercise. Four common juice products were chosen for the exercise: single-strength or ready-to-drink (RTD) apple juice, apple juice concentrate, RTD grape juice, and RTD pear juice. Within the apple juice concentrates, two were collected by FDA investigators, whereas the third concentrate was purchased from a local market (designated AJC1, AJC2, and AJC3, respectively). Of the grape juice samples, two were classified as purple (GJ1 and GJ2) and two as white (GJ3 and GJ4). The RTD apple juice samples were designated AJ1, AJ2, and AJ3, whereas the RTD pear juice samples were designated PJ1, PJ2, and PJ3. The type of each juice was known to the participating laboratories. Unless specified, all juice samples were purchased from local Cincinnati, OH, markets; within each juice type, brands were unique. Samples were not screened for total arsenic or arsenic species before fortification by the organizing laboratory. Selected samples were fortified with various combinations of iAs, DMA, and/ or MMA, and values were not disclosed to participating laboratories (Table 1, fifth column). Levels were selected to mimic those reported in the literature and those previously Collaborative Study

Preparation of Sample and Standard Solutions

Details regarding sample and standard preparation can be found in AOAC First Action Official Method 2016.04 (17). Deviations or clarifications of that method are explained below.