# US 11,442,049 B2 · Method for producing a purple complex for the presence of lead using sodium rhodizonate without use of strong acid > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,442,049 B2 - Document ID: US11442049B2 - Status: Granted - Kind: B2 - Application number: 16/521,829 - Filed: 2019-07-25 - Published: 2021-01-28 - Granted: 2022-09-13 - Earliest claimed: 2019-07-25 - Applicants: Frederic G Dewalt; David C Cox - Inventors: Frederic G Dewalt; David C Cox - Web page: https://patentgrep.com/patent/US11442049B2 ## CPC - G01N 31/22: using chemical indicators (G01N31/02 takes precedence) - G01N 21/78: producing a change of colour - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract A method using ascorbic acid (Vitamin C) as part of a chemical test kit employing sodium rhodizonate as the coloring agent for producing a yellow-orange to purple color transition for detection of lead in various media eliminating the use of strong acid. ## Claims ### Claim 1 A method of detecting lead in media or on objects using ascorbic acid without any use of any strong acid to convert the scarlet lead-rhodizonate compound to the purple (blue-violet complex) that is diagnostic for the presence of lead when using sodium rhodizonate using the following steps: (a) exposing the media or object to an acid to dissolve the lead to form Pb+ ions; (b) exposing the media or object to a tartrate buffer fortified with ascorbic acid; (c) exposing the media or object to rhodizonate, wherein step b must be performed prior to step c); and, (d) monitoring the media or object for a visible color change. ### Claim 2 (depends on 1) The method of claim 1 wherein the color change to purple (blue-violet) is an indicator of the presence of lead. ### Claim 3 (depends on 1) The method of claim 1 wherein the media is paint, dust or soil. ### Claim 4 (depends on 1) The method of claim 1 wherein the object is any surface where the detection of lead is sought. ### Claim 5 (depends on 1) The method of claim 1 wherein for step b) of claim 1, the media or object is instead exposed to a tartrate buffer, wherein the tartrate buffer is not fortified with ascorbic acid; and wherein during step c) of claim 1, the media or object is subsequently exposed to rhodizonate; and wherein said media or object is then exposed to ascorbic acid, to produce a visible color change. ### Claim 6 (depends on 1) The method of claim 1 wherein the tartrate buffer fortified with ascorbic acid has an approximate pH of 2.8 in a solution containing about 0.375 g of tartaric acid, about 0.475 g of sodium tartrate monohydrate, and about 0.5 g of ascorbic acid diluted to 25 mL final volume with water. ### Claim 7 (depends on 6) The method of claim 6 wherein the volume of tartrate buffer fortified with ascorbic acid is increased or decreased by holding constant the ratios of the amounts of about 0.375 g of tartaric acid, about 0.475 g of sodium tartrate monohydrate, and about 0.5 g of ascorbic acid to the 25 mL final volume of water. ### Claim 8 (depends on 1) The method of claim 1, wherein the rhodizonate is a solution containing about 0.06 g of sodium rhodizonate diluted to 25 mL final volume with 0.5% saturated tartrate buffer. ### Claim 9 (depends on 8) The method of claim 8 wherein the volume of rhodizonate is increased or decreased by holding constant the ratio of the amount of about 0.06 g of sodium rhodizonate to the 25 mL final volume of 0.5% saturated tartrate buffer. ### Claim 10 (depends on 8) The method of claim 8 wherein the 0.5% saturated tartrate buffer is about 7.5 g of tartaric acid and about 9.5 g of sodium tartrate monohydrate diluted to 500 mL final volume with water. ### Claim 11 (depends on 10) The method of claim 10 wherein the volume of 0.5% saturated tartrate buffer is increased or decreased by holding constant the ratios of the amounts of about 7.5 g of tartaric acid and about 9.5 g of sodium tartrate monohydrate to the 500 mL final volume of water. ### Claim 12 (depends on 5) The method of claim 5 wherein the tartrate buffer has an approximate pH of 2.8 in a solution containing about 0.375 g of tartaric acid, and about 0.475 g of sodium tartrate monohydrate diluted to 25 mL final volume with water. ### Claim 13 (depends on 12) The method of claim 12 wherein the volume of tartrate buffer is increased or decreased by holding constant the ratios of the amounts of about 0.375 g of tartaric acid, and about 0.475 g of sodium tartrate monohydrate to the 25 mL final volume of water. ### Claim 14 (depends on 5) The method of claim 5 wherein the rhodizonate is a solution containing about 0.06 g of sodium rhodizonate diluted to 25 mL final volume with 0.5% saturated tartrate buffer. ### Claim 15 (depends on 14) The method of claim 14 wherein the volume of rhodizonate is increased or decreased by holding constant the ratio of the amount of about 0.06 g of sodium rhodizonate to the 25 mL final volume of 0.5% saturated tartrate buffer. ### Claim 16 (depends on 14) The method of claim 14 wherein the 0.5% saturated tartrate buffer is about 7.5 g of tartaric acid and about 9.5 g of sodium tartrate monohydrate diluted to 500 mL final volume with water. ### Claim 17 (depends on 16) The method of claim 16 wherein the volume of 0.5% saturated tartrate buffer is increased or decreased by holding constant the ratios of the amounts of about 7.5 g of tartaric acid and about 9.5 g of sodium tartrate monohydrate to the 500 mL final volume of water. ### Claim 18 (depends on 5) The method of claim 5 wherein the ascorbic acid is a solution containing about 0.5 g ascorbic acid diluted to 25 mL final volume with water. ### Claim 19 (depends on 18) The method of claim 18 wherein the volume of ascorbic acid is increased or decreased by holding constant the ratios of the amounts of about 0.5 g of ascorbic acid to the 25 mL final volume of water. ### Claim 20 (depends on 1) The method of claim 1, wherein monitoring for a visible color change is conducted on filter media after pushing some or all of the liquid resulting from steps (a), (b) and (c) applied to the media or object being tested through the filter media. ### Claim 21 (depends on 5) The method of claim 5 wherein monitoring for a visible color change is conducted on filter media after pushing some or all of the liquid from steps (a), (b), (c) and (d) applied to the media or object being tested through the filter media.