Organic Matter Interference Research Articles

Decomposition of tetracycline with peroxymonosulfate activated by an ordered hierarchical pores Fe-N/C catalyst rich in FeNx sites: Insights into singlet oxygen mechanism

FeNx sites show significant superiority in the degradation of antibiotic contaminants, but there are difficulties in successfully constructing highly dispersed FeNx sites. In this work, Fe-N/C catalysts doped with hierarchical ordered pores structure and FeNx active sites were prepared by metal node exchange strategy. Among them, Fe-N/C-2 had more excite species for peroxymonosulfate (PMS) owing to the synergy between Fe and N coordination, which achieved 89.36 % tetracycline (TC) removal rate within 20 min, and its reaction kinetic (k = 0.245 min−1) is 7.66 times more than original PMS system. Moreover, the material exhibited excellent activation performance in a variety of complex water environments, such as the coexistence of multiple anions, strong acids and alkalis (pH = 2.90 ∼ 10.73), and natural organic matter interference. Chemical bond detection confirmed the successful formation of FeNx sites, free radical trapping experiments showed that FeNx was the main catalytic site, and 1O2 was the main active component. Furthermore, the reaction principle of the FeNx site catalyzing the production of 1O2 from PMS was revealed in detail through mechanism exploration. Next, the probable pathways of TC decomposition were elaborated in terms of the intermediates identified by Liquid Chromatograph Mass Spectrometer (LC-MS). This study emphasized the significant potential of synthesizing Fe-N/C catalysts with activated FeNx sites, elucidated mechanism of FeNx in PMS activation, and confirmed its feasibility in TC degradation.

Fluorescent labelling combined with confocal differential Raman spectroscopy to detect microplastics in seawater

As an emerging marine pollutant, microplastics represent a focal point in global monitoring and management efforts. With seawater accounts for 97 % of the total global water resources, scientific assessments of microplastics in seawater are crucial for pollution control and management of marine environments. This study focuses on investigating microplastics in near-shore seawater and proposes a rapid and accurate detection method using a constructed confocal Raman spectroscopy detection system. By optimizing the pretreatment process of seawater microplastic samples, the efficient removal of organic matter interference in microplastic detection is achieved. Employing fluorescent labeling addresses the issues of prolonged detection time and high false positive rates associated with traditional methods, enabling rapid differentiation between microplastics and other substances and significantly enhancing detection efficiency and accuracy. Additionally, the use of differential Raman spectroscopy effectively mitigates fluorescence signal interference, thus improving the signal-to-noise ratio of the spectra. By employing dual-wavelength laser excitation at 784 nm/785 nm, microplastics such as polyethylene (PE), polypropylene (PP), polystyrene (PS) ranging in size from 60 to 500 μm are successfully detected in seawater. The results demonstrate that the proposed pretreatment method for seawater microplastics and novel detection techniques enable rapid screening and comprehensive non-destructive detection of microplastics in seawater, thereby facilitating the characterization of marine microplastics and providing scientific support for enhancing the management of microplastic pollution and ecological risk control.

Quantifying the relative importance of controls and assay conditions for reliable measurement of soil enzyme activities with para-nitrophenol substrates

Since their first application to soils in the late 1960s, assays of hydrolytic enzyme activities in soils using para-nitrophenol (pNP) substrates have become a widespread tool in soil biochemistry. As for any enzymes, the accuracy of measured soil enzyme activities can be strongly influenced by assay methodology (i.e., matrix type and controls) and may further vary by soil and enzyme type. Assay methodology determines time, labor, and reagent costs, and therefore each methodological decision should be weighed against the relative improvement in accuracy. Using recursive partitioning analysis, we determined the relative effect of various enzyme assay controls (abiotic hydrolysis, pNP sorption, dissolved organic matter interference), assay conditions (matrix, substrate concentration), and soil properties (clay, pH, soil organic carbon) on the mis-estimation of phosphomonoesterase and β-glucosidase activities across 26 diverse soils using 7,488 data points. The omission of a control for dissolved organic matter interference enzyme assays was the greatest contributor to the mis-estimation of enzyme activity, an effect that was robust across enzymes and soil properties. The effect of omitting controls for pNP sorption and abiotic hydrolysis varied by matrix type and substrate concentration, but were of secondary importance to the omission of the control for dissolved organic matter interference. Generally, omitting controls entailed lower mis-estimation when using water as the assay matrix than when using modified universal buffer (MUB). Our results provide a quantitative basis for prioritizing which controls should be performed and how much substrate should be used depending on matrix selection and enzyme type.

Organic matter interference with steroid hormone removal by single-walled carbon nanotubes − ultrafiltration composite membrane

Composite adsorbent−ultrafiltration membranes for micropollutant removal are an interesting concept, although water matrix compounds, such as organic matter (OM), may interfere with micropollutant adsorption. To prevent this interference, the adsorbents such as single-walled carbon nanotubes (SWCNTs) can be deposited on the permeate side of an ultrafiltration membrane (UF) that can retain OM. In this study, the ‘shielding’ effect by different UF MWCOs of such an SWCNT−UF composite was evaluated for nine different types of OM. All nine OM types competed with 17β-estradiol (E2) for adsorption to varying extents, and tannic acid (TA, 1.7 kDa) reduced E2 adsorption by SWCNT−UF most drastically. TA interference mechanisms included direct competition with hormones for adsorption sites, and indirect competition via TA−hormone interactions. TA was not fully retained by the composite membrane with an MWCO range of 3−100 kDa, resulting in ineffective shielding. In contrast, humic acid was mostly retained by the composite with low MWCO of 3−10 kDa and allowed high E2 adsorption. This study demonstrates that tailoring composite membranes by carefully choosing UF MWCO can prevent interference of OM types in micropollutant adsorption by permeate-side adsorbents.

High‐Precision Measurement of Stable Cr Isotopes in Geological Reference Materials by a Double‐Spike TIMS Method

Chromium (Cr) isotopes have been widely used in various fields of Earth and planetary sciences. However, high‐precision measurements of Cr stable isotope ratios are still challenged by difficulties in purifying Cr and organic matter interference from resin using double‐spike thermal ionisation mass spectrometry. In this study, an improved and easily operated two‐column chemical separation procedure using AG50W‐X12 (200–400 mesh) resin is introduced. This resin has a higher cross‐linking density than AG50W‐X8, and this higher density generates better separation efficiency and higher saturation. Organic matter from the resin is a common cause of inhibition of the emission of Cr during analysis by TIMS. Here, perchloric and nitric acids were utilised to eliminate organic matter interference. The Cr isotope ratios of samples with lower Cr contents could be measured precisely by TIMS. The long‐term intermediate measurement precision of δ53/52CrNIST SRM 979 for BHVO‐2 is better than ± 0.031‰ (2s) over one year. Replicated digestions and measurements of geological reference materials (OKUM, MUH‐1, JP‐1, BHVO‐1, BHVO‐2, AGV‐2 and GSP‐2) yield δ53/52CrNIST SRM 979 results ranging from −0.129‰ to −0.032‰. The Cr isotope ratios of geological reference materials are consistent with the δ53/52CrNIST SRM 979 values reported by previous studies, and the measurement uncertainty (± 0.031‰, 2s) is significantly improved.

The role of boundary conditions in the bromide-enhanced ozonation process for ammonia nitrogen removal and nitrate minimization

In this study we investigated the effect of some operating conditions, such as the ratio between ammonia nitrogen (AN), ozone and bromide, the initial value of water pH, the amount of bicarbonate used as a buffering substance and the possible interference of organic matter, in a bromide-enhanced ozonation process for the removal of AN. One of the peculiarities of this process is that the oxidation of AN proceeds through the generation of reaction intermediates (bromoamines) and ends with molecular nitrogen (N2) with none or limited generation of nitrate. The results of the ozonation tests carried out at a lab scale demonstrated that nitrate generation could be lowered to less than 10% of the theoretical value when three conditions coexist. Firstly, all the AN was present in the form of ammonium ion (NH4+); this happened when the pH of the system was lower than 8. Secondly, the ratio between bromide and ozone species was optimized, so as to avoid the presence of free ozone and the consequent direct reaction with AN. Finally, the acidification induced by the oxidation of AN was controlled with a buffering substance (bicarbonate). The generation of inorganic bromoamines from the reaction between AN and bromide inhibits the oxidation of bromide to bromate. In fact, in the tests carried out in this study the formation of bromate was limited to values of less than 0.2% of the molar bromate yield.Organic substances in the form of glucose or potassium hydrogen phthalate (KHP) did not affect the removal rate of AN. Conversely, the presence of substances such as phenol and hydroquinone, that had a higher reactivity towards ozone and HOBr, determined a reduced AN removal rate and a bromate generation of one order of magnitude higher than that observed with KHP and glucose. Finally, all the organic substances employed in the study seemed to have a positive effect in reducing the nitrate generation (-30% of the value obtained with sole AN).

Simultaneous activation and magnetization toward facile preparation of auricularia-based magnetic porous carbon for efficient removal of tetracycline

In this work, auricularia-based magnetic porous carbon (AMPC) is achieved via facile simultaneous activation and magnetization strategy. The AMPC shows specific surface area of 823.2 m2 g−1 and pore volume of 0.47 cm3 g−1 nm−1. The hysteresis loop indicates saturated magnetization of AMPC is about 11 emu g−1. The morphology and composition of AMPC were also characterized by SEM, HRTEM, XRD, EDS mapping, XPS, etc. The AMPC exhibits a high adsorption capacity of 397.25 mg g −1 (318 K) for tetracycline (TC). The adsorption data can be fitted well by the Langmuir model and pseudo-second-order kinetic model. Additionally, the AMPC shows acceptable ability to resist ions and natural organic matter interference, and displays good feasibility of reuse by magnetic separation. We believe this facile simultaneous activation and magnetization strategy in converting biomass into a magnetic carbonaceous adsorbent that can remove pollutants from solution is very important for environmental remediation.

Robustness of ANAMMOX granule sludge bed reactor: Effect and mechanism of organic matter interference

The organic matter together with ammonium has become a major concern in the applications of ANaerobic AMMonium OXidation (ANAMMOX) process because of its possible adverse influences. The robustness of ANAMMOX against organic matter interference was found by accident in the ANAMMOX Granule Sludge Bed (GSB) reactor. Under inorganic conditions, Autotrophic ANAMMOX Granular Sludge (AGS) was cultivated, in which ANAMMOX accounted for 89.7% of the total nitrite removal. The bioreactor based on AGS showed an intriguing resistance to organic matter interference, with a stable volumetric nitrogen removal rate (NRR) for a surprisingly long time (|ΔNRR|≤10% for 33 days). Under organic conditions, however, AGS gradually shifted to mixotrophic ANAMMOX granular sludge (MGS), in which ANAMMOX accounted for 51.9% of the total nitrite removal. The bioreactor based on MGS was sensitive to organic matter interference, with a decrease by 20.9% in NRR when the volumetric organic loading rate was 7.5kg COD/(m3d). Beneath the threshold COD/NO2−-N ratio of 1.71, ANAMMOX played its dominant role in MGS (contributed to 68.9% of the total nitrite removal). While above the threshold ratio, ANAMMOX was dramatically inhibited (contributed to less than 34.1% of the total nitrite removal), but it did not disappear completely as expected. The discovery of ANAMMOX robustness in AGS is significant for the development of new ANAMMOX process suitable for the treatment of ammonium-containing wastewaters with coexistence of organic matter.

Positive Thermal Ionization Mass Spectrometric Analysis of Boron Isotope on River/Rain Water with Low Content and Rich Organic Matter

A method for separation and isotopic determination of boron with low content and rich organic matter in the river/rain water samples was developed. Samples were concentrated by ion exchange Amberlite IRA-743 resin. The concentrated solution was subsequently micro-sublimated for 12 h to eliminate the organic matters. Then the boron isotope ratio was determined by measuring positive Cs(2)BO(2)(+) thermal ions. The average recovery was between 97. 5% and 101. 2%. The results that were determined by positive thermal ionization mass spectrometry were closed to those by MC-ICP-MS. The precision of isotopic measurement for boron in river/rain water was better than 0. 05 parts per thousand. The results demonstrated that this method was extremely effective for elimination organic matter interference during boron isotopic analysis with low sample size, high precision and accuracy.

Effective elimination of organic matter interference in boron isotopic analysis by thermal ionization mass spectrometry of coral/foraminifera: micro‐sublimation technology combined with ion exchange

In order to better estimate the effectiveness of micro-sublimation technology on the elimination of organic matter interference during boron isotopic analysis, a series of improved experiments was carried out using simple apparatus. Recovery rates after micro-sublimation were measured for boric acid solutions with different B contents or different B/organic matter ratios. The improved micro-sublimation procedure combined with ion-exchange technology was then used to test natural samples (coral and foraminifera) for the separation of boron. Our results show that the time taken for 100% recovery of different amounts of B differed and that the proportions of B/organic matter within the natural organic matter have little effect on the relationship between the recovery rates of B and the micro-sublimation times. The experiments further confirm that the organic matter does indeed have an effect on boron isotope analyses by positive thermal ionization mass spectrometry and that the use of micro-sublimation can effectively remove interferences from the organic matter during boron isotopic analysis.

Bioavailability of zinc and copper in biosolids compared to their soluble salts

For essential elements, such as copper (Cu) and zinc (Zn), the bioavailability in biosolids is important from a nutrient release and a potential contamination perspective. Most ecotoxicity studies are done using metal salts and it has been argued that the bioavailability of metals in biosolids can be different to that of metal salts. We compared the bioavailability of Cu and Zn in biosolids with those of metal salts in the same soils using twelve Australian field trials. Three different measures of bioavailability were assessed: soil solution extraction, CaCl(2) extractable fractions and plant uptake. The results showed that bioavailability for Zn was similar in biosolid and salt treatments. For Cu, the results were inconclusive due to strong Cu homeostasis in plants and dissolved organic matter interference in extractable measures. We therefore recommend using isotope dilution methods to assess differences in Cu availability between biosolid and salt treatments.

Evaluation of the stability and analysis of halogenated furanones in disinfected drinking waters

A refined method for the sub-nanomolar analysis of 13 halogenated furanones in chlorinated drinking water is proposed which uses liquid–liquid extraction, methylation where necessary, gas chromatographic separation, and either micro-electron capture or ion trap mass spectrometric detection. Liquid–liquid extraction with methyl tert-butyl ether was demonstrated to be effective for recovery of halogenated furanones. Confirmation of the halogenated furanones identity and reduction of natural organic matter interference were achieved by ion trap tandem mass spectrometry. Compound stabilities and procedural efficiencies were evaluated to permit optimization of the method for reasonable sample volumes and a 1000:1 pre-concentration factor that would permit feasible sample collection in the field. Both chlorinated and brominated analogues of MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5 H)-furanone) were included in a suite of compounds targeted in a national occurrence study of disinfection by-products.

Sequential injection system for on-line analysis of total nitrogen with UV-mineralization

An automatic method for the determination of total nitrogen in wastewater by sequential injection analysis and mineralization with UV radiation has been developed. The method is based on the mineralization of the samples with sodium persulphate in basic medium under UV radiation. Small volumes of sample and reagents are firstly aspirated into a single channel and then propelled by flow reversal to the UV reactor and then to the detector. The organic and inorganic nitrogen compounds are oxidized to nitrate that is then measured at 226 nm. The sequential injection procedure has been optimized and the factors affecting the efficiency of the oxidation have been studied with a number of test substances with different chemical structures and properties. Solutions in the concentration range 1–56 g l −1 of nitrogen can be analyzed with the described procedure. The sample rate is of 30–40 samples h −1. The LOD is 0.6 mg l −1 N and the reproducibility is 1.8% (28 mg l −1 N). Organic carbon in the form of glucose was added to a number of test solutions to study the potential interference of organic matter. The method was compared with the Kjeldahl digestion method by analyzing 15 wastewater samples with both methods. The nitrate and nitrite content of the non-oxidized samples were subtracted from the corresponding nitrogen content determined after photo-oxidation and the value compared with the Kjeldahl nitrogen content.

Propriedades químicas e cristalográficas da caulinita e dos óxidos de ferro em sedimentos do grupo barreiras no município de Aracruz, estado do Espírito Santo

As propriedades químicas e cristalográficas detalhadas da caulinita (Ct) e dos óxidos de ferro do solo e dos sedimentos do Grupo Barreiras são pouco conhecidas. Para estudar as características desses minerais em profundidade, coletaram-se 11 amostras (0,7; 1,4; 2,1; 2,8; 3,5; 4,2; 4,9; 5,6; 7,7; 10,5 e 14m) nos horizontes Bt, BC e C de um Argissolo Amarelo no município de Aracruz (ES). As frações argila e silte foram estudadas por difração de raios-X (DRX), análise termo-diferencial (ATD) e microscopia eletrônica. Os teores totais de Fe e outros microelementos (Cr, Mn, Ni, Pb, Ti e Zn) da fração argila foram determinados por espectrometria por emissão por plasma, após digestão da amostra com HF concentrado. Nos extratos resultantes das extrações com oxalato de amônio (OA) e ditionito-citrato-bicarbonato (DCB), determinaram-se os teores de Fe, Al, Si, Cr, Mn, Ni, Pb, Ti e Zn. A composição química da Ct das frações argila (amostra desferrificada) e silte (amostra natural) foi determinada pelo tratamento com NaOH 5molL-1 e pela combinação de aquecimento e extração com NaOH 0,5molL-1 fervente, respectivamente. O teor médio de Fe2O3 da Ct da fração argila (20,7gkg-1) foi superior ao obtido para a fração silte (5,2gkg-1), verificando-se, na menor fração, aumento nos teores de Fe2O3 com a profundidade. Graças ao maior raio iônico, a presença do Fe3+ na estrutura promoveu aumento no espaço interplanar do mineral, sobretudo na direção b. O tamanho das partículas de Ct foi semelhante entre os horizontes amostrados. A Ct apresentou grau semelhante de cristalinidade com a profundidade do solo, com exceção dos horizontes mais superficiais, os quais apresentaram menores valores de índice de cristalinidade, provavelmente por interferências com compostos orgânicos. A redução dos teores de Fe2O3 extraídos pelo DCB e da participação dos teores de FeOA mais FeDCB no Fe total da fração argila com a profundidade foi atribuída à dissolução dos óxidos de ferro, provocada pela umidade nas camadas inferiores dos sedimentos. A substituição isomórfica (SI) de Fe por Al na goethita (Gt) foi cerca de três vezes superior à da hematita (Hm), com maiores valores nos horizontes mais superficiais. A Hm apresentou menor valor de superfície específica (SE) que a Gt, refletindo os maiores valores de diâmetro médio do cristal para a Hm. Baixos valores de cristalinidade e menor tamanho de partículas estão associados à maior atividade e à influência da Ct e dos óxidos de ferro sobre as propriedades físico-químicas do solo. Os óxidos de ferro apresentaram baixa associação com microelementos, sobretudo com Ni, Pb e Ti.

Comparing calcium chloride, barium chloride, and hot water extractions and testing activated charcoal plus azomethine-H dosage for boron determination in Brazilian soils

ABSTRACT Most acid soils have low boron (B) contents which hampers the efficiency of B extraction. The setting of a suitable B extraction method for Brazilian acid soils is important to improve the evaluation of the status of this nutrient in acid soils from Brazil. The extraction of boron with hot water, the standard method, is a hard work method with operational difficulties, alternative methods using saline solutions and microwave oven heating have been tested. The efficiency of CaCl2 5 mmol L−1 as an extractant for determination of B by colorimetry with azomethine-H was evaluated. Boron concentration in extracts from ten Brazilian soils was determined based on the color generated in the reaction of B with azomethine-H. The soil samples were extracted with hot water, barium chloride BaCl2 5 mmol L−1, and calcium chloride (CaCl2) 5, 10, 20 mmol L−1, with and without activated charcoal. For each extractant it was set a completely randomized block design with the treatments arranged in a complete factorial 10 × 2 (soils × presence and absence of activated charcoal in the extraction) with 3 replications. The evaluation of organic matter interference was performed by analysis of variance and extractants were correlated by Pearson's correlation. Regression analysis was performed for selection of the best concentration of CaCl2 for extraction. The extraction with CaCl2 did not remove organic matter interference in the determination of B with azomethine-H. Activated charcoal was required in the B dosage with azomethine-H. The 5 mmol L−1 CaCl2 solution is as effective as BaCl2 in the extraction of B from Brazilian soils.

Sensitive determination of dissolved sulfide in estuarine water by solid-phase extraction and high-performance liquid chromatography of methylene blue

A sensitive method involving solid-phase extraction and HPLC analysis of methylene blue has been developed to measure nanomolar levels of dissolved sulfide in oxic surface waters. The procedure included 1) a preconcentration step, in which methylene blue generated from sulfide reaction with n, n-dimethyl- p-phenylenediamine in acidic conditions in the presence of ferric ion was absorbed onto Waters tC 18 cartridge; and 2) a determination step, in which methylene blue was separated by HPLC in a gradient elution to minimize natural organic matter interference and detected by absorbance. The concentrations of the dissolved sulfide, quantified by standard addition, were about 2.1–4.7 n M in oxic surface waters from Galveston Bay, Texas.

Determination of Seawater Salinity by Ultraviolet Spectroscopic Measurements

A method for the determination of seawater salinity by ultraviolet (UV) spectroscopy is proposed. The effects of single salt concentrations and of salinity on UV absorption in the 190–250-nm range were investigated. These studies revealed that the absorption spectrum of a solution with a given salinity is due mainly, in order, to KBr >MgCl 2>NaCl. The influence of the temperature and salt concentration on UV spectra was studied by using synthetic seawater samples with the salinities ranging from 1 to 50 parts per thousand (%). Results showed that, in the absence of interferences, the most sensitive and reliable conditions for measuring the salinity are at 212 nm and at temperatures in the range of 25–30 °C. Under these conditions this method shows quite linear calibration curves and allows us to perform salinity determinations in seawater solutions at concentrations as low as 4%. Moreover, it requires no sample pretreatment and offers a precision of 0.20%. The proposed method is very simple and rapid for laboratory and on-board analysis. Finally, the interference of organic matter, nitrite, and nitrate species with the salinity determinations was investigated. These studies show that organic matter does not interfere at concentrations of carbon lower than 1 mg/L and at 210 nm. Interferences due to NO− x species can be ignored if these species are dissolved in solution at concentrations lower than ≈0.2 mg/L and the analyses are carried out at wavelengths lower than 212 nm.

Rapid inactivation of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5 H-)-furanone (MX), a potent mutagen in chlorinated drinking water, by sulfhydryl compounds

A refined method for the sub-nanomolar analysis of 13 halogenated furanones in chlorinated drinking water is proposed which uses liquid–liquid extraction, methylation where necessary, gas chromatographic separation, and either micro-electron capture or ion trap mass spectrometric detection. Liquid–liquid extraction with methyl tert-butyl ether was demonstrated to be effective for recovery of halogenated furanones. Confirmation of the halogenated furanones identity and reduction of natural organic matter interference were achieved by ion trap tandem mass spectrometry. Compound stabilities and procedural efficiencies were evaluated to permit optimization of the method for reasonable sample volumes and a 1000:1 pre-concentration factor that would permit feasible sample collection in the field. Both chlorinated and brominated analogues of MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) were included in a suite of compounds targeted in a national occurrence study of disinfection by-products.

N-methyl- N′-nitro- N-nitrosoguanidine induces ultraweak photon emission in Chinese hamster cells

A refined method for the sub-nanomolar analysis of 13 halogenated furanones in chlorinated drinking water is proposed which uses liquid–liquid extraction, methylation where necessary, gas chromatographic separation, and either micro-electron capture or ion trap mass spectrometric detection. Liquid–liquid extraction with methyl tert-butyl ether was demonstrated to be effective for recovery of halogenated furanones. Confirmation of the halogenated furanones identity and reduction of natural organic matter interference were achieved by ion trap tandem mass spectrometry. Compound stabilities and procedural efficiencies were evaluated to permit optimization of the method for reasonable sample volumes and a 1000:1 pre-concentration factor that would permit feasible sample collection in the field. Both chlorinated and brominated analogues of MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) were included in a suite of compounds targeted in a national occurrence study of disinfection by-products.

DIFFERENTIAL PULSE POLAROGRAPHIC EVALUATION OF ALUMINUM IN RENAL INSUFFICIENCY

This work presents several differential pulse polarographic-based methods for the determination of total soluble aluminum in hemodialysis water and post-hemodialysis dialysate. Mineralization was used to overcome the organic matter interference. Samples were also analyzed by graphite furnace atomic absorption spectrometry. Correlation between the electrochemical (Y) and the spectroscopic (X) Al was excellent: Y 0.981X-0.944, r=0.991.