Silicon, an important exposure marker in vivo in silicosis research.

PURPOSE: The degree of silicosis exposure is closely related to the progress of silicosis. At present, we use animal and human studies to explore whether silicon can be an important exposure marker in the development of silicosis. METHODS: Rats were randomly divided into 2 groups: (1) controls; and (2) silicosis. Rats in the silicosis group were killed at 4, 8, 12, 16, 24 h, 3, 7, 14, 21, and 28 days. Hematoxylin-eosin (HE) and immunohistochemistry (IHC) were performed to observe the histomorphology of lung tissue. The expression levels of CC16 and SP-D were detected using ELISA kits. In addition, we conducted a population study. Workers who have been selected to work in an iron mine for more than 1 year as research objects. The population was divided into four groups: silicosis exposure group (workers exposed to silica dust for more than 1 year in an iron mine were selected); patients group (silicosis patients); observation group (evidence of disease not meeting formal diagnostic criteria) and control group. Both the levels of trace silicon in the urine and blood of rats and human subjects were measured with ICP-MS. RESULTS: Serum levels of silicon were immediately increased in rats exposed to silicon dust. Similarly, our population study revealed that the silicon level in the silica exposure group and the observing group (exposed but no obvious symptoms) were significantly increased over that of the control group (P < 0.05). In subjects with extended exposure to silica, the serum and urine silicon level in exposed workers appeared to rapidly increase, reaching its peak in 1-5 years, followed by a gradual decline thereafter. Workers exposed to dust for less than 10 years were divided into subgroups by 2-year limit. The levels of serum silicon, urine silicon, TGF-ß1, and TNF-α were significantly higher than that of control group. CONCLUSION: Changes of the serum levels of silicon occurred earlier than the expression of cytokines such as TNF-α, TGF-ß1, CC16, and SP-D. The level of silicon in workers rapidly increased after exposure to silica, and the change occurred before the expression of TGF-ß1 and TNF-α. As a whole, the findings suggest that determining the level of silicon in vivo might be an effective exposure marker in the diagnosis and pathogenesis of silicosis.

Silicon absorption and excretion is independent of age and sex in adults.

Host factors influencing the absorption and excretion of Si are poorly understood, although previous murine and human studies have suggested that age, sex and oestrogen status may affect Si metabolism and thus function. Here, serum and urine samples were collected from twenty-six healthy adults at baseline and over a 6 h period following ingestion of 17·4mg Si (orthosilicic acid) and analysed by inductively coupled plasma optical emission spectrometry. Fasting baseline serum and urinary Si concentrations were marginally higher in older adults (51-66 years old) compared with young adults (20-47 years old); however, there was no difference in the absorption of Si into serum (overall profile, rate of Si appearance, peak concentration and time to peak) between the different adult groups. The rate of elimination of Si from serum did not significantly differ with age or sex, although serum concentration at 6 h was higher in older adults and significantly correlated with age (r 0·5; P=0·01). There were, however, no significant differences in the excretion of Si into urine (a proxy for overall uptake) between the groups, averaging approximately 45 %. Oestradiol levels did not correlate with any of the above measures of Si. Thus, overall, host age and sex did not appear to markedly influence Si absorption or excretion in human adults and no correlations were found with serum oestradiol status. The marginally higher baseline and 6 h post-dose Si levels in older adults may reflect modestly impaired renal function and/or the loss of Si from connective tissues with ageing.

Relative absorption of silicon from different formulations of dietary supplements: a pilot randomized, double-blind, crossover post-prandial study.

The purpose of the present study was to compare the relative absorption of a new powder presentation of silicon (Si) as orthosilicic acid with maltodextrin (Orgono Powder) compared to usual Si liquid presentations as orthosilicic acid with Equisetum arvense and Rosmarinus officinalis (G5 Siliplant) and orthosilicic acid with aloe vera (G7 Aloe). All dietary supplements were administered at the same Si oral dose (21.6 mg) in a randomized, double-blind, crossover post-prandial study conducted in 5 healthy men. Urine was collected at baseline and over the 6-h post-dose period in 2 separate 3-h collections for the analysis of Si concentration, which was conducted by inductively coupled plasma optical emission spectrometry as the gold standard method. No significant differences in total urinary Si excretion were found after the intake of these 3 dietary supplements; 34.6%, 32.4% and 27.2% of the ingested Si from G7 Aloe, G5 Siliplant and Orgono Powder, respectively, was excreted in urine over the 6-h follow-up period. The 3 different oral Si formulations tested, in powder and liquid presentations, provide highly bioavailable Si and present an equivalent relative absorption in healthy humans.

Absorption of silicon from artesian aquifer water and its impact on bone health in postmenopausal women: a 12 week pilot study.

BACKGROUND: Decreased bone mineral density and osteoporosis in postmenopausal women represents a growing source of physical limitations and financial concerns in our aging population. While appropriate medical treatments such as bisphosphonate drugs and hormone replacement therapy exist, they are associated with serious side effects such as osteonecrosis of the jaw or increased cardiovascular risk. In addition to calcium and vitamin D supplementation, previous studies have demonstrated a beneficial effect of dietary silicon on bone health. This study evaluated the absorption of silicon from bottled artesian aquifer water and its effect on markers of bone metabolism. METHODS: Seventeen postmenopausal women with low bone mass, but without osteopenia or osteoporosis as determined by dual x-ray absorptiometry (DEXA) were randomized to drink one liter daily of either purified water of low-silicon content (PW) or silicon-rich artesian aquifer water (SW) (86 mg/L silica) for 12 weeks. Urinary silicon and serum markers of bone metabolism were measured at baseline and after 12 weeks and analyzed with two-sided t-tests with p < 0.05 defined as significant. RESULTS: The urinary silicon level increased significantly from 0.016 ± 0.010 mg/mg creatinine at baseline to 0.037 ± 0.014 mg/mg creatinine at week 12 in the SW group (p = 0.003), but there was no change for the PW group (0.010 ± 0.004 mg/mg creatinine at baseline vs. 0.009 ± 0.006 mg/mg creatinine at week 12, p = 0.679). The urinary silicon for the SW group was significantly higher in the silicon-rich water group compared to the purified water group (p < 0.01). NTx, a urinary marker of bone resorption did not change during the study and was not affected by the silicon water supplementation. No significant change was observed in the serum markers of bone formation compared to baseline measurements for either group. CONCLUSIONS: These findings indicate that bottled water from artesian aquifers is a safe and effective way of providing easily absorbed dietary silicon to the body. Although the silicon did not affect bone turnover markers in the short-term, the mineral's potential as an alternative prevention or treatment to drug therapy for osteoporosis warrants further longer-term investigation in the future. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01067508.

The comparative absorption of silicon from different foods and food supplements.

Dietary Si (orthosilicic acid; OSA) appears important in connective tissue health, and although the sources and intakes of Si are well established, its absorption is not. Si absorption was measured from eight high-Si-containing sources: alcohol-free beer; OSA solution (positive control); bananas; green beans; supplemental choline-stabilised OSA (ChOSA); supplemental monomethyl silanetriol (MMST); supplemental colloidal silica (CS); magnesium trisilicate British Pharmacopoeia antacid (MTBP). Two of the supplements and the antacid were pre-selected following an in vitro dissolution assay. Fasting, healthy subjects (CS, n 3; others, n > or = 5) each ingested two of the sources separated by a 1-week wash-out period. Blood and urine were collected and measured for total Si concentrations by inductively coupled plasma optical emission spectrometry. Absorption, based on urinary Si excretion, was highest for MMST and alcohol-free beer (64% of dose), followed by green beans (44%), OSA (43%), ChOSA (17%), bananas and MTBP (4%) and CS (1%). Peak serum concentrations occurred by 0.5 h for MMST and green beans, 1.5 h for OSA and alcohol-free beer, 2 h for ChOSA and CS, and 4 h for MTBP. Area under the serum curves correlated positively with urinary Si output (r 0.82; P < 0.0001). Absorption of Si from supplements and antacids was consistent with their known chemical speciation and kinetics of dissolution under simulated gastrointestinal conditions. Monomeric silicates were readily absorbed, while particulate silicates were decreasingly well absorbed with increasing polymerisation. The present results highlight the need to allow for relative absorption of Si from different foods or supplements in subsequent epidemiological and intervention studies.

Relationship Between Dietary Intake and Urinary Excretion of Silicon in Free-Living Korean Adult Men and Women.

Previous studies have reported that silicon (Si) has a positive effect on bone health, immune response, and cognitive health. However, basic and important studies on evaluating dietary intake and urinary excretion of Si are limited. The aim of this study was to evaluate dietary Si intake and urinary excretion according to gender and age in healthy and free-living Korean adults and to investigate the relationship between them with gender. In this cross-sectional study, anthropometric measurements, dietary assessment using a food record, and a 24-h urine collection were conducted in 80 healthy Korean adults (40 males and 40 females; groups of 8 subjects representing each decade of life [20s to 60s]) with self-selected diet. The dietary assessment and 24-h urine collection were performed twice at intervals of 3 days. Daily intake of Si was estimated using a Si database of food composition. Urinary excretion of Si was analyzed using ICP-OES. The mean dietary Si intake was 22.8 mg/day for men and 19.3 mg/day for women without significant difference according to their gender and age. Si intake was the highest from vegetables both in men and women, followed by grains, beverages, and fruits in men and by grains, fruits, and milks in women. Urinary Si excretion was significantly higher in men (9.8 mg/day) than women (9.3 mg/day), and significantly increased with age only in women. Regarding the relationship between dietary Si intake and urinary Si excretion, a significantly positive correlation was found in men, but not in women. Longitudinal and balance studies to elucidate gender differences in Si nutrition are needed.

Trace element loss in urine and effluent following traumatic injury.

BACKGROUND: Few data are available to establish recommendations for trace element supplementation during critical illness. This study quantified the loss of several elements and assessed the adequacy of manganese and selenium in parenteral nutrition (PN). METHODS: Men with traumatic injuries were grouped by renal status: adequate (POLY; n = 6), acute failure with continuous venovenous hemofiltration (CVVH; n = 2), or continuous venovenous hemodiafiltration (CVVHD; n = 4). PN supplied 300 microg/d manganese and 60 microg/d selenium. Urine and effluent (from artificial kidneys) were collected for 3 days and analyzed for boron, manganese, nickel, and silicon using inductively coupled plasma atomic emission spectrometry, and for selenium using atomic absorption spectrometry. RESULTS: POLY manganese and selenium excretion averaged (standard deviation [SD]) 7.9 (3.3) microg/d and 103.5 (22.4) microg/d, respectively. All elements except selenium were detected in dialysate (prior to use). CVVHD effluent contained 3.5 and 7.3 times more manganese and nickel than CVVH ultrafiltrate, respectively. Loss of manganese averaged 2.6%, 21%, and 73% of PN amounts for POLY, CVVH, and CVVHD groups, respectively. DISCUSSION: Minimal loss of manganese compared with the amount in PN suggests that excessive amounts are retained. POLY patients excreted more selenium than was in PN, indicating negative balance. POLY losses of boron and silicon were less than that published for healthy adults, reflecting less than typical intake, whereas loss during CVVH was in the normal reference range, possibly because of added intake from boron contamination of replacement fluids. All patients lost more nickel than amounts published for healthy adults. CONCLUSIONS: Current guidelines of 60-100 microg/d of parenteral manganese may be excessive for trauma patients. The uptake of manganese and nickel from contaminants in CVVHD dialysate should be investigated.

Urinary Excretion of Aluminium and Silicon in Secondary Progressive Multiple Sclerosis.

BACKGROUND: Progressive multiple sclerosis is a chronic autoimmune condition of unknown aetiology and few therapeutic options. Human exposure to aluminium has been linked with multiple sclerosis and affected individuals are known to excrete unusually high amounts of aluminium in their urine. Silicon-rich mineral waters facilitate the removal of aluminium from the body in urine and herein we have tested their efficacy in affecting urinary excretion of aluminium in individuals diagnosed with secondary progressive multiple sclerosis (SPMS). METHODS: Urinary excretion of aluminium and silicon, measured using transversely-heated graphite furnace atomic absorption spectrometry, was determined in 15 individuals diagnosed with SPMS over 24weeks, a 12week baseline period (control) followed by a 12week treatment period, during which individuals consumed up to 1.5L of a silicon-rich mineral water every day. FINDINGS: Individuals with SPMS excreted high amounts of aluminium during the baseline period (135.2nmol/mmol Crt (70.3-222.2, n=180) and females excreted significantly more aluminium than males. Regular drinking of a silicon-rich mineral water increased the urinary excretion of aluminium significantly (349.0nmol/mmol Crt (231.7-524.7, n=180; three-way ANOVA, F1,13=59.17, p-value=0.000003) relative to the baseline period. The majority of individuals, 14 out of 15, excreted more aluminium (µmol/24h) following drinking of a silicon-rich mineral water (independent-test, p<0.05). Silicon-rich mineral waters may be an effective and non-invasive therapy for the removal of aluminium from the body of individuals with SPMS.

Excretion of resorption products from bioactive glass implanted in rabbit muscle.

Bioactive glass granules were implanted in the paraspinal muscle of rabbits to determine the pathway of the silicon released from bioactive glass in vivo. We traced and quantified the silicon released by obtaining 24-h urine and blood samples for up to 6 months after implantation. Furthermore, local muscle tissue as well as the following organs were resected for chemical and histopathological analyses: brain, heart, kidney, liver, lung, lymph nodes, spleen, and thymus. The urinary silicon of the group with implanted granules was significantly higher than in the sham-operated, control group. The average excretion rate was 2.4 mg/day, and as such, 100% of the implanted silicon was excreted in 19 weeks. No elevated concentrations of silicon were found at the implant sites or in the other organs at sacrifice, that is, 24 weeks. The histological appearance of all organs was normal throughout. The concentrations of silicon measured in the urine were well below saturation and because no significant increase in silicon was found in any organ, including kidney, the increased silicon excretion rate was within the physiological capacity of rabbits. Therefore, it can be concluded that the resorbed silica gel is harmlessly excreted in soluble form through the urine.

Digestive absorption of silicon, supplemented as orthosilicic acid-vanillin complex.

SCOPE: Silicon (Si) is an abundant element on earth. It is found naturally in water in the form of orthosilicic acid (OSA), however this form is not stable under certain conditions such as in highly concentrated and non-neutral pH solutions, which lead to its polymerization and reduced bioavailability. This study aimed to assess the bioavailability of Si from OSA stabilized by vanillin (OSA-VC). METHODS AND RESULTS: This was a single-center, double-blind, cross-over randomized controlled trial. Fourteen healthy subjects were recruited and consumed either OSA-VC or a placebo on two separate occasions. Blood and urine samples were collected during 6 h following ingestion and analyzed to determine Si absorption and excretion. Plasma Si area under the curve (0-6 h) was significantly higher after OSA-VC ingestion compared to placebo ingestion (p = 0.0002). Significantly higher urinary Si excretion was also reported over the 6-h period after OSA-VC ingestion compared to placebo (p<0.0001). Approximately 21% of ingested Si was excreted in urine during this period. CONCLUSION: Although many studies have investigated the metabolism and bioavailability of Si supplemented in foods or as a food ingredient, this was the first to investigate and demonstrate the digestibility of OSA administered in a complex form with vanillin.

Dietary silicon intake and absorption.

BACKGROUND: Increasing evidence suggests that silicon is important in bone formation. The main source of silicon for humans is the diet, but the bioavailability of silicon from solid foods is not well understood. OBJECTIVE: We estimated the dietary intake of silicon by adults, separately for men and women and for different age groups. Foods that were major contributors to silicon intake were identified. We then estimated the gastrointestinal uptake of silicon from major food sources and studied how uptake correlated with the silicon contents of the foods. DESIGN: Silicon intakes were determined in cohorts from the original Framingham Study and the Framingham Offspring Study by using a 126-item food-frequency questionnaire. Gastrointestinal uptake of silicon from foods was estimated in 3-8 healthy subjects by using urinary silicon excretion as a surrogate measure of silicon uptake. RESULTS: Mean silicon intakes in men (30 and 33 mg/d in the original Framingham and Framingham Offspring cohorts, respectively) were significantly higher than those in women (24 and 25 mg/d in the 2 cohorts, respectively; P = 0.0001). Silicon intake decreased with age (P < 0.001, adjusted for sex). The major food sources were beer and bananas in men and bananas and string beans in women. Silicon was readily available from foods; a mean of 41% of the ingested silicon was excreted in urine. The silicon content of the foods consumed was significantly correlated with urinary silicon excretion (P = 0.019). CONCLUSIONS: Solid foods are a major source of available silicon. The association between dietary silicon intake and bone health should now be investigated.

Oligomeric but not monomeric silica prevents aluminum absorption in humans.

BACKGROUND: Soluble silica, a ubiquitous component of the diet, may be the natural ligand for dietary aluminum and may prevent its accumulation and toxicity in animals. However, previous studies on the inhibition of aluminum absorption and toxicity by soluble silica have produced conflicting results. We recently identified a soluble silica polymer, oligomeric silica, that has a much higher affinity for aluminum than does monomeric silica and that may be involved in the sequestration of aluminum. OBJECTIVE: By using (26)Al as a tracer, we investigated the effects of oligomeric and monomeric silica on the bioavailability of aluminum (study 1) and compared the availability of silicon from oligomeric and monomeric silica in the human gastrointestinal tract (study 2). DESIGN: In study 1, three healthy volunteers each ingested aluminum alone (control), aluminum with oligomeric silica (17 mg), and aluminum with monomeric silica (17 mg). In study 2, five healthy volunteers ingested both the oligomeric and monomeric forms of silica (34 mg). Serum and urine samples were analyzed for aluminum and silicon. RESULTS: Oligomeric silica reduced the availability of aluminum by 67% (P = 0.01) compared with the control, whereas monomeric silica had no effect (P = 0.40). Monomeric silica was readily taken up from the gastrointestinal tract and then excreted in urine (53%), whereas oligomeric silica was not detectably absorbed or excreted. CONCLUSIONS: The oligomeric, high-aluminum-affinity form of soluble silica reduces aluminum availability from the human gastrointestinal tract. Its potential role in the amelioration of aluminum toxicity in other biological systems requires attention.

Silicon excretion from bioactive glass implanted in rabbit bone.

Bioactive glass granules were implanted in the tibiae of rabbits in order to determine the pathway of the silicon released from bioactive glass in vivo. We traced and quantified the silicon released by obtaining 24-h urine samples and blood samples for up to 7 months after implantation. Bone tissue as well as the following organs were resected for chemical and histopathological analyses: kidney, liver, lung, lymph nodes, and spleen. The urinary silicon of the implanted group was significantly higher than in the control group. From the data, the calculated average excretion rate was approximately 1.8 mg/day, and as such, the amount of implanted silicon was excreted within statistical bounds in 24 weeks. At this point, only elevated concentrations of silicon were found at the implant site and not in the other organs. The concentrations of silicon measured in the urine were well below saturation. Since no significant increase in silicon was found in any of the organs including the kidney, the increased silicon excretion rate was within the physiological capacity of rabbits. Therefore, it can be concluded that the resorbed silica gel is harmlessly excreted in soluble form through the urine.

Silicon metabolism: the basic facts in renal failure.

Silicon levels in plasma and urine have been studied in normal subjects, in chronic renal failure patients, and in regular hemodialysis patients. Plasma levels were elevated in chronic renal failure, and in hemodialysis patients they were three times the control values. Urine silicon excretion is significantly related to creatinine clearance, and to urinary omolality, magnesium and calcium levels. A small amount of residual silicon is found in the hollow fiber artificial kidneys made by some manufacturers. High concentrations of silicon are found in commercial dialysate and pass down a chemical concentration gradient into the blood compartment. It is concluded that silicon is sequestered rapidly in the body during hemodialysis, and that this amounts to 58 g of silicic acid per annum from hemodialysis alone.

Determination of silicon in urine by inductive coupled plasma-optical emission spectroscopy.

We describe an inductive coupled plasma-optical emission spectroscopic method to determine silicon in spot urine specimens. A 6-fold standard addition series of the urine specimen ranging from 0 to 356 micromol/l silicon was applied, and the method meets the requirement of matrix compensation in a frequently changing environment. The inter-assay variation was +/-3.0%, intra-assay variations for three specimens were +/-1.7%, +/-1.1% and +/-0.84%. To compensate for physiological variations of urine density, the silicon concentrations in urine were related to urinary creatinine which was measured in parallel by reversed-phase HPLC. Urinary silicon concentrations were examined in 43 healthy controls from the local population. The 5th-95th percentile was 12.6-237 micromol/mmol creatinine. A follow-up of three people over a period of 14 days showed that intra-individual variations of urinary silicon concentrations were smaller than variations between individuals, especially when silicon is related to creatinine.

Circadian characteristics of dialyzable and non-dialyzable human urinary electrolytes, trace elements and total solids.

Seven clinically-healthy men ranging in age from 21 to 25 years participated in this study. Urine samples were collected at 3 hr intervals over a single 24 hr span. Urines were pooled by using 20% of the total volume collected from each subject over a 3 hr collection span. The resulting 8 pools were analyzed for pH, specific gravity, osmolality, urea N, creatine, uric acid, glucose, phosphorus, chlorides, sodium, potassium, calcium, magnesium, silicon, aluminum, zinc and total solids. Each of the 8 pools was serially dialyzed at pH 7.35 against ammonium-barbituric acid buffer. The non-dialyzable portions were then re-analyzed for the remaining solids, sodium, potassium, calcium, magnesium, silicon, aluminum and zinc. Aliquots of the non-dialyzable fraction were examined by high performance liquid chromatography. Up to twelve discernable fractions were observed in each 3 hr urine by monitoring ultraviolet light absorbance at 280 nm wavelength. Range of change throughout the 24 hr (lowest to highest value) for most variables was 100% or more. In the eight 3 hr pooled urine samples, statistically-significant circadian variation could be described for volume, pH, osmolality, urea nitrogen, creatinine, uric acid, glucose, phosphorus, chlorides, for five of eight non-dialyzed (total) components (Na, K, Ca, Si and solids) and for five of twelve non-dialyzable solid fractions, as well as for total non-dialyzable solids. Single cosinor analysis resulted in description of a significant circadian rhythm in osmolality, urea nitrogen, creatinine, glucose, phosphorus, chlorides, total Na, K, Si and solids; non-dialyzable Si and solids; dialyzable Na, K, Si and solids; and for total solids, as well as their fractions at 23.4 and 25.9 min. These observations are furnished in order to further document the extreme circadian rhythmicity in all aspects of kidney function and as reference for future work which uses any of the investigated urinary endpoints whose circadian time structure is herein described.

A direct current plasma emission spectrometric procedure for the assay of silicon in urine.

A method for the assay of silicon in urine has been developed using direct current plasma emission spectroscopy. Urine is directly aspirated into the argon plasma, and the silicon emission is measured at 251.6 nm. There is a moderate matrix effect which is not compensated by the addition of lithium chloride as an ionization suppressor. The use of calibration standards in an urine-like matrix gives the best analytical results as documented by serial dilution and standard addition studies. The method is linear over the entire range of urine concentrations normally encountered (0 to 50 mg per L). The lower detection limit is 0.05 mg per L and the coefficients of variation at the 2.7 mg per L and 5.9 mg per L levels are 5.8 percent and 11.5 percent, respectively. Urine from ten randomly chosen volunteers shows a considerable between subject variation in silicon concentration (mean 12.5 +/- 8.3 mg per L, range 1.8 to 51.6 mg per L) which is positively associated with vegetable intake. Urine from 39 hospital patients on a standardized diet shows much less variation in concentration (mean 4.1 +/- 3.2 mg per L, range 0.1 to 18.6 mg per L), indicating that the urine silicon assay is likely to be useful in metabolic studies only if diet is controlled.

The role of silicic acid in the renal excretion of aluminium.

The chemical affinity of silicic acid for aluminium (AI) has been shown to reduce the bioavailability of AI in studies of human gastrointestinal (GI) absorption. Investigations were carried out to ascertain whether or not similar interactions may also enhance the renal excretion of AI by assessing the urinary output of both elements. Healthy individuals given monosilicic acid as naturally found in beer, excreted the majority of the silicic acid content (mean 56 percent) within 8 hours, concomitant with a significant increase in AI excretion (P < 0.05). Ingestion of increasing doses of silicic acid resulted in dose related increases in excretion of Si. Excretion of AI reached a maximum and then declined, consistent with depletion of AI body stores. This was confirmed using the 26AI isotope. The low serum but high urine concentration of Si suggests that if AI and Si interact to form an excretable species they do so in the kidney lumen such that Si limits the reabsorption of AI. Silicic acid's effect on the depletion of aluminium stores and reduced GI absorption suggest its addition to municipal water supplies may be a low risk public health measure to reduce the AI burden in the general population.

Silicon analysis in biological specimens by direct current plasma-atomic emission spectroscopy.

A method for the determination of total elemental silicon concentrations in biological fluids by direct current plasma-atomic emission spectrometry (DCP-AES) is presented. The method is linear up to 30 micrograms/mL in blood, serum, plasma, and urine, with a detection limit of 0.2 microgram/mL. Population ranges of silicon concentration in blood, plasma, serum, and urine were found to be less than 0.3 to 33 micrograms/mL, less than 0.4 to 39 micrograms/mL, less than 0.2 to 68 micrograms/mL, and less than 0.3 to 180 micrograms/mL, respectively. Over 50% of all measured concentrations were less than 0.5 microgram/mL for blood, plasma, and serum. Estimates of "normal" population ranges are reported, and potential applicability of this procedure to silicone-related maladies is discussed.

GC/MS analysis of five common benzodiazepine metabolites in urine as tert-butyl-dimethylsilyl derivatives.

A method for the GC/MS confirmation of oxazepam, nordiazepam, desalkylflurazepam, temazepam, and alpha-hydroxyalprazolam in urine is described. The method incorporates a solid phase extraction technique developed by Varian which was found to extract all five metabolites with recoveries exceeding 73%. The extracted metabolites were derivatized with N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA), resulting in the formation of stable tert-butyldimethylsilyl (TBDMS) derivatives. Quantitation was performed by GC/MS using oxazepam-D5, nordiazepam-D5, and alpha-hydroxyalprazolam-D5 as internal standards. The method was found to be linear over the range of 50-2000 ng/mL. Within-run precision, measured as the coefficient of variation at 100 ng/mL, was less than 3% for all analytes except temazepam which was 6% (N = 20).