Evaporative Light Scattering Detector Detection Research Articles

Characterization of ribostamycin and its impurities using a nano-quantity analyte detector: Systematic comparison of performance among three different aerosol detectors

Characterization of aminoglycoside antibiotics like ribostamycin is important due to the complex composition and common toxic impurities. Aerosol detectors are often employed for determination of these non-absorbent analytes. In this work, a robust and cost-effective method was developed for simultaneous detection of ribostamycin and its related substances using high-performance liquid chromatography (HPLC) with a relative new aerosol detector named nano-quantity analyte detector (NQAD). With the introduction of less toxic but more compatible ion-pairs pentafluoropropionic acid (PFPA) and trifluoroacetic acid (TFA) in the eluent, an optimized separation effect was achieved. Compared with the other two aerosol detectors namely ELSD (evaporative light scattering detector) and CAD (charged aerosol detector), method verification and quantitative detection results revealed that NQAD had higher sensitivity than ELSD with a 0.8 μg/mL limit of detection, as well as wider linear range (from 2 μg/mL to 1000 μg/mL) than both CAD (from 2 μg/mL to 200 μg/mL) and ELSD (from 8 μg/mL to 200 μg/mL) detector. The performance of NQAD helped to realize detection of ribostamycin and its impurities with significant concentration differences in a single run. With a cation suppressor to eliminate the ion-suppression caused by the ion-pairs in the eluent, the structure of nine impurities in ribostamycin sample was characterized by liquid chromatography-mass spectrum (LC-MS). Both external standard and area normalization calculation were investigated, and NQAD obtained more accurate results due to its full-range linear response-to-concentration relationship, providing an alternative for routine quality control of multi analyte systems.

Determination of aminoglycoside antibiotics in animal feed by high performance liquid chromatography using evaporative light scattering detector

This study was carried out to develop a method for the simultaneous analysis of 5-aminoglycosides such as streptomycin (STR), neomycin (NEO), kanamycin (KAN), spectinomycin (SPE), and amikacin (AMI) in animal feedstuffs using the (HPLC-ELSD) high performance liquid chromatography with Evaporative Light Scattering Detector detection. The 5-aminoglycoside antibiotics in animal feed samples were extracted with a solvent containing 20% ACN, 1% HCl (v/v). The extract was purified by solid-phase extraction (SPE) with the stationary phase of PCX, at pH 5 which was adjusted by NH3 solution. The 5-aminoglycosides were eluted from the SPR column with 10% NH3 solution. The eluted sample was evaporated to dryness and the residue was dissolved in 20 mM hepta fluorobutyric acid (HFBA) solution followed by filtering through a 0.22 µm membrane prior to analyze by HPLC – ELSD. The 5-aminoglycosides were separated on an Eclipse Plus C18, 1.8 µm, 4.6×100 mm column, an aqueous/acetonitrile containing 15 mM HFBA in gradient mode with ratio of H2O/ACN: 0-1 min fix at 76:25, 1-6 min reduce 55:45, 6-7 min fix at 55-45, 7-8 min increase to 75:25. A carrier gas velocity of the ELSD detector was 1 L/min and the misting temperature was 40oC. This method achieved a detection limit (MDL) of 4 mg/kg and a recovery yield of 87-92% for 5-aminoglycosides in feed sample with the HPLC – ELSD system.

Quantification of phospholipid degradation products in liposomal pharmaceutical formulations by ultra performance liquid chromatography-mass spectrometry (UPLC-MS).

Identification and quantification of excipient related degradation products in the liposomal formulation is important, as they may impact the safety and efficacy of the drug. Phospholipids are one of the major excipients in liposome drugs composing the lipid bilayer, and they are vulnerable to oxidation and hydrolysis reactions. Since phospholipids with saturated fatty acid chain were preferred in most of liposome drug products, the major degradation pathway of phospholipids in liposome formulations are limited to hydrolysis of phospholipids into free fatty acids and lysophospholipids. These hydrolyzed degradation products may form during manufacturing and/or long-term storage of liposomal formulations. Herein, we report development and application of accurate and sensitive methods that can be utilized for the quantitation of saturated free fatty acids (FFA 18:0 and FFA 16:0), lysophosphocholines (LPC 18:0 and LPC 16:0), and lysophosphoglycerol (LPG 18:0) in liposomal formulations. The free fatty acids were separated using a C8 column whereas the LPCs and LPGs were separated using a C18 stationary phase upon direct injection without the need of lipid extraction process. Each analyte was quantified by Q-TOF mass spectrometry. This method was validated according to USP compendial procedures and has been applied to the analysis of four commercial liposomal pharmaceutical formulations. The limit of quantitation (LOQs) of FFA 16:0, FFA 18:0, LPC 16:0, LPC 18:0 and LPG 18:0 are 5ng/mL, 5ng/mL, 6.5ng/mL, 7.0ng/mL, 10ng/mL respectively. Compared to CAD (Charge Aerosol Detector) and ELSD (Evaporative Light Scattering Detector) detection methods in ppm levels, this ultra-performance liquid chromatography (UPLC)-Mass Spectroscopy (MS) method displays precise determination of lysophospholipids in the liposomal formulations with higher accuracy and sensitivity.

Comparison of UV and ELS detectors in HSPEC analysis of natural organic matter in dam water

This project arose out the need for a simple method to analyse natural organic matter (NOM) on a routine basis. Water samples were obtained from the Vaal Dam. Analysis was preceded by separating the NOM into the humic and non-humic fractions. The humic portion was separated further into two fractions by employing a non-ionic DAX-8 resin to separate humic acid from fulvic acid. High-performance size-exclusion chromatography (HPSEC), equipped with a UV detector and an evaporative light scattering detector (ELSD) was used to obtain information on the molecular weight distribution and concentration levels of the two acids. Mixed standards of polyethylene oxide/glycol were employed for calibration. The molecular weight distributions (MWDs) of the isolated fractions of humic and fulvic acids were determined with ELSD detection as weight-average (Mw), number-average (Mn) and polydispersity (ρ) of individual NOM fractions. The Mw/Mn ratio was found to be less than 1.5 in all fractions, indicating that they have a low and narrow size fraction. It is noted that the ELSD detector proved to be far more capable than the UV detector. A finding of interest is that 40% of the total organic carbon in the dam water samples could be attributed to humic substances. The developed method successfully separated the humic substances from water and further separated the humic substances into the component acids, namely, humic and fulvic acids. Molecular weight distribution of these compounds is a powerful indication of how much DOM was present in the dam water. Even though the UV method was useful in characterizing these substances, the ELS detector is recommended because it detects all the organic species present. Keywords: Natural organic matter, dam water, determination, ELSD

Crystallization-induced dynamic resolution R-epimer from 25-OCH3-PPD epimeric mixture.

25-OCH3-PPD is a promising antitumor dammarane sapogenin isolated from the total saponin-hydrolyzed extract of Panax ginseng berry and Panax notoginseng leaves. 20(R)-25-OCH3-PPD was more potent as an anti-cancer agent than 20(S)-25-OCH3-PPD and epimeric mixture of 25-OCH3-PPD. This paper describes the rapid separation process of the R-epimer of 25-OCH3-PPD from its epimeric mixture by crystallization-induced dynamic resolution (CIDR). The optimized CIDR process was based on single factor analysis and nine well-planned orthogonal design experiments (OA9 matrix). A rapid and sensitive reverse phase high-performance liquid chromatographic (HPLC) method with evaporative light-scattering detector (ELSD) was developed and validated for the quantitation of 25-OCH3-PPD epimeric mixture and crystalline product. Separation and quantitation were achieved with a silica column using a mobile phase consisting of methanol and water (87:13, v/v) at a flow rate of 1.0mL/min. The ELSD detection was performed at 50°C and 3L/min. Under conditions involving 3mL of 95% ethanol, 8% HCl, and a hermetically sealed environment for 72h, the maximum production of 25(R)-OCH3-PPD was achieved with a chemical purity of 97% and a total yield of 87% through the CIDR process. The 25(R)-OCH3-PPD was nearly completely separated from the 220mg 25-OCH3-PPD epimeric mixture. Overall, a simple and steady small-batch purification process for the large-scale production of 25(R)-OCH3-PPD from 25-OCH3-PPD epimeric mixture was developed.

Improved evaporative light scattering detection for carbohydrate analysis

Optimization and validation of evaporative light scattering detector (ELSD), aided by response surface methodology (RSM), has been developed for the liquid chromatography analysis of a wide molecular weight (MW) range of carbohydrates, including polysaccharides and oligosaccharides. Optimal experimental parameters for the ELSD detection were: 88.8°C evaporator temperature, 77.9°C nebulizer temperature and 1.1 standard litres per minute nitrogen flow rate. Optimal ELSD detection, used together with high performance size exclusion chromatography (HPSEC) of carbohydrates, gave a linear range from 250 to 1000mgL−1 (R2>0.998), with limits of detection and quantitation of 4.83–11.67 and 16.11–38.91mgL−1, respectively. Relative standard deviation was lower than 1.8% for intra-day and inter-day repeatability for apple pectin, inulin, verbascose, stachyose and raffinose. Recovery ranged from 103.7% to 118.3% for fructo-oligosaccharides, α-galacto-oligosaccharides and disaccharides. Optimized and validated ELSD detection is proposed for the analysis of high- to low-MW carbohydrates with high sensitivity, precision and accuracy.

Flow-injection with enhanced evaporative light scattering detector detection and quantification of human serum albumin using gold nanoparticles

The ELSD response for HSA was enhanced by using GNPs, making it possible to determine HSA by ELSD.

Analysis of non-phthalates plasticizers on porous graphitic carbon by supercritical fluid chromatography using evaporative light scattering detection

The analysis of several plasticizers, widely used in the production of medical devices, was investigated on porous graphitic carbon (PGC) stationary phase in supercritical fluid chromatography (SFC) with an evaporative light scattering detector (ELSD). Due to strong interaction of compounds with the PGC support, solvents of strong eluotropic strength were added to the CO2 supercritical fluid. The effect of alkyl chain (pentane, hexane, heptane) and chlorinated (CH2Cl2, CHCl3, CCl4) solvents was studied on the retention and on the ELSD detection of plasticizers. A co-solvent mixture composed of CHCl3/heptane, eluted under gradient mode, allowed a significant improvement of the ELSD response compared to the use of each solvent individually. Then, a central composite design (CCD) was implemented to optimize both the separation and the detection of plasticizers. The parameters involved were the outlet pressure, the gradient slope, the co-solvent composition and the drift tube temperature of the ELSD. After optimization, baseline separation of plasticizers was achieved in 7min and best signal-to-noise ratios were obtained with outlet pressure and drift tube temperature of ELSD set at 200bar and 31°C, respectively. The co-solvent mixture was also composed of CHCl3/heptane (35/65 v/v) and a gradient from 15 to 60% of co-solvent in 2.2min was employed. The results demonstrated that CCD is a powerful tool for the optimization of SFC/ELSD method and the response surface model analysis can provide statistical understandings of the significant factors required to achieve optimal separation and ELSD sensitivity.

Hydrophilic interaction chromatography with aerosol-based detectors (ELSD, CAD, NQAD) for polar compounds lacking a UV chromophore in an intravenous formulation

In this work, a high performance liquid chromatography (HPLC) method is reported for the separation and quantitation of a drug substance that is highly polar and lacking a chromophore in a mannitol intravenous (IV) formulation. Three polar stationary phases operated in hydrophilic interaction chromatography (HILIC) mode were evaluated in conjunction with an Alltech 800 ELSD detector. These columns were evaluated with respect to chromatographic properties such as buffer, pH and organic concentrations to identify the best stationary phase. The chromatographic method was then validated for the determination of mGlu2/3 receptor agonist (−)-(1R, 4S, 5S, 6S)-4-Amino-2-sulfonylbicyclo [3.1.0] hexane-4,6-dicarboxylic acid (LY404039) content in a mannitol IV formulation with respect to linearity (R2 of 0.9997), repeatability (%RSD of 0.36%), accuracy, solution stability (99.56% after 24h), specificity, intra-assay precision (%RSD 0.48%) and limit of detection (LOD, ∼50μg/mL). In addition to the Alltech 800 ELSD detector, several other aerosol-based detectors were investigated for reproducibility, linearity and LOD. These additional detectors consisted of an Alltech 3300 evaporative light scattering detector (ELSD), a nano quantity analyte detector (NQAD) and a charged aerosol detector (CAD). Based on the data from this report, a feasible isocratic LC method was achieved using a TSKgel Amide-80 column with mobile phase conditions of 30% water with 0.2% trifluoroacetic acid (TFA) and 70% acetonitrile (ACN) using any of the four aerosol-based detectors for detection and quantitation.

Development of a rapid, sensitive and authentic LCMS method for the determination of Dexamethasone, Testosterone and Estrone (E1) in human plasma

A simple, rapid, fast, precise and accurate reverse-phase HPLC method was developed and validated for the simultaneous determination of Dexamethasone, Testosterone and Estrone (E1) in pre-mixture by using RP-HPLC having photon diode array detector, Evaporative Light Scattering Detector (ELSD) and coupled with dual electrospray ionization mass spectrometry Quadrupole time-of-flight (LCMS). The method has shown adequate separation for Dexamethasone, Testosterone and Estrone (E1). Separation was achieved on reverse phase Shodex C18, 3 μm, 4.6 × 100 mm, using isocratic elution mode with a mobile phase Acetonitrile and 0.1% formic acid in water. The flow rate was 1 mL/min and effluents were monitored at 240 and 280 nm, using photodiode array (PDA) detector, ELSD and Ion detection was performed by dual electrospray ionization source (dual ESI) in positive mode. The recovery of steroids was found to be in the range of 98–102%. The described method was linear. The precision, ruggedness and robustness values were also within the prescribed limits.

Counter-Current Chromatographic Separation of Nucleic Acid Constituents with a Polar Volatile Organic-Aqueous Two-Phase Solvent Systems with ELSD Detection

Highly hydrophilic volatile organic/aqueous two-phase solvent systems containing an organic salt such as, acetonitrile/800 mM and 1200 mM ammonium acetate (1 : 1, v/v) were efficiently utilized for high-speed counter-current chromatography (HSCCC) to separate hydrophilic compounds. The retention of the upper and the lower stationary phases in the column of the cross-axis coil planet centrifuge (CCC instrument) was studied by changing the flow-rate of the mobile phase (1.0–3.0 ml/min). Using the acetonitrile/800 mM ammonium acetate two-phase solvent system, the stationary phase was retained at 46.3% relative to the total column capacity of 65 ml by the reversed-phase elution mode at a flow-rate of 1.0 ml/min. The best retention of the stationary upper phase of 51.5% was obtained by the solvent system of the acetonitrile/1200 mM ammonium acetate at the above flow-rate. With the acetonitrile/800 mM ammonium acetate system the base line separation of adenine and adenosine monophosphate (AMP) detected by evaporative light scattering detector (ELSD) and UV was achieved with lower phase mobile at a flow-rate of 1.0 ml/min within 70 min.

HPLC‐ELSD analysis of spectinomycin dihydrochloride and its impurities

A simple, rapid and reliable reversed-phase ion-pair chromatography method by HPLC coupled to an evaporative light scattering detector (ELSD) has been developed to simultaneously determine chloride, spectinomycin and its related substances in a sample. The column was a TSKgel ODS-100V. The mobile phase was ACN/aqueous solution of 15 mM ammonium acetate adjusted with TFA to pH 3.0 (2:98 v/v), in an isocratic mode. The drift tube temperature was set at 50°C and the nebulizing gas flow rate of air was 3.5 L/min for ELSD detection. Almost all of the reported degradation compounds of spectinomycin such as actinamine, actinospectinoic acid and biosynthesis intermediates such as dihydrospectinomycin diastereoisomers were baseline separated. MS was utilized for the identification of spectinomycin and its seven related substances. The method for the assay of spectinomycin was successfully validated with respect to accuracy, precision (RSD less than 2%), linearity (throughout the linear range 0.025-3 mg/mL, r=0.9993), sensitivity (LOD: 100 ng on column) and robustness. The experimental results demonstrated that the simultaneous determination of chloride, spectinomycin and related substances is feasible in a single run, which suggests applicability in routine assays.

Comparison of two aerosol-based detectors for the analysis of gabapentin in pharmaceutical formulations by hydrophilic interaction chromatography

Comparison of hydrophilic interaction chromatography (HILIC) columns coupled with an evaporative light scattering detector (ELSD) or charged aerosol detector (CAD) was done for the detection of gabapentin in pharmaceutical formulations. The chromatographic separations were achieved on four HILIC columns: ZIC HILIC, ZIC pHILIC, Luna HILIC, and Atlantis HILIC. Experimental factors such as mobile phase composition, acetonitrile content, and mobile phase pH were evaluated. Validation of method was done in terms of linearity, sensitivity, accuracy, and precision. The performance of ELSD detection method is comparable to that of CAD. The intra-day and inter-day variations were below 1.7% and 3.2% for CAD and 2.8%, and 3.4% for ELSD, respectively. In addition, detection sensitivities of ELSD, CAD, and UV detectors were also compared for HILIC and reversed phase (RP) modes and the highest sensitivities were obtained in the HILIC mode when connected with CAD and ELSD. The developed HILIC aerosol based detection methods were successfully applied to the analysis of gabapentin in commercial tablets and capsules.

Size exclusion chromatography with evaporative light scattering detection as a method for speciation analysis of polydimethylsiloxanes. I: Influence of selected factors on the signal intensity of the detector

Evaporative light scattering detector (ELSD) is widely recognized as a universal tool in chromatography. In this paper, the characteristics of the ELSD detector response and the influence of different factors on the signal intensity are described. Further, results are presented on the influence of some selected factors on the signal intensity and repeatability of results for linear structure polydimethylosiloxanes (PDMS), differing in molecular weight and viscosity. The following factors were studied: (i) the flow velocity of the nebulising gas, (ii) the temperature of the drift tube and the detection cell, and (iii) the flow velocity of the mobile phase, as they all constitute important parameters of the detector. Based on such studies, the optimal parameters of detector indications can be selected for a specific analysis. The results confirmed the possibility to select one set of values for those parameters that allow for analysis of linear PDMS molecules with viscosities ranging from 10 to 60,000 cSt. The following optimal and common parameter values were specified: temperature drift tube 50 °C, carrier gas pressure (for nebulisation) 140 kPa, and mobile phase flow rate 0.7 ml/min. A high repeatability of the results was demonstrated as the relative standard deviation was less than 2.5%. This type of tests for polydimethylosiloxanes has not been presented in any previous publication.

Evaporative Light Scattering Detector: Toward a General Molecular Weight Cutoff Characterization of Nanofiltration Membranes

An evaporative light scattering detector (ELSD) coupled with HPLC was used for the first time to characterize membranes. Polydispersed PEG-200, 600, and 1000 were selected as probe molecules to study the dependence of membrane retention on molecular weight via a gradient eluted HPLC separation coupled to ELSD detection. The results show that HPLC/ELSD is a really general and powerful technique to study the nanofiltration (NF) process since it does not require any special properties for the solutes (chromospheres or fluorophores) and possesses the required sensitivity. Especially in solvent resistant NF (SRNF), where a wide range of organic solvents is used, the ELSD detector was not affected by the interaction between solvent and solutes, which is a critical issue compared to other more common detectors.

Analysis of triacylglycerols on porous graphitic carbon by high temperature liquid chromatography

The retention behaviour of several triacylglycerols (TAGs) and fats on Hypercarb ®, a porous graphitic carbon column (PGC), was investigated in liquid chromatography (LC) under isocratic elution mode with an evaporative light scattering detector (ELSD). Mixtures of chloroform/isopropanol were selected as mobile phase for a suitable retention time to study the influence of temperature. The retention was different between PGC and non-aqueous reversed phase liquid chromatography (NARP-LC) on octadecyl phase. The retention of TAGs was investigated in the interval 30–70 °C. Retention was greatly affected by temperature: it decreases as the column temperature increases. Selectivity of TAGs was also slightly influenced by the temperature. Moreover, this chromatographic method is compatible with a mass spectrometer (MS) detector by using atmospheric pressure chemical ionisation (APCI): same fingerprints of cocoa butter and shea butter were obtained with LC–ELSD and LC-APCI–MS. These preliminary results showed that the PGC column could be suitable to separate quickly triacylglycerols in high temperature conditions coupled with ELSD or MS detector.

Separation and determination of carbohydrates in drinks by ion chromatography with a self-regenerating suppressor and an evaporative light-scattering detector

Analysis of glucose and other carbohydrates are often performed by use of normal phase HPLC methods with acetonitrile as major eluent coupled with evaporative light-scattering detector (ELSD) or by use of anion-exchange ion chromatography (IC) methods with NaOH as eluent coupled with pulsed amperimetric electrochemical detector. In this work, a novel method for the determination of carbohydrates by IC in conjunction with a self-regenerating suppressor and an ELSD detector was investigated. Three carbohydrates (glucose, fructose, and sucrose) were separated using a KOH eluent generator to avoid the effect of carbon dioxide absorption in the alkaline eluent. Due to the use of the suppressor, non-volatile components were removed and a low salt background (K + ∼0.070 μg/mL) can be obtained so the suppressed eluent could directly go into an ELSD detector without obvious interference of inorganic salts. After examining the changes in retention and resolution, an optimized method was established (for IC: using 32 mM KOH as the eluent at a flow rate of 1 mL/min; for ELSD: operated at 95 °C, 4.0 bar nitrogen with a gas flow rate of 2.0 L/min) and the linearity, reproducibility, and the limit of detection (LOD) for the three carbohydrates were further evaluated. Regression equations revealed acceptable linearity (correlation coefficients = 0.994–0.998) across the working-standard range (100–1000 μg/mL for glucose and sucrose, 150–1000 μg/mL for fructose) and LODs of glucose, fructose, and sucrose were 93, 126, and 90 μg/mL, respectively. This method has successfully been applied to the determination of the three carbohydrates in carbonated cola drinks and fruit juices. The recoveries were between 95 and 113% ( n = 3) for different carbohydrates.

Simultaneous Determination of Glycyrrhizic Acid and Liquiritin in Glycyrrhiza uralensis Extract by HPLC with ELSD Detection

Simultaneous quantitative determination of glycyrrhizic acid and liquiritin in Glycyrrhiza uralensis extract was developed using a high performance liquid chromatography (HPLC) coupled to an evaporative light scattering detector (ELSD). A Luna C18 column was used, along with a mobile phase consisting of acetonitrile and 3.0% (v/v) aqueous acetic acid in a gradient elution mode, at a flow rate of 1.0 mL/min. Parameters of ELSD were 105°C for the drift tube temperature and 2.8 L/min for the gas flow‐rate. Retention times of liquiritin and glycyrrhizic acid were 4.1 and 8.3 min, respectively. Logarithmic calibration curves were obtained for glycyrrhizic acid from 0.50 to 5.72 µg (r2>0.999) with a precision of 0.95% R.S.D and for liquiritin from 0.30 to 6.00 µg (r2>0.999) with a precision of 0.59% R.S.D. The limit of quantitation (LOQ) of glycyrrhizic acid and liquiritin were 168.3 ng and 200 ng (S/N=3), respectively. This method was successfully applied to quality evaluation in licorice raw materials and related commercial formulations.

Direct screening of lyophilised biological fluids for bile acids using an evaporative light scattering detector

The usefulness of lyophilisation for the direct screening of biological fluids for bile acids was investigated. Human serum and urine were lyophilised without losses of the target compounds and further extracted with n-hexane in acidic medium under magnetic stirring. An integrated flow injection-liquid chromatographic system coupled to an evaporative light scattering detector (ELSD) was used for automated screening/confirmation. The continuous module allows sequential filtration of the organic phase, solvent changeover and solid-phase extraction for clean-up and preconcentration purposes. Retained bile acids were eluted with an acetonitrile–methanol (65:35, v/v) stream. For screening purposes, the effluent was directly introduced in the ELSD detector and the total bile acid content of the sample determined. For confirmatory analysis, another aliquot of the sample was processed in the screening module but the effluent was directed to the chromatographic columns, which provided the free bile acid profile of the sample. Fasting serum and urine samples obtained from healthy individuals were lyophilised and processed. Good agreement was obtained in the analysis of the two matrices assayed following the screening and confirmatory methods.

High-performance liquid chromatographic analysis of polydisperse ethoxylated non-ionic surfactants in aqueous samples

An adsorption HPLC method using traditionally reversed-phase solvents and a hybrid column/precolumn has been developed for the quantitative separation and analysis of ethoxylated non-ionic surfactants on the basis of the number of ethoxylate (EO) groups per molecule. This method is demonstrated to separate ethoxylated homologues of broadly distributed linear alcohol ethoxylates and alkylphenol ethoxylates, with numbers of EO groups ranging from 3 to 50 or greater. This method presents a significant advance in non-ionic surfactant analysis because it permits direct injection of aqueous samples, eliminating the need for extensive sample preparation. The method discussed here is optimized for use with an evaporative light scattering detector (ELSD), but works equally well with UV absorbance or fluorescence detectors for the analysis of surfactants with chromophores. ELSD and UV detector operating conditions and calibration methods are discussed.