Precipitation Acidity Research Articles

Long-Term Estimation of Rainfall Acidity in Major African Ecosystems

The paper examines the acidity of precipitation in three major ecosystems in Western and Central Africa, using data from 413 rainfall samples in the dry savanna of Banizoumbou, Niger; 1,056 samples in the wet savanna of Lamto, Ivory Coast; and 578 samples in the equatorial forest of Zoetele, Cameroon. Analyzed at the Toulouse Aerology Laboratory, the findings indicate that rain in Banizoumbou is alkaline (mean pH 6.19), while at Lamto and Zoetele it is acidic (mean pH 5.24 and 5.45, respectively). Despite significant potential acidity, actual acidity (measured by H+ ion concentration) remains low across all sites. The study highlights the importance of a multiphasic process in rainwater neutralization, involving the capture of acidic gases by mineral dust and gas-particle interactions primarily influenced by ammonia (NH3). Notably, the relationship between pH and the ratio of cations to anions varies: in Banizoumbou, they move inversely, whereas in Lamto and Zoetele, they change in the same direction. This suggests that terrestrial dust influences dominate in the dry savanna, while gas-particle conversion processes are more prominent in the wet savanna and equatorial forest.

Modulation of physico-chemical and technofunctional properties of quinoa protein isolate: Effect of precipitation acid

The typically low solubility and gelation capacity of plant proteins can impose challenges in the design of high-quality plant-based foods. The acid used during the precipitation step of plant protein isolate extraction can influence protein functionality. Here, acetic acid and citric acid were used to extract quinoa protein isolate (QPI) from quinoa flour, as these acids are more kosmotropic than the commonly used HCl, promoting the stabilisation of the native protein structure. While proximate analysis showed that total protein was similar for the three isolates, precipitation with kosmotropic acids increased soluble protein, which correlated positively with gel strength. Microstructure analysis revealed that these gels contained a less porous protein network with lipid droplet inclusions. This study shows that the choice of precipitation acid offers an opportunity to tailor the properties of quinoa protein isolate for application, a strategy that is likely applicable to other plant protein isolates.

Influence of Amino Acids on Calcium Oxalate Precipitation in Systems of Different Chemical Complexity

The mechanisms and conditions under which urinary stones, pathological biominerals in the kidneys and bladder, are formed have not yet been fully clarified. This study aims to understand the role of the system complexity and seven different amino acids (alanine, phenylalanine, glycine, serine, cysteine, histidine, and aspartic acid) in the spontaneous precipitation of calcium oxalate. To elucidate these effects, the conditions simulating hyperoxaluria (ci(Ca2+) = 7.5 mmol dm−3 and ci(C2O42−) = 6.0 mmol dm−3) were used for the first time. In this work, systematic research on calcium oxalate precipitation was performed in three systems of different chemical complexities: (a) only calcium and oxalate ions, (b) increased ionic strength, and (c) artificial urine at two initial pHs (pHi = 5.0 and 9.0). In all the investigated systems, the dominant precipitation of calcium oxalate monohydrate (COM) was observed, except in the artificial urine system at pHi = 9.0, in which a mixture of COM and calcium oxalate dihydrate (COD) was obtained. In all the investigated systems, a significant influence of the selected amino acids on the morphology and crystal growth of COM was observed, with more pronounced changes at pHi = 9.0. Overall, polar amino acids and nonpolar phenylalanine inhibit the growth of COM, which is a more pathogenic hydrate form. The artificial urine system proved to be more relevant for the observation of effects relevant to kidney stone formation in the human body.

Development and validation of a rapid and simple HILIC-MS/MS method for the determination of biogenic amines in tuna fish

The production of biogenic amines (BAs), which are markers of both quality and safety in fish and fishery products, is influenced by the harvesting technique, handling, and other operations including those carried out on board the vessel. Scombroid dark-meat fish (e.g. tuna) are the fish species most frequently linked to histamine poisoning. The most commonly found BAs in fish are histamine, tyramine, putrescine, and cadaverine, which are produced when microbes decarboxylate the corresponding free amino acids. In this study, a rapid and cost-effective HILIC-MS/MS method was developed and validated for the determination of putrescine, cadaverine, histamine and tyramine in tuna samples. A simple sample preparation procedure was followed using the solvent mixture MeOH/H2O (50/50, v/v), 0.1 % acetic acid for protein precipitation and analyte extraction. Intra- and inter-day accuracy, expressed as %Recovery (%R), ranged from 88.0 % (Cad) to 102.7 % (Tyr) and from 85.0 % (Cad) to 99.8 % (Tyr), respectively. Intra- and inter-day precision, expressed as %Relative Standard Deviation (%RSD), ranged from 0.4 % (Tyr, Put) to 3.3 % (His) and from 0.7 % (Tyr) to 5.0 % (Cad), respectively. Limits of detection (LOD) and quantification (LOQ) varied from 0.0009 to 0.0940 mg/kg and from 0.0030 mg/kg to 0.3100 mg/kg, respectively, depending on the analyte. Regarding the potential toxic effects linked to biogenic amines in foods, samples examined in this study showed no risk. The proposed method is an important analytical tool for routine analysis of BAs in fish products.

Bacteria in clouds biodegrade atmospheric formic and acetic acids

Abstract. Formic and acetic acids are major organic species in cloud water and affect precipitation acidity. In atmospheric models, their losses are limited to chemical oxidation in the gas and aqueous phases and deposition processes. Previous lab studies suggest that these acids can be efficiently biodegraded in water by atmospherically relevant bacteria. However, the importance of biodegradation as a loss process in the atmospheric multiphase system has not been fully assessed. We implemented biodegradation as a sink of formic and acetic acids in a detailed atmospheric multiphase chemistry model. In our model, biodegradation is considered in 0.1 % of cloud droplets according to atmospheric bacteria concentrations of 0.1 cm−3. We predict that up to 20 ppt h−1 formic acid and 5 ppt h−1 acetic acid are biodegraded. This translates into a concentration change of 20 % and 3 % in addition to that caused by chemical losses. Our sensitivity studies suggest that acetic acid is most efficiently biodegraded at pH > 5, whereas biodegradation is least efficient for formic acid under such conditions. This trend can be explained by the fact that formic acid partitions more efficiently into the aqueous phase due to its higher Henry's law constant (KH,eff(HCOOH)=2×105 M atm−1 vs. KH,eff(CH3COOH)=3×104 M atm−1 at pH = 5). Therefore, under such conditions, formic acid evaporates less efficiently from bacteria-free droplets, resulting in less formic acid in the gas phase for dissolution bacteria-containing droplets to replenish biodegraded acid. Our analysis demonstrates that previous estimates of the importance of atmospheric biodegradation were often biased high as they did not correctly account for such uptake limitation in bacteria-containing droplets. The results suggest that, under specific conditions, biological processes can significantly affect atmospheric composition and concentrations in particular volatile, moderately soluble organics.

Atmospheric precipitation chemistry and environmental significance in major anthropogenic regions globally

In order to investigate the spatiotemporal distribution and influencing factors of global precipitation chemistry, we conducted a comprehensive analysis using multiple data sources, revealing the impact of human activities on the natural environment. The results indicate a decreasing trend in global precipitation acidity over the past 20 years. The distribution of global precipitation is influenced by both natural and anthropogenic factors. Alkaline cation concentrations are higher in desert and arid regions, while high concentrations of SO42− and NO3− are primarily found in industrial areas, and agricultural areas exhibit higher NH4+ concentrations. Coastal regions have higher Na+ and Cl− concentrations compared to inland areas. However, the increased Na + and Cl− concentrations due to inland salinization should not be overlooked. Additionally, influenced by atmospheric circulation, transboundary pollution from South Asia leads to higher SO42− and NO3− concentrations in precipitation over the Tibetan Plateau. Meteorological factors have a weaker influence on precipitation chemistry compared to geographical and human activity factors, although ion concentrations in snowfall are higher than in rainfall.

Comparison of acidity and chemical composition of summertime cloud water and aerosol at an alpine site in Northwest China: Implications for the neutral property of clouds in the free troposphere

Aerosol and cloud acidity are essential to human health, ecosystem health and productivity, as well as climate effects. The main chemical composition of cloud water greatly varies in different regions, resulting in substantial differences in the pH of cloud water. However, the influences of the anthropogenic emissions of acidic gases and substances, alkaline dust components, and dicarboxylic acids (diacids) on the ground concerning the acidity of cloud water in the free troposphere of the Guanzhong Plain, China, remain clear. In this study, cloud water and PM2.5 samples were simultaneously collected in the troposphere (Mt. Hua, 2060 m a.s.l). The results indicated that the cloud water was alkaline (pH = 7.6) and PM2.5 was acidic (pH = 3.2). These results showed the neutral property of clouds collected in the heavily polluted Guanzhong Plain, although most previous studies always considered acidity as a marker of pollution. The sulfate (SO42−), nitrate (NO3−), and ammonium (NH4+) (SNA) of particulate matter and cloud water in the same period were compared. SO42− was dominant in particulate matters (accounting for 63.4 % of the total SNA) but substantially decreased in cloud water (only 30.1 % of the total SNA), whereas NO3− and NH4+ increased from 28.5 % and 8.2 % to 39.8 % and 30.2 %, respectively. This could be attributed to the complex formation mechanism and sources of SO42− and NO3− in the cloud. The results of ion balance indicated that a significant deficit of inorganic anion equivalents was observed in the cloud water samples. The high concentration of diacids in the cloud phase (1237.4 μg L−1) may facilitate the formation of salt complexes with NH4+, thus influencing the acidity of the cloud water. The pH of cloud water has increased in recent decades due to the sustained reduction of sulfur dioxide, which may also affect the acidity of future precipitation.

Legacy sediment as a potential source of orthophosphate: Preliminary conceptual and geochemical models for the Susquehanna River, Chesapeake Bay watershed, USA

Nutrient pollution from agriculture and urban areas plus acid mine drainage (AMD) from legacy coal mines are primary causes of water-quality impairment in the Susquehanna River, which is the predominant source of freshwater and nutrients entering the Chesapeake Bay. Recent increases in the delivery of dissolved orthophosphate (PO4) from the river to the bay may be linked to long-term increases in pH, decreased acidity of precipitation, and decreased acidity, iron, and aluminum loading from widespread AMD. Since the 1950s, baseline pH increased from ~6.5 to ~8 in the West Branch and “North Branch” of the Susquehanna River, which drain bituminous and anthracite coalfields of Pennsylvania. A current baseline pH of ~8 and daily maxima exceeding 9 have been documented along the lower Susquehanna River. In response to improved river quality, bioavailable PO4 now may be released into solution from legacy sediment that has filled major impoundments in lower reaches of the river. At typical pH (5–8) of natural water, aqueous PO4 species tend to be adsorbed by hydrous iron, aluminum, and manganese oxides that coat soil and sediment particles; however, PO4 may be substantially desorbed at pH >8. We created a geochemical model that simulates equilibrium aqueous/solid distributions of PO4 as pH and other solution characteristics change. Considering current conditions in the lower Susquehanna River, the model demonstrates potential for extensive release of adsorbed PO4 at pH >8. Empirical data from laboratory experiments corroborate model results. The transfer of PO4 into the water column may increase algae growth, which removes CO2 and drives pH to higher values, facilitating additional PO4 release and exacerbating the potential for harmful algal blooms. Thus, legacy sediment is a currently unquantified source of PO4 that warrants consideration by resource managers and programs collaborating to reduce phosphorus loads to the bay and similar settings worldwide.

Novel biodegradable polymers modified by humic acids

The possibility of using humic acids (HA) as hybrid modifiers is considered. They were taken from lignite using first sodium pyrophosphate solution, then a 1 % solution of NaOH for extraction, and next mineral acid for precipitation. It has shown that in gelatin–HA hybrid systems, the latter mainly join water molecules and “sequester” them to prevent their interaction with gelatin chains. In the hydroxypropyl methylcellulose (HPMC)-HAs systems, the processes of polymer cross-linking through multipoint chelate interaction with the carboxylate group of HAs have been determined. Hybrid polyvinyl alcohol (PVA)-HAs structures are obtained by the matrix synthesis mechanism. Also, during the hybrid modification of PVA with HAs, additional supramolecular interactions, in addition to hydrogen bonds, occur between their functional groups as a result of crystallization. It was found that hybrid modification of HAs within the matrix synthesis of gelatin-based biopolymer hydrogels allows obtaining polymer hydrogels with an increased swelling degree and gives them antibacterial qualities. The optimal content of HAs in biodegradable polymers based on gelatin, PVA and HPMC is 10 % by mass.

High-performance liquid chromatography with fluorescence detection method for measuring colistin in human serum and its application in critically ill patients treated with colistin methanesulfonate sodium

Colistin, in the form of colistin methanesulfonate sodium (CMS), has a narrow therapeutic window, and colistin levels must be monitored during treatment. The aim of this study was to develop and validate a high-performance liquid chromatography-fluorescence detection (HPLC-FLD) method for measuring colistin in human serum. Colistin was extracted from human serum using trichloroacetic acid and methanol for protein precipitation, followed by in-solid phase extraction derivatization with 9-fluorenylmethyl chloroformate. HPLC-FLD system using a reverse-phase HPLC C18 column and a mobile phase consisting of acetonitrile, tetrahydrofuran, and water (80%:4%:16%) were used for the quantification of colistin A, colistin B, and polymyxin B (internal standard) in human serum. The extraction recoveries were between 71% and 103%. Linear calibration curves were obtained for colistin in concentrations from 0.3 to 8.0 μg/mL, with good fit (r2 = 0.9993). The lower limit of quantitation was 0.3 μg/mL. The intra- and inter-day precision of the assay was 0.5–5% and 3.5–9.4%, respectively. The accuracy ranged from 98% to 100%. This validated method was successfully applied to the analysis of serum-receiving CMS in critically ill patients. This method will be useful to assist colistin dosage adjustment based on individual blood colistin levels for optimization of colistin therapy.

Calcium and ammonium now control the pH of wet and bulk deposition in Ohio, U.S.

As precipitation acidity in the United States has decreased dramatically over the past forty years, new questions have emerged about the role of base cations and nitrogen (N) species in regulating precipitation pH. To address these questions, we studied precipitation chemistry in Ohio, a state with relatively high N deposition and a mix of urban, industrial, and agricultural land use. We used long-term data from the National Atmospheric Deposition Program (NADP) to assess temporal changes in the drivers of wet deposition pH in Ohio. We supplemented our analysis with short-term data on spatial patterns of bulk deposition pH collected along an agricultural-to-urban transect in central Ohio. From 1979 to 2019, wet deposition pH at the Ohio NADP sites increased from 4.22 ± 0.05 to 5.33 ± 0.21, and the cation-to-anion ratio increased from 0.92 ± 0.02 to 1.35 ± 0.06, due to a dramatic decline in measured anions. As correlations between wet deposition pH and the anions SO42− and NO3− weakened, correlations between wet deposition pH and the cations NH4+ and Ca2+ strengthened, suggesting that these cations are playing a larger role in controlling precipitation pH today. In recent years (2021–2022), NH4+ was significantly correlated with bulk deposition pH in all land uses except the urban site, with the strongest correlation at the rural/agricultural site, where the pH was 5.96 ± 0.49. Similarly, Ca2+ was strongly and significantly correlated with bulk deposition pH across all land uses. For Ca2+, the urban site was distinct from the other sites due to the high pH (6.58 ± 0.44) and Ca2+ concentrations at that site, likely driven by high levels of particulate matter deposition. Our results indicate that land use plays a role in the strength and dominant process of acid neutralization, with Ca-rich dust more important in urban areas and reduced N more important in agricultural regions. As precipitation pH increases and land use changes across the country, base cations and reduced N will play an increasingly important role in regulating precipitation pH in the U.S., with important implications for ecosystems continuing to recover from acid rain.

Precipitation of Terephthalic Acid from Alkaline Solution: Influence of Temperature and Precipitation Acid

Precipitation of Terephthalic Acid from Alkaline Solution: Influence of Temperature and Precipitation Acid

Variability in Acidity of Precipitation on the Territory of the Far Eastern Federal District of Russia

Variability in Acidity of Precipitation on the Territory of the Far Eastern Federal District of Russia

Investigation of the chemical nature of precipitation and source apportionment of its constituents in Tehran metropolis, Iran

Precipitation is a key process for purifying the atmosphere of pollutants. However, precipitation chemistry is also a significant environmental catastrophe on a global scale. Tehran Metropolitan Area, Iran's capital, is one of the world's most polluted cities. Nonetheless, little effort has been paid to determining the chemical composition of precipitation in this polluted metropolis. The chemical components and likely sources of trace metals and water-soluble ions in precipitation samples collected from 2021 to 2022 at an urban location in Tehran, Iran, were investigated in this study. The pH of the rainwater samples varied from 6.330 to 7.940 (mean 7.313, volume weighted mean (VWM) 7.523). The following is the order of the VWM concentration of main ions: Ca2+ > HCO3- > Na+ >SO42- > NH4+ > Cl− > NO3- > Mg2+> K+> F−. Furthermore, we discovered that VWM concentrations for trace elements are modest, with the exception of Sr (39.104 eq L−1). The primary neutralizing species for precipitation acidity were Ca2+ and NH4+. Vertical feature mask (VFM) diagrams derived from cloud-aerosol lidar and infrared pathfinder satellite observation (CALIPSO) track data indicated that polluted dust was the most common pollutant in the Tehran sky that might contribute significantly to the neutralization of precipitation. A study of species concentration ratios in seawater and the earth's crust indicated that virtually all Se, Sr, Zn, Mg2+, NO3-, and SO42- were anthropogenic. While Cl− was largely obtained from sea salt, K+ was obtained from both the earth's crust and the sea, with the earth's crust playing a larger role in K+. The earth's crust, aged sea salt, industry, and combustion processes were all verified as sources of trace metals and water-soluble ions by positive matrix factorization analysis.

Model Assessment of Atmospheric Precipitation Acidification in the 20th Century Due to Anthropogenic Sulfur Compounds

Model Assessment of Atmospheric Precipitation Acidification in the 20th Century Due to Anthropogenic Sulfur Compounds

Model Estimate of the Acidity of Atmospheric Precipitation Acidity Due to Anthropogenic Sulfur Compounds in the 20th Century

An analysis of the acidity of precipitation is carried out by using the ChAP-1.0 (Chemistry and Aerosol Processes) atmospheric sulfur cycle scheme developed for Earth System Models of Intermediate Complexity (EMICs)These calculations are forced by monthly mean anthropogenic emissions of sulfur dioxide to the atmosphere in 1850–2000 adapted from the CMIP5 (Coupled Models Intercomparison Project, phase 5) database and by long-term means (taking into account annual variations) of meteorological variables adapted from the ERA-Interim reanalysis for 1979–2015. It was revealed that significant acidity of precipitation (minimum pH of hydrometeors) is typical for regions with high anthropogenic loading of sulfur compounds in atmosphere – Europe, southeast Asia, east North America, southern Africa, and western South America. In these regions in the last decades of the 20th century, typical precipitation values of pH amount from 2.5 to 3.5, which agrees well with the available measurements. The maximum acidity of precipitation (the minimum pH of hydrometeors, which is close to 2) due to anthropogenic sulfur are noted in the eastern Mediterranean region. Atmospheric transport leads to regions with pH 3.5 covering almost all of Eurasia in the last decades of the 20th century. The influence of this transport is also noticeable in other midlatitudinal regions – south of North America and western South America. In general, the ChAP scheme can be used in EMICs, but after a refinement to account for the effect of various types of precipitation on the wet deposition of sulfur compounds from the atmosphere and the effects of orography on the transport of chemical species in the atmosphere

Analyzing Precipitation Acidity Changes Post Train Derailment and Vinyl Chloride Release in East Palestine, Ohio: Exploring Biomedical and Environmental Ramifications

Analyzing Precipitation Acidity Changes Post Train Derailment and Vinyl Chloride Release in East Palestine, Ohio: Exploring Biomedical and Environmental Ramifications

Precipitation chemistry in the westerly domain of the Tibetan Plateau

Based on the interaction of water with natural and anthropogenic airborne particles, precipitation chemistry reflects the degree of pollution in the area. Characterizing the local hydrochemical features and regional geochemical cycle requires an understanding of the chemical characteristics of precipitation and its sources. As a result, major ion concentrations were quantified and their chemical properties were identified in event-based precipitation samples. Ca2+, Mg2+, and K+ were crucial in neutralizing the acidity of precipitation. The order of the ions' concentrations was Na+ > SO42− > HCO3− > Ca2+ > Cl− > Mg2+ > K+ > NO3−. Ionic sources in the region included biomass burning, anthropogenic emissions, crustal dust, and salt. The HYSPLIT trajectory further supports biomass burning and aerosol movement from multiple sites. The National Center for Environmental Prediction Final dataset, clusters of air mass backward trajectory analysis, and source identification suggest that the higher concentration of anthropogenic ions (SO42−) in the study site may have been transported from Xinjiang and nearby locations in Central Asia and the Middle East. These datasets provided an overview for evaluating the regional atmospheric chemistry over the westerly domain of the Tibetan Plateau during the monsoon season based on the ionic characteristics.

Wet depositions of cations in forests across NADP, EMEP, and EANET monitoring networks over the last two decades

Studies focused on emissions and acid deposition of sulfur (S) and nitrogen (N) and the consequent precipitation acidity have a long history. However, atmospheric depositions of cations play a critical role in buffering precipitation acidity, and providing cationic nutrients for vegetation growth lacks sufficient studies equally. The spatiotemporal patterns of cation depositions and their neutralization potential across broad scales remain unclear. Through synthesizing the long-term data in forest sites (n = 128) derived from three monitoring networks (NADP in Northern America, EMEP in Europe, and EANET in East Asia) on wet deposition of cations (Na+, NH4-N, K+, Mg2+, and Ca2+), this study assesses the temporal changes and spatial patterns of cation depositions and their neutralization potential over the last two decades. The results showed that the depositions of cationic nutrients were considerably higher in EANET compared to NADP and EMEP. The depositions of sea salt-associated sodium exhibited a significant transition from marine (> 15 kg ha−1 year−1) to inland (< 3.0 kg ha−1 year−1) forest sites attributable to the precipitation quantity and influences of sea spray. The higher emissions of NH3 and particulate matter in East Asia explained the higher cation depositions in EANET than NADP and EMEP. The annual trends of cations revealed that only 20–30% of the forest sites showed significant changing trends and the sites widely spread across the three networks. Possibly, base cation (BC) deposition has reached a low and stable condition in NADP and EMEP, while it has high spatial heterogeneity in the temporal change in EANET. The difference in BC deposition among the three networks reflects their distinct development of economy. Our synthesis indicates that the annual trends of neutralization factor (NF) in NADP can be explained by the declining of acid potential (AP), not by neutralization potential (NP) as BC deposition has been stably low over the past two decades. Whereas, the concurrent decreases of AP and NP in EMEP or plateau period of both AP and NP in EANET have come to a standstill of acid neutralizing capacity.

Validated UPLC-MS/MS method for the analysis of vitamin B6 pyridoxal 5́-phosphate, pyridoxal, pyridoxine, pyridoxamine, and pyridoxic acid in human cerebrospinal fluid

Vitamin B6 and its metabolites play a crucial role in the development and interaction of brain metabolism. Following diagnostic improvements additional inherited disorders in vitamin B6 metabolism have been identified, most of them leading to a severe epileptic disorder accompanied by progressive neurological deficits including intellectual disability and microcephaly. Since early treatment can improve the outcome, fast and reliable detection of metabolic biomarkers is important. Therefore, the analysis of vitamin B6 metabolites has become increasingly important, but is, however, still challenging and limited to a few specialized laboratories.Until today, vitamin B6 metabolites are measured by liquid chromatography tandem mass spectrometry (LC-MS/MS) using trichloroacetic acid for protein precipitation. In this work, we present the development and validation of a new, accurate and reliable method for analysis and quantification of the vitamin B6 vitamers pyridoxal 5́-phosphate (PLP), pyridoxal (PL), pyridoxine (PN), pyridoxamine (PM) and pyridoxic acid (PA) in human CSF samples using acetonitrile for protein precipitation. The method is based on ultra-performance liquid chromatography-tandem mass spectrometry using electrospray ionization (UPLC-ESI-MS/MS). The calibration was performed in surrogate matrix Ringer solution and metabolites were quantified by their corresponding isotopically labelled internal standards. A protein precipitation by acetonitrile was applied greatly improving chromatographic separation of the metabolites in a 4.7 min chromatographic run. The method was validated following the European Medical Agency (EMA) and Food and Drug Administration (FDA) guidelines for bioanalytical method validation. The metabolites were quantified from 5 to 200 nmol/L with a seven-point calibration curve and minimum coefficient of regression of 0.99. The validation was performed with quality control samples at four concentration levels with surrogate matrix ringer solution and pooled CSF material. Within- and inter-day accuracy and precision in Ringer solution were within 85.4 % (PLP) and 114.5 % (PM) and from 2.6 % (PA) to 16.5 % (PLP). Within- and inter-day accuracy and precision in pooled CSF material were within 90.5 % (PN) and 120.1 % (PL) and from 1.7 % (PA) to 19.0 % (PM). The method was tested by measuring of 158 CSF samples to determine reference ranges. The B6 vitamers PLP and PL were determined in all CSF samples above 5 nmol/L while PN, PM and PA showed concentrations below or near LOQ. Probable supplementation of PLP was detected in eight CSF samples, which revealed high concentrations of PM, PN, PL, or PA, whereas PLP was in the reference range or slightly elevated. The method is suitable for the application within a routine diagnostic laboratory.