Determination of perchlorate anion in foods by ion chromatography-tandem mass spectrometry

Perchlorate in groundwater: a synoptic survey of "pristine" sites in the coterminous United States

Perchlorate is widely used as an oxidant in solid rocket propellants and energetic applications, and it has frequently been detected in groundwaters at concentrations relevant to human health. The possibility of naturally occurring perchlorate has only recently received significant attention. Relying primarily on domestic, agricultural, and recreational wells, we utilized a network of volunteers to help collect 326 groundwater samples from across the coterminous United States. Care was taken to avoid known, USEPA-documented sites of perchlorate use or release, as well as perchlorate contamination due to disinfection using hypochlorite. Using IC-ESI-MS and a Cl18O4- internal standard, we achieved a method detection limit (MDL) of 40 ng/L perchlorate and a minimum reporting level (MRL) of 120 ng/L. Of the 326 samples, 147 (45%) were below the MDL, while 42 (13%) were between the MDL and the MRL. Of the 137 samples that could be quantified, most (109) contained < 1000 ng/L perchlorate; the remaining 28 samples contained from 1000 to 10400 ng/L. Our results support the notion that perchlorate occurs naturally in many groundwaters, but the unusually high concentrations (> 10000 ng/L) previously reported for the west-central Texas area appear to be anomalous. Perchlorate concentrations were positively correlated with nitrate levels (P < 0.001) but not with chloride concentrations. Opportunities exist for follow-up studies of perchlorate's origins using isotope forensics and for further elucidation of the role of atmospheric processes in the formation or transport of perchlorate.

Predicting perchlorate exposure in milk from concentrations in dairy feed

Perchlorate has been detected in U.S. milk samples from many different states. Applying data from a recently reported 9-week experiment in which 16 Holstein dairy cows were administered perchlorate allowed us to derive an equation for the dose-response relationship between perchlorate concentrations in feed/drinking water and its appearance in milk. Examination of background concentrations of perchlorate in the total mixed ration (TMR) fed in addition to the variable dose supplied to treated cows as a ruminal infusate revealed that cows receive significant and variable exposure to perchlorate from the TMR. Weekly examination of the TMR disclosed that a change in ingredients midway through the experiment caused a significant (78%) change in TMR perchlorate concentration. Analyses of the ingredients comprising the TMR revealed that 41.9% of the perchlorate came from corn silage, 22.9% came from alfalfa hay and 11.7% was supplied by sudan grass. Finally, USDA Food and Nutrition Survey data on fluid milk consumption were used to predict potential human exposure from milk that contained concentrations of perchlorate observed in our previous dosing study. The study suggests that reducing perchlorate concentration in dairy feed may reduce perchlorate concentrations in milk as well as the potential to reduce human exposure to perchlorate in milk.

Trace analysis of perchlorate anion in selected food products by reverse-phase liquid chromatography-tandem mass spectrometry

An alternative, rapid, and reproducible method of analysis for perchlorate in selected food products (fruit and vegetable juice, milk, and bottled water) was developed and validated. Improvements over previous methods were achieved by the use of a rugged and inexpensive C18 column, a multi-mode OASIS HLB solid-phase extraction cartridge for sample clean-up, and acetic acid for pH adjustment and protein precipitation. The hydrophobicity of the perchlorate anion gives it good retention and separation characteristics on C18 chromatographic columns. The C18 column allowed for the use of 90% of acetonitrile at a low flow rate (0.3 ml min(-1)), without splitting, and could also be regenerated with organic solvents, unlike an ion-exchange column. Perchlorate levels in selected commercial food samples were: <1.0-2.1 ng g(-1) (fruit and vegetable juices, reported here for the first time), <1.0-5.0 ng g(-1) (milk), and <1.0 ng g(-1) (bottled water).

Fatty acid profile in milk from goats, Capra aegagrus hircus, exposed to perchlorate and its relationship with perchlorate residues in human milk

Polyunsaturated fatty acids (PUFA) in milk are vital for normal growth and development of infant mammals. Changes in fatty acid composition were observed in milk fat from goats dosed with perchlorate (0.1 and 1 mg/kg body weight/day) for 31 days, but the effect was not persistent. Adaptation may be induced in these goats to compensate for the perchlorate effect. In an analysis of fatty acid composition in human milk samples, a weak negative correlation was observed between perchlorate concentrations and total PUFA in 38 human milk samples.

Perchlorate in sewage sludge, rice, bottled water and milk collected from different areas in China

As a new emerging environmental contaminant, perchlorate has prompted people to pay more attention. The presence of perchlorate in the human body can result in improper regulation of metabolism for adults. Furthermore, it also causes developmental and behavioral problems for infants and children because it can interfere with iodide uptake into the thyroid tissue. In this paper, perchlorate in sewage sludge, rice, bottled drinking water and milk was detected for investigating the perchlorate pollution status in China. The places, where the samples were collected, cover most regions of China. Therefore, the final data on perchlorate levels will give an indication of the perchlorate pollution status in China. The final determination of perchlorate was performed by ion chromatography-electrospray tandem mass spectrometry with negative mode. The concentration of perchlorate in sewage sludge, rice, bottled drinking water and milk was in the range of 0.56-379.9 microg/kg, 0.16-4.88 mug/kg, 0.037-2.013 microg/L and 0.30-9.1 microg/L, respectively. The results show that perchlorate has been widespread in China.

Dicationic Ion-Pairing Agents for the Mass Spectrometric Determination of Perchlorate

Perchlorate and other hydrophobic ions can be measured with high sensitivity and selectivity by forming a positively charged ion pair with a dicationic agent. A commercially available reagent, 1,6-bis(trimethylammonium)hexane dibromide (Br(N(CH3)3)(CH2)6(N(CH3)3)Br) allows for the determination of perchlorate by electrospray ionization mass spectrometry as the [(N(CH3)3)(CH2)6(N(CH3)3)ClO4]+ ion. Limits of detection (LODs) are better than those previously observed with custom-synthesized dicationic agents. An LOD of 20 ng/L is readily attainable with a single-quadrupole mass spectrometer.

Occurrence of perchlorate in drinking water sources of metropolitan area in Japan

The occurrence of perchlorate in the Tone River Basin was investigated using an ion chromatograph (IC) coupled with a tandem mass spectrometer (MS/MS). Perchlorate was found at high concentrations in the upper Tone River and its tributary, Usui River, and the maximum concentrations were 340 and 2300 microg/L, respectively. The possible sources of perchlorate in two areas were attributable to industrial effluents. In case of the upper Tone River, perchlorate concentration in an effluent was 1100 microg/L and its concentrations in a tributary (or waterway) directly downstream of the outlet of the effluent ranged from 44 to 1500 microg/L. In case of the Usui River, perchlorate concentration in another effluent was 15,000 microg/L and its concentrations downstream of the outlet of the effluent were 1100-3900 microg/L. Due to the discharge of perchlorate in the upper Tone River Basin, perchlorate concentrations in the river waters of the middle and lower Tone River Basin were generally 10-20 microg/L. Perchlorate concentrations in 30 tap water samples were investigated. Water sources of three tap water samples were other than the Tone River Basin and their perchlorate concentrations were 0.16-0.87 microg/L. On the other hand, water sources of the remaining 27 samples were the upper, middle and lower Tone River Basin and their perchlorate concentrations were 0.06-37 microg/L. Perchlorate concentrations were more than 1 microg/L in 19 tap water samples and more than 10 microg/L in 13 samples. It was shown that tap waters in the Tone River Basin were widely contaminated with perchlorate. To our knowledge, this study was the first to report on perchlorate contamination of environmental and drinking waters in Japan.

Effects of perchlorate on sodium-iodide symporter and pendrin gene expression in deer mice

Effects of perchlorate on sodium-iodide symporter (NIS) and pendrin gene expression in deer mice kidney and stomach were investigated. This was accomplished by isolating a partial cDNA sequence of deer mice NIS gene of 425 bps, and quantitatively analyzing NIS mRNA expression in various deer mouse tissues. The highest NIS expression level was in the stomach, followed by testes, brain, and large intestine; very low expression of NIS was observed in the lung, kidney, heart, and liver. Exposure to perchlorate through drinking water for 28 days did not significantly increase NIS gene expression in the kidney and stomach, and pendrin gene expression in the kidney. In a depuration experiment in which deer mice were exposed to perchlorate for 8-h followed by an 88-h depuration period, no significant difference was observed between the low and high exposure groups in terms of NIS or pendrin gene expression in the kidney or stomach at the end of the experiment. Furthermore, no significant linear relationship was observed between gene expression (either NIS or pendrin) in the kidney and perchlorate mass excreted via urine at day 28, average daily excretion, or total excretion mass over the 28 day exposure. Several factors could influence the effect of perchlorate exposure on NIS and pendrin gene expression in the stomach and kidney, including (1) pre-exposure to trace perchlorate through food and water perhaps resulting in adaptation (or tolerance) in these animals; (2) metabolism of perchlorate in deer mice causing only 46-61% perchlorate excreted into urine. It is also possible that there is no effect of perchlorate exposure and/or urinary excretion on NIS and pendrin gene expression, particularly in the kidney.

Effects of genotype and transpiration rate on the uptake and accumulation of perchlorate (ClO4-) in lettuce

Although evidence of perchlorate accumulation in plants exists, there is a scarcity of information concerning the key factors and mechanisms involved. To ascertain whether genotypic variation in perchlorate accumulation occurs within lettuce, hydroponic plant uptake experiments were conducted with five types of lettuce (Lactuca sativa L.), which were grown to market size atthree perchlorate (ClO4-) concentrations (1, 5, or 10 microg/L). Perchlorate accumulated in the leafy tissues to varying amounts, ranging from 4 to 192 microg/kg fresh weight (FW), and the ranking of perchlorate accumulation was crisphead > butter head > romaine > red leaf > green leaf. The effect of transpiration rate on perchlorate accumulation was further examined using crisphead, butter head, and green leaf lettuce. By growing lettuce in controlled-environment chambers with two climatic regimes, "cloudy, humid, cool" (80% RH, 18/15 degrees C, 250 micromol/m2s photosynthetic photon flux density (PPFD)) and "sunny, dry, warm" (approximately 50% RH, 28/18 degrees C, 500 micromol/m2s PPFD), up to 2.7-fold differences in transpiration rates were achieved. Across all three genotypes, the plants that transpired more water accumulated more perchlorate on a whole-head basis; however, the effect of transpiration rate on perchlorate accumulation was not as great as expected. Despite 2.0-2.7-fold differences in transpiration rate, there were only 1.2-2.0-fold differences in perchlorate accumulation. In addition to whole-head analysis, plants were sectioned into inner, middle, and outer leaves and processed separately. Overall, the ranking of perchlorate accumulation was outer leaves > middle leaves > inner leaves. Transpiration rate has a clear effect on perchlorate accumulation in lettuce, but other factors are influential and deserve exploration.

Influence of soil type and extraction conditions on perchlorate analysis by ion chromatography

Perchlorate is a stable anion that has been introduced into the environment through activities related to its production and use as a solid rocket propellant. Perchlorate is thought to transport through soils without being adsorbed; thus, for determination of perchlorate in soil, samples are typically extracted with water prior to analysis. The completeness of extraction depends on perchlorate existing as a free ion within the soil matrix. In this study, perchlorate extraction efficiency was evaluated with five soil types under two different oxygen states. For each soil, 30% (w/w) slurries were prepared and equilibrated under either oxic or anoxic conditions prior to spiking with a stock solution of sodium perchlorate, and the slurries were then maintained for 1-week or 1-month. At the end of the exposure, slurries were centrifuged and separated into aqueous and soil phases. After phase separation, the soil was washed first with deionized water and then with 50mM NaOH, producing second and third aqueous phases, respectively. Perchlorate concentrations in the three aqueous phases were determined using ion chromatography. The results obtained from this study suggest that matrix interference and signal suppression due to high conductivity have greater effects upon observed perchlorate concentrations by ion chromatography than does perchlorate interaction with soil. Thus, a single water extraction is sufficient for quantitative determination of perchlorate in soil.

Quantification of D-amino acids in the central nervous system of Aplysia californica by liquid chromatography/tandem mass spectrometry

A sensitive, specific and reliable liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed for simultaneous determination of D-amino acids in the central nervous system (CNS) of Aplysia californica. In order to correct for any potential matrix effects on measured signals, deuterium-labeled L-Asp-d3 was used as an internal standard. Pre-column derivatization of the sample with 7-fluoro-4-nitrobenzoxadiazole (NBD-F) allowed both effective in-line pre-concentration and sensitive MS/MS detection of the analytes. An extraction column (50x0.25 mm, 5 microm C18 silica particles) was used to pre-concentrate/stack samples. Enantiomeric separation of amino acid enantiomers was achieved on a chiral column packed with teicoplanin aglycone bonded silica particles (170x0.25 mm, 5 microm) with an MS-friendly mobile phase. The characteristic precursor to product ion transitions, m/z 297-->279 (for NBD-Asp), m/z 269-->223 (For NBD-Ser), m/z 311-->293 (for NBD-Glu) and m/z 300-->282 (for NBD-L-Asp-d3) were monitored for the quantification. Samples from the CNS of A. californica and heart tissues were analyzed. D-Asp was detected at high levels in all the ganglia and nerve tissues, but not in the heart tissue. Further, neither D-Ser nor D-Glu was detected in Aplysia, a widely used neuronal model.

Perchlorate in dairy milk. Comparison of Japan versus the United States

Perchlorate has been considered a potential threat to human health, especially to developing infants and children due to its ability to inhibit iodide uptake by the sodium iodide symporter (NIS) of the thyroid. Although the U.S. has been the prime focus of perchlorate contamination, at least some of the similar sources of perchlorate exist across the world, and it has been detected in many types of foods and beverages worldwide. We present here perchlorate data from cow's milk samples from Japan (mean 9.4 +/-2.7 microg/L, n = 54), which are higher on average than those found in U.S. dairy milk samples reported by a 2004 Food and Drug Administration (FDA) study (5.9+/-1.8 microg/L, n= 104).

Tissue distribution, elimination, and metabolism of sodium [36Cl]perchlorate in lactating goats

Perchlorate has contaminated water sources throughout the United States but particularly in the arid Southwest, an area containing large numbers of people and few water sources. Recent studies have demonstrated that perchlorate is present in alfalfa and that perchlorate is secreted into the milk of cows. Studies in lactating cows have indicated that only a small portion of a perchlorate dose could be accounted for by elimination in milk, feces, or urine. It was hypothesized that the remainder of the perchlorate dose was excreted as chloride ion. The purpose of this study was to determine the fate and disposition of (36)Cl-perchlorate in lactating dairy goats. Two goats (60 kg) were each orally administered 3.5 mg (16.5 muCi) of (36)Cl-perchlorate, a dose selected to approximate environmental perchlorate exposure but that would allow for adequate detection of radioactive residues after a 72 h withdrawal period. Blood, milk, urine, and feces were collected incrementally until slaughter at 72 h. Total radioactive residue (TRR) and perchlorate concentrations were measured using radiochemical techniques and liquid chromatography mass spectrometry (LC-MS-MS). Peak blood levels of TRR occurred at 12 h ( approximately 195 ppb) postdose; peak levels of parent perchlorate, however, occurred after only 2 h, suggesting that perchlorate metabolism occurred rapidly in the rumen. The serum half-life of perchlorate was estimated to be 2.3 h. After 24 h, perchlorate was not detectable in blood serum but TRR remained elevated (160 ppb) through 72 h. Milk perchlorate levels peaked at 12 h (155 ppb) and were no longer detectable by 36 h, even though TRRs were readily detected through 72 h. Perchlorate was not detectable in skeletal muscle or liver at slaughter (72 h). Chlorite and chlorate were not detected in any matrix. The only radioactive residues observed were perchlorate and chloride ion. Bioavailability of perchlorate was poor in lactating goats, but the perchlorate that was absorbed intact was rapidly eliminated in milk and urine.

Reversed-phase liquid chromatograhy/electrospray ionization tandem mass spectrometry for analysis of perchlorate in water

A new reversed-phase liquid chromatograhy/electrospray ionization tandem mass spectrometry method was developed for the analysis of perchlorate in water. The improved separation of perchlorate from common anions along with sample dilution effectively reduced matrix effects, primarily ion suppression caused by common anions. The (18)O-enriched perchlorate used as an internal standard provided further compensation for potential changes associated with instrument sensitivity, retention time shifting, peak broadening, ion suppression, and other matrix effects. The mean recoveries and relative standard deviations were 92-107% and 2.5-9.5% for simulated water matrix spikes at 0.05-1.0 microg/L, and 80-106% and 3.8-13% for real water sample matrix spikes at 2.0 microg/L, respectively. The method detection limits were 0.007 microg/L for reagent water and 0.014 microg/L for the simulated water matrix that contained 100 mg/L of SO(4)(2-), CO(3)(2-), and Cl(-) anions; 2 mg/L of PO(4)(3-) as P and NO(3)(-) as N; and 0.1 mg/L of Br(-), BrO(3)(-), ClO(2)(-), ClO(3)(-), and F(-) anions in reagent water, respectively. When using cartridge pretreatment to remove problematic SO(4)(2-), CO(3)(2-), and Cl(-) anions, the minimum reporting level could be set to 0.05 microg/L or lower. With 10-fold dilution, the minimum reporting level was conservatively set to 0.5 microg/L.

Effect of Mastitis on Milk Perchlorate Concentrations in Dairy Cows

Recent surveys have identified the presence of perchlorate, a natural compound and environmental contaminant, in forages and dairy milk. The ingestion of perchlorate is of concern because of its ability to competitively inhibit iodide uptake by the thyroid and to impair synthesis of thyroid hormones. A recent study established that milk perchlorate concentrations in cattle highly correlate with perchlorate intake. However, there is evidence that up to 80% of dietary perchlorate is metabolized in clinically healthy cows, thereby restricting the available transfer of ingested perchlorate into milk. The influence of mastitis on milk perchlorate levels, where there is an increase in mammary vascular permeability and an influx of blood-derived components into milk, remains unknown. The present study examined the effect of experimentally induced mastitis on milk perchlorate levels in cows receiving normal and perchlorate-supplemented diets. Over a 12-d period, cows were ruminally infused with 1 L/d of water or water containing 8 mg of perchlorate. Five days after the initiation of ruminal infusions, experimental mastitis was induced by the intramammary infusion of 100 microg of bacterial lipopolysaccharide (LPS). Contralateral quarters infused with phosphate-buffered saline served as controls. A significant reduction in milk perchlorate concentration was observed in the LPS-challenged glands of animals ruminally infused with either water or perchlorate. In control glands, milk perchlorate concentrations remained constant throughout the study. A strong negative correlation was identified between mammary vascular permeability and milk perchlorate concentrations in LPS-infused glands. These findings, in the context of a recently published study, suggest that an active transport process is operative in the establishment of a perchlorate concentration gradient across the blood-mammary gland interface, and that increases in mammary epithelial and vascular endothelial permeability lead to a net outflow of milk perchlorate. The overall finding that mastitis results in lower milk perchlorate concentrations suggests that changes in udder health do not necessitate increased screening of milk for perchlorate.

Electrically controlled anion exchange based on polypyrrole and carbon nanotubes nanocomposite for perchlorate removal

A simple and highly effective process for perchlorate removal based on electrically switched ion exchange (ESIX) was developed by using polypyrrole (PPy) deposited on high surface area carbon nanotubes. The redox switching of conducting polymers such as polypyrrole is accompanied by the exchange of ions into or out of the polymer. This effect could be used for the development of an electrically switchable ion-exchanger for water purification, particularly for the removal of anions. In the research presented in this paper, the anion-exchange behavior and ion-exchange capacity of electrochemically prepared polypyrrole on glassy carbon electrodes with and without carbon nanotube (CNT) backbones are characterized using cyclic voltammetry and X-ray photoelectron spectroscopy. It has been found that the presence of carbon nanotube backbone results in an improvement in the anion exchange stability of polypyrrole, which may be due to the stronger interaction between carbon nanotubes and polypyrrole. Chronoamperometric studies show that the process of electrically switched anion exchange could be finished within 10 s. The selectivity of PPy/CNTs films for the perchlorate ion is demonstrated using cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). The results of the present study point to the possibility of developing a green process for removing ClO4- from wastewater using such a novel nanostructured PPy/CNT composite thin film through an electrically switched anion exchange.

Analysis of perchlorate in foods and beverages by ion chromatography coupled with tandem mass spectrometry (IC-ESI-MS/MS)

A new IC-ESI-MS/MS method, with simple sample preparation procedure, has been developed for quantification and confirmation of perchlorate (ClO4-) anions in water, fresh and canned food, wine and beer samples at low part-per-trillion (ng l(-1)) levels. To the best of our knowledge, this is the first time an analytical method is used for determination of perchlorate in wine and beer samples. The IC-ESI-MS/MS instrumentation consisted of an ICS-2500 ion chromatography (IC) system coupled to either an API 2000 or an API 3200 mass spectrometer. The IC-ESI-MS/MS system was optimized to monitor two pairs of precursor and fragment ion transitions, i.e., multiple reaction monitoring (MRM). All samples had oxygen-18 isotope labeled perchlorate internal standard (ISTD) added prior to extraction. Chlorine isotope ratio (35Cl/37Cl) was used as a confirmation tool. The transition of 35Cl16O4- (m/z 98.9) into 35Cl16O3- (m/z 82.9) was monitored for quantifying the main analyte; the transition of 37Cl16O4- (m/z 100.9) into 37Cl16O3- (m/z 84.9) was monitored for examining a proper isotopic abundance ratio of 35Cl/37Cl; and the transition of 35Cl18O4- (m/z 107.0) into 35Cl18O3- (m/z 89.0) was monitored for quantifying the internal standard. The minimum detection limit (MDL) for this method in de-ionized water is 5 ng l(-1) (ppt) using the API 2000 mass spectrometer and 0.5 ng l(-1) using the API 3200 mass spectrometer. Over 350 food and beverage samples were analyzed mostly in triplicate. Except for four, all samples were found to contain measurable amounts of perchlorate. The levels found ranged from 5 ng l(-1) to 463.5+/-6.36 microg kg(-1) using MRM 98.9-->82.9 and 100 microl injection.

Surface-enhanced Raman scattering for perchlorate detection using cystamine-modified gold nanoparticles

Perchlorate (ClO4-) has recently emerged as a widespread environmental contaminant found in groundwater and surface water, and there is a great need for rapid detection and monitoring of this contaminant. This study presents a new technique using cystamine-modified gold nanoparticles as a substrate for surface-enhanced Raman scattering (SERS) detection of perchlorate at low concentrations. A detection limit of 5x10(-6) M (0.5 mg/L) has been achieved using this method without sample preconcentration. This result was attributed to a strong plasmon enhancement by gold metal surfaces and the electrostatic attraction of ClO4- onto positively charged, cystamine-modified gold nanoparticles at a low pH. The methodology also was found to be reproducible, quantitative, and not susceptible to significant interference from the presence of anions such as sulfate, phosphate, nitrate and chloride at concentrations <1 mM, making it potentially suitable for rapid screening and routine analysis of perchlorate in environmental samples.

Streamlined sample preparation procedure for determination of perchlorate anion in foods by ion chromatography–tandem mass spectrometry

A rapid, sensitive, and specific method was developed for the determination of perchlorate anion in foods. The foods included high moisture fruits and vegetables, low moisture foods (e.g. wheat flour and corn meal), and infant foods. Improvements to existing procedures were made in sample preparation that reduced sample test portion size from 100 to 5 or 10 g, extraction solvent volume from 150 to 20-40 ml, and replaced blending extraction-vacuum filtration and their associated large glassware with a simple shakeout-centrifugation in a small conical tube. Procedures common to all matrices involved: extraction, centrifugation, graphitized carbon solid phase extraction (SPE) cleanup, and ion chromatography-tandem mass spectrometry (IC-MS/MS) analysis. A Waters IC-Pak Anion HR column (4.6 mm x 75 mm) was eluted with 100mM ammonium acetate in 50:50 (v/v) acetonitrile/water mobile phase at a rate of 0.35 ml/min. A triple stage quadrupole mass spectrometer, equipped with electrospray ionization (ESI) in the negative ion mode, was used to detect perchlorate anion. An 18O4-labeled perchlorate anion internal standard was used to correct for any matrix effects. The method limit of quantitation (LOQ) was: 1.0 microg/kg in fruits, vegetables, and infant foods; 3.0 microg/kg in dry products. Fortified test portions gave 80-120% recoveries. Determination of incurred perchlorate anion residues agreed well with results for comparable commodities or products analyzed by published methods.

Challenges in determining perchlorate in biological tissues and fluids: Implications for characterizing perchlorate exposure

The ability to measure environmental contaminants in biological tissues and fluids is important in the characterization of exposure. However, the analysis of certain contaminants in these matrices presents significant challenges. Perchlorate (ClO4-) has emerged as a potential contaminant of concern primarily in drinking water and also in contaminated food. Significant advances have been made in the analysis of perchlorate in environmental matrices (water, soil) by ion chromatography (IC). In contrast, the analysis of perchlorate in extracts of biological tissues and fluids (vegetation, organs, milk, blood, urine, etc.) presents several challenges including small sample sizes, extracts with high matrix conductivity, and co-elution of other ions during IC analysis. To be able to detect low concentrations of perchlorate in biological samples, interferences must be removed or minimized, such as through the use of preparative chromatography cleanup techniques and/or alternative analytical methods less susceptible to common interferences (preconcentration or mass spectrometric detection). We present discussion and examples of the challenges encountered in the analysis of tissue extracts and fluids for perchlorate by IC and how some of those analytical challenges have been overcome.

Perchlorate in seawater

There has been no reliable published data on the presence of perchlorate in seawater. Seaweeds are among the most important plant life in the ocean and are good sources of iodine and have been widely used as food and nutritional supplement. Perchlorate is known to inhibit the transport of iodide by the sodium iodide symporter (NIS), present e.g., in the thyroid and mammary glands. With perchlorate being increasingly detected in drinking water, milk and various other foods, increasing the iodide intake through inexpensive natural supplements may be an attractive solution for maintaining iodine assimilation. We report here measurable concentrations of perchlorate in several samples of seawater (detectable in about half the samples analyzed). We also report the iodide and perchlorate concentrations of 11 different species of seaweed and the corresponding bioconcentration factors (BCF) for perchlorate and iodide, relative to the seawater from which they were harvested. All seaweed samples came from the same region, off the coast of Northeastern Maine. Concentrations of iodide and perchlorate in four seawater samples collected from the region near harvest time were 30+/-11 and 0.16+/-0.084 microg l(-1), respectively. Concentrations of both iodide and perchlorate varied over a wide range for different seaweed species; iodide ranging from 16 to 3134 mg kg(-1) and perchlorate from 0.077 to 3.2 mg kg(-1). The Laminaria species had the highest iodide concentration; Laminaria digitata is the seaweed species most commonly used in the kelp tablets sold in health food stores. Our sample of L. digitata contained 3134+/-15 mg iodide/kg dry weight. The BCF varied widely for different species, with Laminaria species concentrating iodide preferentially over perchlorate. The iodide BCF (BCF(i)) to perchlorate BCF (BCF(p)) quotient ranged from 0.66 to 53; L. digitata and L. saccarina having a BCF(i)/BCF(p) value of 45 and 53, respectively, far greater than a simple anion exchange process will allow. Although most seaweed samples contain some amount of perchlorate, the great majority contains iodide in so much higher amount that at least for the commonly used Laminaria species, the iodide/perchlorate ratio is greater than the square of the perchlorate to iodide selectivity factor reported for the mammalian NIS and should thus lead to net beneficial iodine nutrition even in a two-stage mother-infant scenario.

Matrix interference free determination of perchlorate in urine by ion association–ion chromatography–mass spectrometry

Quantitative measurement of perchlorate in biological fluids is of importance to assess its toxicity and to study its effects on the thyroid gland. Whenever possible, urine samples are preferred in toxicologic/epidemiologic studies because sample collection is non-invasive. We present here a pretreatment method for the determination of perchlorate in urine samples that lead to a clean matrix. Urine samples, spiked with isotopically labeled perchlorate, are exposed to UV to destroy/decompose organic molecules and then sequentially treated with an H+-form cation exchange resin to remove protolyzable compounds, with ammonia to raise the pH to 10-11 and finally passed through a mini-column of basic alumina to remove the color and other organic matter. After filtration through a 0.45 microm syringe filter, the sample thus prepared can be directly injected into an ion chromatograph (IC). We use ion association-electrospray ionization-mass spectrometry (ESI-MS) to detect and quantify perchlorate. The proposed sample preparation method leads to excellent limits of detection (LOD's) for perchlorate since there is essentially no dilution of sample and the matrix effects are eliminated. Results of urine samples from both men and women volunteers are reported for perchlorate, as well as for iodide and thiocyanate, which are generally present at much higher concentrations and for which a "dilute and shoot" approach is adequate. The limit of detection (S/N=3) for iodide, thiocyanate and perchlorate by the present method was 0.40, 0.10 and 0.080 microg l(-1), respectively.

Determination of low levels of perchlorate in lettuce and spinach using ion chromatography-electrospray ionization mass spectrometry (IC-ESI-MS)

A sample preparation method was developed to quantify environmentally relevant (low micrograms per liter) concentrations of perchlorate (ClO4(-)) in leafy vegetables using IC-ESI-MS. Lettuce and spinach were macerated, centrifuged, and filtered, and the aqueous extracts were rendered water-clear using a one-step solid-phase extraction method. Total time for extraction and sample preparation was 6 h. Ion suppression was demonstrated and was likely due to unknown organics still present in the extract solution after cleanup. However, this interference was readily eliminated using a Cl(18)O4(-) internal standard at 1 microg/L in all standards and samples. Hydroponically grown perchlorate-free butterhead lettuce was spiked to either 10.3 or 37.7 microg/kg of fresh weight (FW), and recoveries were between 91 and 98% and between 93 and 101%, respectively. Five types of lettuce and spinach from a local grocery store were then analyzed; they contained from 0.6 to 6.4 microg/kg of FW. Spike recoveries using the store-bought samples ranged from 89 to 100%. The method detection limit for perchlorate in plant extracts is 40 ng/L, and the corresponding minimum reporting limit is 200 ng/L or 0.8 microg/kg of FW.

Sample processing method for the determination of perchlorate in milk

In recent years, many different water sources and foods have been reported to contain perchlorate. Studies indicate that significant levels of perchlorate are present in both human and dairy milk. The determination of perchlorate in milk is particularly important due to its potential health impact on infants and children. As for many other biological samples, sample preparation is more time consuming than the analysis itself. The concurrent presence of large amounts of fats, proteins, carbohydrates, etc., demands some initial cleanup; otherwise the separation column lifetime and the limit of detection are both greatly compromised. Reported milk processing methods require the addition of chemicals such as ethanol, acetic acid or acetonitrile. Reagent addition is undesirable in trace analysis. We report here an essentially reagent-free sample preparation method for the determination of perchlorate in milk. Milk samples are spiked with isotopically labeled perchlorate and centrifuged to remove lipids. The resulting liquid is placed in a disposable centrifugal ultrafilter device with a molecular weight cutoff of 10 kDa, and centrifuged. Approximately 5-10 ml of clear liquid, ready for analysis, is obtained from a 20 ml milk sample. Both bovine and human milk samples have been successfully processed and analyzed by ion chromatography-mass spectrometry (IC-MS). Standard addition experiments show good recoveries. The repeatability of the analytical result for the same sample in multiple sample cleanup runs ranged from 3 to 6% R.S.D. This processing technique has also been successfully applied for the determination of iodide and thiocyanate in milk.

Ion chromatographic determination of perchlorate in foods by on-line enrichment and suppressed conductivity detection

Systemic uptake of perchlorate anion, a rocket fuel component and potential thyroid function disruptor, by leafy vegetables and other crops grown in contaminated waters is a public health concern. A column-switching anion-exchange chromatographic method with suppressed conductivity detection, described in this paper, achieved a 3-6 microg/kg method limit of quantitation in analysis of the wet weight edible portion of cantaloupe, carrots, lettuce, and spinach samples with field-incurred perchlorate. A test portion was blended with dilute nitric acid, and the extract was filtered under vacuum. A portion of the measured filtrate was acidified to pH approximately 2 by addition of cation-exchange resin, 4 mL was passed through a graphitized carbon cleanup column, and an aliquot of a collected fraction was pushed through a short precolumn for anion extraction, enrichment, and injection onto the analytical column. Statistical comparison with determination by tandem mass spectrometry-ion chromatography analysis of untreated filtrate revealed that the difference between means was not significant at the 95% confidence level (P value > or = 0.12) for crops tested. In addition, the method was applied to cooked vegetables processed as baby food.

Rapid on-line preconcentration and suppressed micro-bore ion chromatography of part per trillion levels of perchlorate in rainwater samples

The development of a rapid method for the determination of perchlorate in rain and drinking waters is presented. In the optimised method, an on-line preconcentration technique was employed utilising a 10 mm x 4.6 mm Phenomenex Onyx monolithic guard cartridge coated with (N-dodecyl-N,N-dimethylammonio)undecanoate for selective preconcentration, with subsequent elution into a fixed volume injection loop ('heart-cut' of the concentrator column eluate) and separation using an IonPac AS16 (250 mm x 2mm) anion exchange column and a potassium hydroxide concentration gradient. Off-line optimisation studies showed that the coated monolith displayed near quantitative recovery up to 50 microg/L perchlorate level from standards prepared in reagent water. On-line preconcentration of perchlorate obtained detection limits down to 56 ng/L in reagent water, between 70 and 80 ng/L in rainwater samples and 2.5 microg/L in non-pretreated drinking water. After an additional sample sulphate/carbonate removal step, low ng/L perchlorate concentrations could also be observed in drinking water. The complete on-line method exhibited reproducibility for n=10 replicate runs of R.S.D.< or =3% for peak height/area and R.S.D.=0.08% for retention time. The optimised method, of 20 min total duration, was applied to the determination of perchlorate by standard addition in 10 rainwater samples and one drinking water sample. Concentrations of perchlorate present ranged from below the detection limit for four rainwater samples, with another three samples showing perchlorate present at between 70 and 100 ng/L, and one sample showing perchlorate present at 2.8 microg/L. Levels of 1.1 microg/L in the drinking water sample were also recorded.

Optimization of operating conditions for the determination of perchlorate in biological samples using preconcentration/preelution ion chromatography

Perchlorate originates as a contaminant in the environment from the use of salts in the manufacture of solid rocket fuels and munitions. Monitoring potential perchlorate contamination in the environment is of interest, however, very few analytical methods have been developed for perchlorate determination in biological samples. Analysis of complex samples by ion chromatography is complicated by matrix components that can interfere with perchlorate determination. However, a recently developed preconcentration/preelution (PC/PE) ion chromatography method has demonstrated the capability to analyze certain complex samples such as high salinity water, milk, and hydroponic fertilizers. The ability of this method to reduce sample background and lower detection limits in ion chromatography for various biological samples was evaluated in this study. The PC/PE method was applicable to the analysis of kidneys, livers, zebrafish, quail eggs, lettuce, and urine. Optimal operating conditions were determined for each matrix. Ranges of optimal wash volumes were shorter when 15 mM NaOH prewash solutions were used compared with 10mM and good recovery was achieved for most matrices with an injection period > or =60s. Prewash solution concentration did not appear to significantly affect matrix background. The PC/PE method was capable of reducing sample background when compared to EPA Method 314.0, which resulted in detection limits, with the exception of zebrafish and urine, that were two-fold lower than those achieved with EPA Method 314.0.

Fate of dietary perchlorate in lactating dairy cows: Relevance to animal health and levels in the milk supply

Perchlorate is a goitrogenic anion that competitively inhibits the sodium iodide transporter and has been detected in forages and in commercial milk throughout the U.S. The fate of perchlorate and its effect on animal health were studied in lactating cows, ruminally infused with perchlorate for 5 weeks. Milk perchlorate levels were highly correlated with perchlorate intake, but milk iodine was unaffected, and there were no demonstrable health effects. We provide evidence that up to 80% of dietary perchlorate was metabolized, most likely in the rumen, which would provide cattle with a degree of refractoriness to perchlorate. Data presented are important for assessing the environmental impact on perchlorate concentrations in milk and potential for relevance to human health.

Accumulation and perchlorate exposure potential of lettuce produced in the Lower Colorado River region

The Colorado River is contaminated with perchlorate concentrations of 1.5-8 microg/L, an anion linked to thyroid dysfunction. Over 90% of the lettuce (Lactuca sativa L.) consumed during the winter months in the United States is produced in the Lower Colorado River region. Studies were conducted in this region to survey the potential for lettuce perchlorate accumulation and estimate potential human exposure to perchlorate from lettuce. Total uptake of perchlorate in the above-ground plant of iceberg lettuce was approximately 5 g/ha. Exposure estimates ranged from 0.45 to 1.8 microg/day depending on lettuce types and trimming. For all lettuce types, hypothetical exposures were less than 4% of the reference dose recommended by the National Academy of Sciences. Results show the relative iodide uptake inhibition potential because of lettuce nitrate was 2 orders of magnitude greater than that associated with the corresponding trace levels of perchlorate. These data support the conclusion that potential perchlorate exposures from lettuce irrigated with Colorado River water are negligible relative to acute or long-term harmful amounts.

Gas-Phase Ion Association Provides Increased Selectivity and Sensitivity for Measuring Perchlorate by Mass Spectrometry

Perchlorate (ClO4-) competitively inhibits the uptake of iodide by the thyroid gland. Trace quantities of perchlorate are being increasingly detected in food and environmental samples. There is great concern that perchlorate contamination may be far more widespread than believed until now. Increasingly sensitive and unambiguous methods are needed for measuring perchlorate. We report here an ion chromatography-ion association-electrospray ionization-mass spectrometry (IC/IA-ESI-MS) method of substantially greater selectivity and sensitivity than other available single-stage MS approaches. A long chain dipositive cationic agent (D2+) is added postcolumn in low concentration. This ion associates with perchlorate, even in the gas phase. Perchlorate is, thus, detected as DClO4+ in the positive ion mode at an m/z value between 300 and 400 (depending on the choice of D2+). This results in much better S/N and selectivity, as compared to detecting 35ClO4- at m/z 99, where H34SO4- also responds. We show results for various dicationic agents which vary in their selectivity and affinity for ClO4-, typically being at least 1 order of magnitude more selective for ClO4- over HSO4-. For a 100-microL injected standard, limits of detection (LOD, S/N = 3) are as good as 25 ng/L on a single quadrupole mass spectrometer. Calibration for concentrations up to 100 microg/L displays an r2 value of > or =0.9993. We show applicability to various real samples. A number of the studied reagents are suitable for such applications.

Analysis of Perchlorate in Water by Reversed-Phase LC/ESI-MS/MS Using an Internal Standard Technique

A new method was developed for the analysis of perchlorate in water by using reversed-phase liquid chromatograhy/electrospray ionization-mass spectrometry/mass spectrometry (LC/ESI-MS/MS) in the negative ESI mode. Selective and sensitive perchlorate detection was obtained by monitoring the 35ClO4- --> 35ClO3- and 37ClO4- --> 37ClO3- mass transitions. The 35ClO4- --> 35ClO3- transition was quantitated against the internal standard oxygen-labeled sodium perchlorate (NaCl18O4). Sample pretreatment for the removal of major common anions and dissolved metal ions along with internal standard quantitation sufficiently compensated for ion suppression caused by the matrix. The 37ClO4- --> 37ClO3- transition was examined to provide additional specificity. The method sensitivity, accuracy, and precision were investigated by analyzing fortified blank samples, field samples, and performance evaluation samples. The results (1.01-13.5 microg/L) for the proficiency evaluation samples differed from the certified values (1.04-14.1 microg/L) by 3-18%. The developed reversed-phase LC/ESI-MS/MS method was rapid, accurate, and reproducible. The calculated method detection limits were 0.007 microg/L for deionized reagent water and 0.009 microg/L for synthesized reagent water, respectively. The minimum reporting limit was conservatively set to 0.05 microg/L.

Analysis of Perchlorate in Human Urine Using Ion Chromatography and Electrospray Tandem Mass Spectrometry

Because of health concerns surrounding widespread exposure to perchlorate, we developed a sensitive and selective method for quantifying perchlorate in human urine using ion chromatography coupled with electrospray ionization tandem mass spectrometry. Perchlorate was quantified using a stable isotope-labeled internal standard ((18)O(4)-perchlorate) with excellent assay precision (coefficient of variation <5% for repetitively analyzed quality control material). Analytical accuracy was established by blind analysis of certified proficiency testing materials prepared in synthetic urine matrix; calculated amounts deviated minimally from true amounts, with percent differences ranging from 2% to 5%. Selective chromatography and tandem mass spectrometry reduced the need for sample cleanup, resulting in a rugged and rapid method capable of routinely analyzing 75 samples/day. The lowest reportable level (0.025 ng/mL) was sufficiently sensitive to detect perchlorate in all human urine samples evaluated to date, with a linear response range from 0.025 to 100 ng/mL. This selective, sensitive, and rapid method will help elucidate any potential associations between human exposure to low levels of perchlorate and adverse health effects.

The origin of naturally occurring perchlorate: the role of atmospheric processes

Perchlorate, an iodide uptake inhibitor, is increasingly being detected in new places and new matrices. Perchlorate contamination has been attributed largelyto the manufacture and use of ammonium perchlorate (the oxidizer in solid fuel rockets) and/or the earlier use of Chilean nitrate as fertilizer (approximately 0.1% perchlorate). However, there are regions such as the southern high plains (Texas Panhandle) where there is no clear historical or current evidence of the extensive presence of rocket fuel or Chilean fertilizer sources. The occurrence of easily measurable concentrations of perchlorate in such places is difficult to understand. In the southern high plains groundwater, perchlorate is better correlated with iodate, known to be of atmospheric origin, compared to any other species. We show that perchlorate is readily formed by a variety of simulated atmospheric processes. For example, it is formed from chloride aerosol by electrical discharge and by exposing aqueous chloride to high concentrations of ozone. We report that perchlorate is present in many rain and snow samples. This strongly suggests that some perchlorate is formed in the atmosphere and a natural perchlorate background of atmospheric origin should exist.

Current literature in mass spectrometry

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (4 Weeks journals - Search completed at 12th. Jan. 2005).