Anal. Chem. 2000, 72, 2302-2307
A Multicomponent Mobile Phase for Ion Chromatography Applied to the Separation of Anions from the Residue of Low Explosives Janet M. Doyle, Mark L. Miller,* Bruce R. McCord,† David A. McCollam,‡ and George W. Mushrush§
Forensic Science Research and Training Center, FBI Laboratory, Quantico, Virginia 22135
A multicomponent mobile phase utilizing ion-exchange, ion-exclusion, and ion-pairing principles for the rapid isocratic separation of anions in low explosives residue by ion chromatography (IC) has been developed. The notable feature of this system is that an ion-pairing reagent and an ion-exclusion reagent are combined in the same mobile phase. Contrary to expectation, these reagents act independently of each other in solution. The stock mobilephase composition consisted of boric acid, D-gluconic acid, lithium hydroxide, and glycerol. Tetrapropylammonium hydroxide, an ion-interaction reagent was used to achieve pH 8.5. Acetonitrile (ACN) was added to enhance resolution and octanesulfonic acid, an ion-exclusion reagent, was added to adjust the retention time of perchlorate. Separation of a mixture of anions common to low explosives residue was achieved in less than 16 min using a Waters IC-Pak Anion HR column. Optimization studies were performed by changing the concentration of the ACN and by altering the pH or the type of ioninteraction or -exclusion agents. Simulated case studies were performed using postblast residues from pipe bombs. The results show this method to be a valid and reproducible procedure for forensic casework analysis. The practical significance of this system is that a reduction in the analysis time and an improvement in efficiency of lateeluting peaks can be achieved without resorting to gradient elution techniques. For the analysis of anions detected in explosives residue, the Waters IC-Pak Anion HR column has proven to be a suitable replacement for the Vydac 300IC405 column, which has been discontinued by the manufacturer. The significance of characterizing the inorganic anions present in the residue of low explosives has been emphasized by an increase in terrorist bombings in recent years. The ions are the products and reactants of the rapid combustion of fuel and oxidizer that occurs during any explosion. Residue may be used to infer * Corresponding author: (Fax) (703) 632-4557; (e-mail) mmiller@ fbiacademy.edu. † Current address: Department of Chemistry, Clippinger Laboratories, Ohio University, Athens, OH 45701. ‡ Current address: Chemistry Unit, FBI Laboratory, Washington, DC 20535. § Current address: Department of Chemistry, George Mason University, Fairfax, VA, 22030.
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the original composition of the explosive in many instances.1-5 Common water-soluble anions of interest that may be found in explosives residue include chloride (Cl-), nitrite (NO2-), nitrate (NO3-), sulfate (SO42-), chlorate (ClO3-), thiocyanate (SCN-), perchlorate (ClO4-), hydrogen carbonate (HCO3-), cyanate (OCN-), and hydrogen sulfide (HS-).6 These anions may be found in the postblast residue of improvised explosives and commercial explosives such as black powder, Pyrodex, flash compositions,7 and ammonium nitrate-fuel oil mixtures.8 Ion chromatography (IC) has been recognized as a useful method for the separation of inorganic anions since its introduction by Small et al.9 in 1975. Cassidy and Elchuk10 were the first to investigate the advantages of quaternary ammonium-modified reversed-phase columns and conductivity detection for the separation of trace amounts of anions. Schmuckler et al.13 demonstrated the efficacy of a borate and gluconate mobile-phase composition on anionic separations which was determined to be due to the formation of a ring-type borate-gluconate complex. Today, ion chromatography is one of the most powerful techniques for the analysis of water-soluble explosives and explosives residue and is used to detect both the cations and anions that are present in these samples.1,6,11 McCord and Bender described a system for the isocratic separation of anions in low explosives residue utilizing the Vydac 300IC405 anion-exchange column.12 This system was very effective in separating a wide variety of anions in ∼12 min. Due to the (1) Reutter, D. J.; Buechle, R. C.; Rudolph, T. L. Anal. Chem. 1983, 55, 1468A72A. (2) Beveridge, A. D.; Greenlay, W. R. A.; Shaddick, R. C. Proceedings of the International Symposium on the Analysis and Detection of Explosives; FBI Academy: Quantico, VA, 1983; pp 53-8. (3) Selavka, C. M.; Strobel, R. A.; Tontarski, R. E. Proceedings of the Third International Symposium on the Analysis and Detection of Explosives, ICT: Pfinztal, Germany, 1989; pp 3-19. (4) Prime, R. J.; Krebs, J. Can. Soc. Forensic Sci. J. 1984, 17 (2), 35-40. (5) Peterson, G. F.; Dietz, W. R.; Stewart, L. E. J. Forensic Sci. 1983, 28 (3), 638-43. (6) Bender, E. In Forensic Investigation of Explosives; Beveridge, A., Ed.; Taylor and Francis; Bristol, PA, 1998; pp 343-388. (7) Krone, U.; Treumann, H. Propellants, Explos., Pyrotech. 1990, 15, 115-20. (8) Henderson, I. K.; Saari-Nordhaus, R. J. Chromatogr. 1992, 602, 149-54. (9) Small, H.; Stevens, T. S.; Bauman, W. C. Anal. Chem. 1975, 47, 1801-9. (10) Cassidy, R. M.; Elchuk, S. J. Chromatogr. 1983, 262, 311-5. (11) McCord, B. R.; Hargadon, K. A.; Hall, K. E.; Burmeister, S. G. Anal. Chim. Acta 1994, 288, 43-56. (12) McCord, B. R.; Bender, E. In Forensic Investigation of Explosives; Beveridge, A., Ed.; Taylor and Francis; Bristol, PA, 1998; pp 231-65. (13) Schmuckler, G.; Jagoe, A. L.; Girard, J. E.; Buell, P. E. J. Chromatogr. 1986, 356, 413-9. 10.1021/ac991346z CCC: $19.00
© 2000 American Chemical Society Published on Web 04/07/2000
recent discontinuation of this column by the manufacturer, a new isocratic method was developed. The Waters IC-Pak Anion HR column examined in this study allows similar separation to the Vydac column in less than 16 min with nearly a 4-fold increase in the number of theoretical plates for the late-eluting perchlorate peak. Perchlorate and thiocyanate, two anions that have great importance in the analysis of explosives residue, are strongly retained by anion-exchange stationary-phase materials. Separation of thiocyanate and perchlorate was accomplished by Dasgupta14 in 1984 using tetrapropylammonium hydroxide as an ion-interaction reagent; however, gradient elution had to be used in order to shorten the retention times of these ions. The first isocratic description of ClO4- analysis by IC using a Vydac (silica-based quaternary ammonium ion-exchange) column was presented by Verweij et al.15 in 1986. Jupille16 reported the optimum conditions for conductivity detection of the mobile phase for anion separations as consisting of organic acid salts that have low equivalent ionic conductance or hydroxide ions that have very high equivalent ionic conductance. Snyder and Kirkland17 described the instability of anion-exchange column packings and the utility of counterions in ion-pair chromatography to extend column lifetime. The mobile phase developed in this work exploits the positive aspects of all of the above studies. The anions of interest in low explosives residue are separated in less than 16 min with increased resolution and superior peak shape compared to the individual systems described by Schmuckler,13 Dasgupta,14 and Verweij.15 According to Pietrzyk,18 gradient elution was necessary to achieve rapid analysis times, but the use of the mobile phase in this study demonstrates that rapid isocratic separations of anions are possible. Additional benefits of isocratic separation over gradient elution include the elimination of problems with baseline shifts,18 ghost peaks,19 and the necessity for equilibration between runs.20 Jones et al.21 introduced the concept of the isoconductive mobile phase as applied to gradient elution. A pair of eluents that had similar ionic conductance were chosen to effect a gradient anionic separation with a stable baseline in a shorter amount of time than a single isocratic run. The mobile phase in this study employs a different approach through the addition of ion-pairing and ionexclusion reagents to adjust the retention of late-eluting peaks in an isocratic mode. EXPERIMENTAL SECTION The reagents and standards were prepared using 18 MΩ deionized water supplied by an ELGA Maxima SC deionization system (Elga, Bucks, U.K.). The composition of the final mobile phase consisted of 2.75 mM boric acid, 0.37 mM D-gluconic acid, (14) Dasgupta, P. K. Anal. Chem. 1984, 56, 769-72. (15) Verweij, A. M. A.; Verheiiden-de Bruyne, M. M. A.; Klooster, N. T. M. Arch. Kriminol. 1986, 177, 91-4. (16) Jupille, T. In Ion Chromatography; Tarter, J. G., Ed.; Marcel Dekker: New York, 1987; p 26. (17) Snyder, L. R.; Kirkland, J. J. Introduction to Modern Liquid Chromatography, 2nd ed.; Wiley & Sons: New York, 1979; p 427-9. (18) Pietrzyk, D. J. In Handbook of HPLC; Katz, E., Eksteen, R., Schoenmakers, P., Miller, N., Eds.; Marcel Dekker: New York, 1998; p 444. (19) Stevenson, R. L. In Handbook of HPLC; Katz, E., Eksteen, R., Schoenmakers, P., Miller, N., Eds.; Marcel Dekker: New York, 1998; p 520. (20) Snyder, L. R.; Glajch J. L.; Kirkland, J. J. Practical HPLC Method Development; Wiley & Sons: New York, 1988; pp 172-174. (21) Jones, W. R.; Jandik, P.; Heckenberg, A. L. Anal. Chem. 1988, 60, 1977-9.
1.05 mM lithium hydroxide, 1.25 mM glycerol, 5.5 mM octanesulfonic acid, 5% (ACN) (all supplied by Sigma, St. Louis, MO), and 0.6 mM tetrapropylammonium hydroxide (Fluka, Buchs, Switzerland) at pH 8.5. The adjustment of the pH to 8.5 using a 0.5 M solution of tetrapropylammonium hydroxide was accomplished prior to the addition of the acetonitrile (ACN) and the octanesulfonic acid. Isocratic separations were performed at a flow rate of 1 mL/min using a Waters IC-Pak Anion HR 4.6 × 75 mm HPLC column (Waters Corp., Milford, MA). Potassium chloride, nitrite, nitrate, chlorate, perchlorate, sulfate, and thiocyanate (Sigma) were used to prepare standards at a concentration of 1000 ppm each. The individual stock standards were used to prepare a composite standard containing 40 ppm of each anion. Studies to determine the effect of the size of the associated cation on resolution were conducted using 0.5 M solutions of lithium, sodium, cesium, potassium (Sigma), and tetrapropylammonium (Fluka) hydroxide counterions to adjust the pH to 8.5. A similar study was performed using 5.5 mM solutions of methane-, pentane-, hexane-, heptane-, and octanesulfonic acids (Sigma) to determine whether the size of the alkyl substituent groups would effect separation. The potassium salts of azide, chromate, cyanate, dichromate, iodate, permanganate (Fisher Scientific, Fair Lawn, NJ), bromate, iodide (Baker & Adamson, New York, NY), oxalate (Mallinckrodt, St. Louis, MO), and phosphate (Aldrich, Milwaukee, WI); the sodium salts of acetate, cyanide, fluoride, formate, tartrate (Fisher), arsenate (J. T. Baker, Phillipsburg, NJ), benzoic acid (Sigma), and citric acid (Fisher) were used to prepare solutions of ions, that might cause interference in detecting anions from explosives residue, at a concentration of 1000 ppm each. Aliquots of each were diluted to 40 ppm and mixed 1:1 with the standard. Analyses were conducted on a model 600E multisolvent delivery system (Waters Corp.) equipped with a model 7125 injector (Rheodyne, Rohnert Park, CA) containing a 10-µL sample loop. Nonsuppressed conductivity detection was performed using a model 431 conductivity detector (Waters) equipped with a 1.4µL flow cell. Data were collected using the Millenium 32 Chromatography Manager (Waters Corp.) software package. The sample load volume was 20 µL, and isocratic separations were performed at a rate of 1 mL/min as specified by the manufacturer.22 Preblast and postblast explosives samples were prepared as described previously.23 Preblast samples consisting of 0.1 g each of black powder, Pyrodex (black powder substitute: potassium/ perchlorate/nitrate/sulfur/charcoal/dicyandiamide/benzoate), Powermax (emulsion explosive: ammonium nitrate/aluminum/ emulsifier), Powerditch (dynamite: nitroglycerin/ethylene glycol dinitrate/ammonium/nitrocellulose), Trenchrite (water gel: sodium/ammonium/calcium/methylamine nitrate/gelling agent), and two types of Tovex (emulsion explosive: ammonium/sodium/ aluminum/nitrate/methlyamine nitrate/gelling agent) were extracted in 2 mL of deionized water overnight at 4 °C to retard bacterial development. Approximately 10-cm2 sections of previously detonated pipe bombs containing black powder or Pyrodex were swabbed with precleaned cotton cloth moistened with (22) Waters Corp. Waters IC-Pak Column and Guard Column Care and use Manual; Milford, MA, 1994. (23) Doyle, J. M.; McCord, B. R. J. Chromatogr., B 1998, 714, 105-11.
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Figure 1. Anion standard separation using mobile phase consisting of 4 mM octanesulfonic acid. Conditions: 4.6 × 75 mm Waters ICPak Anion HR column; 10-µL injection; nonsuppressed conductivity detection. Peaks: (1) Cl-, (2) NO2-, (3) ClO3-, (4) NO3-, (5) SO42-, (6) SCN-, and (7) ClO4-.
deionized water. The swabs and unused control samples were extracted in 2 mL of deionized water overnight at 4 °C. RESULTS AND DISCUSSION The method described by McCord and Bender12 successfully separated SCN- and ClO4- using the Vydac 300IC405 column for casework analysis. The discontinuation of this column by the manufacturer necessitated the validation of a suitable replacement. A systematic approach was taken to develop a mobile phase that efficiently separates the anions of interest in low explosives residue which achieves a short analysis time for the strongly retained components of SCN- and ClO4-. The Waters IC-Pak Anion HR column with a 4 mM octanesulfonic acid mobile phase was chosen as the starting point of this study (J. Krol, personal communication). This is a reversedphase, ion-exchange (IEC) column with a polymethacrylate packing material containing a quaternary ammonium functional group. The results obtained with the 4 mM octanesulfonic acid mobile phase are shown in Figure 1. Although this method exhibits well-resolved separation, a shorter total analysis time for casework was desired. In an attempt to decrease the elution time for ClO4-, a lithium/ borate/gluconate/1-butanol/ mobile phase was prepared as described in the “care and use” manual that was packaged with the column.22 This mobile phase had not separated thiocyanate and perchlorate even after 60 min. The explanation is probably that thiocyanate and perchlorate are strongly retained because of their large hydrated ionic radii,24 which impede the exchange process. When 1 mM octanesulfonic acid was added to the mobile phase, the perchlorate again eluted in ∼31 min as it did using 4 mM octanesulfonic acid as the eluent. However, the times of the earlier eluting anions were reduced 1.5-2 min. Experiments were conducted to determine the optimum concentration of ACN for the system since column deterioration was observed at 12%. By varying the amount of ACN from 0 to 6%, the optimum concentration was determined to be 5% based on shorter total analysis time and good reproducibility (Figure 2). Reducing the percentage of ACN also increased the life of the
column by decreasing deterioration due to the precipitation of salts in the mobile phase, which could foul it.25 Additional tests at 5% ACN varying the amount of octanesulfonic acid from 0 to 6 mM determined that 5.5 mM was the optimum concentration of this counterion. This evaluation was based on the shortest analysis time in conjunction with the best resolution between ClO3- and NO3- (Figure 3). The results obtained using octanesulfonic acid were compared to those obtained using pentane-, hexane-, and heptanesulfonic acids. Octanesulfonic acid yielded better peak shape than the other sulfonic acids (Figure 4). A study of the size of the cation associated with the hydroxide counterion used to raise the pH of the base composition of the mobile phase from pH 7.6 to pH 8.5 was conducted to determine the effect on resolution. The hydroxides tested were lithium, sodium, potassium, and cesium. The best resolution was obtained when the pH was elevated to pH 8.5 using lithium hydroxide and got progressively worse as the size of the cation of the hydroxide increased (Figure 5). The results indicate that the size of the cation affects the ability of the anion to interact with the charged sites on the stationary phase. The effect on retention factor, resolution, and theoretical plate number obtained by raising the pH of the base mobile-phase composition from pH 7.6 to pH 8.5 using additional lithium hydroxide (LiOH) was compared to that obtained using tetrapropylammonium hydroxide (TPA(OH)), an ion-pairing reagent (Table 1). Elevating the pH of the base mobile phase to pH 8.5 with TPA(OH) resulted in an 89% increase in resolution over the
(24) Smith, F. C., Jr.; Chang, R. C. The Practice of Ion Chromatography; Wiley & Sons: New York, 1983; p 46.
(25) Johnson, E. L.; Stevenson, R. L. Basic Liquid Chromatography; Varian Associates, Inc.; Palo Alto, CA, 1978; p 135.
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Figure 2. Comparison of separation of anion standard using (A) 0 and (B) 5% and 5.5 mM octanesulfonic acid. Other experimental conditions as in Figure 1. Peaks: (1) Cl-, (2) NO2-, (3) ClO3-, (4) NO3-, (5) SO42-, (6) SCN-, and (7) ClO4-.
Figure 4. Comparison of types of sulfonic acids: 5% ACN and 5.5 mM each sulfonic acid. Plates: (A) pentane, (B) hexane, (C) heptane, and (D) octane. Other experimental conditions as in Figure 1. Peaks: (1) Cl-, (2) NO2-, (3) ClO3-, (4) NO3-, (5) SO4-2, (6) SCN-, and (7) ClO4-. Figure 3. Optimization of octanesulfonic acid. Plates: (A) 0, (B) 2, (C) 4, (D) 5, (E) 5.5, and (F) 6 mM. Other experimental conditions as in Figure 1. Peaks: (1) Cl-, (2) NO2-, (3) ClO3-, (4) NO3-, (5) SO42-, (6) SCN-, and (7) ClO4-.
pH 7.6 base mobile phase and a 44% increase over the base mobile phase raised to pH 8.5 with LiOH. Also illustrated is a 4-fold increase in the number of theoretical plates over the base mobile phase at pH 7.6 and a 2-fold increase over the base mobile phase raised to pH 8.5 with LiOH. This is evidence of dynamic coating ion-pair chromatography as described by Haddad and Patsalides26 and Dasgupta27 in which the tetrapropylammonium hydroxide is adsorbed on the stationary phase and provides additional ionexchange sites in the column. By producing a dynamic column coating, the tetrapropylammonium helps to limit irreversible adsorption of sample matrix ions on the stationary phase. With similar usage, the columns in this study that employed TPA(OH) as a component of the mobile phase demonstrated uniform performance for approximately four weeks while those that did not have TPA(OH) in the mobile phase displayed irreversible deterioration after only one to two weeks. Additionally, it is a good choice for adjusting the pH because tetrapropylammonium has a low limiting equivalent ionic conductance which sustains low background noise. (26) Haddad, P. R.; Patsalides, E. J. Chromatogr. Libr. 1992, 51B, B42. (27) Dasgupta, P. K. In Ion Chromatography; Tarter, J. G., Ed.; Marcel Dekker: New York, 1987; p 253.
A selection of anions including acetate, arsenate, benzoate, bromate, chromate, citrate, cyanate, cyanide, dichromate, fluoride, formate, iodate, iodide, oxalate, permanganate, phosphate, and tartrate was analyzed with the anions of interest in explosives residue and no interferences were observed. Comigration of azide with nitrate was the only significant interference found with respect to explosives residue in this study. Attempts were made to resolve these two anions by altering the selectivity of the column using 1 mM triethylamine, 3.7% 2-propanol, and different nalkanesulfonic acids including methane-, pentane-, hexane-, and heptanesulfonic acid. Adjustments in pH from 5.5 to 10 were also performed. Although none of these changes was successful in separating azide and nitrate on the Anion HR column, these anions may be separated using capillary electrophoresis,11 a technique used to confirm the IC results. Ion-exchange packings in general are less stable and offer less reproducibility than those for other liquid chromatography (LC) methods.17 Deterioration of the Anion HR column is due to strongly adsorbed materials which accumulate on the packing. Octanesulfonic acid is a large, bulky counterion which can compete with ClO4- for the exchange sites on the packing material and exclude the ClO4- from being highly retained. It is a good choice for a counterion in this separation because of its high exchange selectivity and its ability to enhance nonsuppressed conductivity detection due to its low limiting equivalent ionic conductance.18,28 These factors help to reduce background noise. Analytical Chemistry, Vol. 72, No. 10, May 15, 2000
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Figure 6. Effect of using tetrapropylammonium hydroxide to elevate pH to 8.5. Other experimental conditions: 2.75 mM boric acid, 0.37 mM D-gluconic acid, 1.05 mM lithium hydroxide, 1.25 mM glycerol, 5.5 mM octanesulfonic acid, and 5% . Peaks: (1) Cl-, (2) NO2-, (3) ClO3-, (4) NO3-, (5) SO42-, (6) SCN-, and (7) ClO4-.
Figure 5. Comparison of the effect of the size of the cation associated with the hydroxide counterion used to adjust pH: 5.5 mM octanesulfonic acid. Plates: (A) lithium, (B) sodium, (C) potassium, and (D) cesium. Other experimental conditions as in Figure 4. Peaks: (1) Cl-, (2) NO2-, (3) ClO3-, (4) NO3-, (5) SO42-, (6) SCN-, and (7) ClO4-. Table 1. Comparison of Chromatographic Parameters for pH-Adjusted Mobile Phase
chromatogr params
unadjusted mobile phase
retention factor (k) resolution (Rs) theoretical plates (N)
1.38 0.997 1610
adjusted to pH 8.5 w/LiOH w/TPA(OH) 1.05 1.31 2689
1.07 1.88 6022
Figure 6 illustrates the enhancements to the separation of anions of interest in low explosives residue using the mobile phase developed in this study. As compared to the method represented by Figure 1, total run time is reduced by more than 50%, facilitating greater sample throughput. There is a significant improvement in peak shape with decreased tailing in the later-eluting peaks. The improved peak shape resulted in increased peak height, which effected nearly a 4-fold increase in the number of theoretical plates (5130 vs 1300) for the late-eluting perchlorate ion as compared to the method of McCord and Bender.12 As compared to a resolution of ∼0.5 between ClO3- and NO3- utilizing the method of McCord and Bender,12 the resolution between these two peaks produced by the mobile phase in the analysis represented by (28) Dean, J. A. Lange’s Handbook of Chemistry, 13th ed.; McGraw-Hill: New York, 1985; pp 6/34-35.
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Figure 7. Examples of pipe bomb extracts. Plates: (A) standard, (B) black powder, (C) Pyrodex CTG, (D) KClO3/sugar, and (E) IMR 4350. Other experimental conditions as in Figure 5. Peaks: (A) (1) Cl-, (2) NO2-, (3) ClO3-, (4) NO3-, (5) SO42-, (6) SCN-, and (7) ClO4-; (B) (1) NO3-, (2) SO42-; (C) (1) Cl- and (2) SO4-2; (D) (1) Cl-, (2) ClO3-, (3) SO42-, and (4) unknown; (E) (1) Cl-, (2) SO42-, and (3) unknown.
Figure 6 is 1.3 (fully resolved peaks have a resolution of g1.5). A reproducibility study consisting of 12 replicate injections was conducted to determine the retention times of seven anions found
Table 2. Anion HR Column Reproducibility Study
mean std dev variance RSD (%)
chloride
nitrite
chlorate
nitrate
sulfate
thiocyanate
perchlorate
2.19 0.04 0.00 1.91
2.53 0.04 0.00 1.62
2.97 0.04 0.00 1.37
3.29 0.04 0.00 1.27
5.41 0.05 0.00 0.93
11.04 0.06 0.00 0.56
15.21 0.09 0.01 0.61
in low explosives residue. Table 2 shows stable retention times for each ion with an RSD of less than 2%. Tests were conducted on water extracts of known preblast (data not shown) and postblast samples of black powder, Pyrodex CTG, IMR 4350, and a mixture of KClO3 and sugar. Figure 7 illustrates typical results obtained for the postblast samples. The expected anions were observed and no interferences were evident. CONCLUSIONS The results of this study demonstrate the utility of combining ion-exchange, ion-exclusion, and ion-interaction methods in one mobile phase for the separation of anions in the residue from low explosives. This system is an improvement over previous methods in that the separation is simplified and the sensitivity is increased. Multicolumns, gradient elution, or suppressed conductivity detection is not necessary. The novel aspect of this dynamic mobile phase is that this is the first instance of an ion-pairing reagent and an ion-exclusion reagent being utilized in the same isocratic method. The separation achieved with this system demonstrates that, contrary to expectations derived from earlier results, each component of the mobile phase acts independently in solution. The benefits of this unusual eluent are short analysis times with increased resolution, reproducibility, and column life. The Waters
IC-Pak Anion HR column has proven to be a suitable replacement for the now discontinued Vydac 300IC405 column for the analysis of anions detected in low explosives residue. Additionally, this method has potential for the analysis of anions from a wide range of other sources such as environmental waste streams, biological fluids, and foodstuffs. ACKNOWLEDGMENT The authors thank Jim Krol of Waters Corp. for suggesting the original separation conditions for the Anion HR column, Kelly Mount of the FBI Chemistry Unit for valuable discourse regarding casework requirements, and the FBI Materials and Devices Unit for supplying the pipe bombs used in this study. This is publication number 00-01 of the Laboratory Division of the Federal Bureau of Investigation. Names of commercial manufacturers are provided for identification purposes only, and do not imply endorsement by the Federal Bureau of Investigation.
Received for review November 22, 1999. Accepted February 17, 2000. AC991346Z
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