spectrometer according to the manufacturer's instructions. Operation is 

 facilitated by the use of an autosampler (P.E. Auto 200) and an ASR-33 

 teletypewriter. To ensure against instrument drift, a cahbration standard is 

 included with each 15 samples. To check for unknown matrix effects, a known 

 spike is added to an aliquot of one of the samples and an equal quantity of 5% 

 nitric acid. From this, a spike recovery is calculated for each group of 15. For 

 each group, a sample of the reference material described in this paper is 

 included. 



Preparation of Reference Material 



Clams (Arctica islandica) were collected by commercial dredge from Block 

 Island Sound, and frozen prior to use. At the time of preparation, they were 

 cleaned, thawed and shucked as if for analysis, except that extracellular fluid 

 was drained and discarded. A total of 637 clam meats was pureed and 

 homogenized in a stainless steel, 40 quart mixer, of the sort found in many 

 commercial kitchens (Hobart VCM-40). Samples of approximately 60 g wet 

 weight were removed, placed in 120 ml acid-stripped polyethylene bottles, 

 sequentially numbered, and frozen for future analysis. This procedure yielded 

 476 samples. 



Characterization of Reference Material 



From the 476 samples, a total of 65 were selected for investigation of the 

 homogeneity of the material. These consisted of every tenth sample, and two 

 blocks of 10 consecutive samples from each end of the sequence. These 

 samples were analyzed for 14 trace elements by the above procedure, and the 

 results examined for homogeneity. 



RESULTS AND DISCUSSION 



The concentrations of 14 metals in the reference material on a wet weight 

 basis are listed in Table 1-1. Only data on a wet weight basis v^ll be discussed 

 because of some anomalous wet to dry weight ratios indicating some samples 

 were not uniformly dried. On the basis of several criteria, the 14 metals may be 

 divided into two groups, A and B. Group A consists of the 10 metals Cd, Cr, 

 Cu, Fe, Mg, Mn, Ni, Pb, V, and Zn, for which the relative standard deviations 

 are less than 7%, as seen in Table 1-2. Three of these metals are graphically 

 represented in Figure 1-1 . Note tlie similarity of the graphs. This similarity may 

 be quantified for these metals by determining the 45 pair-wise correlation 

 coefficients. Almost all of the coefficients indicate positive correlation at the 

 95% confidence level, v^th many of them being much more highly significant. 



