/
111
lo/ 9
/
7
/B&
21 1
I
,
#
200
,
400
600 800 1000 KOVATS RETENTION INDEX
1200
Figure 1. Kovats retention index us. number of boron atoms
6ol
1
'0
1
2
3
4 5
6 7 TIME (mini
6
9 IO 11
Figure 2. Temperature programmed chromatogram of a boron hydride mixture on 6 % OV17 on 80jlOO Chromosorb W.
The temperature programming operation consisted of an initial column temperature of 40 OC; after two minutes of isothermal operation, the temperature was programmed at a rate of 20 "C per minute to a maximum of 180 "C. The final temperature was held constant for five minutes. Compounds were run as individual samples and as mixtures. Kovats retention indices were determined for the commercially available compounds B2H6,B5Hg,and B10H14under the experimental temperature programmed conditions. Under programmed temperature conditions, the Kovats indices of the boron hydrides plotted against the number of boron atoms appears to produce a straight line, Figure 1. This plot can be extremely helpful in tentatively identifying components of a boron hydride mixture. An example of this application can be found when a mixture of boron hydrides was generated from the pyrolysis of diborane (950 ppm in nitrogen), Figure 2. The mixture, of approximately 50 ng for each component, was separated with the experimental programmed temperature technique. A comparison of Kovats indices for the commercially available boron hydrides and the diborane pyrolysis by-products is shown in Table 111. The corresponding Kovats indices for BzHG,B5H9,and BI0Hl4with by-products 1, 2, and 4 tentatively identifies these by-products directly as B2H6,BSHg,and BIOHI4.An application of the plot shown in Figure 1 for the tentative identification of an unknown boron hydride can be found in the case of by-product 3. In this case, the Kovats index of by-product 3 does not correspond directly to that of a commercially available boron hydride; however, the plot shown in Figure 1 relates the Kovats index of byproduct 3 to B6 or hexaborane. Hexaborane was confirmed by mass spectrometry (12). The programmed temperature gas chromatographic conditions used to chromatograph the boron hydrides at trace concentrations, along with the Kovats retention indices, represent a scheme of significant help in the separation and identification of boron hydride mixtures.
RECEIVED for review April 7, 1972. Accepted July 12, 1972. This research was made possible by a grant from the Western Electric Company to Drexel University.
Flow rate isothermally set at SO cm3/min. Temperature program, 2 minutes isothermally at 40 "C followed by programming at 20 "C/min to 180 "C and subsequent isothermal operation. 3.2 X lo-* A full scale. 1. B2H6; 2. BjHi); 3. B6H10; 4. Bi,Hi,
COR R ECTlON
tube and held in place with a small wad of quartz wool. Nitrogen at 5 psig and 30 cm3/min was used to carry decaborane vapors to the gas sampling valve. The hexaborane formed by the pyrolysis of diborane was sampled with the gas sampling valve in the same manner as diborane. RESULTS AND DISCUSSION
Table I1 presents retention time data for boron hydrides isothermally analyzed at two different temperatures on several different column materials. These liquid phases represent a broad spectrum of column materials. As a result, 6 % OV-17 was selected for the programmed temperature separation of boron hydrides in the range of BIHGto BloHI4.
Simultaneous Determination of Sample Concentration and Reagent Blank This note by Max B. Kloster and Clifford C. Hach [ANAL. CHEM., 44,1061 (1972)], contains an error in the explanation of the three cases shown in Figure 3 and discussed in paragraph 3 on page 1064. Case 1 occurs when the reagent blank exceeds the sample concentration, Case 2 occurs when the reagent blank equals the sample concentration, and Case 3 occurs when the reagent blank is less than the sample concentration. Also, in the proposed method, the accuracy is greatest if the two sample/reagent ratios are chosen so that they fall at or near the extremes of the linear portion of the curve.
ANALYTICAL CHEMISTRY, VOL. 44, NO. 13, NOVEMBER 1972
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