Quantitation of tryptophan and other plasma amino acids by automated pre-column o-phthaldialdehyde derivatization high-performance liquid chromatography: improved sample preparation

Plasma Concentrations of Tranexamic Acid in Postpartum Women After Oral Administration

OBJECTIVE

To evaluate the pharmacokinetics of tranexamic acid after oral administration to postpartum women.

METHODS

We conducted a single-center pharmacokinetic study at Teaching Hospital-Jaffna, Sri Lanka, on 12 healthy postpartum women who delivered vaginally. After oral administration of 2 g of immediate-release tranexamic acid 1 hour after delivery, pharmacokinetic parameters were measured on plasma samples at 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 10, and 12 hours. Plasma tranexamic acid concentrations were determined by high-performance liquid chromatography. The outcome measures were maximum observed plasma concentration, time to maximum plasma concentration, time to reach effective plasma concentration, time period effective serum concentration lasted, area under the curve for drug concentration, and half-life of tranexamic acid.

RESULTS

The mean maximum observed plasma concentration was 10.06 micrograms/mL (range 8.56-12.22 micrograms/mL). The mean time to maximum plasma concentration was 2.92 hours (range 2.5-3.5 hours). Mean time taken to reach the effective plasma concentration of 5 micrograms/mL and the mean time this concentration lasted were 0.87 hours and 6.73 hours, respectively. Duration for which plasma tranexamic acid concentration remained greater than 5 micrograms/mL was 5.86 hours. Half-life was 1.65 hours. Area under the curve for drug concentration was 49.16 micrograms.h/mL (range 43.75-52.69 micrograms.h/mL).

CONCLUSION

Clinically effective plasma concentrations of tranexamic acid in postpartum women may be achieved within 1 hour of oral administration. Given the promising pharmacokinetic properties, we recommend additional studies with larger sample sizes to investigate the potential of oral tranexamic acid for the treatment or prophylaxis of postpartum hemorrhage.

Determination of Tryptophan and Kynurenine by LC-MS/MS by Using Amlodipine as an Internal Standard

Tryptophan is an essential amino acid that plays an important role in cell metabolism, and kynurenine is its main metabolic pathway. By using ultra-high-performance liquid chromatography coupled to electrospray ionization triple-quadrupole mass spectrometry, tryptophan and kynurenine were determined using amlodipine as an internal standard. The analysis was carried out on an ACE-C18 (4.6 mm × 50 mm, 5 μm) reversed-phase analytical column using the gradient elution mode. For quantitative determination, amlodipine was used as an internal standard. Detection was performed using multiple reaction monitoring in electrospray ionization mode at m/z 205.1 → 117.7 and 187.9 for tryptophan, m/z 209.1 → 146 and 93.9 for kynurenine, and m/z 409.2 → 294.1 for the internal standard. Good linearity of the analyte to internal standard peak area ratios was seen in the concentration range 1.25-4000 ng/mL for tryptophan and 0.5-1600 ng/mL for kynurenine. The method showed excellent linearity with regression coefficients of 0.99 for kynurenine and 0.996 for tryptophan. The limits of quantification were 0.55 ng/mL for tryptophan and 0.47 ng/mL for kynurenine. The % RSD for all analytes ranged from 0.3 to 3.4% for intraday and 0.4 to 8.9% for interday experiments. A simple LC-MS/MS method has been developed and validated for measuring Kyn and Trp by using an affordable and more easily available internal standard, which is amlodipine.

Amino Acid Loss during Continuous Venovenous Hemofiltration in Critically Ill Patients

BACKGROUND/OBJECTIVES

During continuous venovenous hemofiltration (CVVH), there is unwanted loss of amino acids (AA) in the ultrafiltrate (UF). Solutes may also be removed by adsorption to the filter membrane. The aim was to quantify the total loss of AA via the CVVH circuit using a high-flux polysulfone membrane and to differentiate between the loss by ultrafiltration and adsorption.

METHODS

Prospective observational study in ten critically ill patients, receiving predilution CVVH with a new filter, blood flow 180 mL/min, and predilution flow 2,400 mL/h. Arterial blood, postfilter blood, and UF samples were taken at baseline, and 1, 8, and 24-h after CVVH initiation, to determine AA concentrations and hematocrit. Mass transfer calculations were used to determine AA loss in the filter and by UF, and the difference between these 2.

RESULTS

The median AA loss in the filter was 10.4 g/day, the median AA loss by UF was 13.4 g/day, and the median difference was -2.9 g/day (IQR -5.9 to -1.4 g/day). For the individual AA, the difference ranged from -1 g/day to +0.4 g/day, suggesting that some AA were consumed or adsorbed and others were generated. AA losses did not significantly change over the 24-h study period.

CONCLUSION

During CVVH with a modern polysulfone membrane, the estimated AA loss was 13.4 g/day, which corresponds to a loss of about 11.2 g of protein per day. Adsorption did not play a major role. However, individual AA behaved differently, suggesting complex interactions and processes at the filter membrane or peripheral AA production.

(-)-Hydroxycitric Acid Nourishes Protein Synthesis via Altering Metabolic Directions of Amino Acids in Male Rats

(-)-Hydroxycitric acid (HCA), a major active ingredient of Garcinia Cambogia extracts, had shown to suppress body weight gain and fat accumulation in animals and humans. While, the underlying mechanism of (-)-HCA has not fully understood. Thus, this study was aimed to investigate the effects of long-term supplement with (-)-HCA on body weight gain and variances of amino acid content in rats. Results showed that (-)-HCA treatment reduced body weight gain and increased feed conversion ratio in rats. The content of hepatic glycogen, muscle glycogen, and serum T4 , T3 , insulin, and Leptin were increased in (-)-HCA treatment groups. Protein content in liver and muscle were significantly increased in (-)-HCA treatment groups. Amino acid profile analysis indicated that most of amino acid contents in serum and liver, especially aromatic amino acid and branched amino acid, were higher in (-)-HCA treatment groups. However, most of the amino acid contents in muscle, especially aromatic amino acid and branched amino acid, were reduced in (-)-HCA treatment groups. These results indicated that (-)-HCA treatment could reduce body weight gain through promoting energy expenditure via regulation of thyroid hormone levels. In addition, (-)-HCA treatment could promote protein synthesis by altering the metabolic directions of amino acids. Copyright © 2016 John Wiley & Sons, Ltd.

Automated analysis of primary amino acids in plasma by high-performance liquid chromatography

The concentration of primary amino acids (AAs) in plasma can accurately be determined using high-performance liquid chromatography (HPLC). Before the analysis can be performed, several steps have to be regarded. First, the time and method of blood withdrawal, type of blood tube, use of medication, and differences in dietary intake are important factors that should be standardized. Second, the handling of and the way the blood is transported to the laboratory, the time between blood withdrawal and centrifugation, the method of centrifugation, and the temperature and time of plasma storage have to be noticed. Third, the methods used for deproteinization and derivatization may account for varying results between laboratories.In this chapter, we describe an HPLC method that measures primary amino acids in plasma using automated precolumn derivatization with ortho-phthalaldehyde, and that pays attention to the above-mentioned criteria. This method is relatively fast, simple, sensitive, and reliable. Since with this method we can determine over 40 physiological amino acids with a very good resolution, trace amounts of amino acids can also be determined. In addition, interassay resolution times have very low variation and the use of two internal standards guarantees reliable quantification.

[Determination of total aminothiols and neuroactive amino acids in plasma by high performance liquid chromatography with fluorescence detection]

This paper describes a simple and sensitive reversed-phase HPLC method for the determination of total homocysteine, total cysteine, total glutathione (GSH+GSSG), and neuroactive amino acids (Asp, Glu, Tau, GABA) using precolumn derivatization with ortho-phtaldialdehyde and fluorimetric detection at 360 and 470 nm for emission and excitation, respectively. Derivatization was performed with ortho-phthaldialdehyde in the presence of 2-mercaptoethanol after alkylation of the free sulfhydryl groups with iodoacetic acid. For determination of total aminothiols, the disulfide bonds were reduced and protein-bound thiols were released by addition of dithiothreitol to the plasma sample. The advantage of this method is the simultaneous determination of both homocysteine/cysteine/glutathione and neuroactive amino acids in the sample. The plasma levels of studied compounds were determined in 14 healthy volunteers (20-45 years old) and 55 patients with chronic hepatitis C (20-49 years old) and the resulting numbers were in a good agreement the studies published earlier. The calibration curves were linear over a concentration range of 5-100 microM in plasma (r2 = 0.985-0.996). The intraday and interday coefficients of variation were 3-6% and 4-7%, respectively. The recovery of the standards added to the plasma samples ranged from 94 to 102%. The limits of detection (LOD) were 0.2-0.5 ng per 10 microl injection volume (signal-to-noise ratio of 3).

Analysis of plasma amino acids by HPLC with photodiode array and fluorescence detection

BACKGROUND

Plasma amino acids are usually analyzed by ion-exchange chromatography (IEC), a reproducible but time consuming method. Here, we test whether plasma amino acids can be analyzed using reverse-phase high performance liquid chromatography (HPLC).

METHODS

Filtered plasma, with S-carboxymethyl-l-cysteine as the internal standard, was derivatized and analyzed by an Agilent 1100 HPLC system. Primary amino acids were derivatized with o-phthalaldehyde 3-mercaptopropionic acid (OPA) and detected by a diode array detector. Secondary amino acids were derivatized with 9-fluorenylmethyl chloroformate (FMOC) and detected fluorometrically. Chromatographic separation is achieved by two gradient elutions (two injections per sample), starting at different pHs, on a reverse phase Agilent Zorbax Eclipse C(18) column AAA (4.6 x 150 mm).

RESULTS

The HPLC method evaluated correlated well with IEC (0.89</=r</=1.00) with linearity up to 2500 mumol/l. The between- and within-run CVs were <6.0%. In addition, this method is able to separate argininosuccinic acid, homocystine and allo-isoleucine, rare but clinically significant amino acids.

CONCLUSION

This HPLC method was comparable to IEC and could represent an alternative for amino acid analysis.

Separation methods for taurine analysis in biological samples

Taurine plays an important role in a variety of physiological functions, pharmacological actions and pathological conditions. Many methods for taurine analysis, therefore, have been reported to monitor its levels in biological samples. This review discusses the following techniques: sample preparation; separation and determination methods including high-performance liquid chromatography, gas chromatography, ion chromatography, capillary electrophoresis and hyphenation procedures. It covers articles published between 1990 and 2001.

Analysis of amino acids in human serum by isocratic reversed-phase high-performance liquid chromatography with electrochemical detection

A simple, sensitive and reproducible isocratic high-performance liquid chromatography (HPLC) method has been developed for the determination of amino acids in human serum. The method involves precipitation of the serum proteins with methanol followed by pre-column derivatization of amino acids with o-phthalaldehyde-2-mercaptoethanol or o-phthalaldehyde-sodium sulfite. HPLC separation of the derivatives was performed using an ODS column with an isocratic mobile phase system and electrochemical detection (+0.75 V). The response was linear over the range 5-300 microM for all amino acids. The method allows quantitative determination of glutamic acid, asparagine, serine, glutamine, histidine, taurine, alanine, arginine, methionine, isoleucine, ornithine, leucine, phenylalanine, lysine and tryptophan at concentrations as low as 0.5-5.0 pmol (signal-to-noise ratio=2). Using this method, the levels of amino acids in serum from healthy donors and patients with ischemic stroke were determined.

Plasma tranexamic acid concentrations during cardiopulmonary bypass

Although tranexamic acid is used to reduce bleeding after cardiac surgery, there is large variation in the recommended dose, and few studies of plasma concentrations of the drug during cardiopulmonary bypass (CPB) have been performed. The plasma tranexamic acid concentration reported to inhibit fibrinolysis in vitro is 10 microg/mL. Twenty-one patients received an initial dose of 10 mg/kg given over 20 min followed by an infusion of 1 mg. kg(-1). h(-1) via a central venous catheter. Two patients were removed from the study secondary to protocol violation. Perioperative plasma tranexamic acid concentrations were measured with high-performance liquid chromatography. Plasma tranexamic acid concentrations (microg/mL; mean +/- SD [95% confidence interval]) were 37.4 +/- 16.9 (45.5, 29.3) after bolus, 27.6 +/- 7.9 (31.4, 23.8) after 5 min on CPB, 31.4 +/- 12.1 (37.2, 25.6) after 30 min on CPB, 29.2 +/- 9.0 (34.6, 23.8) after 60 min on CPB, 25.6 +/- 18.6 (35.1, 16.1) at discontinuation of tranexamic acid infusion, and 17.7 +/- 13.1 (24.1, 11.1) 1 h after discontinuation of tranexamic acid infusion. Four patients with renal insufficiency had increased concentrations of tranexamic acid at discontinuation of the drug. Repeated-measures analysis revealed a significant main effect of abnormal creatinine concentration (P = 0.02) and time (P < 0.001) on plasma tranexamic acid concentration and a significant time x creatinine concentration interaction (P < 0.001).

IMPLICATIONS

A 10 mg/kg initial dose of tranexamic acid followed by an infusion of 1 mg.kg(-1).h(-1)produced plasma concentrations throughout the cardiopulmonary bypass period sufficient to inhibit fibrinolysis in vitro. The dosing of tranexamic acid may require adjustment for renal insufficiency.

Derivatization and chromatographic behavior of the o-phthaldialdehyde amino acid derivatives obtained with various SH-group-containing additives

An overview is presented of HPLC methods currently in use to determine amino acids as their o-phthaldialdyde derivatives in the presence of various SH-group-containing additives. Crucial points that proved to influence the stability of the amino acid OPA derivatives have been discussed in detail: (i) the mol ratios of the OPA-SH-group-containing additive amino acid; (ii) the preparation and storage conditions of the OPA reagents; (iii) the optimum pH conditions for the interactions and elutions; (iv) the behavior of the, believed to be, less stable amino acids, such as glycine, beta-alanine, gamma-aminobutyric acid, histidine, ornithine and lysine.

Precise analysis of primary amino acids in urine by an automated high-performance liquid chromatography method: comparison with ion-exchange chromatography

A precise, simple and rapid method for the quantitative determination of primary amino acids in urine based on high-performance liquid chromatography and o-phthaldialdehyde pre-column derivatization is described. All primary urinary amino acids could be determined within 49 min (injection to injection). Amino acid concentrations in 40 urinary samples were measured by this method and the results were compared with those measured by ion-exchange chromatography. The correlation coefficient for the common amino acids was greater than 0.90. This is the first study in which such a detailed comparison has been made on urine samples. It appeared that the method described is an excellent alternative to the classical ion-exchange method for the quantitation of urinary amino acids.

State-of-the-art of high-performance liquid chromatographic analysis of amino acids in physiological samples

Nowadays, the fast and sensitive high-performance liquid chromatographic (HPLC) analysis of derivatized amino acids is a good alternative to the ion-exchange chromatography (IEC) method for plasma amino acids. However, several precautions have to be taken in order to obtain reliable data on the concentration of amino acids in physiological fluids. These include the collection, centrifugation, storage conditions and the method of deproteinization. Furthermore, the method of pre-column derivatization in connection with the protein precipitant used and the choice of the chromatographic system which determines the overall resolution are important factors. HPLC methods using pre-column derivatization with o-phthaldialdehyde were suitable for the accurate determination of many primary amino acids in plasma because of their high sensitivity, simplicity, speed and reliability. When the determination of secondary amino acids and cystine was also necessary, the phenylisothiocyanate method was the preferred technique. The intra-laboratory variability of the HPLC method was satisfactory while the inter-laboratory variation of this method was found to be similar to that of IEC, HPLC methods capable of separating over forty physiological amino acids seem promising for the analysis of urine samples.

Determination of unbound L-tryptophan in human plasma using high-performance liquid chromatography with fluorescence detection

An assay for the measurement of unbound L-tryptophan concentrations in plasma was developed using reverse-phase HPLC with fluorescence detection. Unbound L-tryptophan from plasma was obtained using the Amicon MPS-1 ultrafiltration device. L-tryptophan binding to the membrane in the ultrafiltration device was not significant. A linear relationship between the peak-area ratios (peak-area of L-tryptophan to internal standard) and concentrations of L-tryptophan was obtained in the range of 0.1 microgram/mL to 2.5 micrograms/mL. The intra-assay precision was less than 10% for each control (0.18 microgram/mL, 0.75 microgram/mL and 2.0 micrograms/mL). The inter-assay precision was less than 15% for each control; the accuracy for each control; the accuracy for each control, expressed as percent difference from nominal (%DFN), was less than 12%. This method was used to determine unbound L-tryptophan concentrations in plasma from nine male subjects who participated in a clinical study.

Augmented sensitivity to benzodiazepine in septic shock rats

The purpose of this study was to assess the pharmacological characteristics of the benzodiazepine binding site in the brain of septic animals. We induced endotoxin shock in rats using a caecum ligation and puncture model. Following examination of the physiological state of the rats 24 hr after the caecum ligation and puncture, brain tissue samples were prepared for biochemical assay of amino acids and for the [3H]-diazepam radioligand binding assay. Amino acids assays indicated that the concentration of aromatic amino acids was higher in the CLP group (P< 0.05), the branched chain amino acid concentration was lower in the CLP group (P< 0.05) and the sulfur-containing amino acid concentration was elevated in the CLP group (P< 0.05) than in both the control and the sham-operated groups. [3H]-diazepam radioligand binding assays demonstrated that the number of receptors in the septic rats was increased in the forebrain (CLP rats; 2.37 +/- 0.04 pmol x mg(-1) protein, control rats; 1.45 +/- 0.02 pmol x mg(-1) protein, sham-operated rats; 1.49 +/- 0.03 pmol x mg(-1) protein), cerebellum (CLP rats; 1.55 +/- 0.05 pmol x mg(-1) protein, control rats; 1.05 +/- 0.02 pmol x mg(-1) protein, sham-operated rats: 1.09 +/- 0.02 pmol x mg(-1) protein) and brain stem (CLP rats; 1.21 +/- 0.04 pmol x mg(-1) protein, control rats; 0.61 +/- 0.02 pmol x mg(-1) protein, sham-operated rats; 0.63 +/- 0.02 pmol x mg(-1) protein) compared with the control and sham-operated rats (P< 0.05). In conclusion, it was considered that the increased number of benzodiazepine receptors may be one cause of the neuronal alteration observed in septic shock animals.

Validation of the determination of amino acids in plasma by high-performance liquid chromatography using automated pre-column derivatization with o-phthaldialdehyde

A sensitive and reproducible fully automated method for the determination of amino acids in plasma based on reversed-phase high-performance liquid chromatography and o-phthaldialdehyde pre-column derivatization is described. A 5-microns Spherisorb ODS 2 column (125 x 3 mm I.D.) was selected for routine determination. Over 40 physiological amino acids could be determined within 49 min (injection to injection) and 48 samples could be processed unattended. The coefficients of variation for most amino acids in plasma were below 4%. We were also able to measure trace amounts of amino acids in plasma normally not detected in a routine analysis. The results obtained with the method described compared favourably with those of conventional amino acid analysis (r = 0.997) and were in excellent agreement with those of other laboratories (r = 0.999).

Determination of amino acids in human plasma by liquid chromatography with postcolumn ninhydrin derivatization using a hydroxyapatite cartridge for precolumn deproteination

Amino acids in human plasma were determined by liquid chromatography with postcolumn ninhydrin derivatization using a hydroxyapatite cartridge for precolumn deproteination. S-Carboxymethyl-L-cysteine, D-phenylglycine and S-aminoethyl-L-cysteine were found to be suitable internal standards. The proposed method is simple, rapid (deproteination time less than 1 min) and reproducible [relative standard deviation below 3% except for low-level aspartic acid (n = 3)]. The average recovery of 25 amino acids was above 90%. The elution time of amino acids in human plasma was approximately 2 h. Protein binding of tryptophan was also determined by the proposed method. The analytical data for amino acids in human plasma deproteinated using the proposed and published methods (5-sulphosalicylic acid and ethanol) were compared.

Influence of storage conditions on normal plasma amino-acid concentrations

Conflicting information in the literature is given concerning the optimal preparation and storage conditions of plasma samples for amino-acid analysis. To assess the optimal pre-storage treatment, we compared several methods and studied their influence on plasma amino-acid levels of rats and humans, stored at different temperatures. In rat plasma, the frequently reported degradation of glutamine was not measurable at a storage temperature of -70 degrees C. However, storage of native, not deproteinised plasma at this temperature, resulted in a 32% decrease of arginine and a 30% increase in ornithine after 24 weeks. Deproteinisation prohibited this arginine decay. At -20 degrees C, arginine decay was even more pronounced, whereas glutamine decreased by 14% in untreated plasma, by 10% in sulfosalicylic acid deproteinised plasma and by 3% if the deproteinisation was followed by removal of the protein pellet and subsequent neutralisation. To confirm these unexpected results in humans, we repeated this experiment with plasma of 6 volunteers. In contrast to rat plasma, we did not observe any changes in arginine and ornithine concentrations in human plasma stored at -70 degrees C. At -20 degrees C the reduction in glutamine was only 4-5%. These results suggest that interspecies differences in enxymatic activity exist in plasma. Finally, having assessed the optimal treatment and storage conditions (deproteinisation followed by storage at -70 degrees C), samples were obtained from a total of 112 human volunteers, stratified for age and sex, and amino-acids were measured. In the female group, we found a tendency to a gradual increase in most amino-acid concentrations with advancing age, which however only reached significance for histidine, citrulline, alanine and leucine. These observations demonstrate that plasma samples for amino-acid analysis should be deproteinised and stored at -70 degrees C. Also important interspecies differences appear to exist in plasma enzymatic activity. Finally, control samples should be taken from an age and sex matched control group.

Derivatization of posttranslationally modified amino acids

After a brief overview of posttranslational modifications of protein amino acids, the use of various derivatizing reagents for amino acid analysis is discussed. Derivatization and chromatographic separation of hydroxyproline, methylhistidine, and phosphorylated amino acids are discussed in detail to illustrate some of the strategies that can be applied to the analysis of posttranslationally modified amino acids.

Derivatization reactions for neurotransmitters and their automation

Many reagents suitable for the derivatization of neurotransmitters are selective for the amino function. Others, however, are selective for the carboxyl-, thiol- and hydroxyl function, and recently, reagents selective for more than one function have been produced. Interest persists in the established reagents, with their well understood behaviour which assists automation of analysis as much as new technology. Workers appear reluctant to tackle the optimization of many novel reagents. Chiral reagents may become important if d-amino acids are shown to be significant from a physiological point of view. Solid-phase reagents offer better regulated chemistry and combined derivatization/solid-phase extraction, which make them an exciting prospect.

Novel precolumn deproteinization method using a hydroxyapatite cartridge for the determination of theophylline and diazepam in human plasma by high-performance liquid chromatography with ultraviolet detection

The deproteinization of human plasma was carried out using a hydroxy apatite cartridge as a precolumn. After human plasma had been passed through the cartridge followed by suitable elution, protein-free eluate was obtained within only 1 min without the need for centrifugation. Deproteinization was evaluated by the determination of albumin, gamma-globulin and transferrin in the eluate by high-performance liquid chromatography (HPLC) with UV detection. Determination of theophylline and diazepam in human plasma was performed by HPLC with UV detection. The proposed method was suitable for the determination of these two drugs in human plasma, because it is simple and rapid (retention time of each drugs approximately 15 min) and microamounts of sample are required (50-100 microliters). The calibration graphs for theophylline and diazepam were linear in the range 0.1-10 micrograms and 0.1-65 ng, respectively. Recoveries of both drugs were over 90% by the standard addition method.

Rapid routine determination of amino acids in plasma by high-performance liquid chromatography with a 2-3 microns Spherisorb ODS II column

A rapid fully automated method for the determination of amino acids is described based on high-performance liquid chromatography and pre-column o-phthaldialdehyde derivatization. Using a 150 mm x 4.6 mm I.D. HPLC column filled with a recently introduced 2-3 microns Spherisorb ODS II packing material, 30 physiological amino acids could be determined within 28 min (injection to injection), while 95 samples could be processed unattended within 45 h. For most amino acids, the coefficient of variation (C.V.) for the peak areas measured was below 3%, both in aqueous standards and in plasma. Providing a pre-column change every 200-300 runs, the separation remained unaltered for about 1500-2000 runs on a single column.

Rapid determination of glutamine in biological samples by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of glutamine in biological samples is presented. Glutamine was derivatized with ortho-phthalaldehyde reagent containing 3-mercaptopropionic acid and separated by reversed phase chromatography on a C18 column containing 3-microns particles. No interference from other amino acids was observed. The assay was linear over a range from 1 to 2,000 mumol/l. Analytical recovery of plasma samples spiked with glutamine was 98.6 +/- 3.8%. Within- and between-batch imprecision were 1.5% and 2.2%, respectively. The derivatization step was fully automated. Total analysis time, including derivatization and chromatography, amounted to 6 min. The method can be used for the determination of glutamine in plasma, urine, cerebrospinal fluid and tissue homogenates.

Singlet-oxygen generation at gas-liquid interfaces: a significant artifact in the measurement of singlet-oxygen yields from ozone-biomolecule reactions

Several ozone-biomolecule reactions have previously been shown to generate singlet oxygen in high yields. For some of these ozone-biomolecule reactions, we now show that the apparent singlet-oxygen yields determined from measurements of 1270 nm chemiluminescence were artifactually elevated by production of gas-phase singlet oxygen. The gas-phase singlet oxygen results from the reaction of gas-phase ozone with biomolecules near the surface of the solution. Through the use of a flow system that excludes air from the reaction chamber, accurate singlet-oxygen yields can be obtained. The revised singlet-oxygen yields (mol 1O2 per mol O3) for the reactions of ozone with cysteine, reduced glutathione, NADH, NADPH, human albumin, methionine, uric acid and oxidized glutathione are 0.23 +/- 0.02, 0.26 +/- 0.2, 0.48 +/- 0.04, 0.41 +/- 0.01, 0.53 +/- 0.06, 1.11 +/- 0.04, 0.73 +/- 0.05 and 0.75 +/- 0.01, respectively. These revised singlet-oxygen yields are still substantial.

Quantification of physiological amino acids by gradient ion-exchange high-performance liquid chromatography

A single-column gradient lithium ion-exchange chromatographic method with post-column derivatization and fluorimetric detection for the quantification of physiological amino acids is described. The method runs automatically, requires a minimum of sample preparation, separates all amino acids in plasma and cerebrospinal fluid, and most compounds in brain extract, in addition to some amino acids used therapeutically and in pharmacological studies. About 40 compounds can be quantitated within a run time of 3 h. The within-assay and between-assay coefficients of variations for principal amino acids in plasma samples are satisfactory. The system has performed conveniently and with high stability in the daily routine work and is cost-saving based on laboratory-prepared buffers.