The magnitude of Hg lost while oven drying sediment samples also was 
evaluated. Aliquots of bulk sediments from station M06-13A and aliquots of 
the fine fraction from station M05-16 were analyzed wet and the results 
compared to samples that were oven dried at different temperatures. We found 
no evidence of Hg loss as a result of drying bulk sediments at temperatures 
between 40° and 100°C, but some loss (about 42 percent) was observed when 
drying fine-fraction samples at 100°C. 
Additional methods 
Results of Ba and Cr analyses on selected Georges Bank samples were 
cross-checked by an energy-dispersive X-ray fluorescence technique (Johnson, 
1984). The determination of Ba concentration was made with a Kevex 0/700 
energy-dispersive X-ray fluorescence spectrometer. Powdered samples of about 
1 g were analyzed with a gadolinium secondary target for excitation of the K- 
alpha line. The ratio of Ba intensity to the gadolinium Compton Scatter 
intensity was used to correct for absorption effects. This ratio then was 
compared to a standard calibration curve to determine the concentration of Ba. 
The X-ray fluorescence technique was used on all samples found to have 
more than 500 ppm Ba during the first analysis by acid decomposition and ICP 
spectrometry. The X-ray fluorescence technique is highly accurate in samples 
enriched with BaSO,, which are difficult to dissolve completely. 
Justification of the alternative methods is presented in Bothner and others 
(1982). 
ANALYTICAL ACCURACY AND PRECISION 
Analytical accuracy was determined by analyzing rock standard MESS-1l. 
Excellent agreement occurs between our results and values established by other 
laboratories (table 2). Excellent agreement also exists among aliquots of 
samples submitted as blind replicates (appendix table 2). 
17 
