As part of a large-scale study of nitrate contamination on Kirtland Air Force Base in central New Mexico, the USGS collected groundwater and surface water samples for artificial sweetener analyses. Samples were collected following standard USGS procedures (U.S. Geological Survey, variously dated), filtered to 0.45 microns, and frozen until analysis. Artificial sweeteners analyzed include neotame, acesulfame-K, aspartame, saccharin, and sucralose. Of the 49 sites sampled, 17 sites had measurable detections of artificial sweeteners. Neotame was the most commonly detected sweetener (n=12) followed by saccharin (n=5), acesulfame-K (n=2), aspartame (n=1), and sucralose (n=0). Concentrations ranged from 0.0003–0.011 μg/L for neotame, 0.019–0.63 μg/L for saccharin, 0.84–11 μg/L for acesulfame-K, and 0.0016 μg/L for aspartame. The detection limit of neotame was the lowest (0.0002 μg/L) followed by aspartame (0.001 μg/L), acesulfame-K (0.005 μg/L), saccharin (0.01 μg/L), and sucralose (0.1 μg/L). Three field blanks were collected, and each contained no measurable quantities of any artificial sweetener. Five field replicate pairs were collected and analyzed. Of these, three replicate pairs had no detections of artificial sweeteners above the laboratory reporting limit. A fourth replicate pair had 0.0003 μg/L (slightly above the reporting limit) neotame in the environmental sample and no measurable neotame in the replicate pair. A fifth replicate pair had 0.38 μg/L saccharin in the environmental sample and a small amount of saccharin in the replicate pair just below the reporting limit.
Method:
The Organic Geochemistry Research Laboratory at the USGS Kansas Water Science Center developed a research method, here named LCSU, to analyze a suite of artificial sweeteners in water. Similar to Ferrer and Thurman (2010), water samples were analyzed for acesulfame K, aspartame, neotame, saccharin, and sucralose using solid-phase extraction (SPE) and ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) with electrospray ionization (ESI) using multiple reaction monitoring (MRM). Samples were analyzed in positive ion mode for aspartame and neotame and in negative ion mode for acesulfame K, saccharin, and sucralose. Samples (123 mL) were extracted using 500 mg HLB SPE cartridges (Waters Corp., Milford, Ma). Aspartame-d5, neotame-d3, acesulfame K-d4, saccharin-13C6, and sucralose-d6 were used as surrogate standards. Standard curve, check standards, and blank samples were prepared in type I water (18.2MΩ-cm, <10 ppb TOC).
Samples, standards, and blanks were prepared for analysis by adding 122-mL sample, 900 µL of a 0.1 M phosphate buffer (pH 7), and 100 µL of 10% formic acid. A duplicate sample, matrix spiked sample, and a carryover blank were analyzed after every tenth sample. A check standard was analyzed after every twenty samples and blank samples were interspersed between the environmental samples. All standard solutions, blanks, and matrix spikes were treated the same as the environmental water samples.
SPE cartridges were rinsed with 4 mL methanol followed by 4 mL water. The prepared samples were extracted using a 24-port vacuum rack with Teflon tubing attached to 6-ml SPE cartridge adapters. The SPE cartridges were then allowed to dry for 30 min before being eluted using positive pressure (nitrogen) through a 0.2 micron PTFE filter into glass test tubes with 3 x 4-mL aliquots of methanol. Samples were then evaporated at 45°C to a volume of 25 µL and brought to a final volume of 350 µL with a 95/5 water/methanol solution. The samples were transferred to Waters max recovery vials and stored at 4°C until analysis. Chromatographic separation was performed on a Waters Acquity H-class bio UPLC with a Waters Acquity BEH 2.1 um, 100x1.7 mm column and mobile phase A, 0.3 % formic acid, and B, acetonitrile/methanol (80/20%).
The compounds were analyzed using multiple reaction monitoring (MRM). Compounds were identified using retention times, the m/z of the precursor ion, the m/z of the fragment ions, and the ratio of the fragment ions. The detected compounds were quantitated using the ratio of the area of one ion (quantifying ion) of the analyte to the area of the respective ion of the surrogate internal standard. The reporting levels were: 0.001, 0.0002, 0.005, 0.01, and 0.1 μg/L for aspartame, neotame, acesulfame K, saccharin, and sucralose respectively.
References:
Ferrer, I. and Thurman, E.M., 2010, Analysis of sucralose and other sweeteners in water and beverage samples by liquid chromatography/time-of-flight mass spectrometry: Journal of Chromatography A, v. 1217, issue 25, p. 4127-4134.
U.S. Geological Survey, variously dated, National field manual for the collection of water-quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chaps. A1-A10, available online at http://pubs.water.usgs.gov/twri9A.
