Lab Science News

Background
Today there are two common colorimetric techniques using a Diphenylcarbazide (DPC) solution for determining Hexavalent Chromium (Cr+6) in RCRA site water samples. EPA Method 7196, a colormetric method, analyzes the untreated or filtered sample as is. EPA Method 7199, an ion chromatographic method, separates the Cr+6 ion from interferences and is then followed by post column reaction with DPC. Therefore, colored matrices or matrices containing chemical interferences may be better analyzed by ion chromatography as shown in the following example.

Analytical Challenge
Two highly colored samples were received from a treatability study. They had gone through an oxidative treatment process to remove VOCs. One of the requested analyses was Cr+6. The two samples were analyzed fi rst by EPA 7196. When an acidified sample is reacted with the DPC solution, a pink color (540 nm) appears. The absorbance is measured and its intensity is proportional to the concentration of Cr+6 in the sample. These samples were highly colored, so a background sample was also prepared which contained all of the analytical reagents except for the color reagent. The absorbance of the background sample is subtracted from the color-reacted sample to correct for any color interference. In these samples, after the color reagent was added to the sample, the sample became colorless. This indicated an interference with the normal coloring reaction. The DPC reagent is dissolved in acetone. To rule out a possible interference from the acetone, a third pair of samples were prepared adding acetone without DPC reagent. This experiment showed that the chemical interference in the sample was reacting with the DPC reagent. We suspect the chemical interference in the sample also produced the observed violet color and was from an oxidizing agent used in the treatment process, possibly potassium permanganate, a known method interferent.

The Results
In addition to the EPA 7196 method, the samples were then analyzed for Cr+6 using Ion Chromatography by EPA Method 7199. Using this method, good chromatography and QC data was obtained on these samples. The results have been compared below. A comparison of the results shows the impact of the interferences between the two methods. Because of interferences, the colorimetric method is prone to false negatives and matrix spike recovery failure. The IC method accurately quantitates Cr+6 results with good matrix spike recoveries.

Conclusion
The Ion Chromatography Method, EPA 7199, may be the better choice for the analysis for Cr+6, because it removes color and chemical interferences in samples of potentially diffi cult matrices. The chromatogram in the fi gure below demonstrates the effectiveness in the separation from interferences. In addition, Method 7199 can be performed rapidly, at least four samples per hour, which is very beneficial due to the short (24-hour) hold time specified by the method. In samples containing color and chemical interferences, the Cr+6 value is more accurately reported by method 7199.

Learn more about hexavalent chromium testing…
Learn more about the element chromium…

Columbia Analytical recently conducted a field evaluation of Odor Scan, a suite of methods that has been designed to address compounds that have very low odor thresholds and are irritating at low levels. The suite consists of sampling and analytical methods for carboxylic acids (volatile organic/fatty acids), amines, reduced sulfur compounds and odorous volatile organic compounds (VOCs) such as microbial volatile organic compounds (MVOCs), and high molecular weight aldehydes and alcohols. Two of these methods (ie. amines, carboxylic acids) were developed and validated by Columbia Analytical.

The study was conducted to evaluate the new methods under field conditions and to collect data to profi le the airborne contaminants and odors associated with a composting facility. Due to the wide range of compounds anticipated and the fact that some analyte overlap exists among the methods, this sampling event was also used to compare sampling and analytical methods and sampling media.

The facility composts a variety of materials including green waste, cow manure, construction materials (e.g., sheet rock), and chicken and fish waste. The compost was piled in seven uncovered windrows that were located outdoors on a concrete slab. At this facility, the composting process takes approximately six to seven weeks from the time the material is received until it is ready for screening. Heavy equipment called a SCAT is used to turn the material in the windrows, which helps aerate the product, an important component of the composting process. The final compost product generated is sold for landscaping.

Air samples were collected at the property’s fence line, on top of compost piles and on the SCAT used to turn the compost piles. Sampling media, fl ow rates and analytical methodologies utilized are summarized in Table 1. Calibrated personal sampling pumps were used to collect the solid sorbent samples. For some target compounds (e.g., VOCs, reduced sulfurs), collocated samples were collected using more than one media type.

The analysis of samples for tentatively identifi ed compounds (TICs) by EPA TO-15 and NIOSH 2549 was achieved by comparing the mass spectra of the selected peaks with those from the NIST library, which contains spectra from more than 120,000 compounds. The concentrations of TICs were estimated by comparing the peak area of the compound with that of the nearest internal standard. As the compounds present at the highest concentrations are often not the odorous ones, the analysis was not limited to the 15 largest peaks, as is often the case with these methods. Instead, for method validation purposes, all those peaks with suffi cient response to permit identifi cation of the mass spectra were selected. In some cases, it was not possible to locate the peaks buried in the complex matrix. For some compounds (e.g., carboxylic acids), it was diffi cult to accurately estimate peak area because of the wedge shape of the peaks produced using the EPA and NIOSH methods. The Columbia Analytical Carboxylic Acid method resolves this problem.

Approximately 350 different compounds were identifi ed during the study, including many of the reduced sulfur, carboxylic acid and amine compounds on the OdorScan target lists as well as a diverse mixture of VOCs. Trimethylamine was the predominant amine, while acetic, butyric, propionic and isovaleric acids were the principal carboxylic acids found in many of the samples. When the two VOC methods (NIOSH 2549, EPA TO-15) were compared, more substances were detected in the samples collected on thermal desorption tubes (265 compounds) than in Silco canisters (219 compounds). The types of VOCs identifi ed included higher molecular weight alcohols, aldehydes and ketones (e.g., 2-heptanol, decanal, 2-octanone), terpenes (α & β-pinene, d-limonene, carene), furans, phenols and cresols. Microbial volatile organic compounds were also detected in several of the samples.

As expected, the highest levels were observed in the samples collected near the source: at the top of the compost piles and during the turning of the compost. Samples collected from the newer piles tended to be more complex with respect to the VOCs and reduced sulfur compounds

detected. Based on comparisons with reported odor thresholds, butyric acid, valeric acid, isovaleric acid, acetic acid, propionoic acid, isobutyric acid, dimethyl disulfi de, acetaldehyde, decanal, nonanal, benzaldehyde and, p-cresol were likely contributors to the odor detected at the edge of the property. The preponderance of carboxylic acids present at levels above their odor thresholds was consistent with the sweaty/fecal/sour odor detected.

Although the NIOSH 2549 Method detected the greatest number of compounds, it did not appear to be an effective technique for identifying the presence of amines. The method also underestimated carboxylic acid levels. This study suggests that even a fairly comprehensive method, such as NIOSH 2549, does not effectively capture the full range of compounds that may be contributing to a complex contaminant matrix. The use of the four different methods that comprise OdorScan was a better choice for characterizing the airborne contaminants associated with this odorous source.

Read more about Odor Investigations…

Read more about Odor Compounds at a Compost Facility (PDF)…

Read more about Odor Testing…

On Tuesday, January 11th, 2005 the Committee to Access the Health Implications of Perchlorate Ingestion, convened by the National Research Council at the request of the EPA, DOD, NASA, and the DOE, released their report on the adverse health effects of perchlorate ingestion from clinical, toxicological and public health perspectives. The report also evaluated relevant scientific literature and key fi ndings of the EPA’s 2002 draft risk assessment document on perchlorate. The full report can be found on-line at http:// www.nap.edu/catalog/11202.html.

The committee noted that a noobserved- effect level (NOEL) or lowestobserved- adverse-effect level (LOAEL) identifi ed from a critical study, is used as the basis for establishing a reference dose for daily oral exposures. The committee decided to use a NOEL rather than a LOAEL as the basis for perchlorate risk assessment. They based their reference daily dose on the identified critical study done by Greer, et al (2002)1 in which healthy men and women were given doses of perchlorate of 0.007 to 0.5 mg/Kg body weight per day for 14 days. In this study, the NOEL was found to be 0.007 mg/Kg/day. Using this amount and applying an uncertainty factor of 10 to protect the most sensitive population (identifi ed as pregnant women who may have hypothyroidism or iodide defi ciency), the committee recommended a reference daily dose of perchlorate of 0.0007 mg/Kg of body weight per day from all sources. The EPA’s draft reference daily dose from the 2002 risk assessment was 0.00003 mg/Kg per day. The committee also noted that additional studies are needed, especially long-term, chronic exposure as well as clinical, mechanistic and epidemiological studies.

The release of the report generated a flurry of media reports with widely different safe drinking water levels touted – everything from maximum levels of 3 ppb to 200 ppb. However, as of February 18, 2005, the EPA has set an offi cial reference dose (RfD) of 0.0007mg/kg/day of perchlorate consistant with the National Research Council’s reference dose. The EPA translates the new RfD to a Drinking Water Equivalent Level (DWEL) of 24.5 ppb. As new information becomes available, CAS will post updates at www.caslab.com.

Learn more about Perchlorate Testing…

1 Greer, M/A., G, Goodman, R.C. Pleus, and S.E. Greer. 2002. Health effects assessment for environmental perchlorate contamination: The dose response for inhibition of thyroidal radioiodide uptake in humans. Environ. Health Perspect. 110:927