12
ANALYTICAL CHEMISTRY, VOL. 51, NO. 1, JANUARY 1979
Table V. Determination of the Hydroxyl Content of a Methoxylated Poly(ethy1ene glycol) with Small Quantities of Hydroxyl Terminated Polymer Added. Molecular Weight of Both Polymers: 21.5 x l o 2 H-PEG a d d e d , wt%
hydroxyl content, mmol kg-' ______ ___
0.50
1.00 --___----_--I-.
added 0.0 4.7 9.3
found 4.7
9.3
14.8
calculated (4.7) 9.4 14.0
_______
_I____
From t h e results the confidence limit for one determination is calculated as 3~4.9%( a t t h e 9570 confidence level). This figure, compared with the confidence limit calculated from t h e results listed in Table TI1 (3.1 70),also shows that there is no significant difference in analytical results when using different silylating agents. W e had no other methods of high enough sensitivity to check the small figures found for the hydroxyl content in methylated poly(ethy1ene glycols). Therefore, in a third series of experiments we prepared mixtures of a methylated product of relatively high hydroxyl content (4.7 mmol kg I ) with a hydroxyl terminated polymer of the same molecular weight and analyzed these samples after silylation with l - n a p h thyldimethyl(dimethy1amino)silane. T h e results reported in Table V show t h a t t h e values found experimentally are in satisfactory agreement with those calculated as the sum of t h e hydroxyl concentration in t h e methylated product and t h a t of the hydroxyl terminated additive. In a final series of experiments, we examined the reaction of t h e 1-naphthyldimethyl(dimethy1amino)silane with a few substances containing other functional groups which could interfere with t h e hydroxyl determination. A ketone (3pentanone) and an ester (hexyl acetate) failed t o react with the reagent. On t h e other hand, an acid (hexanoic acid) reacted quantitatively t o give the corresponding silyl ester
acylation titration method. However, since the relative error remains essentially the same for very low hydroxyl concentrations, it can he used successfully in these cases where a titration method would completely fail. T h e lower detection limit can he estimated a t about 10 mol kg considering that a 570 solution of t h e 1-naphthylsiloxy derivative of such a polymer would yield a n absorbance of 0.03. In conclusion, t h e silylation by dimethylaminosilanes is quantitative even a t very low hydroxyl concentrations and proceeds under mild conditions. T h e remarkable ease of the reaction suggests the possibility of its application t o the derivatization of nonchromophoric alcohols for UV detection in liquid chromatography.
',
LITERATURE CITED J. S. Fritz and G. M. Schenk, Anal. Chem., 31, 1606 (1959).
G. M. Schenk and J. S. Fritz, Anal. Chem., 32, 987 (1960). R. S. Stetzler and C. F. Smullin, Anal. Chem., 34, 194 (1962). P. G. Eiving and B. Warchowsky. Anal. Chem.. 19, 1006 (1947). J. A . Fioria, J. W. Dobratz, and J. H. McClure, Anal. Chem., 36, 2053 (1964). S. Siggia. J. G. Hanna. and R . Culrno, Anal. Chem., 33, 900 (1961). D. H. Reed, F. E. CritchfieM, and D. K. Elder, Anal. Chem., 35, 571 (1963). L. Maros, J. Perl, and M. Szaklcs-Pint&, Ann. Univ. Sci. Budap. Robndo fijtvos Nominafae, Sect. Chim., 7, 37 (1965). D. G. Bush, L. J. Kunzelsauer. and S.M. Merrill, Anal. Chem., 35, 1250 (1963). H. P. Keller, Doctoral Thesis No. 165, Ecole Poiytechnique F6d6rale de Lausanne, 1973. H. Kamrnerer and P. N. Grover, Makromol. Chem.. 99, 49 (1966). H. Gilman and C. G. Brannen, J . Am. Chem. SOC.,73, 4640 (1951). M. F. Shostakovskij and Kh. I. Kondratev, Izv. Akad. Nauk. SSSR, Otd. Khim. Nauk., 1956, 967. M. F. Shostakovskii and Kh. I . Kondratev. Izv. Akad. Nauk. SSSR. otd. Khim. Nauk., 1957, 319. A . D. Petrov and T. I . Chernysheva, Izv. Akad. Nauk. SSSR, Otd. Khim. Nauk., 1951, 820 D. Ya. Zhinkin, G. N. Mal'nova, and Zh. V. Gorisiavskaya. Zh. Obshch. Khim., 38, 2800 (1968). N. S. Nametkin, V. M. Vdovin, and E. D. Babich, Khim. Gsterotsikl. Soedin., 1967, 146. C. A . Kraus and R. Rosen, J Am. Chem. Soc , 47, 2746 (1925). R . Fessenden, J . Org. Chem., 25, 2191 (1960). H. Gilman, 6.Hofferth, H. W. Melvin. and G. E. Dunn. J . Am. Chem. Soc., 72, 5767 (1950). H. Gilrnan. G. E. Dunn, H. Hartzfeld, and A. G. Smith. J . Am. Chem. Soc., 77, 1287 (1955).
CONCLUSIONS T h e fact t h a t t h e relative error i5 independent of the hydroxyl content suggests t h a t the precision of t h e method is limited mainly by t h e error of t h e photometric measurement. Therefore, in t h e cases of polymers of high hydroxyl content, the precision may even be inferior t o t h a t of t h e
RECEIVED for review July 24, 1978. Accepted September 18, 1978. This work is a report on p a r t of a project supported by t h e Fonds National Suisse de la Recherche Scientifique.
Separation and Determination of Nanogram Amounts of Inorganic Tin and Methyltin Compounds in the Environment Robert S. Braman' and Michael A. Tompkins Department of Chemistry, University of South Florida, Tampa, Florida 33620
Analytical methods have been developed for the determination of trace amounts of inorganic tin and methyltin compounds. Tin compounds in aqueous solution at pH 6.5 are converted to the corresponding volatile hydride, SnH,, CH,SnH,, (CH,),SnH,, and (CH,),SnH, by reaction with sodium borohydride. These are scrubbed from solution, cryogenically trapped on a U-tube, and separated upon warming. Detection limits are approximately 0.01 ng as Sn when using a hydrogen-rich, hydrogen-air flame emission type detector (SnH band). Parts-per-trillionconcentrations of methyltin compounds were found in a variety of natural waters and in human urine. 0003-2700/79/0351-0012$01.00/0
There is snhstantial interest in the possihle existence of biomethylated compounds of tin. Wood, Ridley, and Dizikes ( I ) have studied the tin hiomethylation process and Nelson, McClain, and Colwell (2) have identified the biological formation of methyltin compounds.
