Last data update: Sep 16, 2024. (Total: 47680 publications since 2009)
Records 1-13 (of 13 Records) |
Query Trace: Whitehead RD Jr [original query] |
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Variability in haemoglobin concentration by measurement tool and blood source: an analysis from seven countries
Rappaport AI , Karakochuk CD , Hess SY , Whitehead RD Jr , Namaste SML , Dary O , Parker ME , Neufeld LM , Larson LM , Newton S , Wegmuller R , Moorthy D . J Clin Pathol 2021 74 (10) 657-663 OBJECTIVE: We explore factors such as the blood sampling site (capillary vs venous), the equipment (HemoCue vs automated haematology analyser) and the model of the HemoCue device (201+ vs 301) that may impact haemoglobin measurements in capillary and venous blood. METHODS: Eleven studies were identified, and bias, concordance and measures of diagnostic performance were assessed within each study. FINDINGS: Our analysis included 11 studies from seven countries (Cambodia, India, The Gambia, Ghana, Laos, Rwanda and USA). Samples came from children, men, non-pregnant women and pregnant women. Mean bias ranged from -8.7 to 2.5 g/L in Cambodian women, 6.2 g/L in Laotian children, 2.4 g/L in Ghanaian women, 0.8 g/L in Gambian children 6-23 months and 1.4 g/L in Rwandan children 6-59 months when comparing capillary blood on a HemoCue to venous blood on a haematology analyser. Bias was 8.3 g/L in Indian non-pregnant women and 2.6 g/L in Laotian children and women and 1.5 g/L in the US population when comparing capillary to venous blood using a HemoCue. For venous blood measured on the HemoCue compared with the automated haematology analyser, bias was 5.3 g/L in Gambian pregnant women 18-45 years and 11.3 g/L in Laotian children 6-59 months. CONCLUSION: Our analysis found large variability in haemoglobin concentration measured on capillary or venous blood and using HemoCue Hb 201+ or Hb 301 or automated haematology analyser. We cannot ascertain whether the variation is due to differences in the equipment, differences in capillary and venous blood, or factors affecting blood collection techniques. |
Retinol-binding protein, retinol, and modified-relative-dose response in Ugandan children aged 12-23 months and their non-pregnant caregivers
Whitehead RD Jr , Ford ND , Mapango C , Ruth LJ , Zhang M , Schleicher RL , Ngalombi S , Halati S , Ahimbisibwe M , Lubowa A , Sheftel J , Tanumihardjo SA , Jefferds MED . Exp Biol Med (Maywood) 2021 246 (8) 906-915 Retinol-binding protein (RBP), retinol, and modified-relative-dose response (MRDR) are used to assess vitamin A status. We describe vitamin A status in Ugandan children and women using dried blood spot (DBS) RBP, serum RBP, plasma retinol, and MRDR and compare DBS-RBP, serum RBP, and plasma retinol. Blood was collected from 39 children aged 12-23 months and 28 non-pregnant mothers aged 15-49 years as a subsample from a survey in Amuria district, Uganda, in 2016. DBS RBP was assessed using a commercial enzyme immunoassay kit, serum RBP using an in-house sandwich enzyme-linked immunosorbent assay, and plasma retinol/MRDR test using high-performance liquid chromatography. We examined (a) median concentration or value (Q1, Q3); (b) R(2) between DBS-RBP, serum RBP, and plasma retinol; and (c) Bland-Altman plots. Median (Q1, Q3) for children and mothers, respectively, were as follows: DBS-RBP 1.15 µmol/L (0.97, 1.42) and 1.73 (1.52, 1.96), serum RBP 0.95 µmol/L (0.78, 1.18) and 1.47 µmol/L (1.30, 1.79), plasma retinol 0.82 µmol/L (0.67, 0.99) and 1.33 µmol/L (1.22, 1.58), and MRDR 0.025 (0.014, 0.042) and 0.014 (0.009, 0.019). DBS RBP-serum RBP R(2) was 0.09 for both children and mothers. The mean biases were -0.19 µmol/L (95% limits of agreement [LOA] 0.62, -0.99) for children and -0.01 µmol/L (95% LOA -1.11, -1.31) for mothers. DBS RBP-plasma retinol R(2) was 0.11 for children and 0.13 for mothers. Mean biases were 0.33 µmol/L (95% LOA -0.37, 1.03) for children, and 0.29 µmol/L (95% LOA -0.69, 1.27) for mothers. Serum RBP-plasma retinol R(2) was 0.75 for children and 0.55 for mothers, with mean biases of 0.13 µmol/L (95% LOA -0.23, 0.49) for children and 0.18 µmol/L (95% LOA -0.61, 0.96) for mothers. Results varied by indicator and matrix. The serum RBP-retinol R(2) for children was moderate (0.75), but poor for other comparisons. Understanding the relationships among vitamin A indicators across contexts and population groups is needed. |
Predictors of anaemia among adolescent schoolchildren of Ghana
Gosdin L , Tripp K , Mahama AB , Quarshie K , Amoaful EF , Selenje L , Sharma D , Jefferds ME , Sharma AJ , Whitehead RD Jr , Suchdev PS , Ramakrishnan U , Martorell R , Addo OY . J Nutr Sci 2020 9 e43 Anaemia is a public health problem in Ghana. We sought to identify factors associated with haemoglobin concentration (Hb) and anaemia among school-attending adolescents. We analysed data from 2948 adolescent girls and 609 boys (10-19 years) selected from 115 schools from regions of Ghana as a secondary analysis of baseline surveys conducted at two time-points. We measured Hb, malaria from capillary blood, anthropometry and used a modified food frequency questionnaire to assess diet. Multivariable linear and Poisson regression models were used to identify predictors of Hb and anaemia. The prevalence of anaemia, malaria and geophagy were 24, 25, and 24 %, respectively, among girls and 13, 27 and 6 %, respectively, among boys. Girls engaging in geophagy had a 53 % higher adjusted prevalence of anaemia and 0⋅39 g/dl lower Hb. There were similar results among those who tested positive for malaria (+52 % anaemia; -0⋅42 g/dl Hb). Among girls, lower anaemia prevalence and higher Hb were associated with consumption of foods rich in haeme iron (-22 %; +0⋅18 g/dl), consumption of iron-fortified cereal/beverages consumed with citrus (-50 %; +0⋅37 g/dl) and being overweight (-22 %; +0⋅22 g/dl). Age was positively associated with anaemia among girls, but negatively associated among boys. Boys who tested positive for malaria had 0⋅31 g/dl lower Hb. Boys who were overweight or had obesity and consumed flour products were also more likely to be anaemic (119 and 56 %, respectively). Factors associated with Hb and anaemia may inform anaemia reduction interventions among school-going adolescents and suggest the need to tailor them uniquely for boys and girls. |
Prevalence and predictors of high blood pressure among women of reproductive age and children aged 10 to 14 years in Guatemala
Pickens CM , Flores-Ayala R , Addo OY , Whitehead RD Jr , Palmieri M , Ramirez-Zea M , Hong Y , Jefferds ME . Prev Chronic Dis 2020 17 E66 INTRODUCTION: Data on the prevalence and predictors of high blood pressure among children and non-pregnant women of reproductive age are sparse in Guatemala. Our objective was to identify the prevalence and predictors of high blood pressure among women of reproductive age and children in Guatemala. METHODS: We analyzed data on blood pressure among 560 children aged 10 to 14 years and 1,182 non-pregnant women aged 15 to 49 from a cross-sectional, nationally representative household survey, SIVESNU (Sistema de Vigilancia Epidemiológica de Salud y Nutrición). We defined high blood pressure among children by using 2004 and 2017 US pediatric guidelines. We defined high blood pressure among women by using 1999 World Health Organization (WHO) and 2017 American College of Cardiology/American Heart Association (ACC/AHA) guidelines. We used multivariable logistic regression to identify significant predictors of high blood pressure. A base model included key covariates (age, ethnicity, socioeconomic index, anthropometric indicators) and accounted for complex sampling. We used backward elimination to identify additional candidate predictor variables. RESULTS: High blood pressure was prevalent among 8.0% (95% confidence interval [CI], 5.4%-10.7%) and 14.0% (95% CI, 10.6%-17.5%) of children using 2004 and 2017 guidelines, respectively; and among 12.7% (95% CI, 10.7%-14.8%) and 41.1% (95% CI, 37.7%-44.4%) of women using 1999 WHO and 2017 ACC/AHA guidelines, respectively. Levels of awareness, treatment, and control of high blood pressure were low in women. Among children, significant predictors of high blood pressure were obesity, overweight, and indigenous ethnicity. Among women, significant predictors of high blood pressure included obesity, overweight, and diabetes. CONCLUSION: The prevalence of high blood pressure was high among Guatemalan women and children. Overweight and obesity were strong risk factors for high blood pressure. Increasing obesity prevention and control programs may help prevent high blood pressure, and expanding high blood pressure screening and treatment could increase awareness and control of high blood pressure in Guatemala. |
Predictors of micronutrient powder sachet coverage and recent intake among children 12-23 months in Eastern Uganda
Ford ND , Ruth LJ , Ngalombi S , Lubowa A , Halati S , Ahimbisibwe M , Mapango C , Whitehead RD Jr , Jefferds ME . Matern Child Nutr 2019 15 e12792 We evaluated predictors of micronutrient powder (MNP) sachet coverage and recent intake using data from a cross-sectional survey representative of children aged 12-23 months in Amuria district, Uganda. In June/July 2016, caregivers were interviewed 12 months after implementation of an integrated MNP and infant and young child feeding pilot (N = 761). Logistic regression described predictors of (a) high-MNP sachet coverage (received at least 60 sachets/6 months) and (b) recent intake (consumed MNP during the 2 weeks preceding the survey) among children who had ever received MNP and had complete data (N = 683). Fifty-nine percent (95% Confidence Interval [CI] [53.8, 64.2]) of children had high-MNP sachet coverage, and 65.4% (95% CI [61.0, 69.9]) had recent intake. MNP ration cards (Adjusted Odds Ratio [AOR] 2.67, 95% CI [1.15, 6.23]), organoleptic changes to foods cooked with soda ash (AOR 1.52, 95% CI [1.08, 2.14]), having heard of anaemia (AOR 1.59, 95% CI [1.11, 2.26]), knowledge of correct MNP preparation (AOR 1.89, 95% CI [1.11, 3.19]), and current breastfeeding (AOR 2.04, 95% CI [1.36, 3.08]) were positively associated with MNP coverage whereas older child age (18-23 vs. 12-17 months) was inversely associated with coverage (AOR 0.32, 95% CI [0.23, 0.50]). MNP ration cards (AOR 2.86, 95% CI [1.34, 6.09]), having heard an MNP radio jingle (AOR 1.40, 95% CI [1.01, 1.94]), knowledge of correct MNP preparation (AOR 1.88, 95% CI [1.04, 3.39]), and the child not disliking MNP (AOR 1.90, 95% CI [1.13, 3.22]) were positively associated with recent intake. Interventions that increase caregiver knowledge and skills and focus on older children could improve MNP coverage and recent intake. |
Predictors of micronutrient powder (MNP) knowledge, coverage, and consumption during the scale-up of an integrated infant and young child feeding (IYCF-MNP) programme in Nepal
Locks LM , Dahal P , Pokharel R , Joshi N , Paudyal N , Whitehead RD Jr , Chitekwe S , Mei Z , Lamichhane B , Garg A , Jefferds ME . Matern Child Nutr 2019 15 e12712 Large-scale programmes using micronutrient powders (MNPs) may not achieve maximum impact due to limited/inappropriate MNP coverage, consumption, and use. We identify predictors of MNP coverage, maternal knowledge of appropriate use, and child MNP consumption in Nepal. A cross-sectional survey was conducted in 2,578 mother-child pairs representative of children 6-23 months in two districts that were part of the post-pilot, scale-up of an integrated infant and young child feeding-MNP (IYCF-MNP) programme. Children aged 6-23 months were expected to receive 60 MNP sachets every 6 months from a female community health volunteer (FCHV) or health centre. Outcomes of interest were MNP coverage (ever received), maternal knowledge of appropriate use (correct response to seven questions), repeat coverage (receipt >/= twice; among children 12-23 months who had received MNP at least once, n = 1342), and high intake (child consumed >/=75% of last distribution, excluding those with recent receipt/insufficient time to use 75% at recommended one-sachet-per-day dose, n = 1422). Multivariable log-binomial regression models were used to identify predictors of the four outcomes. Coverage, knowledge of appropriate use, and repeat coverage were 61.3%, 33.5%, and 45.9%, respectively. Among MNP receivers, 97.9% consumed MNP at least once and 38.9% of eligible children consumed >/=75% of last distribution. FCHV IYCF-MNP counselling was positively associated with knowledge, coverage, repeat coverage, and high intake; health worker counselling with knowledge and coverage indicators; and radio messages with coverage indicators only. FCHV counselling had the strongest association with knowledge, coverage, and high intake. Community-based counselling may play a vital role in improving coverage and intake in MNP programmes. |
Methods and analyzers for hemoglobin measurement in clinical laboratories and field settings
Whitehead RD Jr , Mei Z , Mapango C , Jefferds MED . Ann N Y Acad Sci 2019 1450 (1) 147-171 This paper describes and compares methods and analyzers used to measure hemoglobin (Hb) in clinical laboratories and field settings. We conducted a literature review for methods used to measure Hb in clinical laboratories and field settings. We described methods to measure Hb and factors influencing results. Automated hematology analyzer (AHA) was reference for all Hb comparisons using evaluation criteria of +/-7% set by College of American Pathologists (CAP) and Clinical Laboratory Improvement Amendments (CLIA). Capillary fingerprick blood usually produces higher Hb concentrations compared with venous blood. Individual drops produced lower concentrations than pooled capillary blood. Compared with the AHA: (1) overall cyanmethemoglobin (1.0-8.0 g/L), WHO Colour Scale (0.5-10.0 g/L), paper-based devices (5.0-7.0 g/L), HemoCue(R) Hb-201 (1.0-16.0 g/L) and Hb-301 (0.5-6.0 g/L), and Masimo Pronto(R) (0.3-14.0 g/L) overestimated concentrations; (2) Masimo Radical(R)-7 both under- and overestimated concentrations (0.3-104.0 g/L); and (3) other methods underestimated concentrations (2.0-16.0 g/L). Most mean concentration comparisons varied less than +/-7% of the reference. Hb measurements are influenced by several analytical factors. With few exceptions, mean concentration bias was within +/-7%, suggesting acceptable performance. Appropriate, high-quality methods in all settings are necessary to ensure the accuracy of Hb measurements.This paper describes and compares methods and analyzers used to measure hemoglobin (Hb) in clinical laboratories and field settings. With few exceptions, mean concentration bias was within +/-7%, suggesting acceptable performance. Appropriate, high-quality methods in all settings are necessary to ensure the accuracy of Hb measurements. |
Effects of preanalytical factors on hemoglobin measurement: A comparison of two HemoCue(R) point-of-care analyzers
Whitehead RD Jr , Zhang M , Sternberg MR , Schleicher RL , Drammeh B , Mapango C , Pfeiffer CM . Clin Biochem 2017 50 (9) 513-520 BACKGROUND: In field studies, hemoglobin (Hb) is often measured using a battery-operated, portable HemoCue(R) hemoglobinometer. METHODS: We compared the performance of 2 HemoCue(R) models (Hb-201+ and Hb-301) and investigated effects of preanalytical factors on Hb results by simulating unfavorable field conditions. RESULTS: The Hb-301 produced 2.6% higher results compared to the Hb-201+. Hb had to be measured within 1min of filling the Hb-301 cuvette to avoid artificially elevated concentrations (1.3% per min). The Hb-301 cuvettes withstood elevated temperature (37 degrees C) and humidity (72%) for 3weeks, while the Hb-201+ cuvettes degraded within 10min under those conditions. Both cuvette types withstood elevated temperature for 3weeks. Properly-collected venous and capillary blood produced comparable results. Pooled capillary blood produced comparable results to the second and third but not the fourth drop of blood (3.3% lower). Blood could be stored for ≤4days at 10-30 degrees C before Hb-201+ measurement, but only for 1day at 10-23 degrees C before Hb-301 measurement (≤1% change in Hb). CONCLUSIONS: Higher Hb results obtained with the Hb-301 may influence the interpretation of anemia prevalence in health surveys. While the Hb-301 performed better in high humidity conditions, the Hb-201+ provided more user flexibility regarding delayed Hb reading. |
The loss of 5-methyltetrahydrofolate in human serum under suboptimal preanalytical conditions can only partially be recovered by an oxidation product
Fazili Z , Sternberg MR , Paladugula N , Whitehead RD Jr , Chen H , Pfeiffer CM . J Nutr 2014 144 (11) 1873-9 BACKGROUND: Maintaining folate stability during sample handling is important, yet challenging. OBJECTIVE: We investigated the effects of suboptimal preanalytical conditions on serum folate stability. METHODS: By using an HPLC-tandem MS method we measured folates [5-methyltetrahydrofolate (5-methylTHF), folic acid, MeFox (5-methylTHF oxidation product, pyrazino-s-triazine derivative of 4alpha-hydroxy-5-methylTHF), and other minor folate forms at or below the limit of detection] in human serum exposed to suboptimal conditions. RESULTS: Whole blood samples (n = 21) stored at 32 degrees C for ≤3 d (Expt. 1: delayed processing) showed significant decreases in serum total folate (tFOL; sum of folate forms: 11-32%, 5.5-15.9 nmol/L) and 5-methylTHF (36-62%, 14.5-25.1 nmol/L) and a significant increase in MeFox (346-415%, 7.17-8.63 nmol/L). Serum samples (n = 21) stored at 11 degrees C for 7-14 d (Expt. 2: delayed freezing) also showed significant decreases in tFOL (4.6-10.4%, 2.3-5.1 nmol/L) and 5-methylTHF (8.4-29%, 3.4-11.6 nmol/L) and significant increases in MeFox (88-320%, 1.82-6.62 nmol/L). The molar loss in 5-methylTHF exceeded the gain in MeFox in these 2 experiments. When we exposed 3 serum pools (tFOL: 16.7-58.3 nmol/L) for 24 h to an elevated temperature of 37 degrees C (Expt. 3), the significant decrease in 5-methylTHF (33% on average) was compensated for by an equimolar gain in MeFox. Repeated freeze/thaw cycles (≤3 cycles) of serum [closed (Expt. 4) and open (Expt. 5) vials] showed generally stable folates with small (<1 nmol/L) changes. Long-term (≤12 mo) exposure of 3 serum pools (tFOL: 17.5-63.7 nmol/L) to a suboptimal (-20 degrees C) freezing temperature (Expt. 6) showed significant decreases in tFOL (5% on average) already after 3 mo. The molar loss in 5-methylTHF exceeded the gain in MeFox. Folic acid generally showed good stability. CONCLUSIONS: To avoid folate losses, unprocessed whole blood should be protected from elevated temperatures and serum should not be refrigerated for >2 d or for a long term stored at -20 degrees C. |
A high-throughput LC-MS/MS method suitable for population biomonitoring measures five serum folate vitamers and one oxidation product
Fazili Z , Whitehead RD Jr , Paladugula N , Pfeiffer CM . Anal Bioanal Chem 2013 405 (13) 4549-60 Small specimen volume and high sample throughput are key features needed for routine methods used for population biomonitoring. We modified our routine eight-probe solid phase extraction (SPE) LC-MS/MS method for the measurement of five folate vitamers [5-methyltetrahydrofolate (5-methylTHF), folic acid (FA), plus three minor forms: THF, 5-formylTHF, 5,10-methenylTHF] and one oxidation product of 5-methylTHF (MeFox) to require less serum volume (150 muL instead of 275 muL) by using 96-well SPE plates with 50 mg instead of 100 mg phenyl sorbent and to provide faster throughput by using a 96-probe SPE system. Total imprecision (10 days, two replicates/day) for three serum quality control pools was 2.8-3.6% for 5-methylTHF (19.5-51.1 nmol/L), 6.6-8.7% for FA (0.72-11.4 nmol/L), and ≤11.4% for the minor folate forms (<1-5 nmol/L). The mean (+/-SE) recoveries of folates spiked into serum (3 days, four levels, two replicates/level) were: 5-methylTHF, 99.4 +/- 3.6%; FA, 100 +/- 1.8%; minor folates, 91.7-108%. SPE extraction efficiencies were ≥85%, except for THF (78%). Limits of detection were ≤0.3 nmol/L. The new method correlated well with our routine method [n = 150, r = 0.99 for 5-methylTHF, FA, and total folate (tFOL, sum of folate forms)] and produced slightly higher tFOL (5.6%) and 5-methylTHF (7.3%) concentrations, likely due to the faster 96-probe SPE process (1 vs. 5 h), resulting in improved SPE efficiency and recovery compared to the eight-probe SPE method. With this improved LC-MS/MS method, 96 samples can be processed in ~2 h, and all relevant folate forms can be accurately measured using a small serum volume. |
Urinary concentrations of dialkylphosphate metabolites of organophosphorus pesticides: National Health and Nutrition Examination Survey 1999-2004
Barr DB , Wong LY , Bravo R , Weerasekera G , Odetokun M , Restrepo P , Kim DG , Fernandez C , Whitehead RD Jr , Perez J , Gallegos M , Williams BL , Needham LL . Int J Environ Res Public Health 2011 8 (8) 3063-98 Organophosphorus (OP) insecticides were among the first pesticides that EPA reevaluated as part of the Food Quality Protection Act of 1996. Our goal was to assess exposure to OP insecticides in the U.S. general population over a six-year period. We analyzed 7,456 urine samples collected as part of three two-year cycles of the National Health and Nutrition Examination Survey (NHANES) from 1999-2004. We measured six dialkylphosphate metabolites of OP pesticides to assess OP pesticide exposure. In NHANES 2003-2004, dimethylthiophosphate was detected most frequently with median and 95th percentile concentrations of 2.03 and 35.3 mcg/L, respectively. Adolescents were two to three times more likely to have diethylphosphate concentrations above the 95th percentile estimate of 15.5 mcg/L than adults and senior adults. Conversely, for dimethyldithiophosphate, senior adults were 3.8 times and 1.8 times more likely to be above the 95th percentile than adults and adolescents, respectively, while adults were 2.1 times more likely to be above the 95th percentile than the adolescents. Our data indicate that the most vulnerable segments of our population-children and older adults-have higher exposures to OP pesticides than other population segments. However, according to DAP urinary metabolite data, exposures to OP pesticides have declined during the last six years at both the median and 95th percentile levels. |
Measurement of ethyl methanesulfonate in human plasma and breast milk samples using high-performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry
Montesano MA , Whitehead RD Jr , Jayatilaka NK , Kuklenyik P , Davis MD , Needham LL , Barr DB . J Pharm Biomed Anal 2010 52 (2) 260-4 Ethyl methanesulfonate (EMS) is a mesylate ester, which is known to be a potent mutagen, teratogen, and possibly carcinogen. Mesylate esters have been found in pharmaceuticals as contaminants formed during the manufacturing process and may potentially pose an exposure hazard to humans. We have developed and validated a method for detection of trace amounts (ng/ml levels) of EMS in human plasma and breast milk. The samples were extracted by matrix solid-phase dispersion with ethyl acetate using Hydromatrix and the ASE 200 Accelerated Solvent Extractor. The extracts were separated by high-performance liquid chromatography (HPLC) using a HILIC column. The detection was performed with a triple quadrupole mass spectrometer (TSQ Quantum Ultra, Thermo Electron Corporation) using atmospheric pressure chemical ionization in negative-ion mode and multiple reaction monitoring. The use of a surrogate internal standard in combination with HPLC-MS/MS provided a high degree of accuracy and precision. The extraction efficiency was greater than 70%. Repeated analyses of plasma and breast milk samples spiked with high (100ng/ml), medium (50ng/ml) and low (5ng/ml) concentrations of the analytes gave relative standard deviations of less than 12%. The limits of detection were in the range of 0.5-0.9ng/ml for both matrices. |
Method for measurement of the quaternary amine compounds paraquat and diquat in human urine using high-performance liquid chromatography-tandem mass spectrometry
Whitehead RD Jr , Montesano MA , Jayatilaka NK , Buckley B , Winnik B , Needham LL , Barr DB . J Chromatogr B Analyt Technol Biomed Life Sci 2009 878 (27) 2548-53 We have developed a highly selective and sensitive analytical method to quantify paraquat and diquat by use of high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The sample preparation includes solid phase extraction that uses weak cation exchange cartridges. These highly charged dual quaternary amines were not retained by standard reversed phase columns, but they could be adequately separated through HPLC with a HILIC column. The detection was carried out with a triple quadrupole mass spectrometer with an electrospray ionization probe in positive ion mode in multiple reaction monitoring. Repeated analysis in human urine samples spiked with low (5ng/ml), medium (15ng/ml), and high (30ng/ml) concentrations of the analytes yielded relative standard deviations of less than 9%. The extraction efficiencies ranged from 77.7% to 94.2%. The limits of detection were in the range of 1ng/ml. |
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