Brian De Borba - Academia.edu (original) (raw)

Papers by Brian De Borba

American Laboratory, 2002

Journal of Environmental Monitoring, 2001

Interest in possible sources of perchlorate (ClO4) that could lead to environmental release has b... more Interest in possible sources of perchlorate (ClO4) that could lead to environmental release has been heightened since the Environmental Protection Agency placed this anion on its Contaminant Candidate List for drinking water. Although recent investigations have suggested that fertilizers are minor contributors to environmental perchlorate contamination overall, there is still interest in screening commercial products for possible contamination and quantitating perchlorate when it is found. Ion chromatography (IC) has been used for this application owing to its speed, low detection limits, widespread availability, and moderate ruggedness relative to other techniques. However, fertilizer matrixes complicate the IC analysis relative to potable water matrixes. In this study, the performance of poly(vinyl alcohol) gel resin IC columns (100 mm and 150 mm) was evaluated for fertilizer matrixes using method EPA/600/R-01/026. The NaOH eluent included an organic salt, sodium 4-cyanophenoxide. Detection was by suppressed conductivity. A set of 55 different field samples representing 48 products and previously used by the EPA to assess occurrence of perchlorate in fertilizers (EPA/600/R-01/049) was reanalyzed on the 150 mm column. The 100 mm column was used to further investigate the positive hits. Both columns gave satisfactory performance in fertilizer matrixes, with spike recoveries (+/- 15%), assured reporting levels (0.5-225 microg g(-1) except for one at 1,000 microg g(-1)), accuracy (relative error &amp;amp;amp;lt; 30% always and most &amp;amp;amp;lt; 15%), and precision [injection-to-injection reproducibility &amp;amp;amp;lt; 3% relative standard deviation (RSD)] comparable to those reported in other studies. Performance did not vary substantially between column lengths. Lastly, the results of this investigation provided further evidence in support of the conclusions that had been reached previously by the EPA on the occurrence of perchlorate in fertilizers.

When reporting or using results of quantitative analysis, it is important to understand the uncer... more When reporting or using results of quantitative analysis, it is important to understand the uncertainties associated with the reported values. Every method, no matter how good, has limitations that create some degree of measurement error, which can be manifested as inaccuracy, imprecision, or a combination of these. Relative measurement error tends to increase as analyte concentrations decrease, because analyte responses decrease in relation to background signals. At very low concentrations, analyte signals become difficult to distinguish from background signals, resulting in high rates of false positives (reporting a detection when no analyte is present) and false negatives (reporting no detection when the analyte is present).

Journal of Chromatography A, 2003

The determination of low ng / l sodium in the power industry is critical in identifying and preve... more The determination of low ng / l sodium in the power industry is critical in identifying and preventing corrosive conditions in many power plant components. To address this challenge, we developed an ion chromatographic method to determine sodium at ng / l concentrations in power plant samples. The ion chromatography system used on-line electrolytic eluent generation with a continuously regenerated trap column to minimize system contaminants and therefore allow low detection limits. A 10-ml sample was preconcentrated on a cation-exchange column followed by separation on a high capacity column with 20 mM methanesulfonic acid and detected using suppressed conductivity. Sodium response was linear from 25 to 250 2 ng / l (r 50.9990). Method performance was evaluated by analyzing synthetic samples containing ethanolamine as an additive that are typical of samples encountered in the power industry. Retention time precision for sodium was less than 0.4% (n57) in ultrapure water and simulated sample matrices. The recovery of sodium spiked in synthetic samples at the low ng / l levels was 85-110%. System parameters were optimized to achieve method detection limits in ultrapure water to 3.2 ng / l. 

Journal of Chromatography A, 2007

The determination of biogenic amines in alcoholic beverages is important to assess the potential ... more The determination of biogenic amines in alcoholic beverages is important to assess the potential risks associated with the consumption of high concentrations of these compounds. In addition, product storage conditions and the length of storage can cause the formation of biogenic amines that reduce product quality. We report a new method using cation-exchange chromatography with either suppressed conductivity, integrated pulsed amperometry, UV, or a combination of these detection techniques to determine biogenic amines in alcoholic beverages. The main objective was to provide a direct comparison between IPAD and suppressed conductivity detection for determining biogenic amines in alcoholic beverages. Suppressed conductivity is the simplest detection approach for determining putrescine, cadaverine, histamine, agmatine, phenylethylamine, spermidine, and spermine with good sensitivity (0.004-0.08 mg/l) and was used to evaluate the influence of storage time and conditions on the evolution of biogenic amines in alcoholic beverages. Integrated pulsed amperometric detection (IPAD) detects more biogenic amines than suppressed conductivity detection, enabling the detection of dopamine, tyramine, and serotonin. Tyramine was simultaneously determined by UV detection and IPAD to provide confirmation and ensure the accuracy of the analytical results. The linearity of biogenic amine responses was within 0.1-20 mg/l and peak area precisions were 0.24-4.97% for IPAD, suppressed conductivity-IPAD, and UV detection. The sensitivity for the 10 biogenic amines using the 3 detection techniques varied considerably from 0.004-1.1 mg/l and recoveries were within 85-122%. (B.M. De Borba). amines by acetylation and oxidation reactions mediated by the enzymes monoamine oxidase, diamine oxidase, and polyamine oxidase . However, the consumption of an excess amount of these amines can induce severe toxicological effects and produce various physiological symptoms, such as nausea, respiratory distress, headache, sweating, heart palpitations, and hyper-or hypotension .

Journal of Chromatography A, 2005

Analytical Chemistry, 2000

The practice of determining acid concentrations by titrations has remained unchanged for more tha... more The practice of determining acid concentrations by titrations has remained unchanged for more than a century. We introduce a new approach to the determination of acid concentrations based on cation exchange chromatography. We demonstrate the ability of sulfonated styrene-divinylbenzene based stationary phases to separate the hydrogen ion from other monovalent cations. The eluent is a dilute solution of a neutral salt, sometimes containing a small concentration of the corresponding acid, e.g., sodium ethanesulfonate, pH adjusted with ethanesulfonic acid. The high equivalent conductance (approximately 350 S.cm2/equiv) of H+ and relatively low eluent concentration allows sensitive conductometric detection of H+, down to the 50 microM level under favorable conditions. The conductometric response to H+ can be linear over a wide range of H+ concentrations, from sub-millimolar to several molar concentrations. The system allows the rapid quantitation of strong acids; weak acids can also be determined depending on pKa and injected concentration. The determinations of several strong and weak acids are presented along with factors that govern their chromatographic analysis.

Analytica Chimica Acta, 2006

Two inline matrix diversion methods were developed for the sensitive analysis of perchlorate in a... more Two inline matrix diversion methods were developed for the sensitive analysis of perchlorate in a matrix comprising up to 1000 mg l(-1) of chloride, sulfate and bicarbonate ions using suppressed ion chromatography and conductivity detection. The first method used a cryptand C1 concentrator column, which exhibited a high selectivity for perchlorate ion over the other matrix anions. After retaining the sample anions in a concentrator column derivatized with a crytpand phase, a rinse step was implemented with a weak base to divert the matrix ions to waste while selectively retaining perchlorate in the concentrator column for subsequent analysis. The analysis was done using a 2mm IonPac AS16 or 2 mm IonPac AS20 separator column. The second method was a two-dimensional matrix diversion method with a focus on improving the detection sensitivity. The first dimension was used to achieve some resolution of the matrix ions from perchlorate. The perchlorate ion was then diverted into a concentrator column for subsequent analysis in the second dimension. By pursuing analysis using a 4mm IonPac AS16 or IonPac AS20 column in the first dimension and subsequently pursuing analysis using a 2mm IonPac AS16 or IonPac AS20 column format, excellent sensitivities were achieved when the first and second dimensions were operated at the same linear flow velocity (cm min(-1)). While sensitive detection of perchlorate in the low microg l(-1) regime was achieved by the above methods in the presence of matrix ions, superior recovery for perchlorate was demonstrated under a variety of matrix concentrations by the second method.

Journal of Chromatography A, 2001

The use of on-line dialysis as a sample preparation technique for ion chromatography is described... more The use of on-line dialysis as a sample preparation technique for ion chromatography is described. A fully automated sample preparation device coupled to an ion chromatographic system for the determination of anions and cations in various matrices is presented. The method was based on stopped-flow dialysis, where the samples were continuously dialyzed for 10 min while the acceptor solution was stationary within the recipient channel. The matrices examined, without additional sample treatment, included milk, untreated wastewater, fruit juice, engine coolant, and a multivitamin tablet. The analyte recoveries for anions and cations in various matrices ranged from 87 to 106%. In addition, multiple sample injections were performed and repeatabilities were found in the range of 0.2 to 4%.