~
tI.5
4
~~
Table I. Pb Concentrations in Acids in Parts Per Billion grams Pb per gram acid)
L6
Threads per inch
Figure 1. TFE Teflon connecting block. Fits 32-oz Nalgene, narrow-mouth FEP Teflon bottles (screw cap size 30-430)
I
I I Collecting
Heat lamp
1
bottle
1
A Feed bottle TFE Teflon
Figure 2. Two-bottle Teflon still: ( A ) cleaning position, ( B )collecting position RATE OF DISTILLATION Rate of distillation is determined by a number of factors, including the efficiency of the collecting bottle as a condenser and the amount of condensation in the feed bottle. When these factors are optimized by using an ice-water bath t o cool the collecting bottle and by minimizing condensation in the feed bottle (see above), 600 to 700 ml of HCI or HF can be distilled in 3 t o 4 days, and the same amount of concentrated HNO, in 5 to 6 days. Use of room-temperature water to cool the collecting bottle extends distillation times by a factor of two or three.
6.2N 70z Method 48% H F HCl "03 Two-bottle Teflon stillQ 0.002 0.0015 0.023 (this paper) O.OC5 0.049 Tatsumoto system ( I ) 0.08 ( I ) Isothermal distillation (2) 0 . 2 ( I , 6) Distillation in platinum (3) 0.2-1.0 ( I ) Passage of filtered H F gas into H20 ( 4 ) 0.2-1 .o ( 1 ) Subboiling distillation. in quartz (5) 0.12 (6) 0.18 (6) Starting materials: reagent-grade hydrofluoric acid, singly distilled 6.2N hydrochloric acid, and reagent-grade nitric acid. RESULTS AND DISCUSSION Acids prepared by this method were analyzed for lead by isotope dilution. About 100 ml of acid plus a small amount of enriched *aPb tracer was evaporated in a Teflon beaker under a laminar flow of ultraclean air for each determination. N o corrections were made for lead introduced during evaporation or preparation for the mass spectrometer; thus the figures quoted are maximum values. The results are summarized in Table I. Data for acids prepared by other methods are listed for comparison. The results show that acids of exceptional purity (Pb
