EXPERIMENTAL
Retention times for representative compounds on columns containing the three substrates are given in Table I. Data Obtained With a TEGD are included for comparison. Columns of all three liquids have been programmed up to 175" C. Upper temperature limits for continuous use have not been determined; the nitriles are less stable than the polyether in intermittent use.
Analyses were made with an F & 31 Model 202B gas chromatograph equipped with an oven. Columns were coiled from 10-foot lengths of l/r-inch copper tubing, 4.6-mm. i.d, The three experimental liquids were supported (10% w./w.) on 20- to 80-mesh Haloport F, TEGD (20% w./Fy.) on 30- to 60mesh Ckomo5orb p. "he columns were a t 45" C. (70" C. for the TEGD) for the experiments reported. Helium
flow was 30 ml. per minute, inlet pressure to flow controller 30 p.p.s.i., outlet pressure atmospheric. E. M. BEVILACQUA
E. S. ENGLISH J. S. GALL
~ ~ ~ ~ ~ , & ~co.~ t ~ u b b e r
Wayne, N. J.
R~~~~~~~for review February 27, 1962. Accepted April 4, 1962.
Addition of Sodium Fluoride to Potassium Pyrosulfate Fusions for X-Ray Spectrometric Analysis of Siliceous Samples SIR: In the article entitled "Potassium Pyrosulfate Fusion Technique, Determination of Copper in Mattes and Slags" [ANAL. CHEM.32, 516 (1960)], the recommended particle size of the sample to be fused and the fusion after grinding was -200 mesh. This particle size was desirable because silica present in the sample was insoluble, and if the particles of silica were too large, heterogeneity of the ground and briquetted fusion contributed to the error of the method. Certain slags and ores contain mainly silica or silica compounds, and to determine the elements other than silicon present as accurately as possible, a modification of the fusion technique was desirable. The addition of sodium or potassium fluoride to a potassium pyrosulfate fusion is used in wet analytical methods to break down silica compounds and volatilize the silica as silicon tetrafluoride. The proportion of sodium or potassium fluoride to add to a portion of potassium pyrosulfate for the x-ray spectrometric method is determined by
Table 1. FeO
5
b 0
two factors: an amount, in excess, to volatilize completely the silica present, and the minimum amount needed so that a stable briquet of the ground fusion can be prepared. Since silica is volatilized from the fusion, a positive error on a determination can be expected. This error, prpportional to amount of silica loss will not exceed 2y0 (the portion of the sample present in the fusion-200 mg. of sample in 10.0 grams of fusion mixture). However, in practice, the samples and standards will contain silica contents in a discreate range and the net error will be minor. EXPERIMENTAL DATA
A General Electric XRD-5 x-ray fluorescence spectrometer equipped with a tungsten target x-ray tube operated a t 50 kv. and 50 ma., lithium fluoride crystal, 0.010-inch Soller slit, scintillation counter, and a Victoreen linear amplifier were used to obtain the data. A minimum of 100,000 counts was taken per measurement.
Comparison of Results of Cupola Slag Analysis cu Zn
X-Ray
Chem.4
X-Ray
Chem.*
X-Ray
Chem.c
35.15 38.38 42.66 43.01 44.25 47.00 49.21
35.20 38.16 42.50 42.88 44.30 47.00 49.30
1.10 1.16 1.31 1.23 0.91 0.87 0.73
1.05 1.10 1.33 1.18 0.90 0.83 0.78
3.51 4.23 4.10 2.76 2.10 7.62 10.01
3.66 4.50 4.00 2.80 2.25 7.55 9.85
Titrimetric, K@POI. Photometric, sodium diethylcarbamate. Titrimetric, potassium ferrocyanide.
862
0
ANALYTICAL CHEMISTRY
A fusion mixture of 9.0 grams of potassium pyrosulfate and 1.0 gram of sodium fluoride was determined to meet the requirements of total silica volatilization and production of stable briquets. Fusions were carried out in platinum-clad crucibles a t temperatures between 350" and 700" C. The fusions were ground and 5 grams were briquetted a t 15,000 p.p.s.i., producing a briquet 11/4 inches in diameter. RESULTS
A series of carefully analyzed slags and National Bureau of Standards iron ore samples was used to set up calibrations. The FeO content varied between 20 and 70%, copper 0.5 and 1.6%, and zinc 2 to 12%. Straight line calibrations were obtained by plotting net intensity us. composition. Background corrections were found unnecessary. Two samples of cupola slag were chosen to be standards and are used to recalibrate the system for each series of samples analyzed routinely. Table I shows the accuracy of the method. The average of duplicate x-ray and chemical results is shown. Cupola slags contain 20 to 40% silica. As in the case of straight potassium pyrosulfate fusions, the briquets are stable, and the briquets can be reground and briquetted as handling damage occurs. Matrix effects arising from absorption and enhancement, particle size, homogeneity, and mineralogical history are removed. Total time requirement is about 20 minutes per sample. THOMAS J. CULLEN United States Metals Refining Co. Carteret, N. J.
