Densitometric analysis of rep-PCR data: Insight into genetic variability and transmission of Clostridium perfringens typed with an improved multiplex PCR.

An epidemiological study was conducted in North-East India (part of Indo-Burma biodiversity hotspot) to better understand the distribution, diversity, and transmission of Clostridium perfringens among livestock, pets, wild animals (captive), and humans. A total of 160 C. perfringens isolates were recovered from 642 diarrhoeic faecal samples with an isolation rate of 24.92%. Isolation rate was the highest among captive wild animals (37.5%) followed by dog (34.6%), human (33.8%), pig (32.7%), cattle (20.8%), goat (18.3%) and poultry (9.3%). Isolates were toxin typed using a seven gene multiplex PCR designed for simultaneous detection of cpa, cpb, cpb2, etx, iap, cpe and netB. The majority of isolates, 128 (80%) were of type A, followed by 17 (10.62%), 5 (3.12%), 4 (2.5%), 3 (1.87%), 2 (1.25%) and 1 (0.63%) isolates of type C, D, E, G, F and B, respectively. Beta 2 toxin gene was present in 65 (50%) of type A isolates, followed by 7 (41.2%), 4 (80%), 1(25%), and 1 (100%) of type C, D, G and B isolates, respectively. Beta 2 toxin has a high prevalence among dogs (28.6%), cattle (27.3%), and pig (20.8%) compared to humans, goat, wild animals, and poultry (1.2-14.3%). The prevalence of CPE and NetB toxin-positive strains was low, with only 3 (1.8%) and 5 (3.1%) isolates, respectively. Association of C. perfringens with diarrhoea in Civet Cat, Golden Langur, and Gray Langur has been reported for the first time. The genetic diversity and transmission of isolates were investigated using automated rep-PCR (Diversilab®, bioMérieux) using two densitometry-based matrices: modified Kullback-Leibler (KL) and Pearson's correlation (PC). The PC and modified KL matrices formed three distinct clusters with 59% and 27.2% similarity, respectively. C. perfringens diversity and transmission were best studied using modified KL matrix that placed more emphasis on the presence of bands rather than intensity. However, the PC method was found to be more suitable for differentiating strains within a toxin type, with slightly higher D-values.

Technical note: age estimation by using pubic bone densitometry according to a twofold mode of CT measurement.

In forensic anthropology, age estimation is a major element in the determination of a biological profile and the identification of individuals. Thus, many anatomical structures have been studied, such as the pubic symphysis, which is a source of major interest due to its late maturation. One of the most well-known methods of assessment is the Suchey-Brooks (SB) system based on the morphological characteristics of the pubic symphysis. The aim of this study was to propose linear regression formulae in order to deduce chronological age from bone density, using both Hounsfield unit (HU), and mean bone density (mBD) values of the pubic symphysis. Moreover, we intended to test the reliability and then to explore the feasibility of using HU instead of mBD values for age estimation. We built retrospectively a reference sample of 400 pubic symphyses using computed tomography at a French hospital and a test sample of 120 pubic symphyses. Equations were created to establish linear regression models for age estimation. Inaccuracy and bias were calculated for individuals aged more or less than 40 years. We highlighted homogeneous mean absolute errors for both HU and mBD values, most of them being less than 10 years. Moreover, we reported a moderate overestimation for younger individuals and a very small underestimation for older individuals. This study proposes a correlation between the bone density and age of individuals with a valuable level of reliability. Finally, HU measurements seem to be suitable for linking bone density with the age of individuals in forensic practice.

Methods of assessing body composition in people with limb amputation / Métodos de avaliação da composição corporal em pessoas com amputação de membros

Objective: Identify which methods of have been used to assess the body composition individuals with limb amputation from the literature review. Method: In order to reach the defined objective, the Pubmed and Scielo databases were used, through the descriptors (in combination with amputation) body composition, fat mass and lean mass from 1986 to 2019. Results: Found articles went through the inclusion and exclusion criteria and 17 articles were selected, all of them using anthropometric measures (body mass and stature), followed by bone densitometry (DXA) and thickness of skinfolds. It can also be observed that most of the studies are focused on the health aspect which focused on nutrition and risk factors. Conclusion: Through this review we observed that the anthropometric methods were mostly used to evaluate body composition in individuals with limb amputation followed by bone densitometry. However, the studies were scarce and many procedures were not so clear to make a more careful analysis unfeasible. In addition, there is a lack of longitudinal studies and especially in the area of sports performance in this population, indicating an important gap to be explored.

Objetivo: Identificar quais métodos foram utilizados para avaliar a composição corporal de indivíduos com amputação de membros a partir da revisão da literatura. Método: Para atingir o objetivo definido, utilizou-se as bases de dados Pubmed e Scielo, através dos descritores (em combinação com amputação) composição corporal, massa gorda e massa magra de 1986 a 2019. Resultados: Os artigos encontrados passaram pela inclusão e critérios de exclusão e 17 artigos, todos utilizando medidas antropométricas (massa corporal e estatura), seguidas de densitometria óssea (DXA) e espessura das dobras cutâneas. Pode-se observar, também, que a maioria dos estudos está focada no aspecto saúde, com foco em nutrição e fatores de risco. Conclusão: Através desta revisão, observou-se que os métodos antropométricos foram utilizados principalmente para avaliar a composição corporal em indivíduos com amputação de membros, seguida de densitometria óssea. No entanto, os estudos eram escassos e muitos procedimentos não eram tão claros para inviabilizar uma análise mais cuidadosa. Além disso, faltam estudos longitudinais e, principalmente, na área do desempenho esportivo nessa população, indicando uma lacuna importante a ser explorada.

Associação de força de preensão palmar e osteoporose avaliada por densitometria óssea (DXA) em idosos quilombolas: um estudo seccional / Association between handgrip strength and osteoporosis assessed by bone densitometry in elderly quilombolas: a sectional study

Objetivo: Verificar a associação de força de preensão palmar e osteoporose em idosos quilombolas. Método: Trata-se de um estudo seccional com 70 participantes (idade 65,58 ± 6.67 anos) de ambos os sexos. A densidade mineral óssea (DMO), massa muscular (MM) e o percentual de gordura foram analisados pela absortometria de raios-x de dupla energia (DXA) e a força de preensão palmar (FPP) por meio do dinamômetro de mão. O ponto de coorte adotado para identificação de osteoporose foi o da Organização Mundial de Saúde (OMS). A identificação do status da sarcopenia foi realizado para caraterização da amostra e para o diagnóstico foi utilizado os critérios propostos pelo European Working Group on Sarcopenia in Older People (EWGSOP). A FPP foi associada positivamente e significativamente com a DMO. Resultados: A osteopenia foi identificada em 42,8% da amostra e a osteoporose em 20%, sem diferença entre as frequências segundo o sexo (p = 0,161). Conclusão: Nos idosos quilombolas a baixa FPP esteve positivamente associada com baixa DMO. Portanto, sugerindo que a FPP pode ser considerada um fator de risco importante de estado ósseo em idosos quilombolas.

Objective: The aim of this study was to verify the association between handgrip strength and osteoporosis in elderly quilombolas. Method: It is a sectional study with 70 participants (aged 65.58 ± 6.67 years) of both sexes. Bone mineral density (BMD), muscle mass and fat percentage were analysed by dual-energy X-ray absorptiometry (DXA) and handgrip strength by a hand dynamometer. Subjects were classified as having osteoporosis according to World Health Organization (WHO) cutoff point. The identification of sarcopenia was performed to characterize the sample and the diagnosis was done according to the European Working Group on Sarcopenia in Older People (EWGSOP) criteria. Results: Osteopenia was identified in 42.8% of the sample and osteoporosis in 20%, with no difference between sex (p = 0.161). HGS was positively associated with BMD. Osteopenia was identified in 42.8% of the sample and osteoporosis in 20%, with no difference between the frequencies according to sex (p = 0.161). Conclusion: In the elderly quilombolas low HGS was positively associated with low BMD. Therefore, suggesting that HGS may be considered an important risk factor for bone state in this population.

Drilling resistance: A method to investigate bone quality.

PURPOSE: Bone drilling is a major part of orthopaedic surgery performed during the internal fixation of fractured bones. At present, information related to drilling force, drilling torque, rate of drill-bit penetration and drill-bit rotational speed is not available to orthopaedic surgeons, clinicians and researchers as bone drilling is performed manually. METHODS: This study demonstrates that bone drilling force data if recorded in-vivo, during the repair of bone fractures, can provide information about the quality of the bone. To understand the variability and anisotropic behaviour of cortical bone tissue, specimens cut from three anatomic positions of pig and bovine were investigated at the same drilling speed and feed rate. RESULTS: The experimental results showed that the drilling force does not only vary from one animal bone to another, but also vary within the same bone due to its changing microstructure. Drilling force does not give a direct indication of bone quality; therefore it has been correlated with screw pull-out force to provide a realistic estimation of the bone quality. A significantly high value of correlation (r2 = 0.93 for pig bones and r2 = 0.88 for bovine bones) between maximum drilling force and normalised screw pull-out strength was found. CONCLUSIONS: The results show that drilling data can be used to indicate bone quality during orthopaedic surgery.

A field-to-desktop toolchain for X-ray CT densitometry enables tree ring analysis.

BACKGROUND AND AIMS: Disentangling tree growth requires more than ring width data only. Densitometry is considered a valuable proxy, yet laborious wood sample preparation and lack of dedicated software limit the widespread use of density profiling for tree ring analysis. An X-ray computed tomography-based toolchain of tree increment cores is presented, which results in profile data sets suitable for visual exploration as well as density-based pattern matching. METHODS: Two temperate (Quercus petraea, Fagus sylvatica) and one tropical species (Terminalia superba) were used for density profiling using an X-ray computed tomography facility with custom-made sample holders and dedicated processing software. KEY RESULTS: Density-based pattern matching is developed and able to detect anomalies in ring series that can be corrected via interactive software. CONCLUSIONS: A digital workflow allows generation of structure-corrected profiles of large sets of cores in a short time span that provide sufficient intra-annual density information for tree ring analysis. Furthermore, visual exploration of such data sets is of high value. The dated profiles can be used for high-resolution chronologies and also offer opportunities for fast screening of lesser studied tropical tree species.

Densidad ósea volumétrica vertebral obtenida sin fantoma en estudios de rutina de tomografía computarizada de abdomen: correlación con los valores medidos por densitometría ósea areal por rayos X / Phantom-less volumetric vertebral density obtained from routine abdominal ct studies: correlation with data obtained by DXA

La densidad mineral ósea (DMO) por tomografía computarizada cuantitativa (QCT) mide con exactitud y precisión de corto plazo la densidad volumétrica (DMOv) de secciones axiales de los cuerpos vertebrales lumbares valiéndose de un fantoma de calibración. Existe evidencia de que la densitometría por TC sin fantoma convirtiendo las unidades Hounsfield en g/cm3 aplicando un coeficiente específico para cada equipo, presenta muy alta correlación con la DMO por QCT y que es confiable para evaluar la densidad ósea vertebral. Apoyándonos en ello, correlacionamos DMO y CMO estimados a partir de estudios de TC con los obtenidos por DXA. Se incluyeron 28 mujeres (edad: 63,4±10,3 años, rango: 37-85) que habían realizado una TC de abdomen y previamente una DMO en un lapso previo no mayor de 6 meses. Se midieron: 1) TC: DMOv promedio integral (trabecular + cortical) en un corte axial medio vertebral de 10 mm de espesor y el área en cm2 . Se multiplicó la densidad por el área, obteniendo un valor equivalente al CMO de la sección (CMO-TC) y 2) DXA: se consideraron la DMOa y CMO en una RI de 10 mm de altura a nivel del centro de la vértebra L3. Las correlaciones entre los parámetros homólogos obtenidos por ambos métodos fueron significativas: resultó superior para CMO [DMOv vs. DMOa r: 0,67 (p=0,005) y CMO-TC vs. CMO-DXA r: 0,75 (p=0,00063)]. El estudio complementa los ya existentes y abre la posibilidad de utilizar estudios de rutina de TC de abdomen para evaluar la densidad ósea, para lo cual deberán establecerse valores de referencia sexo y edad específicos. (AU)

Conventional quantitative computed tomography (QCT) uses a calibration phantom scanned simultaneously with the anatomical region of interest and measures bone density accurately and with short-term high precision. Evidence supports that phantom-less volumetric BMD highly correlates with QCT BMD and is a reliable method for assessing bone density of vertebral bodies. Assessment of BMD in routine abdominal CT scans has been investigated in recent years. The aim of the study was to correlate BMD and bone mineral content (BMC) obtained from CT studies with data obtained by DXA. Twenty eight women (age 63.4±10.3 years old, range: 37-85) who underwent abdominal CT for different reasons and DXA measurements within 6 months were included. A simple manual region of interest (RI) which delineated the edge of the vertebral body was applied to L3. We measured 1) CT: Volumetric integral density (BMDv) -trabecular and cortical bone- of the axial section and area (A) in cm2 . Density was multiplied by area to obtain a value equivalent to BMC. 2) DXA: BMD and BMC in a RI of 10 mm height in the middle of L3. All parameters obtained by CT correlated significantly with the corresponding to DXA : BMDv vs BMDa r: 0.67 (p=0.005) y BMC-CT vs BMC-DXA: r: 0.75 (p=0.00063). This study complements previous reports and opens the possibility of using routine abdominal CT studies to assess bone density. For that purpose reference values (age and gender) must be established. (AU)

Stimulus edge effects in the measurement of macular pigment using heterochromatic flicker photometry.

Heterochromatic flicker photometry (HFP) is the most common technique of measuring macular pigment optical density (MPOD). Some data strongly suggest that HFP samples MPOD specifically at the edge of center-fixated circular stimuli. Other data have led to the conclusion that HFP samples over the entire area of the stimulus. To resolve this disparity, MPOD was measured using HFP and a series of solid discs of varying radii (0.25 to 2.0 deg) and with thin annuli corresponding to the edge of those discs. MPOD assessed with the two methods yielded excellent correspondence and linearity: Y=0.01+0.98X , r=0.96. A second set of experiments showed that if a disc stimulus is adjusted for no-flicker (the standard procedure) and simply reduced in size, no flicker is observed despite the higher level of MPOD in the smaller area. Taken together, these results confirm that MPOD is determined at the edge of the measuring stimulus when using stimulus sizes in the range that is in dispute (up to a radius of 0.75 deg). The basis for this edge effect can be explained by quantitative differences in the spatial-temporal properties of the visual field as a function of angular distance from the fixation point.

Photopigment self-screening and the determination of macular pigment absorbance using heterochromatic flicker photometry.

PURPOSE: Heterochromatic flicker photometry (HFP) is commonly used to determine macular pigment optical density (MPOD). Since HFP in this application is a locus comparison method, an identical relative spectral response at each locus is required for a perfect measure. We know this requirement cannot be strictly true since the optical density of photopigments increases as the foveal center is approached. Thus, the self-screening effect would result in an underestimate of MPOD. An earlier study concluded that the underestimate is on the order of 30%. We examined this issue by manipulating photopigment optical density, and consequently the degree of selfscreening. METHODS: A continuously exposed, 470 nm, background bleached cone photopigments over a range from 0 to 80%. MPOD was determined 10' and 30' from the foveal center. Two subjects were used in the main experiment. Five additional subjects were studied with just the 0% and 80% bleach levels. Spectral measures were obtained at 0% and 70% bleach levels for the two primary subjects. RESULTS: Subjects in the main experiment showed MPOD estimates that increased with increasing bleaching. The effect, however, was small: one observer's MPOD increased 0.08 and 0.02 for the 10' and 30' loci, respectively; the other observer's values were 0.04 and 0.01 for the same loci. Comparable values were obtained for the other five subjects using the 0% and 80% bleach conditions. Spectral measures were consistent with the findings of the main experiment. CONCLUSIONS: When self-screening is nearly abolished (80% bleach), a relatively small underestimation is revealed for the unbleached state. For the 1° target we show about 2-3% underestimation. Our 20' target reveals a larger underestimate (8-9%), consistent with longer photoreceptor outer-segments nearer the foveal center. We conclude that HFP yields values essentially independent of self-screening for targets of 1° diameter or greater. Smaller targets are less than 10% underestimated for near-zero bleach conditions.

Inertial imaging with nanomechanical systems.

Mass sensing with nanoelectromechanical systems has advanced significantly during the last decade. With nanoelectromechanical systems sensors it is now possible to carry out ultrasensitive detection of gaseous analytes, to achieve atomic-scale mass resolution and to perform mass spectrometry on single proteins. Here, we demonstrate that the spatial distribution of mass within an individual analyte can be imaged--in real time and at the molecular scale--when it adsorbs onto a nanomechanical resonator. Each single-molecule adsorption event induces discrete, time-correlated perturbations to all modal frequencies of the device. We show that by continuously monitoring a multiplicity of vibrational modes, the spatial moments of mass distribution can be deduced for individual analytes, one-by-one, as they adsorb. We validate this method for inertial imaging, using both experimental measurements of multimode frequency shifts and numerical simulations, to analyse the inertial mass, position of adsorption and the size and shape of individual analytes. Unlike conventional imaging, the minimum analyte size detectable through nanomechanical inertial imaging is not limited by wavelength-dependent diffraction phenomena. Instead, frequency fluctuation processes determine the ultimate attainable resolution. Advanced nanoelectromechanical devices appear capable of resolving molecular-scale analytes.

Intraoperative mechanical measurement of bone quality with the DensiProbe.

Reduced bone stock can result in fractures that mostly occur in the spine, distal radius, and proximal femur. In case of operative treatment, osteoporosis is associated with an increased failure rate. To estimate implant anchorage, mechanical methods seem to be promising to measure bone strength intraoperatively. It has been shown that the mechanical peak torque correlates with the local bone mineral density and screw failure load in hip, hindfoot, humerus, and spine in vitro. One device to measure mechanical peak torque is the DensiProbe (AO Research Institute, Davos, Switzerland). The device has shown its effectiveness in mechanical peak torque measurement in mechanical testing setups for the use in hip, hindfoot, and spine. In all studies, the correlation of mechanical torque measurement and local bone mineral density and screw failure load could be shown. It allows the surgeon to judge local bone strength intraoperatively directly at the region of interest and gives valuable information if additional augmentation is needed. We summarize methods of this new technique, its advantages and limitations, and give an overview of actual and possible future applications.

Outdoor solar UVA dose assessment with EBT2 radiochromic film using spectrophotometer and densitometer measurements.

Direct measurements of solar ultraviolet radiations (UVRs) have an important role in the protection of humans against UVR hazard. This work presents simple technique based on the application of EBT2 GAFCHROMIC(®) film for direct solar UVA dose assessment. It demonstrates the effects of different parts of the solar spectrum (UVB, visible and infrared) on performed UVA field measurements and presents the measurement uncertainty budget. The gradient of sunlight exposure level permitted the authors to establish the mathematical relationships between the measured solar UVA dose and two measured quantities: the first was the changes in spectral absorbance at the wavelength 633 nm (A633) and the second was the optical density (OD). The established standard relations were also applied to calculate the solar UVA dose variations during the whole day; 15 min of exposure each hour between 8:00 and 17:00 was recorded. Results show that both applied experimental methods, spectrophotometer absorbance and densitometer OD, deliver comparable figures for EBT2 solar UVA dose assessment with relative uncertainty of 11% for spectral absorbance measurements and 15% for OD measurements.

Integrated protocol for reliable and fast quantification and documentation of electrophoresis gels.

Quantitative analysis of electrophoresis gels is an important part in molecular cloning, as well as in protein expression and purification. Parallel quantifications in yield and purity can be most conveniently obtained from densitometric analysis. This communication reports a comprehensive, reliable and simple protocol for gel quantification and documentation, applicable for single samples and with special features for protein expression screens. As major component of the protocol, the fully annotated code of a proprietary open source computer program for semi-automatic densitometric quantification of digitized electrophoresis gels is disclosed. The program ("GelQuant") is implemented for the C-based macro-language of the widespread integrated development environment of IGOR Pro.

Application of an online-biomass sensor in an optical multisensory platform prototype for growth monitoring of biotechnical relevant microorganism and cell lines in single-use shake flasks.

In the context of this work we evaluated a multisensory, noninvasive prototype platform for shake flask cultivations by monitoring three basic parameters (pH, pO2 and biomass). The focus lies on the evaluation of the biomass sensor based on backward light scattering. The application spectrum was expanded to four new organisms in addition to E. coli K12 and S. cerevisiae [1]. It could be shown that the sensor is appropriate for a wide range of standard microorganisms, e.g., L. zeae, K. pastoris, A. niger and CHO-K1. The biomass sensor signal could successfully be correlated and calibrated with well-known measurement methods like OD600, cell dry weight (CDW) and cell concentration. Logarithmic and Bleasdale-Nelder derived functions were adequate for data fitting. Measurements at low cell concentrations proved to be critical in terms of a high signal to noise ratio, but the integration of a custom made light shade in the shake flask improved these measurements significantly. This sensor based measurement method has a high potential to initiate a new generation of online bioprocess monitoring. Metabolic studies will particularly benefit from the multisensory data acquisition. The sensor is already used in labscale experiments for shake flask cultivations.

Portable digital lock-in instrument to determine chemical constituents with single-color absorption measurements for Global Health Initiatives.

Innovations in international health require the use of state-of-the-art technology to enable clinical chemistry for diagnostics of bodily fluids. We propose the implementation of a portable and affordable lock-in amplifier-based instrument that employs digital technology to perform biochemical diagnostics on blood, urine, and other fluids. The digital instrument is composed of light source and optoelectronic sensor, lock-in detection electronics, microcontroller unit, and user interface components working with either power supply or batteries. The instrument performs lock-in detection provided that three conditions are met. First, the optoelectronic signal of interest needs be encoded in the envelope of an amplitude-modulated waveform. Second, the reference signal required in the demodulation channel has to be frequency and phase locked with respect to the optoelectronic carrier signal. Third, the reference signal should be conditioned appropriately. We present three approaches to condition the signal appropriately: high-pass filtering the reference signal, precise offset tuning the reference level by low-pass filtering, and by using a voltage divider network. We assess the performance of the lock-in instrument by comparing it to a benchmark device and by determining protein concentration with single-color absorption measurements. We validate the concentration values obtained with the proposed instrument using chemical concentration measurements. Finally, we demonstrate that accurate retrieval of phase information can be achieved by using the same instrument.

Repeatability of lens densitometry using Scheimpflug imaging.

PURPOSE: To evaluate the repeatability of different lens densitometry analysis modes performed with Scheimpflug imaging using the Pentacam HR device. SETTING: University eye hospital, Frankfurt am Main, Germany. DESIGN: Cross-sectional study. METHODS: Eyes were analyzed under mydriasis during 2 examinations performed by the same examiner. Three single measurements were taken to assess lens densitometry via 3 modes as follows: peak (maximum), linear (vertical axis), and 3-dimensional (3-D). Measurements were also taken using 3 cylindrical reference blocks (P) with different diameters (2.0 mm, 4.0 mm, 6.00 mm) composing the whole lens depth. Repeatability was tested using Bland-Altman analysis. As statistical parameters, the coefficient of repeatability (CoR) and the relative repeatability (RR) were applied. RESULTS: The study analyzed 105 eyes. The CoR of the peak modus was 5.6 (RR, 29.8%); of the linear modus, 0.9 (RR, 8.8%); and of the 3-D modus, 0.36 (RR, 3.6%). The values of the P mode were lower, with a CoR between 0.19 and 0.30 (RR, 2.1%-3.3%). CONCLUSIONS: Lens densitometry using Scheimpflug imaging was highly repeatable. However, repeatability was dependent on the analysis mode used. Repeatability decreased with increasing opacification.

In-situ detection of density alteration in non-physiological cells with polarimetric tilted fiber grating sensors.

Tilted fiber Bragg grating (TFBG) biosensors can be used as a cost-effective and relatively simple-to-implement alternative to well established biosensor platforms for high sensitivity biological sample measurements in situ or possibly in vivo. The fiber biosensor presented in this study utilizes an in-fiber 12° tilted Bragg grating to excite a strong evanescent field on the surface of the sensor over a large range of external medium refractive indices. The devices have minimal cross-sensitivity to temperature and their fabrication does not impact the structural integrity of the fiber and its surface functionalization. Human acute leukemia cells with different intracellular densities and refractive index (RI) ranging from 1.3342 to 1.3344 were clearly discriminated in-situ by using the differential transmission spectrum between two orthogonal polarizations for the last guided mode resonance before "cut-off", with an amplitude variation sensitivity of 1.8 × 10(4) dB/RIU, a wavelength shift sensitivity of 180 nm/RIU, and a limit of detection of 2 × 10(-5)RIU. The detection process was precisely controlled with a micro-fluidic chip which allows the measurement of nL-volumes of bio-samples. The proposed in-fiber polarimetric biosensor is an appealing solution for rapid, sub-microliter dose and highly sensitive detection of analytes at low concentrations in medicine, chemical and environmental monitoring.