The microextraction/ion chromatographic (IC) method developed in this study involves extraction o... more The microextraction/ion chromatographic (IC) method developed in this study involves extraction of 9 haloacetic acids (HAAs) from aqueous samples (acidified with sulfuric acid to a pH of < 0.5 and amended with copper sulfate pentahydrate and sodium sulfate) with methyl tert-butyl ether (MTBE), back extraction into reagent water, and analysis by IC with conductivity detection. The separation column consists of an Ion Pac AG-11 (2 mm id x 50 mm length) guard column and an Ion Pac AS-11 (2 mm id x 250 mm length) analytical column, and the concentration column is a 4 mm id x 35 mm length Dionex TAC-LP column. Use of the 2 mm id Dionex AS-11 column improved detection limits especially for trichloracetic acid (TCAA), bromodichloroacetic acid (BDCAA), dibromochloroacetic acid (DBCAA), and tribromoacetic acid (TBAA). The peak interfering with BCAA elutes at the same retention time as nitrate; however, we have not confirmed the presence of nitrate. Stability studies indicate that HAAs are...
Journal - Association of Official Analytical Chemists
Method 8080, as published in the Second Edition of &quot;Test Methods for Evaluating Solid Wa... more Method 8080, as published in the Second Edition of &quot;Test Methods for Evaluating Solid Waste,&quot; EPA Manual SW-846, has been evaluated in a single-laboratory study. The Florisil procedure recommended in Method 8080 for sample cleanup does not separate organochlorine pesticides (OCPs) from the polychlorinated biphenyls (PCBs). Consequently, gas chromatographic analysis of OCPs on the packed column recommended in the method may result in false identifications or in no identifications at all when PCBs are present. Therefore, silica gel was substituted for Florisil, a capillary column was substituted for the packed column, and a sulfur cleanup procedure was incorporated in the method. The revised method was evaluated with samples spiked at 3 concentrations. Precision and accuracy indicate that the revised method can be reliably applied to the determination of OCPs and PCBs in liquid and solid matrixes. Detection limits for liquid matrixes range from 0.02 to 0.09 micrograms/L for OCPs and from 0.5 to 0.9 micrograms/L for PCBs. Detection limits for solid matrixes range from 1 to 6 micrograms/kg for OCPs and from 60 to 70 micrograms/kg for PCBs.
A joint U.S. Environmental Protection Agency (USEPA)-AOAC interlaboratory method validation study... more A joint U.S. Environmental Protection Agency (USEPA)-AOAC interlaboratory method validation study was conducted on USEPA National Pesticide Survey (NPS) Method 6, &quot;Determination of Ethylene Thiourea (ETU) in Finished Drinking Water by Gas Chromatography with a Nitrogen-Phosphorus Detector.&quot; The purpose of the study was to determine and compare the mean recoveries and precision for determination of ETU in reagent water and finished drinking waters. The study design was based on Youden&#39;s nonreplicate plan for collaborative tests of analytical methods. The waters were spiked with ETU at 6 concentrations levels, prepared as 3 Youden pairs. In the method, the test water is extracted by passing the sample through an absorbent matrix type tube. ETU is recovered from the tube with methylene chloride, the extract is solvent-exchanged to ethyl acetate, and an aliquot of each extract is analyzed by gas chromatography using a nitrogen-phosphorus detector. Twelve laboratories participated in the study. Data were analyzed using a USEPA computer program, which measured recovery and precision for ETU and compared the performance of the method between the 2 water types. Over the concentration range tested, the mean percent recoveries of ETU were 82-92% in reagent water and 85-98% in finished drinking water. The range of the between-laboratory relative standard deviations (RSDR) for the 6 concentrations was 5-24% in reagent water, but was only 4-9% in finished drinking water. The range of the within-laboratory relative standard deviations (RSDr) was 6-14% for reagent water and 6-10% for finished drinking water. Results for the 2 water matrixes showed no statistically significant differences.(ABSTRACT TRUNCATED AT 250 WORDS)
Journal - Association of Official Analytical Chemists
A joint U.S. Environmental Protection Agency/AOAC interlaboratory method validation study was con... more A joint U.S. Environmental Protection Agency/AOAC interlaboratory method validation study was conducted on EPA Method 508, Determination of Chlorinated Pesticides in Water by Gas Chromatography with an Electron Capture Detector, to determine the mean recovery and precision for analyses of 29 pesticides in reagent water and finished drinking water. The study design was based on Youden&#39;s nonreplicate plan for collaborative tests of analytical methods. The waters were spiked with 29 pesticides at 6 concentration levels, as 3 Youden pairs. Eleven volunteer laboratories extracted the spiked test waters with methylene chloride, performed a solvent exchange with methyl tert-butyl ether, and analyzed an aliquot of each extract by gas chromatography with electron capture detection. Results were analyzed using an EPA computer program, interlaboratory Method Validation Study (IMVS), which measured recovery and precision for each of the 29 pesticides and compared the performance of the method between water types. Method 508 was judged acceptable for all analytes tested. Only 3 analytes (alpha-chlordane, 4,4&#39;-DDE, and methoxychlor) exhibited practical significant matrix effects. The method has been adopted official first action.
Journal - Association of Official Analytical Chemists
A joint U.S. Environmental Protection Agency/AOAC interlaboratory method validation study was con... more A joint U.S. Environmental Protection Agency/AOAC interlaboratory method validation study was conducted on EPA Method 507, Determination of Nitrogen- and Phosphorus-Containing Pesticides in Finished Drinking Water by Gas Chromatography with a Nitrogen-Phosphorus Detector, to determine the mean recovery and precision for analyses of 45 nitrogen- or phosphorus-containing pesticides in reagent water and finished drinking waters. The study design was based on Youden&#39;s nonreplicate plan for collaborative tests of analytical methods. The waters were spiked with 45 nitrogen- or phosphorus-containing pesticides at 6 concentration levels, prepared as 3 Youden pairs. Ten volunteer laboratories extracted the spiked test waters with methylene chloride, performed a solvent exchange with methyl tert-butyl ether, and analyzed an aliquot of each extract by gas chromatography using a nitrogen-phosphorus detector. Results were analyzed using an EPA computer program, which measured recovery and precision for each of the 45 pesticides and compared the performance of the method between water types. Method 507 was judged acceptable for all analytes tested except merphos, which thermally decomposed in the injection port of the gas chromatograph. Five compounds (carboxin, disulfoton, metolachlor, pronamide, and simazine) exhibited statistically significant matrix effects for the finished drinking water. The method has been adopted official first action by AOAC.
Supercritical fluid extraction (SFE) of the marine red alga Plocamium cartilagineum, which is kno... more Supercritical fluid extraction (SFE) of the marine red alga Plocamium cartilagineum, which is known to contain complex mixtures of halogenated monoterpenes, was investigated. P. cartilagineum samples were extracted by SFE with carbon dioxide and modified carbon dioxide containing up to 10% methanol at different pressure and temperature conditions to establish the optimum conditions for extraction. These conditions were then used in the extraction of halogenated monoterpenes from 2 different samples of P. cartilagineum: one from Davenport, CA, and the other from Casa Beach (San Diego, CA). Several halogenated monoterpenes isolated by conventional solvent extraction with methanol and purified by column chromatography were used as the reference compounds for the determination of the extraction efficiency in the SFE experients. Plocamium cartilagineum belongs to the red alga family--Plocamiaceae, and has been found to contain a large number of halogenated monoterpenes, whose structures typically contain 1-6 bromine and/or chlorine atoms. P. cartilagineum grows along the Pacific coast from Washington to Chile, the British Isles, Australia, and Spain. Interestingly, P. cartilagineum collected from different geographical areas in the world are all reported to produce halogenated monoterpenes, but of different structural types and halogen substitution patterns. Most of these halogenated monoterpenes have been found to exhibit varied biological activities, including antifungal, antimicrobial, and molluscicidal activity.
An extraction technique, involving homogenization of a sediment sample with dichloromethane at du... more An extraction technique, involving homogenization of a sediment sample with dichloromethane at dual pH and phase separation by centrifugation, was used in the determination of fifty-one organic priority pollutants as identified in a standard reference sediment sample. The extract containing the base/neutral compounds was fractionated by gel permeation chromatography (GPC). Separation and identification of individual compounds in the silica gel fractions was accomplished by gas chromatography/mass spectrometry (GC/MS). Method precision and accuracy are discussed. Tentative identifications of other organic compounds found in the sediment are given.
Matrix metalloproteinases (MMPs) are a family of zinc-dependent proteolytic enzymes that degrade ... more Matrix metalloproteinases (MMPs) are a family of zinc-dependent proteolytic enzymes that degrade extracellular matrix (ECM) components like collagen, fibronectin, and laminin. While this activity is important for normal development, morphogenesis, and wound healing, deregulation of MMP activity has been implicated in a number of cardiovascular diseases, including congenital heart defects, atherosclerosis, myocardial infarction, and congestive heart failure. MMPs are good potential diagnostic indicators of cardiovascular disease, but current detection methods are time consuming and quite laborious. This review will discuss MMP biology, current methods for detection of MMPs from patient samples, and potential new developments in multiplexed analysis of MMPs.
... Chromatography/Mass Spectrometry Viorica Lopez-Avila,* Pat Hirata, Susan Kraska, Michael Flan... more ... Chromatography/Mass Spectrometry Viorica Lopez-Avila,* Pat Hirata, Susan Kraska, Michael Flanagan, and John H. Taylor, Jr. Acurex Corporation, Energy and Environmental Division, 555 Clyde Avenue, Mountain View, California 94039 ...
Disposable cartridges containing 1 g of Florisil are investigated for cleanup of extracts obtaine... more Disposable cartridges containing 1 g of Florisil are investigated for cleanup of extracts obtained from various environmental matrices. Elution patterns and recoveries are determined for 22 chlorinated hydrocarbons and 16 phthalate esters in the presence of interferents such as corn oil, diesel hydrocarbons, organochlorine pesticides, and chlorinated phenols. Hexane, hexane/diethyl ether (1:1), hexane/acetone (9:1), and various combinations of hexane/methylene chloride are used as eluants.
... 468 Reproduction (photocopying) of editorial content of this journal is prohibited without pu... more ... 468 Reproduction (photocopying) of editorial content of this journal is prohibited without publisher&#x27;s permission. Viorica Lopez-Avila* and NS Dodhiwala Mid-Pacific Environmental Laboratory, 625-B Clyde Avenue, Mountain View, California 94043 ...
... Viorica Lopez-Avila Midwest Research Institute, 425 Volker Boulevard, Kansas City, Missouri 6... more ... Viorica Lopez-Avila Midwest Research Institute, 425 Volker Boulevard, Kansas City, Missouri 641 10 Ronald A. Hites&amp;#x27; School of Public and Environmental Affairs and Department of ... Wastewater samples were collected in 1-gal, amber glass bottles directly from the clarifier tank. ...
The microextraction/ion chromatographic (IC) method developed in this study involves extraction o... more The microextraction/ion chromatographic (IC) method developed in this study involves extraction of 9 haloacetic acids (HAAs) from aqueous samples (acidified with sulfuric acid to a pH of < 0.5 and amended with copper sulfate pentahydrate and sodium sulfate) with methyl tert-butyl ether (MTBE), back extraction into reagent water, and analysis by IC with conductivity detection. The separation column consists of an Ion Pac AG-11 (2 mm id x 50 mm length) guard column and an Ion Pac AS-11 (2 mm id x 250 mm length) analytical column, and the concentration column is a 4 mm id x 35 mm length Dionex TAC-LP column. Use of the 2 mm id Dionex AS-11 column improved detection limits especially for trichloracetic acid (TCAA), bromodichloroacetic acid (BDCAA), dibromochloroacetic acid (DBCAA), and tribromoacetic acid (TBAA). The peak interfering with BCAA elutes at the same retention time as nitrate; however, we have not confirmed the presence of nitrate. Stability studies indicate that HAAs are...
Journal - Association of Official Analytical Chemists
Method 8080, as published in the Second Edition of &quot;Test Methods for Evaluating Solid Wa... more Method 8080, as published in the Second Edition of &quot;Test Methods for Evaluating Solid Waste,&quot; EPA Manual SW-846, has been evaluated in a single-laboratory study. The Florisil procedure recommended in Method 8080 for sample cleanup does not separate organochlorine pesticides (OCPs) from the polychlorinated biphenyls (PCBs). Consequently, gas chromatographic analysis of OCPs on the packed column recommended in the method may result in false identifications or in no identifications at all when PCBs are present. Therefore, silica gel was substituted for Florisil, a capillary column was substituted for the packed column, and a sulfur cleanup procedure was incorporated in the method. The revised method was evaluated with samples spiked at 3 concentrations. Precision and accuracy indicate that the revised method can be reliably applied to the determination of OCPs and PCBs in liquid and solid matrixes. Detection limits for liquid matrixes range from 0.02 to 0.09 micrograms/L for OCPs and from 0.5 to 0.9 micrograms/L for PCBs. Detection limits for solid matrixes range from 1 to 6 micrograms/kg for OCPs and from 60 to 70 micrograms/kg for PCBs.
A joint U.S. Environmental Protection Agency (USEPA)-AOAC interlaboratory method validation study... more A joint U.S. Environmental Protection Agency (USEPA)-AOAC interlaboratory method validation study was conducted on USEPA National Pesticide Survey (NPS) Method 6, &quot;Determination of Ethylene Thiourea (ETU) in Finished Drinking Water by Gas Chromatography with a Nitrogen-Phosphorus Detector.&quot; The purpose of the study was to determine and compare the mean recoveries and precision for determination of ETU in reagent water and finished drinking waters. The study design was based on Youden&#39;s nonreplicate plan for collaborative tests of analytical methods. The waters were spiked with ETU at 6 concentrations levels, prepared as 3 Youden pairs. In the method, the test water is extracted by passing the sample through an absorbent matrix type tube. ETU is recovered from the tube with methylene chloride, the extract is solvent-exchanged to ethyl acetate, and an aliquot of each extract is analyzed by gas chromatography using a nitrogen-phosphorus detector. Twelve laboratories participated in the study. Data were analyzed using a USEPA computer program, which measured recovery and precision for ETU and compared the performance of the method between the 2 water types. Over the concentration range tested, the mean percent recoveries of ETU were 82-92% in reagent water and 85-98% in finished drinking water. The range of the between-laboratory relative standard deviations (RSDR) for the 6 concentrations was 5-24% in reagent water, but was only 4-9% in finished drinking water. The range of the within-laboratory relative standard deviations (RSDr) was 6-14% for reagent water and 6-10% for finished drinking water. Results for the 2 water matrixes showed no statistically significant differences.(ABSTRACT TRUNCATED AT 250 WORDS)
Journal - Association of Official Analytical Chemists
A joint U.S. Environmental Protection Agency/AOAC interlaboratory method validation study was con... more A joint U.S. Environmental Protection Agency/AOAC interlaboratory method validation study was conducted on EPA Method 508, Determination of Chlorinated Pesticides in Water by Gas Chromatography with an Electron Capture Detector, to determine the mean recovery and precision for analyses of 29 pesticides in reagent water and finished drinking water. The study design was based on Youden&#39;s nonreplicate plan for collaborative tests of analytical methods. The waters were spiked with 29 pesticides at 6 concentration levels, as 3 Youden pairs. Eleven volunteer laboratories extracted the spiked test waters with methylene chloride, performed a solvent exchange with methyl tert-butyl ether, and analyzed an aliquot of each extract by gas chromatography with electron capture detection. Results were analyzed using an EPA computer program, interlaboratory Method Validation Study (IMVS), which measured recovery and precision for each of the 29 pesticides and compared the performance of the method between water types. Method 508 was judged acceptable for all analytes tested. Only 3 analytes (alpha-chlordane, 4,4&#39;-DDE, and methoxychlor) exhibited practical significant matrix effects. The method has been adopted official first action.
Journal - Association of Official Analytical Chemists
A joint U.S. Environmental Protection Agency/AOAC interlaboratory method validation study was con... more A joint U.S. Environmental Protection Agency/AOAC interlaboratory method validation study was conducted on EPA Method 507, Determination of Nitrogen- and Phosphorus-Containing Pesticides in Finished Drinking Water by Gas Chromatography with a Nitrogen-Phosphorus Detector, to determine the mean recovery and precision for analyses of 45 nitrogen- or phosphorus-containing pesticides in reagent water and finished drinking waters. The study design was based on Youden&#39;s nonreplicate plan for collaborative tests of analytical methods. The waters were spiked with 45 nitrogen- or phosphorus-containing pesticides at 6 concentration levels, prepared as 3 Youden pairs. Ten volunteer laboratories extracted the spiked test waters with methylene chloride, performed a solvent exchange with methyl tert-butyl ether, and analyzed an aliquot of each extract by gas chromatography using a nitrogen-phosphorus detector. Results were analyzed using an EPA computer program, which measured recovery and precision for each of the 45 pesticides and compared the performance of the method between water types. Method 507 was judged acceptable for all analytes tested except merphos, which thermally decomposed in the injection port of the gas chromatograph. Five compounds (carboxin, disulfoton, metolachlor, pronamide, and simazine) exhibited statistically significant matrix effects for the finished drinking water. The method has been adopted official first action by AOAC.
Supercritical fluid extraction (SFE) of the marine red alga Plocamium cartilagineum, which is kno... more Supercritical fluid extraction (SFE) of the marine red alga Plocamium cartilagineum, which is known to contain complex mixtures of halogenated monoterpenes, was investigated. P. cartilagineum samples were extracted by SFE with carbon dioxide and modified carbon dioxide containing up to 10% methanol at different pressure and temperature conditions to establish the optimum conditions for extraction. These conditions were then used in the extraction of halogenated monoterpenes from 2 different samples of P. cartilagineum: one from Davenport, CA, and the other from Casa Beach (San Diego, CA). Several halogenated monoterpenes isolated by conventional solvent extraction with methanol and purified by column chromatography were used as the reference compounds for the determination of the extraction efficiency in the SFE experients. Plocamium cartilagineum belongs to the red alga family--Plocamiaceae, and has been found to contain a large number of halogenated monoterpenes, whose structures typically contain 1-6 bromine and/or chlorine atoms. P. cartilagineum grows along the Pacific coast from Washington to Chile, the British Isles, Australia, and Spain. Interestingly, P. cartilagineum collected from different geographical areas in the world are all reported to produce halogenated monoterpenes, but of different structural types and halogen substitution patterns. Most of these halogenated monoterpenes have been found to exhibit varied biological activities, including antifungal, antimicrobial, and molluscicidal activity.
An extraction technique, involving homogenization of a sediment sample with dichloromethane at du... more An extraction technique, involving homogenization of a sediment sample with dichloromethane at dual pH and phase separation by centrifugation, was used in the determination of fifty-one organic priority pollutants as identified in a standard reference sediment sample. The extract containing the base/neutral compounds was fractionated by gel permeation chromatography (GPC). Separation and identification of individual compounds in the silica gel fractions was accomplished by gas chromatography/mass spectrometry (GC/MS). Method precision and accuracy are discussed. Tentative identifications of other organic compounds found in the sediment are given.
Matrix metalloproteinases (MMPs) are a family of zinc-dependent proteolytic enzymes that degrade ... more Matrix metalloproteinases (MMPs) are a family of zinc-dependent proteolytic enzymes that degrade extracellular matrix (ECM) components like collagen, fibronectin, and laminin. While this activity is important for normal development, morphogenesis, and wound healing, deregulation of MMP activity has been implicated in a number of cardiovascular diseases, including congenital heart defects, atherosclerosis, myocardial infarction, and congestive heart failure. MMPs are good potential diagnostic indicators of cardiovascular disease, but current detection methods are time consuming and quite laborious. This review will discuss MMP biology, current methods for detection of MMPs from patient samples, and potential new developments in multiplexed analysis of MMPs.
... Chromatography/Mass Spectrometry Viorica Lopez-Avila,* Pat Hirata, Susan Kraska, Michael Flan... more ... Chromatography/Mass Spectrometry Viorica Lopez-Avila,* Pat Hirata, Susan Kraska, Michael Flanagan, and John H. Taylor, Jr. Acurex Corporation, Energy and Environmental Division, 555 Clyde Avenue, Mountain View, California 94039 ...
Disposable cartridges containing 1 g of Florisil are investigated for cleanup of extracts obtaine... more Disposable cartridges containing 1 g of Florisil are investigated for cleanup of extracts obtained from various environmental matrices. Elution patterns and recoveries are determined for 22 chlorinated hydrocarbons and 16 phthalate esters in the presence of interferents such as corn oil, diesel hydrocarbons, organochlorine pesticides, and chlorinated phenols. Hexane, hexane/diethyl ether (1:1), hexane/acetone (9:1), and various combinations of hexane/methylene chloride are used as eluants.
... 468 Reproduction (photocopying) of editorial content of this journal is prohibited without pu... more ... 468 Reproduction (photocopying) of editorial content of this journal is prohibited without publisher&#x27;s permission. Viorica Lopez-Avila* and NS Dodhiwala Mid-Pacific Environmental Laboratory, 625-B Clyde Avenue, Mountain View, California 94043 ...
... Viorica Lopez-Avila Midwest Research Institute, 425 Volker Boulevard, Kansas City, Missouri 6... more ... Viorica Lopez-Avila Midwest Research Institute, 425 Volker Boulevard, Kansas City, Missouri 641 10 Ronald A. Hites&amp;#x27; School of Public and Environmental Affairs and Department of ... Wastewater samples were collected in 1-gal, amber glass bottles directly from the clarifier tank. ...
Uploads
Papers by Viorica Lopez-avila