sults were obtained with the use of this apparatus in the esterification of fatty acids (8). The application of this type of unit for pyrolysis esterification offers several advantages over those cited earlier. First, the unit is commercially available and easily adapted to many types of chromatographs. Second, the configuration of the probe is such that, if necessary, repetitive additions to the probe tip of sample aliquots are easily accomplished prior to pyrolysis with a delay only for the solvent to evaporate. Since no degradation of the dry salts of these acids was observed on the probe, as many aliquots as were necessary could have been added, thus reducing the need to concentrate samples. Tme
(Minutes)
Figure 1. Chromatogram of a mixture of (1) pyrolysis degradation products, (2) methyl methylfluorophosphinate, and (3) di-
methyl methylphosphonate
0.8 l.Ol 1
0.6-
CONCLUSIONS While most workers have focused their work with this technique on the determination of carboxylic acids, the data suggest that the technique can be applied to phosphorous-containing acids. The method appears ideally suited to the analysis of moderately dilute aqueous solutions of these acids where the approach is to conduct the analysis through gas chromatography of their methyl esters.
P
Received for review August 22, 1973. Accepted October 26, 1973.
e
0.4 .c
-
t 0.2 0
(8) P. H . Latimer and W. L. Clapp, R . J. Reynolds Tobacco Company, unwblished work, 1968. 200 Probe
400
600
Temperoture
000
1000
(" C )
Figure 2. Yield of dimethyl methylphosphonate as a function of pyrolysis probe temperature
Table I. Effect of Sample Size on Yield of Methyl Methylfluorophosphinate Sample size, pg
100 75 37.5 11.3 a
Yield: %
*
99 1 99 Zk 1 98 2 97 3
+
*
Each analysis is the average of three Chromatograms.
Table 11. Effect of Sample S i z e o n Yield of Dimethyl Methylphosphonate Sample size, pg
100 50 30 10 a
Yield: %
99 Zk 1 99 i 1 52 Zk 2 10 Zk 5
Each analysis is the average of three chromatograms.
was less than 50 Fg. When the tetramethylammonium salts of both methylfluorophosphinic acid and methylphosphonic acid were pyrolyzed simultaneously, esterification was quantitative for both acids over the entire concentration range. An attempt was made to esterify phosphoric acid under these same conditions but low, erratic yields were obtained, probably because of an inability to neutralize the thud acid group. Pyrolysis Probe. The nature of the pyrolysis unit was the key to the study. By producing a rapid, yet well-defined, probe temperature, reproducible injection port esterification was possible. In an earlier study, similar re614
ANALYTICAL CHEMISTRY, VOL. 46, NO. 4, A P R I L 1974
CORRECT1ON Resolution by Gas-Liquid Chromatography of Diastereomers of Five Nonprotein Amino Acids Known to Occur in the Murchison Meteorite In this article by G. E. Pollock, Anal. Chem., 44, 2368 (1972), an error in nomenclature was made. The ( + ) - 2 alkanols have an S ( + ) configuration in the Cahn-Ingold system, not R(+) as written in this paper. The following changes should be made: p 2368, column 2, lines 11 and 12 the N-trifluoroacetyl-(SR)-aminoacid (S)-2-butyl esters p 2369, column 1 under Reagents, line 4, , optically active S - (+)-2-alkanols p 2371, Tables I11 and IV, bottom of table Peak 1-RS for N-methylalanine, p-amino-n-butyric, Peak 2-SS and pipecolic acids. Peak 1-SS for isovaline and P-aminoisobutyric acid Peak 2-RS p 2372, column 1, lines 9-15, l . e . , the RS peak elutes first and the S S peak second. Isovaline and /3-aminoisobutyric acid, however, show a reversal of elution pattern, the SS peak elutes first and the RS peak second. Up to this time, only one case of reversal of elution order has been reported. Charles-Sigler and coworkers ( I O , 13) report that N-TFA(RS)-phenylglycine-(S)(+)-%octanol ester has a reversed elution order while the S ( +)-2-butanol ester is normal. I wish to thank Dr. E. Gil-Av for calling to my attention this error in nomenclature.
