Harvey Indyk - Academia.edu (original) (raw)

Papers by Harvey Indyk

Research paper thumbnail of Determination of Biotin and Folate in Infant Formula and Milk by Optical Biosensor-Based Immunoassay

Journal of AOAC INTERNATIONAL, 2000

Biomolecular interaction analysis was evaluated for the automated analysis of biotin- and folate-... more Biomolecular interaction analysis was evaluated for the automated analysis of biotin- and folate-supplemented infant formulas and milk powders. The technique was configured as a biosensor-based, nonlabeled inhibition immunoassay using monoclonal antibodies raised against analyte-conjugate. Sample extraction conditions were optimized and antibodies were evaluated for cross-reactivity. Performance parameters included a quantitation range of 2–70 ng/mL, recoveries of 86–102%, agreement against assigned reference values for National Institute of Standards and Technology Standard Reference Material 1846, between-laboratory reproducibility relative standard deviation of 9.1% for biotin and 8.1% for folate, respectively, and equivalence against reference microbiological assay methods for both analytes.

Research paper thumbnail of High performance liquid chromatographic analysis of lactose-hydrolysed milk

Research paper thumbnail of Determination of Vitamin K1 Isomers in Foods by Liquid Chromatography with C30 Bonded-Phase Column

Journal of AOAC INTERNATIONAL, 2002

Vitamin K1 was determined in a variety of foods by using reversed-phase liquid chromatography wit... more Vitamin K1 was determined in a variety of foods by using reversed-phase liquid chromatography with a C30 column followed by post-column reduction to the fluorescent hydroquinone derivatives. Lipids were removed by lipase digestion, followed by single extraction into hydrocarbon, and the protocol was extended to selected natural and processed foods. Biologically active trans- and inactive cis-vitamin K1 isomers were measured individually to evaluate the true nutritional status of the products. Method performance parameters confirmed the validity of the technique. The use of the triacontylbonded C30 phase for selective phylloquinone isomer measurement extends previously validated AOAC Method 999.15 for vitamin K1 in milk and infant formula to a wider range of foods important in the human diet. The cis-vitamin K1 isomer contributes up to about 15% of total phylloquinone in certain foods.

Research paper thumbnail of Taurine Analysis in Milk and Infant Formulae by Liquid Chromatography

Journal of AOAC International, 80, 860-865, 1997

Research paper thumbnail of Biosensors: making sense of food

Journal of AOAC International

Research paper thumbnail of Committee on food nutrition. Nonvitamin micronutrients

Research paper thumbnail of Determination of vitamin K in milk and infant formulas by liquid chromatography: Collaborative study

Journal of AOAC International, 2000

A simple procedure for determination of vitamin K1 was developed for routine compliance monitorin... more A simple procedure for determination of vitamin K1 was developed for routine compliance monitoring of supplemented infant formula and measurement of endogenous levels in milk and milk powders. Samples are digested with lipase and extracted into hexane; and aliquot is evaporated, reconstituted in methanol, and analyzed by reversed-phase LC. Post-column zinc reduction of phylloquinone facilitates detection by fluorescence. The procedure was subjected to an AOAC collaborative study involving 8 materials, each in blind duplicate, across the range of 5-120 micrograms/100 g solids and including NIST 1846 reference material. Thirty-three laboratories returned valid data which were then statistically analyzed for outliers and precision parameters. Mean RSDR (%) was 6.53 (4.33-10.94), with a mean HORRAT value of 0.33 (0.23-0.43) and RSDr:RSDR ratio of 0.74. K1 isomers (cis and trans) were aggregated with conventional C18 columns, but may be selectively estimated with use of the C30 column.

Research paper thumbnail of Rapid Determination of Thiamine, Riboflavin, Pyridoxine and Niacinamide in Infant Formulas by Liquid Chromatography

Journal AOAC International, 85, 945-951, 2002

A simplified, simultaneous determination of vitamins B1, B2, B3, and B6 in supplemented infant fo... more A simplified, simultaneous determination of vitamins B1, B2, B3, and B6 in supplemented infant formulas was developed from a single deproteinized sample extract, with analysis by reversed-phase, ion-pair chromatography with an acidified methanol-water mobile phase. The dioctylsulfosuccinate counter-ion facilitates unique retention of the pyridine-based vitamins (niacinamide and pyridoxine) and allows for concurrent measurement of both the pyridoxal and riboflavin 5'-phosphate endogenous components of milk. Other naturally occurring undetected vitamin congeners have minimal analytical significance. UV detection is used for niacinamide, and programmed fluorescence detection is used for riboflavin and the B6 vitamins. Thiamine is routinely determined sequentially under modified elution conditions.

Research paper thumbnail of Determination of total vitamin C in fruit juices and related products by liquid chromatography: Interlaboratory study

Research paper thumbnail of Determination of choline in milk and infant formulas by enzymatic analysis: collaborative study

Journal of AOAC International, 2000

Research paper thumbnail of A Rapid Method for the Determination of Biotin and Folic Acid in Liquid Milk, Milk Powders, Infant Formula, and Milk-Based Nutritional Products by Liquid Chromatography-Tandem Mass Spectrometry

Journal of AOAC International, Jan 31, 2018

Biotin and folate are B-group vitamins that play a critical role in numerousmetabolic reactions, ... more Biotin and folate are B-group vitamins that play a critical role in numerousmetabolic reactions, and they are supplemented to infant and adult nutritional formulas as free biotin and folic acid. We describe a rapid method for the analysis of biotin and folic acid that is applicable to liquid milk, milk powders, infant formula, and milk-based nutritional products. Samples are autoclaved, centrifuged, filtered, and analyzed by HPLC-MS/MS, with quantitation accomplished by the internal standard technique. The method was shown to be accurate, with acceptable spike recovery (biotin: 96.5-108.2%; folic acid: 92.6-104.4%), and no bias (α = 0.05) against either a certified reference material (biotin: = 0.70; folic acid: = 0.23) or established analytical method (biotin: = 0.10; folic acid: = 0.48) was found. Acceptable precision was confirmed with repeatability relative standard deviation (RSD) and Horwitz ratio (HorRat) values (biotin: RSD = 0.5-5.6%, HorRat = 0.1-0.6; folic acid: RSD = 2.0...

Research paper thumbnail of {"__content__"=>" (SMPRs®) 2018.003: Quantitation of Milk by ELISA-Based Methods.", "i"=>{"__content__"=>"Standard Method Performance Requirements"}}

Journal of AOAC International, 2018

Research paper thumbnail of Analysis of Vitamin D2 and Vitamin D3 in Infant and Adult Nutritional Formulas by Liquid Chromatography-Tandem Mass Spectrometry: A Multilaboratory Testing Study

Journal of AOAC International

A multilaboratory testing study was conducted on AOAC First Action Method 2016.05 “Analysis of Vi... more A multilaboratory testing study was conducted on AOAC First Action Method 2016.05 “Analysis of Vitamin D2and Vitamin D3in Fortified Milk Powders, Infant Formulas, and Adult/Pediatric Nutritional Formulas by Liquid Chromatography-Tandem Mass Spectrometry.” Nine laboratories participated in the analysis of duplicate samples of 20 nutritional products. The samples were saponified at high temperature with lipid-soluble components extracted into isooctane; an aliquot was washed and vitamin D derivatized with 4-phenyl-1,2,4-triazoline-3,5-dione to form a high-molecular mass, easily ionizable adduct, extracted into acetonitrile and analyzed by reversed-phase LC-tandem MS. Stable isotope-labeled internal standards were used for quantitation to correct for losses in extraction and variation in derivatization and ionization efficiencies. Acceptable precision as RSD was demonstrated; repeatability ranged from 1.9 to 5.8% RSDr and reproducibility values ranged from 6.4 to 12.7% RSDR, with sampl...

Research paper thumbnail of Analysis of Vitamin D2 and Vitamin D3 in Fortified Milk Powders and Infant and Nutritional Formulas by Liquid Chromatography–Tandem Mass Spectrometry: Single-Laboratory Validation, First Action 2016.05

Journal of AOAC International, 2017

Research paper thumbnail of Analysis of Vitamin D<sub>2</sub> and Vitamin D<sub>3</sub> in Fortified Milk Powders and Infant and Nutritional Formulas by Liquid Chromatography-Tandem Mass Spectrometry: Single- Laboratory Validation, First Action 2016.05

Journal of AOAC International, Jan 25, 2016

A method for the determination of vitamin D2 and vitamin D3 in fortified milk powders and infant ... more A method for the determination of vitamin D2 and vitamin D3 in fortified milk powders and infant and adult nutritional formulas is described. Samples are saponified at high temperature and lipid-soluble components are extracted into isooctane. A portion of the isooctane layer is transferred and washed, and an aliquot of 4-phenyl-1,2,4-triazoline-3,5-dione is added to derivatize the vitamin D to form a high-molecular-mass, easily ionizable adduct. The vitamin D adduct is then re-extracted into a small volume of acetonitrile and analyzed by RPLC. Detection is by tandem MS, using multiple reaction monitoring. Stable isotope-labeled vitamin D2 and vitamin D3 internal standards are used for quantitation to correct for losses in extraction and any variation in derivatization and ionization efficiencies. A single-laboratory validation of the method using AOAC Stakeholder Panel on Infant Formula and Adult Nutritionals (SPIFAN) kit samples was performed and compared with parameters defined a...

Research paper thumbnail of The routine, enzymatic estimation of total choline in milk and infant formulas

Journal of Micronutrient Analysis, 1990

Research paper thumbnail of The analysis of pantothenic acid in milk and infant formulas by HPLC

Food Chemistry, May 1, 2000

Research paper thumbnail of Liquid chromatographic method for the determination of lutein in milk and�pediatric formulas

International Dairy Journal, Sep 1, 2008

Research paper thumbnail of Rapid determination of thiamine, riboflavin, pyridoxine, and niacinamide in infant formulas by liquid chromatography

Journal of Aoac International, 2002

A simplified, simultaneous determination of vitamins B1, B2, B3, and B6 in supplemented infant fo... more A simplified, simultaneous determination of vitamins B1, B2, B3, and B6 in supplemented infant formulas was developed from a single deproteinized sample extract, with analysis by reversed-phase, ion-pair chromatography with an acidified methanol-water mobile phase. The dioctylsulfosuccinate counter-ion facilitates unique retention of the pyridine-based vitamins (niacinamide and pyridoxine) and allows for concurrent measurement of both the pyridoxal and riboflavin 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-phosphate endogenous components of milk. Other naturally occurring undetected vitamin congeners have minimal analytical significance. UV detection is used for niacinamide, and programmed fluorescence detection is used for riboflavin and the B6 vitamins. Thiamine is routinely determined sequentially under modified elution conditions.

Research paper thumbnail of Development and application of an optical biosensor immunoassay for a-lactalbumin in bovine milk

Research paper thumbnail of Determination of Biotin and Folate in Infant Formula and Milk by Optical Biosensor-Based Immunoassay

Journal of AOAC INTERNATIONAL, 2000

Biomolecular interaction analysis was evaluated for the automated analysis of biotin- and folate-... more Biomolecular interaction analysis was evaluated for the automated analysis of biotin- and folate-supplemented infant formulas and milk powders. The technique was configured as a biosensor-based, nonlabeled inhibition immunoassay using monoclonal antibodies raised against analyte-conjugate. Sample extraction conditions were optimized and antibodies were evaluated for cross-reactivity. Performance parameters included a quantitation range of 2–70 ng/mL, recoveries of 86–102%, agreement against assigned reference values for National Institute of Standards and Technology Standard Reference Material 1846, between-laboratory reproducibility relative standard deviation of 9.1% for biotin and 8.1% for folate, respectively, and equivalence against reference microbiological assay methods for both analytes.

Research paper thumbnail of High performance liquid chromatographic analysis of lactose-hydrolysed milk

Research paper thumbnail of Determination of Vitamin K1 Isomers in Foods by Liquid Chromatography with C30 Bonded-Phase Column

Journal of AOAC INTERNATIONAL, 2002

Vitamin K1 was determined in a variety of foods by using reversed-phase liquid chromatography wit... more Vitamin K1 was determined in a variety of foods by using reversed-phase liquid chromatography with a C30 column followed by post-column reduction to the fluorescent hydroquinone derivatives. Lipids were removed by lipase digestion, followed by single extraction into hydrocarbon, and the protocol was extended to selected natural and processed foods. Biologically active trans- and inactive cis-vitamin K1 isomers were measured individually to evaluate the true nutritional status of the products. Method performance parameters confirmed the validity of the technique. The use of the triacontylbonded C30 phase for selective phylloquinone isomer measurement extends previously validated AOAC Method 999.15 for vitamin K1 in milk and infant formula to a wider range of foods important in the human diet. The cis-vitamin K1 isomer contributes up to about 15% of total phylloquinone in certain foods.

Research paper thumbnail of Taurine Analysis in Milk and Infant Formulae by Liquid Chromatography

Journal of AOAC International, 80, 860-865, 1997

Research paper thumbnail of Biosensors: making sense of food

Journal of AOAC International

Research paper thumbnail of Committee on food nutrition. Nonvitamin micronutrients

Research paper thumbnail of Determination of vitamin K in milk and infant formulas by liquid chromatography: Collaborative study

Journal of AOAC International, 2000

A simple procedure for determination of vitamin K1 was developed for routine compliance monitorin... more A simple procedure for determination of vitamin K1 was developed for routine compliance monitoring of supplemented infant formula and measurement of endogenous levels in milk and milk powders. Samples are digested with lipase and extracted into hexane; and aliquot is evaporated, reconstituted in methanol, and analyzed by reversed-phase LC. Post-column zinc reduction of phylloquinone facilitates detection by fluorescence. The procedure was subjected to an AOAC collaborative study involving 8 materials, each in blind duplicate, across the range of 5-120 micrograms/100 g solids and including NIST 1846 reference material. Thirty-three laboratories returned valid data which were then statistically analyzed for outliers and precision parameters. Mean RSDR (%) was 6.53 (4.33-10.94), with a mean HORRAT value of 0.33 (0.23-0.43) and RSDr:RSDR ratio of 0.74. K1 isomers (cis and trans) were aggregated with conventional C18 columns, but may be selectively estimated with use of the C30 column.

Research paper thumbnail of Rapid Determination of Thiamine, Riboflavin, Pyridoxine and Niacinamide in Infant Formulas by Liquid Chromatography

Journal AOAC International, 85, 945-951, 2002

A simplified, simultaneous determination of vitamins B1, B2, B3, and B6 in supplemented infant fo... more A simplified, simultaneous determination of vitamins B1, B2, B3, and B6 in supplemented infant formulas was developed from a single deproteinized sample extract, with analysis by reversed-phase, ion-pair chromatography with an acidified methanol-water mobile phase. The dioctylsulfosuccinate counter-ion facilitates unique retention of the pyridine-based vitamins (niacinamide and pyridoxine) and allows for concurrent measurement of both the pyridoxal and riboflavin 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-phosphate endogenous components of milk. Other naturally occurring undetected vitamin congeners have minimal analytical significance. UV detection is used for niacinamide, and programmed fluorescence detection is used for riboflavin and the B6 vitamins. Thiamine is routinely determined sequentially under modified elution conditions.

Research paper thumbnail of Determination of total vitamin C in fruit juices and related products by liquid chromatography: Interlaboratory study

Research paper thumbnail of Determination of choline in milk and infant formulas by enzymatic analysis: collaborative study

Journal of AOAC International, 2000

Research paper thumbnail of A Rapid Method for the Determination of Biotin and Folic Acid in Liquid Milk, Milk Powders, Infant Formula, and Milk-Based Nutritional Products by Liquid Chromatography-Tandem Mass Spectrometry

Journal of AOAC International, Jan 31, 2018

Biotin and folate are B-group vitamins that play a critical role in numerousmetabolic reactions, ... more Biotin and folate are B-group vitamins that play a critical role in numerousmetabolic reactions, and they are supplemented to infant and adult nutritional formulas as free biotin and folic acid. We describe a rapid method for the analysis of biotin and folic acid that is applicable to liquid milk, milk powders, infant formula, and milk-based nutritional products. Samples are autoclaved, centrifuged, filtered, and analyzed by HPLC-MS/MS, with quantitation accomplished by the internal standard technique. The method was shown to be accurate, with acceptable spike recovery (biotin: 96.5-108.2%; folic acid: 92.6-104.4%), and no bias (α = 0.05) against either a certified reference material (biotin: = 0.70; folic acid: = 0.23) or established analytical method (biotin: = 0.10; folic acid: = 0.48) was found. Acceptable precision was confirmed with repeatability relative standard deviation (RSD) and Horwitz ratio (HorRat) values (biotin: RSD = 0.5-5.6%, HorRat = 0.1-0.6; folic acid: RSD = 2.0...

Research paper thumbnail of {"__content__"=>" (SMPRs®) 2018.003: Quantitation of Milk by ELISA-Based Methods.", "i"=>{"__content__"=>"Standard Method Performance Requirements"}}

Journal of AOAC International, 2018

Research paper thumbnail of Analysis of Vitamin D2 and Vitamin D3 in Infant and Adult Nutritional Formulas by Liquid Chromatography-Tandem Mass Spectrometry: A Multilaboratory Testing Study

Journal of AOAC International

A multilaboratory testing study was conducted on AOAC First Action Method 2016.05 “Analysis of Vi... more A multilaboratory testing study was conducted on AOAC First Action Method 2016.05 “Analysis of Vitamin D2and Vitamin D3in Fortified Milk Powders, Infant Formulas, and Adult/Pediatric Nutritional Formulas by Liquid Chromatography-Tandem Mass Spectrometry.” Nine laboratories participated in the analysis of duplicate samples of 20 nutritional products. The samples were saponified at high temperature with lipid-soluble components extracted into isooctane; an aliquot was washed and vitamin D derivatized with 4-phenyl-1,2,4-triazoline-3,5-dione to form a high-molecular mass, easily ionizable adduct, extracted into acetonitrile and analyzed by reversed-phase LC-tandem MS. Stable isotope-labeled internal standards were used for quantitation to correct for losses in extraction and variation in derivatization and ionization efficiencies. Acceptable precision as RSD was demonstrated; repeatability ranged from 1.9 to 5.8% RSDr and reproducibility values ranged from 6.4 to 12.7% RSDR, with sampl...

Research paper thumbnail of Analysis of Vitamin D2 and Vitamin D3 in Fortified Milk Powders and Infant and Nutritional Formulas by Liquid Chromatography–Tandem Mass Spectrometry: Single-Laboratory Validation, First Action 2016.05

Journal of AOAC International, 2017

Research paper thumbnail of Analysis of Vitamin D<sub>2</sub> and Vitamin D<sub>3</sub> in Fortified Milk Powders and Infant and Nutritional Formulas by Liquid Chromatography-Tandem Mass Spectrometry: Single- Laboratory Validation, First Action 2016.05

Journal of AOAC International, Jan 25, 2016

A method for the determination of vitamin D2 and vitamin D3 in fortified milk powders and infant ... more A method for the determination of vitamin D2 and vitamin D3 in fortified milk powders and infant and adult nutritional formulas is described. Samples are saponified at high temperature and lipid-soluble components are extracted into isooctane. A portion of the isooctane layer is transferred and washed, and an aliquot of 4-phenyl-1,2,4-triazoline-3,5-dione is added to derivatize the vitamin D to form a high-molecular-mass, easily ionizable adduct. The vitamin D adduct is then re-extracted into a small volume of acetonitrile and analyzed by RPLC. Detection is by tandem MS, using multiple reaction monitoring. Stable isotope-labeled vitamin D2 and vitamin D3 internal standards are used for quantitation to correct for losses in extraction and any variation in derivatization and ionization efficiencies. A single-laboratory validation of the method using AOAC Stakeholder Panel on Infant Formula and Adult Nutritionals (SPIFAN) kit samples was performed and compared with parameters defined a...

Research paper thumbnail of The routine, enzymatic estimation of total choline in milk and infant formulas

Journal of Micronutrient Analysis, 1990

Research paper thumbnail of The analysis of pantothenic acid in milk and infant formulas by HPLC

Food Chemistry, May 1, 2000

Research paper thumbnail of Liquid chromatographic method for the determination of lutein in milk and�pediatric formulas

International Dairy Journal, Sep 1, 2008

Research paper thumbnail of Rapid determination of thiamine, riboflavin, pyridoxine, and niacinamide in infant formulas by liquid chromatography

Journal of Aoac International, 2002

A simplified, simultaneous determination of vitamins B1, B2, B3, and B6 in supplemented infant fo... more A simplified, simultaneous determination of vitamins B1, B2, B3, and B6 in supplemented infant formulas was developed from a single deproteinized sample extract, with analysis by reversed-phase, ion-pair chromatography with an acidified methanol-water mobile phase. The dioctylsulfosuccinate counter-ion facilitates unique retention of the pyridine-based vitamins (niacinamide and pyridoxine) and allows for concurrent measurement of both the pyridoxal and riboflavin 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-phosphate endogenous components of milk. Other naturally occurring undetected vitamin congeners have minimal analytical significance. UV detection is used for niacinamide, and programmed fluorescence detection is used for riboflavin and the B6 vitamins. Thiamine is routinely determined sequentially under modified elution conditions.

Research paper thumbnail of Development and application of an optical biosensor immunoassay for a-lactalbumin in bovine milk