Douglas T. Heitkemper

Arsenic extraction and speciation in carrots using accelerated solvent extraction, liquid chromatography and plasma mass spectrometry

Arsenic present in freeze-dried carrots was extracted using accelerated solvent extraction (ASE). Several parameters, including selection of the dispersing agent, extraction time, number of extraction cycles, particle size and extraction temperature, were evaluated to optimize the ASE method. Filtering and treatment with C-18 SPE cartridges were also evaluated as part of the sample preparation procedure before speciation analysis. The method was validated by spiking single arsenical and mixed arsenical standards on the dispersing agent and on portions of freeze-dried carrot prior to extraction. LC-ICP-MS was used to determine individual arsenic species in the carrot extracts. A weak anion-exchange column was used for the separation of As(III), As(v), monomethylarsonic acid (MMA), dimethylarsinic acid and arsenobetaine. Optimized sample preparation conditions were applied to the extraction of arsenic in nine freeze-dried carrot samples. Total arsenic concentration in the carrot samples ranged from less than 20 ng g(-1) to 18.7 microg g(-1), dry mass. Extraction efficiency, defined as the ratio of the sum of individual arsenic species concentrations to total arsenic, ranged from 80 to 102% for freeze-dried carrots with arsenic concentrations greater than the limit of quantitation. Inorganic As(III) and As(v) were the only species found in samples that contained less than 400 ng g(-1) total arsenic. MMA and an unidentified arsenic compound were present in some of the samples with higher total arsenic content.

An evaluation of extraction techniques for arsenic species from freeze-dried apple samples.

The extraction of arsenic from freeze-dried apples and subsequent determination of individual arsenic species by HPLC-ICP-MS is described. Solvent extraction with sonication using various aqueous and aqueous/solvent mixtures was initially evaluated by measuring total arsenic extracted by ICP-MS. A two step procedure using overnight treatment with alpha-amylase enzyme followed by sonication for 6 h with 40:60 acetonitrile-water was found to provide good extraction efficiency. The concentration of arsenic extracted was compared with the concentration of total arsenic in the samples determined using ICP-MS after microwave digestion in order to calculate extraction efficiency. Individual arsenic species in the extracts were measured using HPLC-ICP-MS. The three most abundant arsenic species found were arsenite, arsenate and dimethylarsinic acid. Total arsenic concentrations in the freeze-dried apple samples ranged from 8.2 to 80.9 micrograms kg-1 As, dry mass. By HPLC-ICP-MS, the relative amount of inorganic arsenic in the samples ranged from 73 to 90% of the sum of the arsenic species detected in each sample.

Practical applications of element-specific detection by inductively coupled plasma atomic emission spectroscopy and inductively coupled plasma mass spectrometry to ion chromatography of foods

Three practical examples are presented to demonstrate the utility of element-selective detection for ion chromatography (IC). The determination of As species in a liquid health food supplement by IC with inductively coupled plasma atomic emission spectroscopy (IC-ICP-AES) is shown to confirm results obtained for total As. IC-ICP-AES is also used to investigate the identity of an unknown peak in a sample of shrimp commercially treated with tripolyphosphate. Finally, results are presented for the determination of residual bromate in baked goods by IC with inductively coupled plasma mass spectrometry detection.

Investigation of arsenic speciation in algae of the Antarctic region by HPLC-ICP-MS and HPLC-ESI-Ion Trap MS

An investigation into presence and nature of As species in algae originating from the Antarctic region is presented in this work. Arsenic speciation information in Antarctic algae samples was obtained by using anion- and cation-exchange chromatography with on-line detection by inductively coupled plasma spectrometry (ICP-MS) or electrospray ionization ion trap mass spectrometry (ESI-ITMS). Total arsenic concentrations found by ICP-MS in the Antarctic algae samples ranged from 8.4 to 29.3 μg As g−1 (dry weight). Arsenic species were efficiently extracted (83–108%) by using an MeOH : H2O (1 : 1) mixture. Anion-exchange chromatography utilizing gradient elution with 25 mM ammonium bicarbonate adjusted to pH 10 was used to separate the anionic As species present in the algae extracts. Additionally, gradient cation-exchange chromatography was performed using 4 mM pyridine solution adjusted to pH 2.4. This allowed the separation of neutral and cationic As species present in the algae extracts. High volatility of the mobile phases allowed sample introduction compatibility with both ICP-MS and ESI-ITMS detectors. Three arsenosugar species (arsenosugar–OH, –SO3, and –PO4) previously reported in marine algae samples accounted for ∼50–80% of the total extractable arsenic in 4 of the 5 samples studied. In one algae sample, the presence of a previously unreported arsenic-containing compound in algae samples was confirmed by ESI-ITMS isolation and fragmentation as 5-dimethylarsinoyl-β-ribofuranose. This compound has been identified previously in marine bivalves but, to our knowledge, not in algae samples.

Survey of total arsenic and arsenic speciation in US-produced rice as a reference point for evaluating change and future trends

Rice generally contains higher levels of arsenic than most terrestrial-based foods. Studies related to dietary intake of arsenic from rice must take into account arsenic speciation due to toxicity differences in arsenic species. In this study, microwave-assisted extraction with trifluoroacetic acid was used to prepare rice samples for arsenic speciation analysis by high-performance liquid chromatography-inductively coupled plasma mass spectrometry. Fifty-three samples collected directly from the fields in four major rice-producing states in 1980 and 1981 were analysed for total and speciated arsenic and the results were compared with each other and with results for several more recently collected samples from local markets. The average content of total arsenic was 210 ± 190 ng As g−1. This study demonstrates that US rice samples with higher levels of total arsenic have higher levels of dimethylarsinic acid; however, inorganic arsenic levels, regardless of the total arsenic content, rarely exceed 150 ng As g−1 dry weight. These data are consistent with more recent findings, thus establishing trends that arsenic content in US-grown rice has been relatively constant throughout the last 30 years. To the authors’ knowledge, the presented data are unique in that they provide a historical reference point for arsenic distribution in US-produced rice. These data would be invaluable for several applications including long-term arsenic exposure studies, environmental clean-up assessments, and to establish models for future trends in arsenic contribution in total diet studies.

Detection of chemical warfare agent degradation products in foods using liquid chromatography coupled to inductively coupled plasma mass spectrometry and electrospray ionization mass spectrometry.

The following work presents the exploration of three chromatographic separations in combination with inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of chemical warfare agent degradation products (CWADPs). The robust ionization of ICP is virtually matrix independent thus enabling the examination of sample matrices generally considered too complicated for analysis by electrospray ionization (ESI) or atmospheric pressure chemical ionization MS with little to no sample preparation. The analysis was focused on detecting CWADPs in food matrices, as they present possible vehicles for terrorist contamination. Due to the specific detection of (31)P by ICP-MS, resolution of analytes of interest from other P-containing interferences (H(3)PO(4)) was a crucial part of each separation. Up to 10 CWADPs were separated in the presence of H(3)PO(4) with detection limits in the low part per billion levels using the methods described. Additionally, one method was tailored to be compatible with both ICP-MS and ESI-MS making structural verification possible.

Investigating the non-enzymatic methylation of arsenite by methylcobalamin B12 using high-performance liquid chromatography on-line with inductively coupled plasma-mass spectrometry

In this study, we have demonstrated the use of HPLC-ICP-MS as a powerful tool for studying the reaction of arsenite with methylcobalamin in the presence of glutathione. Even though this reaction has previously been investigated using radioactive 73As, HPLC-ICP-MS provides considerable advantages relating to sample throughput, sensitivity, and separation efficiency of the arsenic-containing reaction products. As a result of these advantages, kinetic studies were easily conducted, potentially providing valuable insight into the reaction itself. In addition, the HPLC-ICP-MS approach allowed for the tentative identification of methylarsonous acid, an arsenic species that had escaped detection in previous studies of the same reaction. Overall, this study confirmed that methylcobalamin acts as a methylating agent for arsenite in the presence of glutathione in an abiotic environment. A series of methylated arsenic species, identified as methylarsonic acid, dimethylarsinic acid and methylarsonous acid were detected.

Use of ion chromatography for the verification of drug authenticity

Abstract Investigations of drug authenticity focus on both bulk drugs and finished products. Excipients and contaminants from manufacturing processes may be used as “chemical fingerprints” to track drug sources. This paper describes the ion chromatographic determination of sodium lauryl sulfate, chloride, phosphate and citrate in drug formulations as applied to drug authenticity cases.

Determination of saccharin in shrimp by ion chromatography and capillary gas chromatography-mass spectrometry

Abstract A procedure is described for the detection, identification and determination of saccharin in shrimp. Undeclared use of this regulated substance has been noted. Shrimp is extracted with water, and the extract is treated with a C18 solid-phase extraction cartridge and a chloride removal cartridge. The method detection limit is 2 μg/g saccharin in shrimp. Recovery of a 16 μg/g saccharin spike averaged 91 ± 6%. The identity of saccharin is confirmed by gas chromatography-mass spectrometry of the methyl derivative which is prepared using an on-column methylating agent.

Estimating Inorganic Arsenic Exposure from U.S. Rice and Total Water Intakes.

Background: Among nonoccupationally exposed U.S. residents, drinking water and diet are considered primary exposure pathways for inorganic arsenic (iAs). In drinking water, iAs is the primary form of arsenic (As), while dietary As speciation techniques are used to differentiate iAs from less toxic arsenicals in food matrices. Objectives: Our goal was to estimate the distribution of iAs exposure rates from drinking water intakes and rice consumption in the U.S. population and ethnic- and age-based subpopulations. Methods: The distribution of iAs in drinking water was estimated by population, weighting the iAs concentrations for each drinking water utility in the Second Six-Year Review data set. To estimate the distribution of iAs concentrations in rice ingested by U.S. consumers, 54 grain-specific, production-weighted composites of rice obtained from U.S. mills were extracted and speciated using both a quantitative dilute nitric acid extraction and speciation (DNAS) and an in vitro gastrointestinal assay to provide an upper bound and bioaccessible estimates, respectively. Daily drinking water intake and rice consumption rate distributions were developed using data from the What We Eat in America (WWEIA) study. Results: Using these data sets, the Stochastic Human Exposure and Dose Simulation (SHEDS) model estimated mean iAs exposures from drinking water and rice were 4.2μg/day and 1.4μg/day, respectively, for the entire U.S. population. The Tribal, Asian, and Pacific population exhibited the highest mean daily exposure of iAs from cooked rice (2.8μg/day); the mean exposure rate for children between ages 1 and 2 years in this population is 0.104μg/kg body weight (BW)/day. Conclusions: An average consumer drinking 1.5 L of water daily that contains between 2 and 3 ng iAs/mL is exposed to approximately the same amount of iAs as a mean Tribal, Asian, and Pacific consumer is exposed to from rice. https://doi.org/10.1289/EHP418