Development and validation of two LC-MS/MS methods for the detection and quantification of amphetamines, designer amphetamines, benzoylecgonine, benzodiazepines, opiates, and opioids in urine using turbulent flow chromatography

In the context of driving ability diagnostics in Germany, administrative cutoffs for various drugs and pharmaceuticals in urine have been established. Two liquid chromatography–tandem mass spectrometry methods for simultaneous detection and quantification of amphetamines, designer amphetamines, benzoylecgonine, benzodiazepines, opiates, and opioids in urine were developed and validated. A 500-μL aliquot of urine was diluted and fortified with an internal standard solution. After enzymatic cleavage, online extraction was performed by an ion-exchange/reversed-phase turbulent flow column. Separation was achieved by using a reversed-phase column and gradient elution. For detection, a Thermo Fisher TSQ Quantum Ultra Accurate Mass tandem mass spectrometer with positive electrospray ionization was used, and the analytes were measured in multiple-reaction monitoring mode detecting two transitions per precursor ion. The total run time for both methods was about 15 min. Validation was performed according to the guidelines of the Society of Toxicological and Forensic Chemistry. The results of matrix effect determination were between 78 % and 116 %. The limits of detection and quantification for all drugs, except zopiclone, were less than10?ng/mL and less than 25 ng/mL, respectively. Calibration curves ranged from 25 to 200 ng/mL for amphetamines, designer amphetamines, and benzoylecgonine, from 25 to 250 ng/mL for benzodiazepines, from 12.5 to 100 ng/mL for morphine, codeine, and dihydrocodeine, and from 5 to 50 ng/mL for buprenorphine and norbuprenorphine. Intraday and interday precision values were lower than 15 %, and bias values within?±?15 % were achieved. Turbulent flow chromatography needs no laborious sample preparation, so the workup is less time-consuming compared with gas chromatography–mass spectrometry methods. The methods are suitable for quantification of multiple analytes at the cutoff concentrations required for driving ability diagnostics in Germany.     

Efficiency of a miniaturized silica monolithic cartridge in reducing matrix ions as demonstrated in the simultaneous extraction of morphine and codeine from urine samples for quantification with liquid chromatography-tandem mass spectrometry (LC-MS/MS)

Presence of matrix ions could negatively affect the sensitivity and selectivity of liquid chromatography‐tandem mass spectrometer (LC‐MS/MS). In this study, the efficiency of a miniaturized silica monolithic cartridge in reducing matrix ions was demonstrated in the simultaneous extraction of morphine and codeine from urine samples for quantification with LC‐MS. The miniaturized silica monolith with hydroxyl groups present on the largely exposed surface area function as a weak cation exchanger for solid phase extraction (SPE). The miniaturized silica cartridge in 1 cm diameter and 0.5 cm length was housed in a 2‐ml syringe fixed over a SPE vacuum manifold for extraction. The cleaning effectiveness of the cartridge was confirmed by osmometer, atomic absorption spectrometer, LC‐MS and GC‐TOFMS. The drugs were efficiently extracted from urine samples with recoveries ranging from 86% to 114%. The extracted analytes, after concentration and reconstitution, were quantified using LC‐MS/MS. The limits of detection for morphine and codeine were 2 ng/ml and 1 ng/mL, respectively. The relative standard deviations of measurements ranged from 3% to 12%. The monolithic sorbent offered good linearity with correlation coefficients > 0.99, over a concentration range of 50–500 ng/ml. The silica monolithic cartridge was found to be more robust than the particle‐based packed sorbent and also the commercial cartridge with regards to its recyclability and repeated usage with minimal loss in efficiency. Our study demonstrated the efficiency of the miniaturized silica monolith for removal of matrix ions and extraction of drugs of abuse in urinary screening. Copyright © 2011 John Wiley & Sons, Ltd.     

UPLC - ESI MS/MS法测定动物饲料中苯二氮卓类药物

建立了超高效液相色谱-电喷雾串联质谱(UPLC - ESI MS/MS)同时检测动物饲料中地西泮、奥沙西泮、硝西泮、三唑仑、艾司唑仑和咪达唑仑6种苯二氮卓类药物的方法.饲料样品采用碱性叔丁基甲醚提取,Oasis MCX固相萃取柱净化,反相色谱柱分离,以0.1％甲酸和乙腈为流动相进行梯度洗脱,正离子模式扫描,多反应监测模...     

Rapid screening of drugs of abuse and their metabolites by gas chromatography/mass spectrometry: application to urinalysis

This paper describes a rapid gas chromatographic/mass spectrometric (GC/MS) screening method for the detection of drugs of abuse and/or their metabolites in urine. Synthetic stimulants, opiates, cocaine metabolites, cannabinoids--and specifically the acid metabolite of tetrahydrocannabinol (THC-COOH)--can be simultaneously extracted by a single liquid/liquid separation step, at alkaline pH, and assayed as trimethylsilyl derivatives by GC/MS in SIM (selected ion monitoring) mode. All the analytes show a good linearity (R2 > 0.99 for most of the considered substances) in the range 25-1000 ng/mL, with a good reproducibility of both the retention times (CV% <0.7) and the relative abundances of the characteristic diagnostic ions (CV% <13). The limit of detection (LOD) of the method is 25 ng/mL of target compound in human urine for most of the substances investigated, 3 ng/mL for THC-COOH, and 10 ng/mL for norbuprenorphine. Validation of the method allows its application to different fields of forensic analytical toxicology, including antidoping analysis.     

LC–MS/MS method for simultaneous determination of serum p‐cresyl sulfate and indoxyl sulfate in patients undergoing peritoneal dialysis

p‐Cresol sulfate (pCS) and indoxyl sulfate (IS) are protein‐bound uremic toxins that accumulate in patients with chronic kidney disease (CKD). They are closely associated with the mortality rate of CKD and morbidity of cardiovascular disease. In the present study, we established a rapid method for determination of pCS and IS by HPLC‐MS/MS in serum samples from 205 CKD patients undergoing peritoneal dialysis. In brief, serum was extracted by acetonitrile and spiked with hydrochlorothiazide. The prepared sample was eluted through HPLC column (Agilent Zorbax SB‐C₁₈, 3.5 μm, 2.1 × 100 mm) with a mobile phase of acetonitrile and 10 mm ammonium acetate solution (10:90, v/v) for subsequent detection of pCS and IS by MS/MS. The linearity ranged from 50 to 10,000 ng/mL for pCS (r > 0.99), and from 500 to 10,000 ng/mL for IS (r > 0.99). The lower limit of quantification was 50 ng/mL for pCS, and 500 ng/mL for IS. Relative standard deviation (RSD) of intra‐ and inter‐day precision was within ±15%. The results showed that pCS and IS levels were partially correlated with renal function in CKD patients, and IS was directly related to serum creatinine and estimated glomerular filtration rate.     

聚[2-(丙烯酰氧基)乙基]三甲基氯化铵-乙二醇二甲基丙烯酸酯整体柱固相萃取结合高效液相色谱法测定尿液中3种苯二氮（卄卓）类药物

以[2-（丙烯酰氧基）乙基]三甲基氯化铵（DAC）为单体,乙二醇二甲基丙烯酸酯（EDMA）为交联剂在注射器中制备聚合物整体柱,用其固相萃取尿液中溴西泮（BRZ）、劳拉西泮（LRZ）和地西泮（DZP）3种苯二氮（卄卓）类药物（BZDs）,并采用高效液相色谱法（HPLC）分析。实验考察了整体柱聚合时间及固相萃取条件（淋洗溶液、洗脱溶剂种类和体积）对BZDs萃取效率的影响。结果表明,仅聚合4 h得到的整体柱对BZDs吸附效率为100%。取尿液样品4 mL上样,用4 mL H₂O冲洗,1 mL乙酸乙酯洗脱,采用高效液相色谱分析。在最优条件下,3种BZDs在4.0~1000 ng/mL范围内线性关系良好（r=0.999）,检出限（S/N=3）和定量限（S/N=10）分别为1.0~1.2 ng/mL和3.3~4.0 ng/mL;在10、25和50 ng/mL加标水平下回收率为81.4%~102%,日内（n=3）和日间（n=3）相对标准偏差分别为1.2%~4.5%和2.5%~8.3%。该整体柱可对尿液中3种BZDs有效净化,且富集达12~15倍。方法构筑的聚合物整体柱制备简单,萃取高效,可成功用于尿液中3种BZDs的分析。     

Liquid chromatography/mass spectrometric bioanalysis of a modified gamma-cyclodextrin (Org 25969) and Rocuronium bromide (Org 9426) in guinea pig plasma and urine: its application to determine the plasma pharmacokinetics of Org 25969

A sensitive and specific liquid chromatography/mass spectrometry (LC/MS) method has been developed and validated for the quantification of the modified gamma-cyclodextrin Org 25969 and Rocuronium bromide (Roc or Org 9426) in the plasma and urine of guinea pigs. The assay was linear and reproducible over the range 25-10000 ng/mL for both compounds. The lowest limit of quantification (LLOQ) for both compounds in urine was 25 ng/mL. In plasma, the LLOQ was 25 ng/mL for Org 9426 and 50 ng/mL for Org 25969. The inter- and intra-day variation was lower than 20%. The physicochemical properties of both compounds imposed different modes of extraction from plasma. The modified gamma-cyclodextrin was extracted by trifluoroacetic acid (TFA) precipitation while Rocuronium was extracted by acetonitrile precipitation. Both compounds were quantified in urine by direct injection onto the column. The LC/MS analyses of Org 25969 and Org 9426 were performed using two different assay conditions. It was not possible to quantify the complex of cyclodextrin and Roc as it dissociated on the LC column. The use of LC/MS conferred great advantage to the quantification of both Org 25969 and Org 9426, as they were not chromogenic enough to afford the sensitivity and specificity required for the assay.     

Determination of trace levels of benzodiazepine in urine using capillary electrochromatography-time of flight mass spectrometry

This paper details a method for the separation and determination of ten benzodiazepines in urine using CEC-MS(TOF) and an hexyl acrylate-based porous monolith. The TOF mass spectrometer provides an exact mass of protonated benzodiazepines to three decimal places (1-6 ppm). This high selectivity along with the CEC separation, provides an effective method for the identification of benzodiazepines. Linearity is satisfactory for all compounds in the concentration range of 25-500 ng/mL for lorazepam and 12.5-500 ng/mL for the others. The RSDs are between 1.4-2.3% for retention times and 1.1-9.2% for relative areas. Using the monolithic stationary phase, a preconcentration step is achievable and permits an 75-140-fold improvement in sensitivity. This strategy permits the quantification of these drugs down to 1 ng/mL in urine. This method was used for the analysis of benzodiazepines in spiked urine samples.     

Extraction of amphetamines and methylenedioxyamphetamines from urine using a monolithic silica disk-packed spin column and high-performance liquid chromatography-diode array detection

To overcome the limitations of solid-phase extraction, we developed a device comprising a spin column packed with octadecyl silane-bonded monolithic silica for extracting amphetamines and methylenedioxyamphetamines from urine. Urine (0.5mL), buffer (0.4mL), and methoxyphenamine (internal standard) were directly put into the preactivated column. The column was centrifuged (3000rpm, 5min) for sample loading and washed. The adsorbed analytes were eluted and analyzed by high-performance liquid chromatography, without evaporation. The results were as follows: linear curves (drug concentrations of 0.2-20microg/mL); correlation coefficients >0.99; detection limit, 0.1microg/mL. The proposed method is not only useful for drugs from biological materials but also highly reproducible for the analysis of these drugs in urine.     

Development of a multi-target screening analysis for 301 drugs using a QTrap liquid chromatography/tandem mass spectrometry system and automated library searching

A new multi-target screening (MTS) procedure for drugs in blood and urine for toxicological analysis has been developed using a hybrid triple-quadrupole linear ion trap mass spectrometer (QTrap) for the fast detection and identification of 301 forensically important drugs, e.g. tranquilizers (benzodiazepines), hypnotics, drugs of abuse (opiates, cocaine, amphetamines, cannabinoids), antidepressants, neuroleptics, and some cardiac drugs, in one single liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis. Samples were extracted either with liquid-liquid extraction or solid-phase extraction. A multiple reaction monitoring (MRM) as survey scan and an enhanced product ion (EPI) scan as dependent scan were performed in an information-dependent acquisition (IDA) experiment. Finally, drug identification was carried out by library search with a newly developed MS/MS library based on EPI spectra at three different collision energies in positive mode. The advantage of this newly developed method is the possibility to detect and identify 301 drugs in one single LC/MS/MS run.     

海洛因滥用者唾液中毒品代谢物的SPE-GC/MS-SIM分析

本文首先考查了不同类型不同厂家的固相萃取柱的萃取效果,采用提取效果较好的50 mg/mL的Clean-screen CSDAUL01混合型强阳离子固相萃取柱,对唾液中的吗啡、可待因、6-单乙酰吗啡等3种鸦片类毒品进行提取后,将提取液吹干;再经MBTFA衍生化后,进行GC/MS-SIM检测。以乙基吗啡为内标,3种毒品的线性相关系数均大于0.99,线性范围为10～1000 ng/mL,相对回收率分别为85%～110%、94%～107%和75%～92%;相对标准偏差小于10%。3种毒品的检测限分别为2 ng/mL、1 ng/mL和2 ng/mL。该方法灵敏度高、重现性好、操作简便,可用于鸦片类毒品滥用者及中毒者唾液中的毒品及其代谢物的检测。     

Analyses of benzodiazepines and their metabolites in various biological matrices by LC-MS(/MS)

Benzodiazepines are among the most frequently prescribed drugs due to their sedative, hypnotic, anxiolytic, muscle relaxant and antiepileptic properties. Because of the high consumption of benzodiazepines worldwide, this class of drugs and their metabolites are frequently present in both clinical and forensic cases. For these reasons, the analysis of benzodiazepines and their metabolites in biological fluids is of great interest to clinicians and forensic toxicologists. This paper reviews procedures for multi-analyte single-stage (LC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) using different mass analyzers for the screening, identification and/or quantification of drugs, poisons and/or their metabolites in blood, plasma, serum or urine published since 2001. Basic information about the biosamples assayed, work-up, LC column, mobile phase, ionization type, mass spectral detection mode, matrix effects and validation data for each procedure is summarized. The feasibility of using LC-MS(/MS) techniques to identify and quantify benzodiazepines and their metabolites is also discussed.     

苯硼酸双柱固相微萃取-超高效液相色谱-串联质谱分析单胺类神经递质

本文构建了苯硼酸双柱固相微萃取-超高效液相色谱-串联质谱分析3种单胺类神经递质的方法。苯硼酸固相微萃取柱以4-乙烯基苯硼酸和甲叉双丙烯酰胺原位聚合法制备,该介质对含有顺式二羟基分子的化合物能够进行特异性捕获,并采取扫描电镜,红外光谱对其进行表征,研究了影响富集的各种条件。在优化条件下,线性度好,相关系数大于0.9971,检出限为23.6~152 pmol·L^-1,相对标准偏差(RSD)不大于5.9%。采用该方法对人体尿液和大鼠血清样品中3种单胺类神经递质进行分析,加标回收率为82.9%~113%,RSD为2.6%~7.7%。本文方法分析效率高,灵敏度高,准确度好,适用于尿液和大鼠血清样品中痕量单胺类神经递质的测定。     

Simultaneous LC–MS/MS analysis of eicosanoids and related metabolites in human serum,sputum and BALF

The differences among individual eicosanoids in eliciting different physiological and pathological responses are largely unknown because of the lack of valid and simple analytical methods for the quantification of individual eicosanoids and their metabolites in serum, sputum and bronchial alveolar lavage fluid (BALF). Therefore, a simple and sensitive LC–MS/MS method for the simultaneous quantification of 34 eicosanoids in human serum, sputum and BALF was developed and validated. This method is valid and sensitive with a limit of quantification ranging from 0.2 to 3 ng/mL for the various analytes, and has a large dynamic range (500 ng/mL) and a short run time (25 min). The intra‐ and inter‐day accuracy and precision values met the acceptance criteria according to US Food and Drug Administration guidelines. Using this method, detailed eicosanoid profiles were quantified in serum, sputum and BALF from a pilot human study. In summary, a reliable and simple LC–MS/MS method to quantify major eicosanoids and their metabolites was developed and applied to quantify eicosanoids in human various fluids, demonstrating its suitability to assess eicosanoid biomarkers in human clinical trials.     

Detection of Delta9-tetrahydrocannabinolic acid A in human urine and blood serum by LC-MS/MS

Delta9-tetrahydrocannabinolic acid A (Delta9-THCA-A) is the precursor of Delta9-tetrahydrocannabinol (Delta9-THC) in hemp plants. During smoking, the non-psychoactive Delta9-THCA-A is converted to Delta9-THC, the main psychoactive component of marihuana and hashish. Although the decarboxylation of Delta9-THCA-A to Delta9-THC was assumed to be complete--which means that no Delta9-THCA-A should be detectable in urine and blood serum of cannabis consumers--we found Delta9-THCA-A in the urine and blood serum samples collected from police controls of drivers suspected for driving under the influence of drugs (DUID). For LC-MS/MS analysis, urine and blood serum samples were prepared by solid-phase extraction. Analysis was performed with a phenylhexyl column using gradient elution with acetonitrile. For detection of Delta9-THCA-A, the mass spectrometer (MS) (SCIEX API 365 triple-quadrupole MS with TurboIonSpray source) was operated in the multiple reaction monitoring (MRM) mode using the following transitions: m/z357 --> 313, m/z357 --> 245 and m/z357 --> 191. Delta9-THCA-A could be detected in the urine and blood serum samples of several cannabis consumers in concentrations of up to 10.8 ng/ml in urine and 14.8 ng/ml in serum. The concentration of Delta9-THCA-A was below the Delta9-THC concentration in most serum samples, resulting in molar ratios of Delta9-THCA-A/Delta9-THC of approximately 5.0-18.6%. Only in one case, where a short elapsed time between the last intake and blood sampling is assumed, the molar ratio was 18.6% in the serum. This indicates differences in elimination kinetics, which need to be investigated in detail.     

Rapid and simultaneous determination of multiple classes of abused drugs and metabolites in human urine by a robust LC‐MS/MS method – application to urine drug testing in pain clinics

A simple LC‐MS/MS method was developed and validated for quantitatively analyzing six classes of 26 abused drugs and metabolites in human urine: (1) illicit drugs; (2) opiates; (3) synthetic opioids; (4) sedative; (5) stimulants; and (6) γ‐aminobutyric acid analogs. All urine samples were diluted with a mixture of isotope‐labeled internal standards, hydrolyzed with β‐glucuronidase and directly injected in a gradient chromatographic run. The mobile phase was composed of 0.1% formic acid in water and 0.1% of formic acid in methanol. A 4.9 min run time using the multiplexing driver and ultra‐biphenyl column (50 × 2.1 mm, 5 µm, RESTEK) allowed all drugs to have sufficient resolution in a short elute time. The overlapping liquid chromatography runs and scheduled multiple reaction monitoring acquisition method resulted in a higher overall throughput for the system. The result was linear over the studied range (2–16,000 ng/mL) for all compounds with correlation coefficients r² ≥ 0.995. The intra‐day and inter‐day precisions and accuracies were within 15% and recovery was between 83 and 115% for all analytes. Freeze–thaw stability for three cycles and long‐term stability (57 days, ?20°C) were established for all analytes. The cross‐validation between College of American Pathologists and in‐house was validated (0.06% ≤ bias ≤ 12.3%). The applicability of the method was examined by analyzing urine samples from chronic pain patients (n = 610). Copyright © 2013 John Wiley & Sons, Ltd.     

Development of LC‐MS/MS method for the determination of dapiprazole on dried blood spots and urine: application to pharmacokinetics

A rapid and highly sensitive liquid chromatography–tandem mass spectrometric (LC‐MS/MS) method for determination of dapiprazole on rat dried blood spots and urine was developed and validated. The chromatographic separation was achieved on a reverse‐phase C₁₈ column (250 × 4.6 mm i.d., 5 µm), using 20 mm ammonium acetate (pH adjusted to 4.0 with acetic acid) and acetonitrile (80:20, v/v) as a mobile phase at 25 °C. LC‐MS detection was performed with selective ion monitoring using target ions at m/z 326 and m/z 306 for dapiprazole and mepiprazole used as internal standard, respectively. The calibration curve showed a good linearity in the concentration range of 1–3000 ng/mL. The effect of hematocrit on extraction of dapiprazole from DBS was evaluated. The mean recoveries of dapiprazole from DBS and urine were 93.88 and 90.29% respectively. The intra‐ and inter‐day precisions were <4.19% in DBS as well as urine. The limits of detection and quantification were 0.30 and 1.10 ng/mL in DBS and 0.45 and 1.50 ng/mL in urine samples, respectively. The method was validated as per US Food and Drug Administration guidelines and successfully applied to a pharmacokinetic study of dapiprazole in rats. Copyright © 2013 John Wiley & Sons, Ltd.     

Combined quantification of paclitaxel,docetaxel and ritonavir in human feces and urine using LC‐MS/MS

A combined assay for the determination of paclitaxel, docetaxel and ritonavir in human feces and urine is described. The drugs were extracted from 200 μL urine or 50 mg feces followed by high‐performance liquid chromatography analysis coupled with positive ionization electrospray tandem mass spectrometry. The validation program included calibration model, accuracy and precision, carry‐over, dilution test, specificity and selectivity, matrix effect, recovery and stability. Acceptance criteria were according to US Food and Drug Administration guidelines on bioanalytical method validation. The validated range was 0.5–500 ng/mL for paclitaxel and docetaxel, 2–2000 ng/mL for ritonavir in urine, 2–2000 ng/mg for paclitaxel and docetaxel, and 8–8000 ng/mg for ritonavir in feces. Inter‐assay accuracy and precision were tested for all analytes at four concentration levels and were within 8.5% and <10.2%, respectively, in both matrices. Recovery at three concentration levels was between 77 and 94% in feces samples and between 69 and 85% in urine samples. Method development, including feces homogenization and spiking blank urine samples, are discussed. We demonstrated that each of the applied drugs could be quantified successfully in urine and feces using the described assay. The method was successfully applied for quantification of the analytes in feces and urine samples of patients. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantitative determination of metformin,glyburide and its metabolites in plasma and urine of pregnant patients by LC‐MS/MS

This report describes the development and validation of an LC‐MS/MS method for the quantitative determination of glyburide (GLB), its five metabolites (M1, M2a, M2b, M3 and M4) and metformin (MET) in plasma and urine of pregnant patients under treatment with a combination of the two medications. The extraction recovery of the analytes from plasma samples was 87–99%, and that from urine samples was 85–95%. The differences in retention times among the analytes and the wide range of the concentrations of the medications and their metabolites in plasma and urine patient samples required the development of three LC methods. The lower limit of quantitation (LLOQ) of the analytes in plasma samples was as follows: GLB, 1.02 ng/mL; its five metabolites, 0.100–0.113 ng/mL; and MET, 4.95 ng/mL. The LLOQ in urine samples was 0.0594 ng/mL for GLB, 0.984–1.02 ng/mL for its five metabolites and 30.0 µg/mL for MET. The relative deviation of this method was <14% for intra‐day and inter‐day assays in plasma and urine samples, and the accuracy was 86–114% in plasma, and 94–105% in urine. The method described in this report was successfully utilized for determining the concentrations of the two medications in patient plasma and urine. Copyright © 2014 John Wiley & Sons, Ltd.     

Automated on-line column-switching HPLC-MS/MS method for measuring environmental phenols and parabens in serum

We developed a method using on-line solid phase extraction (SPE) coupled to high performance liquid chromatography–isotope dilution tandem mass spectrometry (HPLC–MS/MS) to measure the serum concentrations of seven environmental phenols and five parabens: bisphenol A; ortho-phenylphenol; 2,4-dichlorophenol; 2,5-dichlorophenol; 2,4,5-trichlorophenol; benzophenone-3; triclosan; and methyl-, ethyl-, propyl-, butyl-, and benzyl-parabens. The phenols and parabens present in serum were retained and concentrated on a C18 reversed-phase size-exclusion SPE column, back-eluted from the SPE column while the eluate was diluted through a mixing Tee (analyte peak focusing), separated using a pair of monolithic HPLC columns, and detected by isotope dilution-MS/MS. Sample preparation did not require protein precipitation, only dilution of the serum with 0.1 M formic acid. This method, which combines an on-line SPE with analyte peak focusing feature and the selective atmospheric pressure photoionization MS detection, resulted in limits of detection ranging from 0.1 to 0.5 ng/mL for most of the analytes. The high throughput and adequate sensitivity with yet a relative low serum volume used (100 μL) confirm that analytically it is possible to measure simultaneously these phenols and parabens with the precision and accuracy at sub-parts-per-billion levels required for biomonitoring. However, important additional factors, including validated sample collecting, handling, and storing protocols, as well as toxicokinetic data, are required if these measures are used for exposure assessment.