1792 Table
ANALYTICAL CHEMISTRY, VOL. 57, NO. 8, JULY 1985
In conclusion, the proposed method offers several advantages over the titrimetric method cited as well as a viable method for IC users who do not wish to invest in expensive UV-vis detectors to analyze urea solutions. Registry No. Urea, 57-13-6.
VII. A m m o n i u m - N R e s u l t s in A b o v e A n a l y s e s
% "3-N
N-P-K analysis % NH3-N IC 41-04' 37-24' 17-0-23' 22-7-10 24-5-8
NA NA NA 7.82 7.08
% NH3-N titr
NA NA NA NA NA
claim
0.0 0.0 0.0
LITERATURE CITED
7.98 6.96
because both species are commonly found as major nutrients in chemical fertilizers. Analysis of urea in the presence of ammonium ion was found to be accurate and precise (Table V) using prepared laboratory samples. These results were very encouraging and it was decided to attempt the analysis of actual fertilizers. A variety of samples were chosen for this purpose the results are found in Tables VI and VII. It should be made clear that the sums of the urea-N and the ammonium-N of the last two samples do not equal the total-N claim because the balance of the nitrogen is present as nitrate-N. The advantage of the proposed method over that of the comparison method is clearly accuracy and precision. A second advantage is the low concentration and small sample size needed in IC analyses. The advantage of this method over deterination of urea on the IC using UV-vis detection is purely monetary, but this is often a very important consideration when deciding upon analysis methods.
(1) Honitz, W., Ed. "Officlal Methods of Analysis of the Assocation of Offlcial Analytical Chernlsts", 12th ed.; AOAC: Washlngton, DC, 1975; Method 2.081, (2) Falls, J. H.; Barnacascel, W. R.; Britt, P. W. J. Assoc. Off. Anal. Chem. 1978, 59, 1045-1047. (3) Watt, G. W.; Chrisp, J. D. Anal. Chem. 1954, 26,452-453. (4) Anigbohu, V. C.; Dietz, M. L.; Syty, A. Anal. Chem. 1983, 55, 535-539. (5) Abramova, E. L.; Aulesheva, M.; Saibova, M. T. Deposited Document, 1976, VINITI 3748-76 (Russ). (6) Barbera, A.; Disaro E.;'Bottacin, E. Chim. Ind. (Milan) 1981, 63, 163-166 (Eng). ( 7 ) Singh, K.; Saksena, V. P. Indlan J. Agric. Res. 1979, 13, 1-6 (Eng). (8) Schilbach, U.; Kirmse, E. M. Chem. Anal. (Warsaw) 1978. 23, 1025-1028 (Ger). (9) Sloan, D. M.; Veales, R. W. J. Assoc. Off. Anal. Chsm. 1977, 60, 876-880 . __. (10) Tagami, S.; Matsuba, A.; Sawada, T.; Nakano, T.; Shlbo, D. Yakagaku Zasshi 1974, 94, 1384-1388 (Eng). (11) Gehrke, C. W.; Klllingley, J. S.; Wall, L. L. Adv. Aufom. Anal., Technlcon Inc. Congr. 1972 1973, 7 ,33-49. (12) Marecek, J.; Paviik, P.; Kosarkova, J. Chem. Rum. 1975, 25,69-71 (Czech). (13) Rud, T. A. Sb. Nauchn. Tr., DonskoiS-kh. Inst. 1975, IO,95-101 (Russ).
RECEIVED for review February 19,1985. Accepted April 22, 1985.
ADDENDUM Analysis of Polynuclear Aromatic Mixtures by Liquid Chromatography/Mass Spectrometry Kenneth J. Krost (Anal. Chem. 1985,57, 763-765). The following material was inadvertently omitted from the publication: EXPERIMENTAL SECTION Materiqls. The chromatogrphic columns used were obtained from E. I. du Pont de Nemours, Inc., Wilmington, DE (Zorbax ODS, CI8octadecylsilane, bonded to SIL silica particles, 4.6 mm i.d. X 25 cm length), and Varian Instrument Corp., Walnut Creek, CA (Micropak, MCH-10, octadecylsilane bonded to 10-pm silica particles, 4.0 mm i.d. x 30.0 cm length). The reverse-phase solvents, water and methanol, were obtained from Burdick and Jackson, Muskegan MI, HPLC grade. The following compounds were obtained from Aldrich Chemical Co. Inc., Milwaukee, WI: benzo[a]pyrene, 99+%;
The equipment used was a Finnigan 3200 mass analyzer combined with the standard Kaplon belt-driven interface. Data were acquired using a Fihnigan/Incos 2300 data system. The high-performance Iiquid chromatograph used was a Varian Model 5000 combined with a Varian Vista 401 dedicated computer/terminal. Electron ionization spectra were taken with a standard Finnigan CI source at pressures of 5 X lo4 torr. RESULTS AND DISCUSSION Eluent Flow and Composition. A schematic of the system used in this study is shown in Figure 1. A split ratio of 1:5 between the analyzer and waste solvent was generally maintained. A wide variance in flow, composition, and pressure was used for the eluents. Of particular importance was the flow-pressure curve for water and hexane (Figure 2). Clearly, when water was used in reverse-phase separations, severe flow and compositional restrictions occurred. However, at the other extreme, the system accommodated hexane with no significant rise in analyzer pressure.
