Preparation and Certification of Hydrogen in Titanium Alloy Standard Reference Materials

A series of three hydrogen in titanium alloy Standard Reference Materials (SRMs 2452, 2453, and 2454) was prepared with hydrogen mass fractions bracketing the hydrogen specification limit of 125?mg/kg. Commercial titanium alloy Ti6Al4V (6?pct aluminum and 4?pct vanadium) was heated under vacuum in a furnace to remove native hydrogen, then it was doped with a measured quantity of hydrogen. Prompt gamma-ray activation analysis was used to determine hydrogen in the degassed material and finished SRMs. A combination of preparation data and PGAA measurement was used to certify the hydrogen mass fraction of each. The certified hydrogen mass fractions are 62.5?mg/kg?±?1.6?mg/kg for SRM 2452, 114?mg/kg?±?5?mg/kg for SRM 2453, and 211?mg/kg?±?4?mg/kg for SRM 2454.     

Determination of calcium by inductively coupled plasma-atomic emission spectrometry, and lead by graphite furnace atomic absorption spectrometry, in calcium supplements after microwave dissolution or dry-ash digestion: method trial

A 3-laboratory method trial was conducted to evaluate 2 sample digestion procedures and instrumental determination parameters for analysis of calcium and lead in Ca supplements. Calcium supplements were treated by dry-ash digestion or microwave dissolution prior to spectrometric analysis. In each case, Pb was determined by graphite furnace atomic absorption spectrometry and Ca by inductively coupled plasma-atomic emission spectrometry. Blind duplicates of 6 Ca supplement samples were analyzed after each sample treatment procedure. Matrix pairs contained dissimilar Pb levels to cover the analyte range encountered during method development. Calcium content of the Ca supplement samples also reflected the range seen during method development. Stock solutions of Ca and Pb were supplied to collaborators for preparation of quantitation standards to remove a variable external to the method. National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1486, bone meal, was included to assess method accuracy and recovery at NIST certificate Ca and Pb levels for this material (26.58 +/- 0.24% Ca and 1.335 +/- 0.014 micrograms Pb/g). Analyses of the NIST SRM yielded 25.9 +/- 1.1 and 27.2 +/- 2.3% Ca and 1.53 +/- 0.19 and 1.26 +/- 0.19 micrograms Pb/g for dry-ash and microwave procedures, respectively. Statistical analyses of data indicated acceptable repeatability and reproducibility for determination of Pb and Ca in various Ca supplements. With either sample preparation technique, the method is appropriate for determining Pb or Ca in Ca supplements.     

国外固体矿产勘查基本分析样品质量控制探讨

随着中国矿业市场对外开放与走出去战略的实施,越来越多的固体矿产勘查项目必须满足西方上市机构认可的质量控制体系要求。在简述基本分析样品控制因素的基础上,详细介绍了国外固体矿产勘查工作过程中基本分析样品质量控制的系统方法：在勘查过程中,通过取孪生检查样、野外重复样来评价采样质量;在送样批次中通过插入粗粒空白样、粗粒重复样来监控样品加工质量与污染;样品分析前,通过插入标样、细空白样和细重复样来评价分析质量。根据上述基本分析样品质量控制系统方法,结合广东高枨铅锌银矿详查具体项目实际情况,通过插入各类检查样,监控评价采样、加工和化验质量,满足加拿大证券交易所NI43-101规范QA/QC要求,结果可靠,样品分析数据得到独立咨询机构认可,有一定的借鉴意义。     

校准曲线和观测方式对电感耦合等离子体原子发射光谱法测定不锈钢中镍、铬和锰的影响

装饰装修用不锈钢材料主要为200和300系列不锈钢,其化学元素含量对其性能影响较大,其中镍、铬、锰 3种元素扮演着举足轻重的作用,因而能否对这些元素含量准确测定意义重大。不锈钢材料中化学元素含量测试主要依据SN/T2718-2010、GB/T 18705-2002、SN/T 3343-2012标准进行测定,此类方法均运用铁基体匹配的系列混合标准溶液绘制校准曲线、电感耦合等离子体原子发射光谱(ICP-AES)法进行测定。用这种方法绘制校准曲线,实验前期准备工作繁琐,而且用于绘制校准曲线的溶液成分与实际待测样品溶液的成分不完全一致,造成样品中成分测定的不确定度大。因此,实验采用系列不锈钢标准样品绘制校准曲线后测定不锈钢中镍、铬、锰含量, 并对比了这两种绘制校准曲线方法和测定时观测方式对测定结果的影响。结果表明,采用系列不锈钢标准样品绘制的校准曲线测定镍、铬、锰的含量,准确性明显优于用单标准溶液(样品)绘制的校准曲线,而且配制方法简单,可以大大缩短检测时间。ICP-AES测定的观测方式对不锈钢成分的测定结果有影响,径向观测比轴向观测更适用于不锈钢中镍、铬、锰含量的测定。     

Enhancement of motility by treating spermatozoa with an antioxidant solution (Sperm-Fit) following ejaculation

Oxygen radical generation is known to be detrimental to sperm function, especially motility, through the lipid peroxidation of the membranes. Generation of reactive oxygen species can be induced by leukocyte contamination, sperm centrifugation and the presence of abnormal spermatozoa with excess residual cytoplasm. This study aims to evaluate the effect on sperm motility of incubation in an antioxidant-containing solution, during liquefaction and centrifugation. Thirty semen samples were each divided into two equal parts: one mixed with Tyrode's solution, the other with a salt solution containing antioxidants (Sperm-Fit; Ellios Bio-Media, Paris, France). All the procedures were identical in the two groups. The ratio of leukocytes to spermatozoa was significantly correlated with the motility after liquefaction and after a 24 h incubation in routine in-vitro fertilization (IVF) medium and with the number of motile spermatozoa recovered after Percoll preparation. Moreover, when this ratio was > or = 0.2, all motility parameters were lowered. Incubation with Sperm-Fit allowed a higher percentage of motility after Percoll preparation when the ratio was > or = 0.2 (48 +/- 5% versus 41 +/- 6% for Sperm-Fit and Tyrode's solution respectively; P < 0.05) and a greater number of motile spermatozoa recovered after Percoll preparation, whatever the ratio (3.2 +/- 1.0 x 10(6) versus 2.4 +/- 0.7 x 10(6) for Sperm-Fit and Tyrode's solution respectively when ratio > or = 0.2; 18.1 +/- 3.4 x 10(6) versus 14.4 +/- 2.9 x 10(6) for Sperm-Fit and Tyrode's solution respectively when ratio < 0.2; P < 0.05). These results show that incubation with antioxidants during liquefaction and centrifugation increases recovery of motile spermatozoa.     

Assay of thiamine in foods, using manual and semiautomated fluorometric and microbiological methods

Three methods for the determination of thiamine in foods were evaluated for accuracy, recovery, and precision: a manual fluorescent method, a semiautomated fluorescent method, and a Lactobacillus viridescens microbiological assay. Thiamine in the samples was destroyed with clam tissue thiaminase; a known amount of thiamine hydrochloride was then added to the extract; and the thiamine recovery was determined. For 14 commerically processed food products analyzed by the manual and semiautomated methods, the mean per cent recovery values and standard deviations were 91.2 +/- 8.92 and 99.3 +/- 3.13%, respectively. Eight of these products were analyzed by all 3 methods. The mean per cent recoveries and standard deviations for these 8 samples were 90.7 +/- 8.97, 101 +/- 2.52, and 99.9 +/- 1.03%, respectively, for the manual, semiautomated, and microbiological methods. The microbiological method with L. viridescens gave the best results for the products tested. The concentration of vitamin which can be measured is such that samples of low label declaration present no problems. The semiautomated method offers a rapid and accurate method of thiamine assay. The chemical reactions are identical to those of the official method. The major difference between the methods is in the sample cleanup. It is postulated that the low recovery observed for the manual method is due to incomplete elution of thiamine in the column purification step.     

Transport of amino acid aryl amides by the intestinal H+/peptide cotransport system, PEPT1

The oxygen tension (PO2) in the renal cortex and outer renal medulla in 26 rats was studied by use of oxygen microelectrodes before and after injection of x-ray contrast media (CM). The CM, iopromide, ioxaglate and iotrolan were administrated intravenously in iodine equivalent doses (1,600 mg iodine/kg body wt). Ringer's solution was used as the control. In the outer medulla, all three CM induced a decrease in PO2: iopromide (N = 6) from 30 +/- 3 to 18 +/- 4 mm Hg; ioxaglate (N = 7) from 32 +/- 6 to 15 +/- 4 mm Hg; and iotrolan (N = 6) from 36 +/- 3 to 14 +/- 4 mm Hg. All these decreases were significant. After the injection of Ringer's (N = 7) there was an increase from 34 +/- 3 to 35 +/- 3 mm Hg. In the cortex a slight decrease was noted for injection of CM, but this was significant only after injection of iotrolan. All tested contrast media decrease PO2 in the outer renal medulla, which may partly explain contrast medium-induced acute renal failure.     

Radiographic assessment of knee osteoarthritis: reproducibility and sensitivity to change

OBJECTIVE: To determine the cross sectional and longitudinal reproducibility of various measures used for assessing radiographic knee osteoarthritis (OA) and to compare the sensitivity to change over a one year period of these measures. METHODS: We studied 55 patients referred to hospital with knee OA (clinical and radiographic ACR criteria). Anteroposterior radiographs at baseline and after 12 months were read by methods both qualitative (Kellgren and Lawrence grading scale, joint space narrowing scale) and quantitative (joint space width measurement at 3 different points). All qualitative methods used standardized atlases. The intraclass correlation coefficient and the graphical method of Bland and Altman were used to assess cross sectional and longitudinal reproducibility. Reproducibility was tested using 2 readers (interreader) and 2 readings for one of the readers (intrareader). Sensitivity to change was assessed using standardized response mean (SRM). RESULTS: All methods tested were shown to be reproducible both for cross sectional and longitudinal data. Intrareader was higher than interreader reproducibility for most radiographic features. Significant changes were observed after one year for methods measuring joint space narrowing. The sensitivity to change of the methods assessing joint space narrowing (joint space narrowing scale and joint space width measurement) was higher, with SRM varying from 0.37 to 0.57, than for the Kellgren and Lawrence grading system (SRM 0.19 and 0.23). CONCLUSION: These data suggest that methods measuring narrowing should be preferred as outcome measures in clinical trials or longitudinal epidemiologic studies; and show that in a particular subset of patients with very active disease, significant radiographic changes in knee OA can be detected after a one year period.     

Determination of nanogram amounts of iodine in foods by radiochemical neutron activation analysis

Three different neutron activation analysis methods have been developed for the determination of ppb levels of iodine in food samples. The methods are based on the separation of iodine using (i) toluene extraction followed by bismuth sulfide coprecipitation; (ii) bismuth sulfide coprecipitation followed by radiochemical purification with palladium iodide; and (iii) radiochemical isolation by bismuth sulfide coprecipitation. The accuracy of these methods was evaluated by analysing replicate samples of reference materials. The measured values of iodine in A-11 Milk Powder, H-4 Animal Muscle and H-9 Mixed Human Diet from the International Atomic Energy Agency (IAEA) are statistically indistinguishable from the IAEA recommended values, and those for the Standard Reference Materials 1571 Orchard Leaves and 1577 Bovine Liver from the National Institute of Standards and Technology (NIST) are in good agreement with the NIST information values. The precision, in terms of relative standard deviation, is 5% at 50-100 ppb and 10% at 5-20 ppb levels of iodine. The absolute detection limits of these methods vary between 0.5 and 10 ng of iodine. All three methods were used to measure the iodine content of several food samples. The method involving bismuth sulfide coprecipitation followed by radiochemical purification provides the best detection limit and highest precision.     

Comparison between a lyse-and-then-wash method and a lyse-non-wash technique for the enumeration of CD34+ hematopoietic progenitor cells

The flow cytometric enumeration of CD34+ hemopoietic precursor cells (HPC) present in samples used for transplantation of HPC has proven to be the most powerful single parameter for prediction of engraftment. At present, several different methodological approaches are used for the flow cytometric enumeration of CD34+ HPC. In the present study we have compared two of these methods as regards enumeration of CD34+ HPC and their CD34+/CD19- and CD34+/CD19+ subsets: a lyse-non-wash procedure based on the use of a recently commercialized red cell lysing solution (Quicklysis, Cytognos, Salamanca, Spain) and a lyse-and-then-wash method in which the Becton Dickinson (San Jose, CA) FACS Lysing Solution was used. For that purpose a total of 52 samples corresponding to 20 G-CSF mobilized peripheral blood (PB) samples and 21 PB-derived leucapheresis products from patients undergoing autologous PB stem cell harvest, together with 11 bone marrow (BM) samples from healthy volunteers were analyzed. Our results show that for each of the three types of samples analyzed the use of the lyse-and-then-wash method is associated with significantly lower numbers of both total CD34+ HPC (P < or = 0.003) and its major CD34+/CD19- subset (P < or = 0.01) while no significant changes are detected in the number of CD34+/CD19+ HPC in BM samples (P > 0.05). The use of an internal standard (reference beads) added just prior to data acquisition, showed that the differences between both methods are due to a selective loss of CD34+ HPC and its major CD34+/CD19- subset in BM (P=0.002 and P=0.003), PB (P < 0.0001 and P < 0.0001) and PB-derived leucapheresis products (P < 0.0001 and P=0.0001). Finally, addition of a centrifugation and washing step to a group of 11 leucapheresis samples lysed with Quicklysis showed that they did not significantly affect the overall number of total CD34+, CD34+/CD19- and CD34+/CD19+ HPC obtained. In line with these findings elimination of centrifugation and washing steps when FACS Lysing Solution was used to lyse mature red cells almost corrected for the selective loss of CD34+ HPC. In spite of these differences a significant degree of correlation (r > 0.83 in all cases) was found between both methods regarding the total number of CD34+, CD34+/CD19- and CD34+/CD19+ HPC present in the BM, PB and PB-derived leucapheresis samples analyzed in this study.     

Iodine deficiency in the Cirque of Salazie (Reunion Island). Analysis of nutritional causes and study of their consequences

Randomized subjects (n = 294), (35 young children, 6-30 months old--91 children 8.6 +/- 0.7 years, 116 teenagers 13.2 +/- 1.9 y--52 young women 28.5 +/- 6.1 y) leaving in a mountainous area of Reunion Island (Cirque de Salazie) were evaluated according to the following: a questionnaire related to food intake, cervical palpation for thyroid size evaluation and collections of urine and foods (natural and mineral water, breast and commercial milk and salt) for iodine measurement. Neonatal TSH of 308 new borns in Salazie were compared to TSH of 300 new-borns of Lille (France). The prevalence of goiter increases with age (0% in young children, 12.1% in children, 23.3% in teenagers, 38.4% in women) whereas median urinary iodine (microgram/dl) decreases in the same groups (12-7.8-5.6-4.2). The intake of milk and dairy products significantly decreases from children to adults. Neonatal TSH values are significantly higher in Salazie than in Lille (p < 0.005). Natural and mineral water, breast milk and salt contain little iodine. In conclusion iodine deficiency is present in this area of Reunion Island with a significant increment of neonatal TSH values.     

Ultrasonic nebulization of hypertonic solution: a new method for obtaining specimens from nasal mucosa for morphologic and biochemical analysis in allergic rhinitis

Various techniques are used to collect specimens from the nasal mucosa for morphologic and biochemical analysis. The purpose of this study was to devise a method that overcomes some of the disadvantages (e.g., invasive procedure, samples not suitable for cytologic and biochemical analysis, lack of standardization, and poor reproducibility) of these techniques. The new method requires subjects, with neck extended, to inhale an ultrasonic nebulization of a hypertonic (3% NaCl) solution (UNHS) for 5 min. They then blow their nose into a Petri dish, one nostril at a time with the other one blocked. The secretions are dispersed with 0.1% dithiothreitol in phosphate buffer solution for 20 min. Total cell count (TCC) is evaluated, and the cellular suspension is divided into two aliquots: one is centrifuged and the supernatants are collected for eosinophil cationic protein (ECP) measurements; the other is cytocentrifuged and the slides, stained with Diff-Quik, are used for differential cell count. The results obtained with the UNHS and nasal lavage (NL) methods were compared. Eleven nonatopic healthy subjects and 19 allergic rhinitic patients were studied. Total cell count (x10(5)) was significantly higher with UNHS than with NL (13.0+/-12.3 vs 1.9+/-1.6; P<0.01) The differential cell count was similar with the two procedures. ECP levels (microg/l) were higher with UNHS than with NL (39.1+/-38.2 vs 16.7+/-41.2; P<0.01). For evaluation of reproducibility, four healthy and six rhinitic subjects underwent UNHS on two occasions within 5 days, and the results of two samples (sample 1 vs sample 2) were analyzed. Reproducibility was good as to TCC, differential cell count, and ECP.     

镀锌板粗糙度和形貌的工业在线测量

为了实现钢带表面尤其是粗糙度(Ra)的连续控制,进而改善钢带的表面性质,冶金研究中心（CRM）开发了一种表面粗糙度传感器（SRM）,并在AMEPA实现了工业化。SRM用于测量不同工业线上整条钢带的粗糙度参数。选取的测量方法基于三角测量原理：一条很细的线被投影到表面,然后通过分析线的变形确定凸现。本方法通过与机械触针参照测量法对比得到验证,SRM与触针的相关范围为+/-10%。SRM被安装于不同的线和各种产品上：连续退火线、伸线（抹油表面）、镀锌线（高反射表面）和轧辊间（高反射和粗糙表面）。同样涉及的还有涂层的、未涂层的、随即（例如EDT）和确定（例如EBT）表面等。最终得到一个用于测量形貌学的在线传感器。这个传感器不久前用于欧洲某些公司及其他线的日常生产,四个传感器安装于中国某公司的连续镀锌线以及连续退火线上,这有助于理解不同生产参数对钢带表面的影响,有可能实现过程的直接控制。     

Human thyroglobulin reference material (CRM 457). 2nd Part: Physicochemical characterization and certification

This report describes the characterization of a purified human thyroglobulin (Tg) reference material, and details the procedures used in its certification. The purified Tg is intended to be used as a primary reference material to establish calibration of working serum based reference material for immunoassay procedures. The programme involved the participation of 15 European laboratories and one laboratory from the United States. The physicochemical characterization showed by polyacrylamide gel electrophoresis and immunoblotting that the purified Tg had for the major part the expected molecular size of 660 kDa with traces of lower molecular forms. The amino acid composition was close to that demonstrated for the cDNA and the content of iodine was in keeping with a moderately to highly iodinated Tg. The mass concentration in reference material RM 457 is certified to be (0.324 +/- 0.018) g/L on the basis of protein determined by the Lowry method and supported by nitrogen determination, absorbance measurement, and amino acid analysis. This reference material is considered the first step towards decreasing the interlaboratory variability between Tg methods of measurement.     

Automated chemical synthesis of biologically active tRNA having a sequence corresponding to Ascaris suum mitochondrial tRNA(Met) toward NMR measurements

RNA samples corresponding to Ascaris suum mitochondrial tRNA(Met) were chemically and automatically synthesized in amounts sufficient for NMR measurement. Conventional and rapid deprotection methods gave tRNA samples with the same amino acid-accepting activity as those prepared by other method; enzymatic synthesis, and enzymatic ligation of chemically synthesized fragments. The synthetic tRNA showed the same 1H-NMR spectrum in the iminoproton region as the ligated tRNA. This rapid and reliable preparation method thus provides biologically active tRNA for NMR measurement, and further, it is applicable for synthesis of other large synthetic RNAs, by combining the site-specific isotopic labeling method.     

A modified electrometric method for measurement of erythrocyte acetylcholinesterase activity in sheep

A modified method was compared with an original electrometric method for measurement of erythrocyte acetylcholinesterase (EChE) activity in sheep. The mean +/- SD (pH/30 min) of EChE activity of 8 sheep measured by the modified procedure (0.70 +/- 0.15) was not significantly different from that of the original method (0.64 +/- 0.12). The inherently low plasma cholinesterase activity of the sheep as measured by the 2 methods were also not significantly different from each other (0.09 +/- 0.04 vs 0.10 +/- 0.04). The coefficient of variation of the modified method in measuring EChE activity was 8%. The method was used to demonstrate in vitro inhibition of sheep EChE activity by the organophosphorus and carbamate insecticides dichlorvos and methomyl, respectively. The method could be well-suited for rapid measurement of EChE activity in sheep, especially in cases of organophosphate and possibly carbamate poisoning.     

Iodine deficiency in cardiovascular diseases

The thyroid hormone deficiency on cardiovascular function can be characterized with decreased myocardial contractility and increased peripheral vascular resistance as well as with the changes in lipid metabolism. 42 patients with cardiovascular disease (mean age 65 +/- 13 yr, 16 males) were investigated if iodine insufficiency can play a role as a risk factor for the cardiovascular diseases. The patients were divided in 5 subgroups on the ground of the presence of hypertension, congestive heart failure, cardiomyopathy, coronary disfunction and arrhythmia. Urine iodine concentration (5.29 +/- 4.52 micrograms/dl) was detected with Sandell-Kolthoff colorimetric reaction. The most decreased urine iodine concentration was detected in the subgroups with arrhythmia and congestive heart failure (4.7 +/- 4.94 micrograms/dl and 4.9 +/- 4.81 micrograms/dl, respectively). An elevated TSH level was found by 3 patients (5.3 +/- 1.4 mlU/l). An elevation in lipid metabolism (cholesterol, triglyceride) associated with all subgroups without arrhythmia. In conclusion, the occurrence of iodine deficiency in cardiovascular disease is frequent. Iodine supplementation might prevent the worsing effect of iodine deficiency on cardiovascular disease.     

Taurine in rat posterior pituitary: localization in astrocytes and selective release by hypoosmotic stimulation

The design of biomaterials containing specific ligands on the surface offers the possibility of creating materials that can interact with and potentially control mammalian cell behavior. Biodegradable materials further provide the significant advantage that the polymer will disappear in vivo, obviating long-term negative tissue responses as well as the need for retrieval. In earlier studies we synthesized and characterized arginine-glycine-aspartic acid (RGD) peptide-modified poly(lactic acid-co-lysine) (PLAL). In this study, both bulk properties and surface features have been characterized, with a focus on surface analysis as a means of interpreting observed changes in cell behavior. Bulk peptide attachments were performed using 1,1'-carbonyldiimidazole (CDI). Amino groups were measured using colorimetric assays and X-ray photoelectron spectroscopy (XPS). Peptides were measured by incorporating iodine into the peptide as a distinct elemental marker for use with XPS. Typical samples contained 13 +/- 4 pmol/cm2 of amino groups and 4 +/- 0.2 pmol/ cm2 of peptides, as calculated from XPS measurements of nitrogen and iodine. The wettability and crystallinity of the samples were determined by contact angles and differential scanning calorimetry, respectively. Wettability and crystallinity were not altered by the incorporation of lysine or peptides. After incubating bovine aortic endothelial (BAE) cells for 4 h on surfaces with RGD-containing peptides, the mean spread cell area increased from 77 +/- 2 microns2 to 405 +/- 29 microns2 compared to 116 +/- 11 microns2 on poly(lactic acid), 87 +/- 4 microns2 on PLAL, and 105 +/- 4 microns2 on surfaces with RDG-containing (control) peptides. The significance of this work is that the first synthetic interactive, resorbable biomaterial has been developed, and use of this material to control cell behavior has been demonstrated.     

Maternal iodine status and thyroid volume during pregnancy: correlation with neonatal iodine intake

Differences in pregnancy-associated alterations in thyroid volume and urinary iodine (UI) excretion have been attributed to geographical variations in dietary iodine intake. In this study, ultrasound-measured thyroid volume and UI excretion were assessed during the 3 trimesters of pregnancy, at delivery, and at 6 weeks postpartum. Urine specimens also were obtained from mothers and both breast- and formula-feeding infants at 3 days after delivery. Thyroid volume showed a significant increase (maximum 47.0%), compared with nonpregnant control values over the 3 trimesters of pregnancy, which occurred as early as the first trimester and was paralleled by increased UI excretion, followed in turn by a precipitous fall at delivery. UI excretion in breast-feeding neonates (100 +/- 6.8 micrograms/L) was significantly higher than in their mothers (76 +/- 5.6 micrograms/L; p < 0.01) but was significantly lower (43 +/- 3.5 micrograms/L) in formula-fed infants. The results suggest that in an area of moderate dietary iodine intake, UI loss during pregnancy may result in maternal thyroid enlargement. The ability of the breast to transport iodine compensates for this loss in breast-fed infants, but this protection may be lost in formula feeding.     

Serum concentrations of retinol, d-alpha-tocopherol and beta-carotene: effects of storage at -70 degrees C for five years

To investigate the effects of prolonged storage of serum samples at -70 degrees C on concentrations of micronutrients, we measured concentrations of retinol, d-alpha-tocopherol, and beta-carotene in serum samples drawn in 1986. We compared values we measured in 1991 to values we obtained in 1986, using the same analytical methods. The relative concentrations obtained in 1991 (mean +/- S.D.) were: retinol 99.7 +/- 12.6% (n = 23), d-alpha-tocopherol 100.7 +/- 6.4% (n = 19), and beta-carotene 103.4 +/- 13.7% (n = 28). Using these techniques of sample preparation and high-performance liquid chromatographic analysis, we found that the effects of storage of serum at -70 degrees C for five years appear insignificant in a small population of patients. However, we did identify clinically important changes in concentration (> 20% difference) in several individual subjects.